The present invention relates to a high-strength galvamiealed steel sheet and a 10 method of manufacturing the same. . 15 Priority is claimed-on Japanese Patent Application No. :2009-200467, filed August 31, 2009, Japanese Patent Application No. 2009-217578, filed September 1 R, 2009, and. Japanese Patent Application No. ioo9-2169f6, filed September 1&, 2009, the content of which are incorporated herein by reference .A typical example of a plated steel, sheet ha~g favorable corrosion resistance is ' ~ ,- . . I ' a galvannealed steel sheet. The galvannealed steel sheet is generally manufactured by 20 degreasing a steel sheet, preheating the steel sheet in a non-oxidizing furnace or direct fired fumac·e, carryhlg out reduction annealing in a reduction furnace for cleaning the surface and securing the material quality, immersing the steel sheet in a galvanizing bath, controlling the adhered amount of molten zinc;' and carrying out alloying. Since the steel sheet has excellent corrosion resistance, plate adhesiveness;and the like, the steel 25 sheet is widely used mainly for automobiles, construction materials, and the like. Patticularly, in recent years, iri order to both secure a function for protecting passengers in case of collision and reduce the weight for improving the gas mileage in ·the automobile field, there has been a demand for an increase in the strength of a plated 5 steel sheet. However, generally, an increase in the strength results in degradation of the formability, and thus there has been ·a demand to establish a method for incre~ing the strength while the formability is maintained . [0004] --.-- ... -······ -------- . ~-- .. --- ···- --·. ~- . -- ... . Examples of the method for increasing the strength while the formability is 10 maintained include methods as described in Patent Documents 1 and 2. .These methods are for increasing the strength and obtaining favorable formability at the same time by dispersing residual austeni.te in steel and using the fact that the residual austenite causes a stress indu<:tion and deformation induction dming a prrcess. In the steel sheet as described in Patent Documents 1 and 2, C, Si, and Mn are used as basic alloy elements, IS annealing is can·ied out. in a two-phase region offerrite (a.)+ austenite (y), and then a· thermal treatment is carried out in a temperature region of approximately 300°C to 450°C, thereby using·a bainite tnirisfoi:niatiml' and obtaining· residual austenite even at room temperature. However, since carbides, su_vh as. cementite, tend to be precipitated during ' ! . the thermal treatment of300"C to 450°C, and austenite is decomposed, it is necessary to 20 add Si or AI. [0005] However; since Si and AI are more liable to be oxi~d than Fe, it is likely that · oxides containing Si or Al.are formed on the surface in the above stee!.sheet These oxides have poor wetting propertie.s with molten Zn, and thus, in steel sheets containing 25 · Si orAl, there. is a problem in that non-plated portions are liable to be formed. In lr 1~ '~ 4 · · ·addition, the above oxides delay the !'lloying reaction between Zn and Fe. Therefore, in steel sheets containing Si or AI, long alloying treatment with a high-temperature is required compared with mild steel sheets, degradation of the productivity is caused, austenite is decomposed into a bainite sb.ucture including pearlite and c.arbides by long 5 alloying treatment with the high-temperature, and an excellent formability cannot be obtained. [0006] Patent Document 3 describes a method for solving the above problems. This - ·-- .. -···- ... --- ··--- --· .. ·- ···----~---·- ·- ----------- ····--··· ---- ... ·--- -··· .. -. -· -- . . . ·-- --·-" -·· -··· -- --··-· .... -· method is for improving the wetting properties of steel sheets and molten Zn and 10 accelerating the alloyi.ng reaction by adding an appropriate concentration of AI to molten [0007] This method makes it possible to suppress prcpagation of fatigue cracking that propagates through soft ferrite by structural strengthening that strengthens soft ferrite 15 using a hard structure, such as hard martensite or residual austenite, and thus this method . contributes to improving the fatigue durability up to a certain fraction of.hard phases. 20 However, since fatigue cracking propagate~ through soft structures, there is a limit to increasing the fatigue limit simply with an increase in the fraction of hard. structures. . -· . . ·'' . AB a result, when the fraction of hard stn1c~es reacheJ a certain extent or more, the; . strength o. f the steel sheet is increased, but the fatigue limit i.s . not increas. ed.- Therefore) it was difficult to achieve both an increase in the strength and fatigue durability to a high . . level (for example, refer to Non Patent Document 1). [0008] Meanwhile, since steel sheets used for autumoliiles or construction materials · 25 have a thin sheet thickness, there are cases in which, when fatigue cracking is forrned, the 5 sheet thickness is immei:liate!y penetrateroving the bending properties, but 3 minutes or more of the isothermal treatment is essential, and this method carri~d out using a continuous plating li facility causes a significant degradation of productivity. 5 [0018] In Patent Documents 11 and 12, the structure or C concentration in t~e ferrite portion is controlled in order to improve the plating properties. . These documents focus to the surface properties of the ferrite while plating is carried out. . However, these ······--·--------·--···--···-- ·-····-··-. ····-····· -- ·-·-··------------···· --··-·-···--··-·-···----·- ····.··--- ·documents do not sufficiently disclose the analysis, which is carried out after the plating, " . 10 of the properties of the ferrite portion that directly adjqins the interface with the plate. In the method of Patent Document 12, it is difficult to measure the. concentration of C irrunediately below the intetface, particularly, at a depth of 1 }lJll or less. I Citation List 15 Patent Documents . -... -_' ~~;i~i [0019] · [Patent Document 1] Japanese Unexamined Patent Application, First · Publication No. HOS-70886 . - ·.· . ! [Patent Document 2) Japanese Unexamined Patent Application, First 20 Publication No. HOS-195143· [Patent DocUm.ent 3) Japanese Unexamined. Patent Application; First Publication No. 2003-105516 · lPatent Document 4) Japanese Unexamined PatentApplication,First Publication No. 2006-57120 25 [Patent Document 5) Japanese Unexamined Patent Application, First ---"- -- - ~ :-:: :_:_,~__'_ -- ::::::-::-: :-:-_c;:::_ ~--:: ': -_~:-~-~-=-- :'-:- : ~~-: ----~-- 9 I'hb!ication No. 2005~194586 [Patent Document 6] Japanese Unexamined Patent Application, First Publication No.· 2003-171752 [Patent Documen~ 7] Japanese Unexamined Patent Application, First 5 Publication No. H04-276057 [Patent Document 8] Japanese Unexamined Patent Application, Fir~ Publication No. H03-28359 [Patent Document 9] Japanese Unexamined Patent Application, First • --· •• - 7"" ·····-··-··· --·---·--··---·---------------------·--- -··------- Publication No. H03-64437 10 [I' a tent Document 1 0] Japanese Unexamine(l Patent Application, First Publication No. 2006-9057 [Patent Document 11] Japanese Unexamined Patent Application, First J Publication No: 2002~088459 [Patent Document 12] Japanese Unexamined Patent Application, First 15 Publication No. 2003-073772 Non Patent Documents .. [0020] . [Non Patent Document 1] The pr-~print of till;, ~Oth academic conference by The ' . . . . . ' ~ I . . . I Japan Institute of Metals, written by Yokomaku Toshinori and three other authors, 1991, 20 page 16 Disclosure of the invention Technical Problem [0021] 25 In order to improve the fatigue durability of a steel sheet, it is necessary to :..: . I I I I I I _-,____;:: - 10 . . ' ' . - - - . - . . · suppress fonnation of cracking on the surface, but it was difficult to stably suppress · fonnation of cracking on the surface in the related art. The present invention has been made in consideration of such a circumstance, and an object o_fthe present invention is to provide a high-strength galvannealed steel sheet that can stably produce favorable fatigue 5 durability. Solution to Problem [0022] In order to solve the above problem, aspects o~ the present invention are as 10 follows: (1) Afrrst aspect of the present invention is a galvanized steel sheet having a tensile strength of 770 JvlPa or more including a steel.sheet portion containing, by mass%-, C: 0.05% to 0.50%, Si: 0.005% to 2.5%,Mn:j0.01% to 3.0%,Al: O%to 0.5%, ' Ni: 0% to 2.0%, Cu: 0% to 2.0%, Cr: 0% to 2.0%, Mo: 0% to 2.0%, B: 0% to 0.002%, '15 - Ti: 0% to 0:1%, Nb: 0% to 0.1%, V: 0% to 0.1%, REM: 0% to 0.1%, and Ca:.O% to 0.1% . . a remainder of Fe and inevitable impurities,' in which P, S, and Ji are limited to 0.03% or less, 0.02% 'or less, and 0.0060% or less respectively, ·and a plated layer formed on the surface of the steel sheet portion, in which j}le plated layer is a galvanized plated layer or . . I a galvannealed plated layer, the galvanized plated layer containing AI: 0.01% to 1.5% 20 and one or more selected from Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu,'Li, Ti, Be, Bi, and REM in total of 0% to 3.5% with the remainder of Zn and inevitable impurities, and . the galvannealed plated layer containing Fe: 5% to 15%, AI: 0:01% to I% and one or · more selected from Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and REM in a total of0%to 3.5%with the remainder of Zn and inevitable impurities, the steel- · 25 sheet portion has a soft layer that directly adjoins tl1e interface with the plated layer imd -- ------"·--~--- ·r 11 an inside layer that is other than the soft layer, the thickness D of the soft layer is 0.001% to 5% of the thickness t 0fthe steel sheet portion, and, when the hardness of the soft layer measured by the nano-indentation method is indicated by H1, and the representative hardness of the steel sheet portion measured by the naco-indentation method is indicated 5 by Ha in a cross section that goes along the thickness direction of the steel sheet portion, · HI is 5% to 75% ofHa. (2) In the galvanized steel sheet according to the above (1), when an oxide including one or two of Si and Mn is. present in the steel sheet surface layer portion . - ···-·.--- ... --- .. -·----- ······ -- --------·-. ··- --··· .... - -----. .. . .. - . •'· .. . . --· . --------·-·· ---·-- within a depth d or Jess from the plate/ferrite interface, _the depth d in which the oxide is 10 present and D may satisfy d/4 $ D $ 2d. (3) In the galvruiized steel sheet according to the above (1 ), the steel sheet · portion may further contain more tlian 0.10% to 0.50% of C. (4) In the galvanized steel sheet according to ~e above (1), the C concentration in the soft layer may be 10% to le.ss than 30% of the C concentration of the entire steel 15 sheet portion. · (5) A second aspect of the present invention is a method of manufacturing the · galvanized steel sheet according to the above (1 ), in which ihe conditions for_ annea.lirig ahead of plating in a continuous galvanizin_.gline for the steel sheet portion are: the peak . I . . sheet temperature is controlled to 650°C tIG 1 is a microscopic photograph showing the result of etching the cross section of the typical steel sheet and observing the same using an optical microscope. ,. Qescription ofEmbodiments [0025] 25 Any of the above related art does not consider improvement in the fatigue ., c••cc'~L"Lccc"cc;LLL ,cL'cC:c•.,·.·13 dunibility of a plated steel sheet The fatigue· durability is a deformation characteristic in a case in which a sufficiently low stress is repeatedly added with respect to the tensile strength, and is an indispensible characteristic .for structural members that receive a repetitive stress, such as automobiles, construction machines, and conStruction materials. 5 · When a steel sheet receives a repetitive stress, fine deformation occurs in the steel sheet even when the intensity of the stress is smaller than the yield stress, and accun~illation of the def01mation results in fracture of the steel sheet.. Tbis fracture is caused by cracking that is formed on the surface and propagates into the steel sheet. From this fact, it ·--------·-·--- -------------· ................................ ····-·. ·; ·- ·-------·-····-' ---. ~--··-·····- -·· ·. ·- . becomes importaut to suppress formation of fatigue cracking or suppress propagation of 10 cracking in order to improve the fatigue durability. [0026] Particularly, in a case in which application to automobile members is taken into consideration, there is a concern that even fine crackin~ may act as a starting point of fracture in case of collision of a vehicle body. In tllis case, since there is a concern that ·,- • 15 predetermined collision stability may not be ob~ined, it is considered to be important to suppress-fine cracking in order to improve the collision characteristics .. Therefore, it · bec~mes particularly importaut to suppress formation Of cracking on the surface to improve fatigue durability. .. In order to suppress formation of c~acking, the 1 characteristics of the plated steel 20 sheet, particularly in a portimi immediately below the plate interface (a portion that directly adjoins the plate) are important. The steel sheet portion immediately below the i.n terface, p. articularly in. a range of 1 fliD or less from the· plate interface sometimes bas a . different hardness from that ofthe entire steel sheet due to a plurality of causes, such as the increased C concentration compared with the en lire steel sheet, accumulation of 25 oxi'des, and formation of a different composition. of the steel structure from the inside of 0 '< j .i .i -~ ~,- .. -~ -:::-~-:----~~-Y~:-~~ ~~- ----~~~- -~~~~--~---~ ~-"-. ,.__ ~ .. -~OJ .............. ··-·-·---~--~----~---.-.~ ... -- ···-·-·-~---- --. ••• ~-.-.-.···· 14 the steel sheet: Therefore, it was fo\md that it is difficultto obtain a "stable fatigue durability of a plated steel sheet if the manufacturing method and the quhlity are n<;~t controlled based on an accurate measurement of the hardness of the steel sheet immediately below the plate interface. 5 [0027) In the related art, when investigation on a steel portion below the plat~ interface was carried out, for example, a method in which the plate is removed using an ~ inhibitor-containing solution, the steel sheet is dissolved up to a depth of approximately 5 Jlm, and an average carbon concentration and the like of the dissolved.steel sheet are 10 measured was used. ··However, iii the measurement r~sults by the present inventors, there were cases in which a stable correh1tion between the measurement results and the . fatigue durability was not obtained particularly in high-strength steel sheets having a tensile strength of 770 MPa or more. As a result of apditional investigations, it was found that the characteristics of the steel sheet in a portion of a depth of 1 Jlffi or less '15 .. from the interface are accurately correlated·with the fatigue durability;-''' In a 20 measurement according to the related art, the range of tneasuretnent of a portion of a . depth of 5 fim oileis is to'o broiul, and therefore the characteristic. ofihe Steel sheet .. . immediately below the interface cannot beinve~tigated ·sufficiently, which is considered ! to be a cause of the poor correlation. [0028) In addition, as a result of repetitive thorough studies regarding improvement in the fatigue durability of a high-strength galvannealed steel sh~et, the inventors found that the fatigue durability can be improved without degrading the formability by forming a microstructure, in which the area ratio of ferrite is 95% or more, in the interface between 25 the high-strength steel sheet and the galvannealed plated layer in an average thickness of I 5 ---'-'--:-:-:, 15 0. 0 lJJ.m to 10 JJ.m. . P~icularly, as•1ong as the are·a·r~tio of ferrite is. appropriately controlled immediately below the interface, fuat is, at a depth of 1 f!ID or less, the fatigue durability can be stably improved. [0029] In addition, fue inventors found fuat it is possible to reduce only fue hardness of a close-to-interface layer, which is the steel sheet surface (fue vicinity of the plate interface) portion that does not affect fue strength offue steel. sheet, by adjusting the steel ductility of the close-to-interface layer, suppress the OC9Urrence of cracking, and further ~ 0 · improve hydrogen entbrittlement resistance. In addition, it was found _that generation of oxides ofSi and Mn in the vicurlty of the steel sb~et surface layer (in fue vicinity of~. 15 close-to-interface layer) can improve fue hydrogen embrittlement resistance su;ce·the oxides suppress propagation of cracking even when cr~clcing occirrs, ruid, furthermore, fmmation of the oxides inside the steel sheet can secure favorable plating properties. · detail. [0030] (First embodiment) ·Hereinafter; a"flrst embodiment" Of the present invention will be deilctibed in -· ·'• •. Firstly, fue reasons w]ly the components offue steel sheet are limited will be 20 described, Furthermore, % in fue present invention refers to mass% unle~s ofu~rwise specified. [0031] (Steel sheet components) · C is an essential element in a case in which increasing the strength of tl1e steel 25 sheet is attempted through structural strengthening which is achieved by martensite or ' -j • 16 - -·r---~ . . . residual austenite. The reasonwhy!the amount of Cis set to 0.05% or more is that, when the amount of C is less than 0.05%, cementite or pearlite is liable to be generated in a galvanizing line in which it is difficult to quench the steel sheet from the annealing temperature using mist or water jets as a cooling medium, and it is difficult to secuie the s- _· : ·~i~ce5sary tensile strength. In order to stably achieve a high strength of 770 MPa or more, the c amount is preferably set to more than 0.08%, and more preferablY. to more than 0.1 0%. On the other hand, the reason why the amount of C is set to 0.50% or less is that, when the amowit of C exceeds 0.50%, the weldability is significantly degraded. ·. ·-· ·-----~----~ -·-· ------··-- ----·-·- ...... -·····-. -- ...... - '" "Meanwhile, in a case in which a: more preferably weldability is required, the amount of C · _10 is set to 0.25% or less, and more preferably to 0,20% or less .. [0032] Si is an element that increas~s the strength without significantly impairing the formability, particularly elongation of the steel sheet, tnd is added at 0.005% to 2.5%; The reason ~hy the arnount.ofSi is set to 0.005% or more is to secure a sufficient tensile 15· strength. Furthermore, in order to stably obtain a tensile strength of770 MPa or more, _. .. ·. the amount of Si is more preferably set to 0.5% or more, and still more preferably to 1.0% or more. The reason why the upper limit of the ammmt of the Si is set to 2.5% or · · · less is .that, as long a8 the upper limit is wiftrin ~he above range, the effect of increasing I ' the strength is not saturated, and the ductility is not degraded. Patticularly, in order to 20 obtain favorable weldability and plating properties, the upper limit of Si· is more · preferably set to 2.0%, and still more preferably to ~.s%. In addition, when Si is added four times or more than the amount of C, the . . . progress of the pearlite and bainite transformation is significantly delayed by reheating for an alloying treatment, which is carried out immediately.after the plating, a 25 microstructm:e in which one or two kinds of 5% to,70% of martensite or residual ........ -_ -.::____ - ~- ---------:::::( 17 austenite by the area ratio is inoludell in ferrite even after the steel sheet is cooled to room [0033] temperature, and it becomes easy to secure a sufficient strength. The range of the Mn amount is set to O.Ol%to 3.0% by mass%. The lower 5 limit at which the effect of increasing the strength is exhibited was set to 0.01 %, and the upper limit was set to 3.0% from the viewpo. int of manufacturing costs. Me'!l'while, . since Mn decreases the free energy of austenite· together with C, Mn is more preferably added at 1.5% or more, and still more preferably at 2.0% or more for the purpose of "-······-···· '·· ···--·--.. -~---~----· .. ·-·-··.··--~···----·-···---· .............. , __ , ________ ,_, ___________ ,, stabilizing austenite until the steel sheet is immersed in a plating bath. In addition, io a 10 case in which Mn is added 12 times or mort\ than the a_mount of C, the progress of the pearlite and bainite transformation is significantly delayed in reheating for an alloying 20 treatment, which is carried out immediately after the plating, a microstructure in which one or two kinds of5%to 70% of martensite or resid'f austenite bye the area ratio is included in ferrite even after the steel sheet is cooled to room temperature, and it becomes easy to secure a sufficient strength. However, when the added amount becomes excessive, since cracking is liable to occur~ the slab~ and the ~eldabilityis also deteriorated, the upper limit is more preferably set to ·2.8%, and still more preferably -to 2.5% in a case in which the strength, forQlability, an9- .costs are taken ioto ' . . .~ . . . consideration. ! [0034] Generally, Pis included in steel as an inevitable impurity; however, when the amount ofP exceeds 0.03%, the spot weldability is significantly deteriorated .. In addition, in this case, in a high-strength steel· sheet having a tensile strength of more than 770 MPa, such as the embodiment, both the toughness and the cold rolling properties are 25 significantly deteriorated. Therefore, the amount ofP is set to 0.03% or less. · A 18 smilller· amount of P results in a more favorable fonnabili1y, and the amount of P is more preferably set to 0:02% or Jess, and still more preferably to 0.01% or less. On the other hand, since reduction of the amount ofP to less than 0.00-I% excessively increasesthe refinement costs, the lower limit of the amouot is set to 0.00 I%. The amouot of P is 5 preferably set to 0.003% to 0.01% in terms of the balance among the strength, the formability, and the costs .. [0035] S is also, generally, included in steel as an inevitable impurity, and, when the ···--·----· ··-----~····· ------------····-····-···-····---··········- .. --------------- -----·--· .......... ___ _ amount thereof exceeds 0.02%, MnS stretched in the r~Jiing direction is significantly I 0 generated, and the bending properties of the steel sheet are adversely affected. Therefore, the arnounf of S is limited to 0.02% or less. The amount of S is more preferably set to 0.01% or less, and still more preferably to 0,005% or Jess. However, it costs money to reduce the amouotof S. From the vifwpoint of the formability and the plate adhesiveness, it is not necessmy to excessively reduce the amount of S, and the t 5 amount of S may be reduced to.a level necessary for the conditions of the hot rolling fonnability, corrosion resistance, and the like. [0036] N is also, genenilly, included i11 steel as an iney)table impurity. When the .~ . . . . . J . f amount ofN exceeds 0.0060%, e.l.o ngation and brittleness are deteriorated, and therefore 20 the amount"ofN is limited to 0.0060% or less. Particularly, in a case in Which a favorable formability is required, the amount ofN is more preferably set to 0.004% or less, _and still more preferably to 0.003% or Jess. A smaller amount ofN is preferred, but reducing the amount to ~ess than 0.0005% increases the costs excessively, and therefore the lower limitofthe amount is set to 0.0005%. 25 [0037] l_ I ~----- --~-- - . -----~--~ ~---····-··- ---·-----~-----~--~-- 19 Addition of Al is not essential; however, in a case in which AI is added, Al is added as a deoxidizing element of stee~ and exhibits an effect of the refinement of a hot-rolled material throughAlN and suppressing the coarsening of crystal grains in~ series of thermal treatment processes, thereby improving the material quality. In: a case 5 in which this effect is required, Al needs to be !!{lded at 0.005% or more, and preferably 10 0.01.% or more. However, when more than 0.5% orAl is added, since the costs are increased, and the surface properties are deteriorated, the_ amount of Al is set to 0.5% or . _ ,l_es~,.~refer_~b!_Y. t? ~.3 o/o .o.r_lf:SS: _D':lor.~_?r~f~r~~~y !o_ ~·-1~ .. ?r less,_ ~d sti~ ll'lo!~ pr_ef,e_r~lY, .. to 0.05% or less. [0038] In addition, one or rnore ofNi, Cu, Cr, Mo, B, Ti, Nb, V, REM (for example, La and 'Ce), and Ca may be added to steel containing the above elements as the main components. ~ Containing tb.ese elements does not im~air the effects of the embodiment, and, also, there ate preferable cases in which the strength or foimability is improved 15 ·depending on the amounts thereof. Specifically; the amounts are as follows: Ni: 0.05% ·~. 20 to 2.0%, Cu: 0.05% to 2.0%, Cr: 0.05% to 2.p%, Mo: 0.05% to 2.0%, B: 0.0001% to . 0.002%, Ti: 0.001%-to 0.1%, Nb: 0,001% to 0.1%, V: 0.001% to 0.1%; REM: 0.0001% ~ tci 0.1%, and Ca: 0.0001% to 0.1%. -· [0039] .•. ' ' A-ddition ofNi, ·cu, Cr, and Mo is not essential; however, in a case in which Ni, Cu, Cr, and Mo are added, similarly to Si, there is a tendency of delaying the generation of carbides, and remaining of austenite is helped. In addition, these alloy elements lower the martensite transformation start temperature of austenite. Therefore, addition cifNi~ Cu, Cr, and Mo is effective for increasing the fomiability or fatigue strength. 25 However, in a case in which the added amount of each of the alloy elements is less than --~20 . 0.05% ' -the above effects are not sufficient, and therefore ifis.desirable to set 0.05% as . · the lower li~it values of the added amounts of these elements. On the other hand, when the added amount is increased, since the effect of increasing the strength is saturated, and the deterioration rate. of the ductility is increased, it is desirable to set 2% as the upper 5 · limit. value of the added amount of each of" these elements. [0040] In addition, when the total added amount of elementS Ni, Cu, Cr, andMo exceeds 3.5%, since the hardenability of a steel material is increased more than necessary, . -- --~------~---.- .... ---- -·.- -· ... ---------. ·- ... -. '. . -.- .. ----- -- ···-- . ·--- ---- ...... -- . ·- ·-· ······-· ---.- it becomes difficult to manufacture a steel sheet that mainly includes ferrite and has a 10 favorable.formability,,and an increase in the costs for i:Jle steel material is caused. Therefore, the upper limit value of the total added amo\mt of the above alloy elements is preferably set to 3.5%. [0041] Addition ofB is not essential, but B is known as an element that increases the '!5 hardenability when added, and it is desirable to adcLO.OOOl% onnore ofB in order to delay the pearlite and bainite transfmmation when reheating is carried out for an alloying ·treatment. · However, when the added amount exceeds· 0.005%, since ·a ·sufficient area · · ratio of ferrite is not grown during cooling .f rom. t he tw<;l~phase coexisting temp'erature . .. ' ' ~ . ! ' I region of ferrite and austenite, and it becomes difficult to manufacture a steel sheet tliat 20 mainly includes ferrite and has a favorable formability, it is desimble to set 0.005% as the upper limit value, and it is more desirable to set 0.002% as the upper limit value . . [0042] Addition ofTI, Nb, and V is not essential, but these elements are effective for increasing the strength of a steel sheet since the elements form carbides and nitrides (or 25 carbonitrides), and strengthen the ferrite phase. i-J:owever, in a case in which the added ~' 21 amount of each of these alloy elemehts is less than 0.001%, the above effects are not sufficient, and therefore, it is desirable to set 0.001% as the lower limit values of the · added amounts of these elements. On the other hand, in a case in which more than · 0.1% is added, since an increase in the costs for a steel material is caused, the.effect of 5 . increasing the strength is saturated, and, furthermor~, C is unnecessarily wasted, it is 10 ·' ,. : ... 15 desirable to set 0.1% as' the upper limit value of the added amount of each of t)le elements. [0043] ..... -. ·----· ··-------···- ····--·--------------------- -----··· -··· .... ----- ···.·-- In addition, similarly, in a case in which Ti, Nb, and V are added in a total of more than 0.20%, since an increase in the costs for a st.e el material is caused, the effect of ' increasing the strength is saturated, and, f11rthermore, Cis unnecessarily wasted, it is desirable to set the upper limit value of the total added amount of these alloy elements to 0.2%. [0044] Addition of REM and Ca is not essential, but REM.anrl Ca ·combine with S so as. to spheroidize inclusions, B?d improve_ the cold workability or fatigue durability. ··However, in a case in which the added amount of each of them is less 1han 0.0001%, the· effects are not sufficient. Therefore, 0.000!% is set a~ the lowerlimit of the added . -· . • • . ! I amount. In addition, when these elements are excessively added, since the effects are · 20 saturated, and defects in welded portions are increased, the upper limit value of the added amount of each is set to 0.1 %. [0045] Next, the galvanoealed plated layer will be described. In the embodiment, the galvannealed plated layer refers to a plated layer that mainly includes a Fe"Zn alloy 25 generated by dispersion of Fe in steel during Zn plating, which is caused by the alloying • I ' 1 I i . ·.• c:---- ~~ ~-~-- =·=--=~=-:-:::~=---~>---'--- --- ----- ---=--]-- --- I 22 l F_-- reaction. ·111e amount of Fe Is set tb i% to 30%." Wheii an amount of Fe in the plate of ' . less than 7 mass%, there are cases in which a soft Zn-Fe alloy is formed on the plated smface, and the press fmmability is deteriorated, and, when the amoUllt of Fe exceeds 15 mass%, there are cases in which a brittle alloy layer is developed excessively in the 5 felTite interface, and the plate adhesiveness is deteriorated. Therefore, the amount of Fe is more preferably 7 mass% to 15 mass%. [0046] In addition, when galvanizing is carried out, since AI is added to a plating bath -. ······· .. ··--- ··--···---- ·--·-------· ............. ---·--·-··. ·····-··········---·-----~----. in order to suppress the alloying reaction in the plating bafu..0.01 %to 1.5 mass %of AI 10 is inclUded in the plate. This is because, when the adped amount ofAl is less than O.Ql %, Zn oxide-dominant dross is significantly generated on surface of the plating bath, and the appearance after plating is degraded.· Since the effect of suppressing the · generation of dross is saturated at the added amount o~ more than 1.5%, the upper limit was set to 1.5% from the vie\vpoint of manufacturing costs. The added amoUllt of Al is 15 ... , more preferably 0.05% to 0.50%, and still more preferably 0.10% to 0.30%: .In addition, since diffusion of Fe and diffusion ·of elements added to steel occur·at the same time in the pwcess of alloying, these elements are also included in the plate. [0047] .. · ,•, f . ' The adhered amount of the plate is not particularly linlited, but a single surface 20 thickness is preferably 1 ~or more, and more preferably 3 11m or more from the viewpoint of co!Tosion resistance. ·rn addition, the single surface adhered amount is preferably 20 11m oi less from the viewpoint of formability, w~ldability, and ~nomic efficiency. [0048] 25 Meanwhile, it is still within the scope of the embodinlent to plate a top layer or .· .·.•.··---------··~ -------------------·-.·-·-·-----·-····-~-----~-... ~~ 23 C!lifY out a variety of chemical conversion treatments, for exani.ple, a phosphate treatment, .a weldability-improvi.)lg treatment, a lubricity-improving treatment, or the like on the plated steel sheet of the embodiment in order to improve the painting properties and weldability. s· [0049J . The steel s)leet of the embodiment does not impair the effects of the ~mbodiment even when the total of3.5% or less of one or more ofPb, Sb, Si, Sn, Mg, Mn, N.i, Cr, Co, . _______ .. _ (";~~ < In addition, the .... ·····''"' 20 25 steel sheet of the embodiment is preferably a high-strength steel sheet in which the · ·tensikstrength TS is 490 MPa; and the relationship between the tensile strength TS. (MPa) and the elongation EL (%) satisfies '-I;S x .E L ~ 19000. Still more desirable is TS . I ~ 590 MPa, and most preferable is TS ~ 770 MPa and TS x EL~ 20000 . . [0052] In order to obtain more favorable fatigue durability, a microstructure having ferrite at an area ratio of 95% or more may be formed on the ~eel sheet side of the interface between the steel sheet and the galvruinealed plated hyer in an average thickness (arithmetic average) of 0.01 J.lill to 10 Jlm. [0053] •. ~--- I ' 25 :l ..... .. .~., ~_cc~cc7•L~.,_,_ . _~,,_~:_-_~ •,c;-·c_~·- ~·-·····------ol The reason why the fatigue aurabllity is improved by fanning the microstructure, in which the area ratio of ferrite is 95% or more, in the interface between the steel sheet and the galvanoealed plated layer is considered that this layer acts as a buffer zone. Since the galvannealed plated layer is hard and brittle, there are cases in which cracking 5 that have occurred in the galvannealed plated layer advances into the steel sheet due to load stress, and the steel sheet is finally fractured. On the other hand, when ~soft layer . ·,;.. (for example, a ferrite layer) is present below the galvannealed plated layer, the cracked -~~·;· fenite layer is defonned, and stress concentration is prevented, whereby it becomes ---·--·-·--------------·-···-··------··· --·- ...... ··-·--· -· - ·- .. ······-···--··-·.···--- ---········-- ···- -···. possible to prevent the cracking from advancing into the steel sheet. 10 [0054] As a result of investigating the_ relationship between the fatigue durability and microstructure of the galvannealed steel sheet using steels having a variety of components, the inventors found that, when galvanneafing is· ·carried out on a complex . . . structure steel sheet that includes ferrite as the major phase and has one or two of is martensite and residual austenite. at an m·ea ratio of 5% to 30%, more favorablafatigue durability can be obtained by foiming a microstructure in which the area ratio of ferrite is · 95% or more on the steel sheet side of tlie interface betweep. the steel sheet and the · galvannealed plated layer in an average thi~,kne~s 'of 0,01 1-1m to 10 1-lffi· . . I . , In addition, itis pat1icularly importantto set the area ratio of ferrite in a range of 20 1 1-1fU from immediately below the plate interface toward the steel sheet side to 95% or more in order to stabiy obtain the fatigue durability. When the ferrite layer is 0.05 1-1m or more separated fr.om the interface with the plated layer, there are cases in which. the fatigue durability is adversely affected. [0055] . 25 The reason why the average thickness of the microstructure'in which the area 26 ratio of ferrite is 95% or more is set to 0.01 J.Lil1 or more is that, in a case in·which the average thickness of the microstructure in which the area ratio of ferrite is 95% or more is less than 0.01 f1m, the effect of improving the fatigue duraqility is not shown. On the other hand, when the average thickness of the microstructure in which the area mtio of 5 ferrite is 95% or more exceeds 10 iJ.ID, t}l.e effect of improving the fatigue durability bewns to degrade. This is considered to be because; when the microstructure having lin·· area ratio of ferrite of 95% or more is thick, slipping that has occurred in the ferrite grain ... boundaries grow~ while repe.titive..stresses are. loaded, and, acts as. the."staiting.point oL ...... ·-·· .... _ ... . cracking. In contrast to the above, it is considered that, in a case in which the average· 10 of the microstructure ·in_ which the area ratio of ferrite is 95% or more is 10 11m orless, since the growth of slipping in graphite grains is significantly suppressed due to the influence of a compressive stress by the galvrumealed plated layer having a hard si.rrface, the slipping does not act as the starting point of ~racl4g. . That ;;, it is considered that ·forming a soft microstructure below the hard galvannealed:plated layer in an average of 15 ... --o·:tfi"flm to 10 ~can suppress 1:he occurrence ~d advancement of cnicklngiifthe ~ 20 . -du~ to the synergistic effect, and favorable fatigue durability can be obtained. More . .. .. . - .. -.' ' . ·-·' .. -... . . preferably, when the average thickness of the microstructure in which the area ratio of fen-it~ is 95% or more is set to 3 !l!p- or lesS~ the-fatigue;dur~bility is more stably improved. (0056] Therefore, a higher area ratio of ferrite increases the effect of iniproving the : fatigue durability, and it is desirable to form a microstructure in wbi~h the area ~atio of ferrite is 98% or more in an average thickness ofO.Ol11m to 10 11m. In addition, since . . . the thickness of the microstructure in which the area ratio offeriite is not less than 95%. I I 5 10 15 I__ " c-~ ·-·- --------- -------- _ ................. ---------- ----·--~· ..... ..... I 27 or ·not less than 98% is affected by tHe thickness of the plated layer, the thickness of the microstructure is preferably twice or Jess the thickness of the plated layer. The thicklless of the microstructure is still more preferably 0.1 1-1-m to 8 1-1-ffi· [0057] In the embodiment, a method of manufacturing the microstructure in which the area ratio of ferrite is not less than 95% or not less than 98% is not particularly limited as. long as the microstructure is formed on the steel sheet side of the interface between the_ In order to ni:ore reliably improve the fatigue durability, the area ratio of ferrite ·in the steel sheet portion inrmediately below the interface of the plated layer, particularly, in-tbe portion at a depth of 1 ]-LID or Jess from the interface with the plated layer iS more preferably not Jess than 95% or not J~ss than 98'?(. [0058] 'The microstrUcture in Which th6' area ratio of ferrite is not Jess than 95% 'of'nOf'-: less than 98"/o can be :formed on the smface layer at the same time when a thermal max:imum area ratio, and one or more of bainite, martensite, and residual austenite mixed • I , · therein, as long as a Fe layer having a low carbon concentration is formed 6n the surface 20 layer of a high-stren~ steel sheet before annealing. [0059] . . In addition,- the microstructure in which the area ratiQ of ferrite is not less than 95% or not less than 98% can be easily observed from a cross section. FIG. I shows the results of observation of a cross section of a representative steel sheet after etching using 28 an optical microscope. Since the nl.icrostructure in whl6h the:" area ratio offerrite is not less than 95% or not less than 98% has a characterisii.c that ferrite grains significantly , grow compared with the complex structure that includes ferrite as the major phase and has one or more of bainite, martensite, and residual austenite mixed therein, the 5 microstructure can be easily partitioned using an optical microscope. Furthermore, in a case in which the fraction of the inside structure is obtained, the fraction can ~e obtained by observing the structure using an "SEM or TEM. [0060] A method of manufacturing a multi-layer steel sheet having a Fe layer having a 10 low carbon concentration formed on the surface layer \s not particularly limited. It is possible to fonn a Fe layer having a low carbon concentration on a slab or the steel. sheet surface layer by a variety of methods, such as rolling, explosive bonding, decarburizatio11, overlaying, cast boning, and the like. . TI1e cheapest urethod is the addition of Fe only to ' tl).e surface during continuous casting. That is, firstly, a direct current magnetic field '15 that traverses the thickness of a slab is applied to molten steel fed in a continuous casting_· mold at a location below the meniscus in the casting direction so as to form a direct · · current .m agnetic field zone. ·Mol. ten steel is supplied to a·molten steel pool on the top.· side and a molten steel pool on the bottom _s.ide !hat are_ partitioned by the direct current ' ' ! ! magnetic field through two nozzles having different lengths, and the molten steel is ' 20 solidifted and drawn to carry out continuous casting. In the continuous casting, the 25 concentration of Fe is increased only in the surface layer portion by adding Fe to the molten steel pool on the top side. As a method of adding Fe~ a wire-shaped Fe or Fa alloy and the like can be continuously supplied. [0061] The slab of the mnlti-layer steel sheet cast by the above continuous casting I l -~-~-- 0 -~~- :-:---c::--r--r:: _-_-:::=-::-~ ~-~~-~- -------- - _-_-__ :_:_-:::-=:' __ ':--- -5 -------- - -·-~-----~--~~~---~-···- . ····-·--·~··--·-·-·--·····-···---·--··-----~--~·""'-''-·"'= 29 method is processed into a thin sheet·by an· ordinary hot rolling or cold rolling method, and then plated in a continuous galvanizing line. A niethod of manufacturing a plated steel sheet is not particularly limited, and an ordinary non-oxidation furnace or all - radiant-type galvanizing method can be applied. [0062] Furthennore, the steel sheet of the embodiment sufficiently exhibits the effects with no regard to whether the steel sheet is manufactured into a cold-rolled steel sheet or ~-; rIi I I _. -~ __ --~ .. ___ h?t-~~lle~ ~~~~l s~~~~ ~Y 811. o!~i~ proc~s, _and_ !lJ.e. e.tt:~~t~ do not sj~?.cm.-~ly ~Ill).'- . _ ... _ .. _ I with the history of the steel sheet. In addition, in the embodiment, the thickness of the .......... :•.: 10 steel sheet does not impose any limitation on the emb~diment, and the embodiment can be applied as long as the steel sheet has an ordinarily-used ·sheet thickness. The ordinary sheet thickness is between 0.4 nun to 3.2 rom, but is preferably between 1.0 mm to -3.2 rom in consideration-of the load of a rolling mare or productivity~ [0063] '15 ln addition, the hot rolling-conditions, the cold rolling conditions, and the like 20 may be appropriately selected according to the dimensions and necessary strength of the steel sheet, and the effects of the steel sheet of the embodiment are not impaired by the· · hot rolling conditions, the cold rolling conditions, and tjl.e l~ke. . . - . ....~ . . . ' [0064] I' In addition, when annealing is carried out in an in-line annealing type continuous galvanizing line, the annealing conditions are that the steel sheet has a complex structure in which ferrite has the maximum area ratio, and one or more of bainite, martensite; and residual austenite are mixed as the microstructure, and the .,' selected conditions enable the obtainment of a complex structure in which the area ratio 25 of one or two of the martensite and residual austenite is 5% to 70%. ·--------------- 30 [0065) .. ',_I,,:, .... ;, o ,,,;, ·- ,• ,. 1'- o • ' Specifically, annealing is carried out in the two-phase coexisting region of ferrite and austenite of 700°C to 850°C, and cooling is carried out from the peak temperature to 650°C at an average rate of 0.5°C/s to 1 0°C/s, and, subsequently, from 650°C to the 5 platlng bath at an average rate of 1 °C/s to 20°C/s. As described above, as long as an Fe layer haying a low carbon concentration is formed on the surf~elayer of the - -high-strength steel sheet before annealing, at the same time, it becomes possible to form _______________ a rnicrostructut:e. in which the .area ratio _of:ferrite_is not less than 95% or not less _than 10 98% on the surface layer during the thermal treatment._ [0066] As the temperature of the plating bath for galvanizing, the condition in the rela:ted art may be applied. For example, the condition of 440°C to 550°C can be applied.·. 'fu ad_f_-_1~~0 _t~~_s _t()} 9_0900 _t!!lles .. _ after a cross section of the steel sheet in a rolling direction or a cross section in the right 10 .angle direction of the-rolling direction was etched using a Nita! reagent and the reagent as disclosed in Japanese Unexamined Patent Application, First Publication No. 859-219473. · In addition, the kind and volume of the microsh'UCture in the inside and_ surface layer of the steel sheet were also observed using a FE-TEM haying a magnification of 10000 - - . times to 1000000 times after a cross section sample was manufactured by the 15 FIBfl-sarnpling method. Twenty or more sites were observed in: each of the samples. In addition, the area ratio was specified by the point counting method or an image analysis.- -The average thickness 'of the microstructure in which the'iirea ratio of ferrite.- was 95% or more was also, similarly, obser.ved ~sing an.optical microscope having a - I ' magnification of 400 times to 1000 tinles and a 8EM having a magnification of 1000 20 times to 100000 times after a cross section of the steel sheet in a rolling direction or a cross section in the right angle direction of the rolling direction was etched using a Nita! reagent arid the reagent as disclosed in Japanese Unexamined Patent Application, First - - Publication No. 859-219473. In addition, th.ethickness of a thin sample was also observed using a FE-TEM having a magnification of 10000 times to 1000000 times after 25 a cross section sample was manufactured by the FlBfl-sampling method. ! I I I [0077]. .. . I· • ---_:----1 -_-__ ::---::._----- 36 The fatigue durability was evaluated using ratios of fatigue limit to tensile strength (fatigue ratios). In the specification, the ratio offatigue limit to tensile strength is a value of the 2 x·107 time strength, which is obtained by .carrying out a fatigue test 5 according to TIS Z 2275 on No; 1 test specimen as defined in JIS z·2275 having a parallel portion of30 mm, a sheet thickness of2 rnm, and a radius curvature oflOO mm, . divided by the tensile strength. Steel sheets having a ratio offatigue limit to tensile _ ..... _ --· ·-. .. . . _sl!.ellgth ahoy~ ~· 7:- 0. OO_D3 x TS were eva~uat~d. I >!.;:1-:: :, I I I I '.'.1. :w.j• i I" ! f: i I:! ,' ,:1 I ,, -:-: ;c I Table 1 ( 2 / 2) Symbol Ni A B c D -E F G H I J K o.so L M N 0 ·p Q R s T u v w X y z A2 ·. Cu Cr Me ' 0.80 ' •. .• 0.80 0.60 . 0.4~ 0.50 .. 0.20 0.60 Chemical components (mass%) Nb Ti v Ca ' i ' ' ! 0.02 ··-. . . 0.02 0.02 0.02 . 0.01 0.05 ·. 0.003 ' : 0.02 ' 0.01 0.02 I 0.02 0.01 ' 0.03 0.04 O.Q2 ' ' ' REM B ' 0.01 0.002 0.001 ••-.· -,-,- ·-,; ; ,-,.,-~-·,.. -.-,.-,' ---~ ,r~,, ,..- -~,--- r 'tl.' ,., ''·:· i:·: i 1 •:· : ' ,. r,: -_-_--_-:: -_:_:_: .:.::-:-:-~-~~~~~ :.=~-:: , -:, ccc ccc' <~ccc=cc=·cc=ccc~::.-.cc~cc'-'- ,-:C:C~_,.'='==~~~--·,=,c;=·;_=c_:=c,:-.,_.-Cc_..- :..~:.· ~,,=:·-:.:c--c..= ,_c-::?"'cc-::.:•_.~- _ -.c·=-•c·_,•·Ccccy -·-·····---- - ---- ----------------·--···-------------------.-.:~:.-. -----~-:-::---~-~~---=-- .-. ~~:-: .. ··::-.----- . 8 d I. ·-· ·-------.... ------- ·------------~----- . ~_. ................ , ........ .. · ·'• I I ~- ~ ·.'~ ......,.' Table 2 ( 1 I 2) Steel sheet material properties Microstructure in lhe steel sheet Finthes~e No .. Steel sheet yp TS E1 F B M Other . M+y . layer symbol r (MPa) (MPa) (%) (%) (%) (%) (%) (%). (%) (%) l A 371 607 33 91 9 9 97 2 B 395 604 38 89 5 l 5 6 97 3 c 448 805 :28 78 10 2 10 12' 95 4 D 389 621 36 90 4 2 ' 4 6 98 5 E 427 788 27 . 84 " 15 1 16 95 6 ·F 462 824 31 08 11 11 11 93. 7 G 485 812 ,29 74 12 2 12 14 94 I 8 H 735 9.07 ·33 '65 16 3 16 19 91 9 I 764 976 33 61 18 3 18 21 91 !0 J 471 777 27 82 " 18 18 95 ' II K 589 961· ·23 77 ·_ 23 23 92 .J: U1 12 r.: 581 89~ 23 78 22 22 91 13 M 595 916 . 23 75 24 1 25 92 14 N 587 924 .24 .74 24 ' 2 26 93 '15 0 534 '822: 26 . 82 18 • 18 95 . 16 p 531 817 26 82 18 18 94 17 Q 558 858 24 82 ., 18 18 92 18 R 537 826 ·25 82 18 18 95 19 s 472 781 27 82 18 . ·18 94 20 T 468 778 27 82 .. 1.8 !8 95 21 ·u 548 .. 843 .25 79 21 21 94 22 v 570 877 •24 79 21 21 93 23 w 597 918 23 78 22 ·' 22 93 24 X 573 •882 '24 80 20 20 93 ·25 y .607 934 ·22 77 23 23 92 26 z 694 1069 19 --__ 74 .. 25 1 ._ 26 91 -- - --- --·- ---- .--.... -., ,-....... -.- -1'~-- :~~~ -~" ,-,:::;~.::~"';~-- . .:;;;::;-:··:: ,-.,- ''·{··;··· 27 A2 296 423 :38 100 28 B2 321 459 '34 90 29 C2 308 431 35 91 30 D2 441 816 26 82 31 E2 555 843 25 80 32 F2 578 906 24 75 ~· ' ''•- l 9 9 1 18 19 l 23 2 '' ----,- ,-,,-,-. ·--.-.,-.;;-- --.-.-- - 0 0 0 ' 18 20 25 99 99 99 96 92 93 I J::l "' ' : I I I ~.~.~- · ~oc· ::~c-cc.=ccc•,c:•-···-·· ,: ..... ::cc:r i!'i':·:' I !::. Table 2 ( 2/ 2) Thickness of1he No. Steel sheet Surface layer C surface layer symbol (mass%) (!'Il1) I A 0.022 0 .2 B 0.035 0 3 c 0.037 3.8 4 D 0.020 0 5 E 0.033 4.1 6 F 0.041 8.6 7 G 0.045 5.7 8 R 0.059 1.2 9 I 0.062 9.4 10 J 0.026 0.8 11 K 0.02.7 ' '· 6.1 12 L 0.031 . 5.9 13 M 0.028 2.2 14 N 0.027 7.8 15 0 0.024 : 0.5 16 p 0.028 4.6 17 Q 0.029 1.4 18 R 0.024 9.5 19 s 0.030 3.7 20 T 0.027 8.3 21 u 0.026 4.2 22 v 0.027 7.6 23 ·W 0.027 . 6.8 24 X 0.027 ·- 2.9 25 y 0.028 8.4 26 z 0.025 3.5 Nano hardness Fatigue ratio Steel sheet inside Smface layer .. (GPa) (GPa) 0.57 3.02 2.74 0.57 3.01 2.71 ' 0.51 4.17 2.81 0.56 3.05 ' 2.67 ' 0.51 4.00 2.82 • 0.5 4.39 2.87 ' 0.49 5.04 2.83 ' 0.48 5.65 2.94 • 0.46 7.16 2..93 ' 0.51 3.90 2..78 ' 0.48 5.64 2.91 ' ' ;· 0.48 5.37 2.94 : ; 0.48 5.81 2.93 I 0.47 5.97 . 2.89 0.49 4.36 2.79 • 0.5 4.30 2.84 0.49 4.83 2.90 0.5 4.41 2.81 0.55 3.93 2.85 0.55 3.91 2.8 0.5 4.63 2.83 0.49 5.12 2.89 0.47 5.85 2.87 0.49 5.20 2:88 0.47 6.17 2.89 0.43 10.08 2.94 ==--~- .. --- Surface layer! inside Note I ! 0.91 Comparative example I 0.90 Comparative example 0.67 Invention example 0.88 Comparative example 0.71 Invention example 0.65 Invention example 0.56 Invention example 0.52 Invention example -- 0.41 Invention example 0.71 Invention example 0.52 . Invention example· 0.55 Invention example 0.50 . Invention example 0.48 Invention exauiple 0.64 Invention exarnp le 0.66 Invention example 0.60 Invention example 0.64 Invention example 0.73 Invention example · 0.72 Invention exmnple 0.61 Invention ex~ple 0.)6 Invention example 0.49 Invention example 0.55 Invention example OA-7 Invention example 0.29 Invention example --------- .I: "!-I 27 A2 28 B2 29 'C2 30 D2 31 E2 32 F2 0.007 0.018 0.019 0.048 0.031 0.0~-- L.... . .'· ·o . 0.61 2.83 0 0.59 2.85 ·o 0.62 2.84 o.o-s . 0.45 . 4.03 11.7 0.44 4.75 -0 ---L____0-42_ 5.87 .:_ 2.66 ' 0.94 2.66 0.93 2.65 ' 0.93 2.99 0.74- 2.51 ; 0.53 4.59 - 0.78 Comparative example , Comparative example Comparative example ~ Comparative Cxample ~ Comparative example; Comparative example _ --~7~- ( ·•! i _j .j ~ - ..t" 00 1:< ::, :: I i :-:: I 1': I : '' ::::'"''' '"' •--,,""•,-••-.,,-, -.·-,,,•,r ...t..! 0) i ' ! ' ~ i I Table 3 ( 2/2) Surface Steel sheet layer C No. symbol (mass%) I J - 2 J 0.490 3 J 0.Q26 4 J 0.024 5 J 0.025 6 J 0.027 7 J 0.026 8 J 0.026 9 J 0.026 10' J '0.026 11 J 0.026 12 J - 0.026 13 J 0.026 14 J - ·.0.026 15 J - 16 J 0.026 17 J 0.026 18 J 0.026 Plate Present Present Present Present Present Present Present Present Present Present Present Present Present Present Absent Absent Absent Absent _! .. ·.~:-:· •.;.:·.·:::-. ~·:.:: ·. Fatigue ratio - 0.42 0.48 0.5 0.51 0.51 0.51 0.52 0.52 0.52 0.52• 0.49 0.45 0.5 0.44--- 0.47 0.46 0.45 0.44 .... Nano hardness Steel sheet inside Surface layer Surface layer(mside (GPa) (GPa) : 3.90 - I - 3.89 2.78 ! 0.71 3.91 2.77 0.71 3.88 2.79 0.72 ~.90 2.78 0.71 3.89 2.78 0.71 3.87 2.79 0.72 3.9 2.80 0.72 3.88 2.77 0.71 3.86 2.78 : 0.72 3.92 2.78 0.71 3.87 2.79 0.72 3.89 2.76 0.71 3.90 .2.78 0.71 3.96 ·, - - 3.95 2.77 0.70 3,96 2.78 0.70 L___ __3_:9±_ - 2.76 .L. 0.70 '· Note ,;1 :I Comparative example 1 Invention example Invention example ·I Invention example Invention· example Invention example Invention example Invention example_ Invention example Invention example Invention example Comparative example Invention example Comparative example Comparative example Comparative example Comparative example Comparative example - TJ"l~ 0~ j ! 1 •I ~ i' Q ;, ! ! ! ~ ~ ~ !, T-- I' i I I '" __ ,_,_,,, ..... ~- .. ·.··~'"'-''-'-""-'-' ··~-......... .,._ ~··--····~······• . ' , . • Table4 Steelsheet No. S1 S2 S3 .S4 85 S6 87 88 S9 -S10 Sll S12 . . . S1~. ' .. - Sl4 SIS S16 817 . 818 819 820 821 822. 823 824 S25 826 827. 828 829 830. C in steel(%) 0.10 0.15 0.20 0.25 0.30 0.40 0.50 0.10 0.15 . 0.20 0.25 0.30 ... 0.4_0 . - 0.50 0.10 0.15 0.20 025 0.30 0.40 0.50 ·0.10 0.15 0.20 0.25 -- 0.30 0.40 0.50 ·0.20 0.05 51 Si in ~tee!(%) 0.01 0.10 0.10 0.10 0.50 0.50 0.50 1.00 1.00 1.00 2.00 2.00 . . f1.oo . . - O.QJ 0.10 0.10 0.10 . 0.50 0.50 0.50 1.00 1.00 1.00 2.00 2.00 2.00 O.QJ 0.10 ' 1:20 . 0.10 ,.· Mn in steel(%) 0.50 0.10 0.50 1.00 2.00 3.00 0.01 0.10 0.50 1.00 2.00 3.00 . .. ()_.0)- .... 0.10 0.50 - 1.00 2.00'. 3.00 0.01 0.10 0.50 l.OOf 2.00' ' 3.00 0.01 0.10 0.50 1.00 1.50 0.50 .·, Sheet thickness t (mm) 1.20 1.60 1.80 2.00 2.30 2.70 3.20 1.00 1.60 1.80 2.00 2.30 . ···-· - . - 2.7Q .. ·- . - 3.20 1.20 1.60 1.80 2.00 2.30 2.70 3.20 1.20 !.60 1.80 2.00 2.30 2.70 3.20 !.00 1.80 .· ·' ' .... -.-L .. •' -.. ,_,, -, ,.,-· ' - .. -~ If Table 5 (.1/3) Steel sheet Plate No. Hydrogen during Ajmealing temp: ("C) No. annealing(%) Ml SI J 800 M2 S2 2 - . 900 M3 S3 4 &50 M4 S4 6 800 M5 S5 8 750 M6 S6 10 700 M7 S7 l 650 M8 S8 4 900 M9 89 6 850 M\0 810 & 800 Mil S!l 10 750 M12 Sl2· 2 700 ' Ml3 SJ3 4 650 Ml4 Sl4 6 900 MIS SIS 8 .. 850 Ml6 Sl6 10 800 Ml7 Sl7 2 750 Ml8 SIS 4 700 Ml9 Sl9 6 ·- : 650 M20 S20 8 900 : M21 • S21 10 850 M22 S22 2 ' &00 1 M23 S23 3 900 M24 S24 5 &50 ' M25 S25 7 800 M26 S26 10 750 M27 S27 5 700 M2& S2& 10 650' M29 S29 5 •. 750 M30 S24 · 5 500. M31 S25 5 600 . . Dew point during annealing ("C) 1 5 10 15 20 25 30 40 50 l 5 10 15 20 25 30 40 . 50 1 5 10 15 20 25 30 40 50 30 -20 -2 60 Plate thicknOss (}liD) AI in plate (%) I 2 : 0.39 6 0.45 8 . ' 0.37 10 ' 0.41 12 . 0.46 6 . 1.18 7 : 0.34 8 . 0.63 10 • 0.38 6 0.47 7 : 0.36 8 : l-14 9 - 0.49 I 10 . 0.37 _j 6 0.31 7 '0.35 8 0.33 . 9 ; D.44 10 . o.n 4: 0.42 I , 0.47 20: 0.36 . 6 I 0.37 7 : 0.45 8 ' 0.34 ' 9 • 0.38 !0 : 0.49 6 ! 0.35 7 ; 0.36 8 : 0.4 9 . . 0.39- I ··--... ---~ ~ '·-·,-.-·,., -.~., -" ,-..·..- .- ,-,-.,C ~'C'i ·~·""'"''- •-.-.-.-.-,, -- ~ I' ' ! I 01! !" -·--.-... ---,- (': !···· M32 526 5 M33 S26 0 M34 525 3 M35 S27 20 M36 530 5 M37 S30 20 .- 800 85Q 920 .. 800 800 800. '• \:lg/ " .. '!' ·~ 'i -40 10 ~ 2 6 . 65 7 . -20 8 : -20 9 -20 10 •---- - c,-, ---•• 0.47 0.53 0.51 0.44 0.42 ' ·0.43 ·-,,,-, -,,,-.,, ~("'".".,"-··,-,,,~,-.-. ,"":~" •,-,,-.,-,,-- c-,-.-.. ~'C--;;'''c :; U11 <..:N~ I I I I. I I I ! Table 5 ( 2 f 3 ) Plate No. Steel sheet No. D (JJ.m) d (J.lm) Ml Sl 0.16 0.09. M2 S2 0.62 .0.38 M3 S3 1.35 0.9 M4 S4 1.5 1.2 M5 S5 1.46 1.42 M6 86 2.8 1.8 M7. ·S7 5.6 3.6 M8 S8 2.5 2.6 M9 S9 16 4.2 MIO SIO 4.9 ~.1 Mil Sll 1.05 1.1· M12 512 51- 1.4 M13 813 3.5 3.7 Ml4 S14 3.9 4.5 MIS SIS 1.3 • • 1.5. M16 S16 2.2 . !'.6 M17 S17 2 3.2 M18 SIS 7.2 4.4: M19 819 4.?:' -- 3.& M20 S20 3.7 2.8 M21 821 5.2 4.8 ' M22 S22 8.3 8.1 . M23 S23 4.4 4.3 M24 S24 8.2 6.7. M25 S25 100 16. M26 526 9.5 12 M27 S27 2.2 3.4 M28 S28 23 . 2.3 M29 529 - - M30 · 524 I 0.85 M31 825 . '--20.5 8.5 - ·Tensile test value Evaluation of hydrogen TS (MPa) El (MPa) embrittlement resistance 783 .: 13 3 827 ° 15 3 856; 18 3 918 20 . 3 1064 18 3 1249 17 : 4 1580 6 4 805 Is ·5 833 24 .. 4 861 27 .4 932 25 4 1027 22 4 1629 6 5 1573 4 5 795 13 4 816 ' 12 5 988. 10 5 1204, 8. 5 1550'' 5 5 1591 5 4 !642 6 5 812 25 5 930 22 5 979 22 5 1375 7 5 1561·. 6 4 1597i· 5 5 1606~ . 6 5 978; 20 . 1 1042 22 I . 1359 7 . I ';.' :o C in surface layer (mass%) 0.028 0.043 0.053 0.063 0.214 0.116 0.128 0.029 0.041 0.052 0.070 ' 0.086 0.114 0.133 . 0.025 0.041 ' 0.058 0.064 . 0.089 ' 0.108 0.130 ! 0.028 ; 0.045 0.057 0.066 ' 0 .. 075 ' 0.!10 : 0.145 - ' 0.059 ' 0:068 - I ·: ·-... -..-. . -...- .... -.,. ---, ·, "~"'·:.--.-.-.·.. - .- .-,, ~~ _, - ,.,._-.- .-.--;n;--;;---,. ~' "'''' ..I;~ ~ ~ i ~ I j l j 1 i j ·.~ .:::._:r ~I ,i::; ( .. :.:· ~ ' ' i I I " !'' -M32 S26 0.51 - M33. S26 0.02 0.1 M34 S25 228 . 6: M35 S27 . - - M36 S30 o· 1.3 M37 S30 0 - . '· -- 1594. 6 -1 1585 6 1 1408 7 1 1616 5 1 453- 36 5 447 36 5 ,, 0.256 0.238 0.064 : - 0.016 . '0.017 "\J"\' 1',',' 1:: Table 5 ( 3 I 3) Steel sheet Plate No. No. Steel sheet inside (GPa) Ml Sl 3.95 M2 S2 4.42 M3 83 4-.80 M4 54 5.85 M5 S5 9.89 M6 S6 ']1.80 M7· S7 14.10 M8 S8 4.17 M9 S9 4.50 MlO SlO 4.88 Mil Sll 6.13 Ml2 S12 8.62 Ml3 · S13 14.30 M14 S14 13.90 MIS SIS T ·~. 4.07 Ml6 S16 . 4.29 M!7 S17 7.47 M18 Sl8 11.90 M19 519 .> 13.70 M20 520 13.80 M21 . 521 14.00 M22 S22 . 4.25 M23 S23 6.@9 M24 524 7.23. M25 .S25 13.40 M26 S26 14.20 M27 S27 . 13.90 M28 S28 14.10 M29 S29 . 7.21 M30 S24 9.11 M31 S25 12.70 Nano hardness Surface layer ( GPa) SUrface layer/inside . 2.86 0.73 2.37 0.65 2.84 0.59 . 2.85 . 0.49 3.00 0.30 3.50 030 4.18. 0.30 2.87 0.69 2.84 0.63 2.84 0.58 2.93. 0.48 3.04 0.35 6.06 0.42 4.50 0.32 ·. 2.78 0.68 2.84 0.66 2.99 0.40 3.03 0.25 5.78 0.42. 4.85 0.35 4.77 0.34 . 2.85 0.67 2.97 0.49 2.97 0.41 3.53 0.26 3.93 0.28 5.14 0.37 6.12 0.43 2.90 0.4-0 . 3.03 0.33' 3.56 0.28 . Note lnvention example Invelltion example !nventioh example Invention example Invention example Invention example· I Invention example Invention exam?le Invention example ' Invention example I~ention example Invention example Invention example Invention example Invention example Invention example Invention example Invention example Jnvention example Invention example Invention example Invention example Invention example Invention example Invention example • Inven_tion example InveU.tion example Invention example Comparative example Comparative example Comparative example lJC' "~'TC'•, ,-..- ·.~ -.- ,-.. -.. ~, .. -.. ,-,,.-..- ,-.- -,;·--.- -.,~ -.~ .-,- - i i I . ·../ ' ' . '· M32 826 M33 -826 M34. 825 M35 827 M36 830 M37 830 .- ' •'· 13.80 !3.90 . !3.10 14.30 2.84 2.84 4.44 5.29 3.% 6.60. 2.65 2:66 ·.-;-~ ,0.32 Comparative example 0.38 Comparative example 0.26 ComParative example 0.46 Comparative example 0.93 Comparative example 0.94 Comparativ~ exam~l~ -- -- ____ .. ---.-..- -- ------.--. ,.--~~ ' -.-.-. --- \11 -tJI -----r--- !·: I I I ! !::· - --_---- -----·-·-·--·------- :·:--::-:c-:-:-:-_-:-:----::~:o_-_-l_ __________ ----- :-: __ :::1 -T 58 /II Table 6 Steel sheet No. C in steel (%) Si in steel(%) Mn in s(eel (%) Sheet thickness t (rom) 81 0.10 0.50 0.01 1.20 S2 0.15 0.005 0.10 1.60 83 0.20 0.10 0.50 1.80 S4 0.25 0.10 1.00 2.00 ss . 0.30 0.50 2.00 2.30 86 0.40 0.50 3.00 2.70 S7 0.50 0.50 0.01 . 3.20 . 88 0.10 1.00 0.10 . 1.00 .. 89 0.15 1.00 0.50 1.60 I SIO 0.20 1.00 1:oo 1.80 811 0.25 2.00 2.00 2.00 I 81;2, 0.30 2.00 3.00 2.30 813 0.40 2.00 O.ol 2.70 Sl4 0.50 0.01 0.10 - 3.20 SIS 0.!0 0.10 0.50 1.20 816 .. o:)5 0.10 1.00. 1.60 817 020 0.10 2.00 1.80 818 0.25. 050 3.00 2.00 S19 0.30 0.50 O.ol 2.30 '820 . 0.40 0.50 0.10. 2.70 821 . 0.50 1.00 o.so 1 3.20 822 0.10 1.00 1.00' 1.20 823 0.15 1.00 2.00 !.60 824 0.20 2.00 3.00 1.80. 825 0.25 2.00 0.01 2.00 826 0.30 2.00 0.10 2.30 827 0.40 0.01 0.50 2.70 S28 .. 0.50 0.10 !..00 . . 3.20 S29 0.20 1.20 1.50 1.00 S30 0.05 0.10 0.50 ·'• 1.80 - :>: I) ~: ·~ '---'---' ,;·,.~ ; Table 7 C-1/3) .. ' i~ '·( ' Plate No: Steel :sheet.No. Hydrogen during Annealing temp.· Dewpoint~g Plate thickness AI in plat9 Fe in plate aonealing (%) ("C) . annealing ("C) (J.Ull) (%) (%) ~ Ml Sl 3 .. 800 1 2 . 0.20 5 .::i i1 M2 82 I . 900 5 6 0.25 7 :~ • M3 S3 3 850 10 8 0.19 12 '?: M4 S4 5 BOO 15 ' 10 . 0.20 10 j M5 . S5 7 750 20 IZ· 0.25 . 12 M6 S6 10 700 25 6 . 1.00 5 M7 · S7 1 650 30 7·' ' 0.01 15 MB . S8 3 900 40 8 0.50 5 ~ j il II ~ M9 S9 5 850 50 10 0.20 }0 i M10 SJO 7 BOO I 6 0.25 . I) Mll 811 10 750 5 7 0.19 12 M12 812 I . 700 40 8 !.00 10 I ; ':1 MJ3 S13 3 650 15 9 0.25 12 I 'l Mi4 Si4 5 900 20 10' 0.19 10 VI '.JZ) MIS SiS 7 I ~, B5b 25 6 0.01 . 11 Mi6 S16 10 . 800 30 7 0.05 : 12 Ml7 817 1 750 40 8 0.20 10 M18 SIB 3 700 5Q 9 . 0.25 . 12 M!9 Sl9 5. .- 650' 1 10 0.19 ' 10 .. M20 820 7 900 5 4 0.20 11 M21 S21 10 850 10 . 1 0,25 I 12 .• M22 S22 1 800 15 20 0.19 . 10 M23 823 3 900 20 6 0.20 12 . M24 S24 5 850 25 7 0.25 ; 5 M25 825 7• 800 30 8 0.19 . 7 ,1, M26 S26 10 750 40 9 0.20 ' 12 M27 827 5 700 50 10 0.25 ; 10 M28 S28 10 650 30 6 0.19 : 11 M29 S29 s· 750 -20 . 7 0.18 . !0 M30 S24· 5 500 -2 8' 0.20 J1 M31 S25 5 600 60 9. 0.20 ' s· i:.: I I 1:., ~-· - - - -- - - ----- --·- ,- ,•·n-,- ,. -,, -..- - ...-... -....... ·--.-.-.... -.. -, M32 826 M33 826 M34 525 M35 S27 M36 S30 M37 830 5 0 3 20 5· 20 .. ' &00 &50 920 . 800 &00 . 800 ~.·~ -40 10. 2 6 65 7 -20 8 15 9 . ·20 10 0.24 5 0.30 ; 0.05 0.30 10 0.22 : 10 0.22 ' 10 0.22 10 r::,. ~:yfJ ' '· ~~ ~ ~ t; -.. ~ r:: ~ H :'- i i.': \~_ r ·~: .,, , r:~ 'f: 1:; 0"\r 0 :•. j) ';j ;.i il :: ~ ;oZO¥ '" ""g;;: ,,. o ... ,.-~:s,.., .• ..,c .. ::s., ~,·.~W!iliiQiiliJllili;)Jf!jjji._;,•i':.' . ._-,;, :,.·:,:, i 1. :_: '' I /" ( ' r~,-,:' ,. .:,· ~ :: ';: ,. h I' [ I i' i~ 1~ ->- Table7 (2/3) Plate No. Steel sheet No. PC~)_ M1· Sl 0.1 M2 S2 0.2 M3 S3 0.4 M4 S4 0.5 M5 85 0.1 M6 S6 2.5 M7 87 4.5 M8 S8 2.1 M9' S9 15 MlO SJO 4.2 Mil Sll 0.2 M12. 812 50 Ml3 513 2.4 MI4 814 '3.8 MIS SIS ' ·~- 0.6 MI6 Sl6 1.4 Ml7 SJ7 1.2 . ' ·MIS 818 6.1 M19 SI9 :-3.2 M20 S20 3.3 . M2! 821 5.1 M22 S22 6.3 M23 S23 3.7 M24 824 7.8 M25 8~ !00 M26 826 8.4 M27 827 1;2 ·M28 828 1.6 M29 S29 .. - M30 . 824 0.!6 M31 825 20 d~) . -- 0.2 0.3 0.025 1.5 2.5 2.2 3.2 2.4 0.3 0.4 2.6 4.4 0.8 0.8 2.4 3.3 2.8 2.4 4.7 6.1 3.6 6.3 15 11 2.4 1.6 " O.Ql 8 -~a~ Tensile tost value TS(MPa) El (MPa) 783 13 827 15 856 18 918 20 .< 1064 !8 1249 17 1580 6 805 15 833 24 . 861 27 .. 932 25 L027 22 1629 . 6 1573 4 795 ]3 816 12 988 10 1204 8 1550 5 1591 5 1642 6 .812 25 930 22 979 22 1375 7 !56! 6 1597 5 !606 6 978 . 20 - -~ 1042 22 1359 7 C in surface layer (mass%) 0.028 0.043 0.053 0.063 0.214 '. 0.! 16 ' 0.!2,8 0.030 0-041 0.052 0.070. 0.087 ;· 0.114 0.133 0.025 ' 0.041 0.058 0.064 0.085 ' . 0.!08 ' 0.!30 0.028 0.043 0.057 . 0.066 ' O.o75 0.110 0.!45 ' - 0.059 I -' 0.068 ! ' -·.' r·.~~-" (I' 1 -c.·..~. ~ ... -.. ~-•. ,_.,,, ,.,, __ .., =;:••..-.. -.-. ~,,..,,,~- I i:· ~· I ,-,1 M32 S25 O.Ql - . 1594 5 0.255 M33 ' S26 0.02 0.1 1585 6 0.238 M34 S25 22 5.2 1408 7 0.064 M35 S27 - - 1616 5 - ·::'·': ,/,i: M36 S30 0 0.3 453 36 0.015 ' M37 S30 0 - ' 447 . 35 0.017 1- ::·,:,, . l i ·;_· ::·:: I . ' I (I' I . l·i 1'-' ·- ;: ,'· !:''::I i,:::-',1 -- .''.'.I :.;:i l '·· . ~~--.. ~- --c-,-.-~- - -·~~;~'-- ·-... -, --, ~-~,-- :·: !,,i t) i f; r ::j :.: 8 :.:: ~ ::. ,, :-: r: ' ?j t' H t: fl ll II Table 7 ( 31 ;:n Plate No. Steel sheet No. Ml, Sl M2 82. M3 S3 M4 S4 M5 55 M6 86 M7 87 MS $8 M9 89 MID S10 'Mil Sll Ml2 812. M13 813 Ml4 '814 MIS 815 . •. Ml6 Sl6 . Ml7 S17 MIS 818 M19' Sl9' .· MZO 820 M21 821 M22 S22 M23 · 823 M24 824 M25 825 M26 S26 M27 827 M28 828 M29 829.- M30 824 M31 825 . ti'ii Steel sbeet inside (GPa) 3.95 4.42 4.80 5.85 9.89 11.80 14.10 . 4.17 4.50 ., 4.88· 6.13 8.62 14.30 13.90 4.07 4.29 . 7.47 . "11.90 : 13.70 ·13.80 ,14.00 4.25 6.09 7.23 13.40 . 14.20 13.90 14.10 7.21 . 9.11 12.70 ... Nano hardness S1Jl"fitce layer (GPa) Surface layer/ inside 2.86 0.72 2.87 0.65 2.84 0.59 2.85 0.49 3.00 0.30 3.50 0.30 4.18 . 0.30 . 2.87 0.69 2.84 0.63 ' 2.84 0.58 2.93 0.48 ' 3.04 0.35 6.06 0.42 4.50 0.32 I .2.78 0.68 2.84 0.66 2.99 0.40 3.0J 0.25 5.78 0.42 : . 4.85 0.35 ,: 4.77 0.34 2.85 0.67 ' 2.97 0.49 : . :2.97 0.41 I 3.53 0.26 ' 3.93 0.28. ' •.5.14 0.37 6.12 0.43 : 2.90 0.40 ' 3.03 0.33 3.56 . 0.28 Bent portion rating 3 4 ' 3 3 3 4 4 4 5 5 3 3 4 4 3 4 4 5 5 4 4 5 5 5 '5 . 5 s· 5 1 . 1 . 1 Beot portion cross section rating 3 3 3 4 4 5 5 5 5 5 4 4 5 5 4 5 5 5 5 5 5 5 5 5 5 4 4 4 1 1 1 I I ' 0" ~ i ti : ~ t 11 ' '!! :~ t,:, M32 M33 M34 M35 M36 - M37 __ 826 826 825 827 S30· 830 - -· . '· 13.80 4.44 0.32 13.90 5.29 0.38 13.10 3.46 0.26 . 14.30 6.60 0.46 2.84 2.65 0.93 2.84 2.66 0.94 - ,. , 1 1 1 , 1 ' I 5 ; 5 1 1 I I 5 5 -- -- - ,.. ,J; ! ! ,. :::·1 1:: I " '·' i.l i:: lj !:::, !'"':I '::/ ·::: ;.:·: ·~~~ j':_: l i, " ::·:' I' ,I. I Note Invention example ·: Invention exairiple Invention example lnvent'ion example i Invention example Invention example Invention example Invention example Invention example Invention example Invention example Invention example Invention example. ·Invention example Invention eXample Invention example Invention example Invention example Invention example Invention example Invention example lnve!ltion example Invention example Invention example Invention example Invention example Invention example Invention exo.mplc Comparative example Comparative example InVention example . ' ~~w:· ·• ,. ' .·: .• :;:-= ~~ IT' IJ'I I . I I~ ! i'' I. I r !::: ~. ~.~~--- -------"=~ i ~ c. ~ ~ u u > > 'Cs 'iii :a c. "' f: E 0 0 u u ---- -~~-:: ~c~:: ~:: ~c~:_:~_:: ~~,~=:~~.-::___~~~.~::- ~--:~c'l~=·~=~-~,~~,~-:_~c~~~~~~~~~-~~,~, ~~-~c_~- --~-.~.~ ---~=~~-~-~~=----~. ~~, ·,~.· ~~~ ~~ ~~~~~. -~~~~~~~,~:_:_::_-:! ____ ~_- ~-~= .!! ~ .!! c. Q. c. ~ ~ ~ ~ ~ " .. ..> , > .~ -~ ~ .. ~ "' Q. c. 8 E e 0 0 0 u u u .-· ~ Q. ~ 1l !' ·~ a c. E 0 u ·'• ·, ' [ I ' f' I ::-:-:::-:-_-_-___ - -- 5 67 (Second embodiment) Hereinafter, a second embodiment of the present invention will be described m detail. Firstly, the reason why the components of the steel sheet used m the embodiment are limited will be described. [0093] The reason why the range of the C amount was set to 0.10% to 0.50% by mass% is that the lower limit of the C amount was set to 0.10% in order to secure the strength, and 0.50% was set as the upper limit, at which the weldability can be maintained . . ··--~------·-· [0094] 10 The reason why the range ofthe Si amount W!'S set to 0.005% to 2.0% by mass% is that.the lower lin1it of the Si amount was set to 0.005% in order to secure the strength, and the upper limit was set to 2.0%, at which the weldability and plating properties are not :idversely affected. [0095] The reason why the range of the Mn amount was set to 0.01% to 3.0% by mass% is that the lower limit was set to 0.01%, atvduch the effect of increasing the · · strength is exhibited, and the upper limit was set to 3;0% from the viewpoint of manufacturing costs. .. .· . [0096] 20 J;', S, Al, andN are inevitably contained as elements other than the above. One or more ofTi, Nb, Mo, W, Co, Cu, Cr, Ni, Sn, V, B, and REM may be contained in a · range of 0% to 3.5 in total according to necessity. [0097) Next, the reason why the galvanized plated layer used in the embodiment is 25 · limited will be described. 68 [0098] The reason why the range of the Al amount in the plated layer is set to 0.01% to 1.5% by mass% is tltat, when tbe Al amount is less tban 0.01 %, Zn oxide-dominant dross is significantly generated on tlte surface of the plating bath, and the appearance after 5 plating is degraded. Since the effect of suppressing the generation of dross is saturated ·'(':1 when the Al ammmt exceeds 1.5%, the upper limit was set to 1.5% from the '1evl'point of ~]'"I manufacturing costs. [0099] . . .... -----·-··· ··- ----·· ····-. ------------·- ... '-·. --.--- ····- ...... - "-·- . . . . .... . The adhered amount of the plate is not particularly lin;lited, but is preferably 1 10 J.lm or more in thickness on a single surface from the ~iewpoint of corrosion resistance. 15 20 25 In addition, the adhered amount on a single surface is preferably 20 J.lffi or less from tbe viewpoint of the formability, weldability, and economic efficiency. [0100] . I Meanwhile, it is still within the scope of the embodiment to plate a top layer or carry out a variety of chemical conversion treatments, for example, a phosphate treatment, a weldability-improving treatment; a lubricity-improving treatment, or the-Jike on the · · ·plated steel sheet Of the embodiment in order to improve the painting properties and · we;:ldability. .·._ [0101] The range of the sheet thickness t (rnm) excluding the plated layer is not . - particularly limited. · The range of the sheet thickness t is ordinarily between 0.4 mm to . 3.2 mm, but is preferably between 1.0 mm to 3.2 mrn in consl~eration ofthe productivity or the load on a rolling machine. [0102] Measurement by the nano-indentation method was carried out by the same -----::::J -- -_-_-_ _-:-_- -:-: ~::: :__ __ _-_.:_:..: ---~.._L_ - "_,__:-~=-=~=-=_:: _:_:_:__-~=---:- =~= -_ -- 69 method as in the first embodiment. I As a result, when the thickness of the softened layer (aiso expressed as the surface layer) in the ferrite portion of the steel sheet from the plate/ferrite interface was indicated by D (mm), and the thickness of the entire steel sheet excluding the plated layer was indicated by t (mm), a prefetTed range ofD was set to 5 0.001% to 5% oft. Din the above range produces an effect of improving the hydrogen embrittlement resistance of the steel sheet The detailed reason thereof is no! clear, but . it is considered that the presence of the soft layer ori the surface layer. affects the ____ -·-· _ .. _ .. __ _J::yd:ogen~mb~i~eiT1entresistance: __ Inadditi_~n! ~~en the thickness J) ~!tb~ ~O.ft~~-e predetermined depth in the surface layer portion of the steel sheet, thereby enabling 15 stable obtainment of favorable hydrogen enibrittlement resistance. When the hydrogen : 20 in the annealing atmosphere is controlled in a range of2% to 8% by volume%, there is a . te~dency for favorabie hydrogen einbrittiement resistance tO be more stabiy obtaitie(( .. which is preferable. Since generation of Si oxi.des is suppressed on the surface of the ! steel sheet after the annealing, the plate wetting properties are also favorable. [0111] •. . . 11te holdittg time at the peak sheet temperature is dependent on the mechanical properties r~quired for the steel sheet, and thus not particularly limited to a certaitt range; however, generally, it is preferable to select the holding time necessary to obtain necessary mechanical properties from 10 seconds to 20 minutes. The holdittg time is --::_;:,_______-:- 72 pi-eferably between 20 seconds to 15,0'seconds from"the viewpoint of the productivity. [0112] The annealed steel sheet is cooled to a range of350°C to 550°C, inunersed in a plating bath of 440°C to 480°C, drawn from the bath, controlled to have a predetermined 5 plate amount, and cooled. [Example 3] [0113] example are one example of the conditions employed f~r confirming the feasibility and 10 effects of the embodiment, and the embodiment is not limited to this example of the conditions. The embodiment can employ a variety of conditions within the gist of the embodiment as long as the object of the embodiment is achieved. [0114] f Other elements that are not shown in Table 4 are not added, but included in steel is only at a· small amount as inevitable impurities. Steel sheets having the steel components and the sheet thicknesses as shown in · Table 4 were· subjected to ail.' annealing treatment at the arinealirig temperatures; hydrogen concentrations, and dew points as shown ~.Tab~e 5, inunersed in a molten Zn plating . - . ' ! ~ bath of a bath temperature of 450°C for 3 seconds, drawn from the bath, controlled to 20 . have an adhered amount on a single surface of 1 J.Lm to 20 J.LID by gas wiphi.g, and, subsequently, subjected to a treatment for cooling to room temperature using nitrogen gas. After the plate ·on the obtained plated steel sheet was dissolve~ by an acid, the .results of chemical analyses were as shown in Table 5 as A1 (%)in the plate. . [0115] 5 10 . ' 15 .[Table4]" "'-·· ··• · - - ·-:-[ 0116] [Table 5] "[0117] 73 In addition, the plated steel sheet was cut in the thickness direction, and the hardness of the steel sheet on a cross section was measured by the nano-indentation - method up to a depth of 1/3 of the sheet thickness of the steel sheet from the plate/ferrite interface. How to use the nano-indentation-method for measurement is pursuant to the ·-···--~ ······-··---· ·-·········~-. ,. -- ·············-··· ··------·----········-···-··· first embodiment. [OU8] The depth d (J-lm) from the plate/ferrite interface at which the oxide including one or two of Si and Mn was present in steel was obtained by observing a cross section of the plated _steel sheet using a scanning electron mic,scope (S-800, manufactured by . Hitachi, Ltd.) and confmning a location in which one or more of the oxides identified by an energy dispersion-type X-ray spectrum were present in 100 J-lm' The results are ~hown in Table 5. [0119) .. The hydrogen embrittlement resist.~ nce was ev~)uated as follows: The plated -- . ' ! layer was peeled off using a 5% hydrochloric acid solution, cathodic charging was 20 carried out for.24 hours in a CH3COOH-CH3COONa buffer solution having a pH of 4.5 at a current density of 2 A/dm2 using the steel sheet as the cathode and a galvanostat (HAB-151, manufactured by Holruto Denlco Corporation), subsequently, Cd electroplating was carried out, the steel sheet was cut into a size of20mm x 100 rnm, and a ~otch having a depth of 50% of the sheet thickness was introduced at the central 25 portion in the longitudinal direction, thereby producing a test specimen. The steel sheet ., - -----------····-------- - -----------~~-- ---·--·---'"'~-~--·~"·•-·-'--~· ... ~ ·-·-·-·-·-·-·-·--.·--······-.-• ......-:.-:<.·. ----~, 74 · .... · wrudracrured in a iliiee~pou;tbertdmgtest:using an 1nstron testing machine (type number 33&0), the fractured surface was .observed using !l SEM (S-800, manufactured by Hitachi Ltd.), and the area ratio of the brittle fractured surface at the observation site was obtained, thereby evaluating the hydrogen embrittlement resistance. Ratings of 3 or 5 higher represent excellent hydrogen embrittlemeut resistance. ,, [0120] 10 15 20 25 Rating 1: the area ratio of the brittle fractured surface is niore than 50%. Rating 2: the area ratio of the brittle fractured surface is more-than. 30% to 50%. Rating 3: the area ratio of the brittle fractured surface is more than 20% to 30%. Rating 4: the. area ratio of the brittle fractured surface is more than 10% to 20%. . . Rating 5: the area ratio ofthe brittle fractured sUrface is 10% or less, [0121] It is found from the evaluation results' in TablT-5 that the plated steel sheet of the ' embodiment is excellent in terms of the hydrogen embrittlement resistance. [0122] (Third embodiment) Herejnafter, a thrrd embodll:nent of the present invention will be. descii.bed ill detail. Firstly, the components of the st.e e...l. she.e t used. i ll the embodll:nent are th~ same as in 'the second ernbodll:nent, and thus will-not be desclibed .. [0123] Next, the reason why the plated layer used in the embodiment is limited will be described. The same reason for the limitation as in the second embodiment will not be described, and only the differences will be described. [0124] The reason why the range of the AJ amount in the plated layer is set to 0.01% to ----------- .......................... .____ ----------- --- ·- ----·- ----- - ---- ---·- -···-· ~-···- ~-.----·-···•"""~--- -------------·- 75 1 "fo i~ ilia\ when the Alam6oot is le~s than O.Dl %; Zll oid"de~dominant dross is significantly generated on the surface of the plating bath, and the appearance after the plating is degraded. When the Al amount exceeds 1%, Fe-Zn alloying on the plated layer becomes significantly suppressed, the line speed of the continuous plating line is 5 reduced, and the ~roductivity is degraded. 10 [0125] 'the plated layer used in the embodiment is the same. as the galvannealed plated layer in the first embodiment. ... --------.-----. ··------- --------------- [0126] The reason why the range of the thickness Ii pf the soft layer (softened layer) in which the nano hardness generated at this time is 75% or less of that at the inside of the steel sheet is set to d/4 s D :S: 2d is that the bending properties are more favorable in this range .. ··The detailed reason Is ·not cieru~ but it is consjdered that the above fact results ' . from the effect of the oxides present in this range for suppressing propagation of 15 cracking. 20 [0127] . The method of manufacturing the ·galvanized steel sheet having excellent bending properties of the embodin1e~t wilJ,be ~escrib~. The same portions as in the 1 ' second embodiinent Vl~ll not be described, and only the difference will be described: The composition of the steel sheet, the casting conditions, and the processes through annealing are the same as in the second embodiment. [0128] The annealed steel sheet is cooled to a range of 350°C to 550°C, immersed in a plating bath of 440°C to 480°C, drawn from the bath, controlled to have a predetermined 25 plate amount, and subjected to a heating treatment for 10 seconds to 60 seconds at a sheet , I I ,. ---r:-- ------- ---- ---- ----- ----- - -----:-:-:.o:_]_ 76 - . . .... --··•. .... . .. temperature of 400'C to 600'C, the1eby diffusing Fe in the plated layer and forming an alloyed plated layer containing a predetermined-concentration of Fe.· As the conditions . of the alloying, the heating treatment is preferably carried out for 10 seconds to 60 seconds at a sheet temperature of 410'C to 530'C from the viewpoint of securing the · 5 quality of the steel sheet, and is preferably carried out for 10 seconds to 40 seconds from the vieWPoint of suppressing the growth of a f phase in the plated layer. [Example4] ...... ____________ [DJ29] .......... . Next, an example of the embodiment will be described, _but the conditions of the ·10 example are one example of the conditions employed for confirming the feasibility and . 15 effects of the embodiment, and the embodiment is not limited to this example ofthe conditions. The embodiment can employ"a vanety of conditions within the gist of the embodin1ent ~s long as the object of the embodiment /s achieved. [0130] Other elements that are not included in Tl!ble 6 are not added, and inCluded only at a small amount as inevitable impurities . . Steel sheets having the steel compmients and the sheet:'tbiclaiesses ·a.s shOWn in Table 6 were subjected to an armealing tr~trnent at the annealing temperatures, hydrogen . , I ' ' concentrations, and dew points as showri in Table 7,- immersed in a molten Zn plating - 20 bath of a bath temperature. of 450'C for 3 seconds, drawn from the bath, controlled to have an adhered amount on a single surface to .1 fl-ID to 20 11m by gas wiping, rel\eated up to a sheet temperature of 400'C to 600'C for diffusing Fe in the plated layer, and then cooled up to room temperature using nitrogen gas. After the plate on the· obtained plated steel sheet was dissolved by an acid, the results of chemical analyses were as ----- ------ --l ,_ 77 shown in Table 7 as Al (%)iii the phite and Fe(%) in the plate. "" [0131] [Table 6) [0132) ' 5 [Table 7] [0133] Meanwhile, the thickness of the steel sheet is slightly reduced by the diffusion of Fe from the steel sheet due to the alloying-treatment after the plating, but the reduced ... -···· ~--- .. ··· ····-. ·- -- ---···-- -····· .. ~ -··~---~-·. __ .,- --- ·-·- ... -----·-·-· - ......... -- .. -· .. - ·- ... ·-···~·-·· -- amount is a maximum of 5 [liD, and there is no substan?al influence, Therefore, in the .1 0 present application, "the sheet thickness of the original sheet before the plating is treated to be the-same as the sheet thickness t excluding the thickness of the plate of a product steel sheet" - [01"34] . -.:· .=.- · .-- In addition, the plated steel sheet was cut in the thickness direction, and the 15 hardness of the steel sheet on a cross section was measured by the nano-indentation method up to a depth of 113 of the sheet thickness of the steel sheet from the plate/ferrite ·- it1terface: · ·Howe to use the nano-indentation method for measurement is pursuant to the · [lrst embodiment. _.. .. •'• [0135] 20 The depth d (J.lm) from the plate/ferrite interface at which the oxide including one or two of Si and lvfn was present in the steel was obtained by observing the cross . section of the plated steel sheet using a scanning electron mic:roscope (S-800,_ manufactured by Hitachi, Ltd.) and confinning a location in which one or more of the oxides that was identified by an energy dispersion-type X-ray spectrogram were present 25 in 100 JliD. The results are shown in Table 7. 78 [Oi36] ·. ~ ... . The bending properties were evaluated as follows: . The plated steel sheet was cut into a size of70 nun x 30 mm so 3§ to produce a sample, and a30-degree V bending test in which a punch having a V shape that has a width of 30 rom and an angle of30 5 degrees was pressed at the center of the 70 nun-long side was carried out. The angleR of the V-shaped punch was set to he constant, 1.0 rom. After the test, the surface at the . bent p01tion was photographed, cracked portions and robust portions were binarized in ....... ______ . ___ th(!_ob~ervll:ti()n_photo? ~e-~~a ratios :ve~~ o?~aiJ;ed fi:oii!:_":'l ~1e o~serva~oll_~it_e_s o~ _the_ .. cracked portions, thereby evaluating the bending prope_rties. The obtained cracked area · 10 ratios were given ratings according to the following index, and rates of 3 or higher were set as having reached the pass level . . [0137] Furthermore, the bent portion was implanted in a resin, and the cross section of . I ' the bent portion was observed using an optical microscope, thereby observing the 15.· advancing state of cracking. In the observation orthe cross section, among the observation sites, the depth of cracking that had advanced farthest :frOm the surface layer ·was measured, and the ratio of the crack depth to the sheet thickness of the steel-sheet was used as a crack advancing rate. The gl;>tained crack advancing rate was given a . . . . ! '· rating according to the following index, and ratings of 3 or higher were set as having' 20 reached t~e pass level. The results are shown in Table 7 . . [0138] Observation of the surface of the bent portion Rating 1: the area ratio of cracking is more than 20%. Rating 2: the area ratio of cracking is more than 10% to 20%: 25 Rating 3: the area ratio of cracking is more than 5% to 10%. i ·--·.·.·-~····--~- ... ..-----~--····:.·-·-·.· ._._,._._._..,._,._._.,._..., ___ ~----~~~-~-·~~- ·-~-------- -~------ ------ 79 Rating_ 4; the area ratio of dracking is more than 1% to 5%.: Rating 5; the area ratio of cracking is 1% or less. [0139] Observation of the cross section of the bent portion Rating 1; the advancing rate of cracking is more than 20% . . . Rating 2; the advancing rate of cracking is more than 10% to 20%. Rating -3; the advancing rate of cra~king is more than 5% to 10%. Rating 4; the advancing rate of cracking is more than 1% to 5%. ····-------·······--········-··----·"'''-·--------·-·-·.---:·--·----·-········-----------··· --------------· -···--··- ... _,,,_, . Rating 5; the advancing rate of cracking is 1 o/~ or less. 10 [0140} ·It is found from the evaluation results in Table 7 that the plated steel sheet of the . present invention is excellent in terms of the bending properties.· Industrial Applicability [0141} . ;.-··.· According to the present invention, it is possible to provide a plated steel sheet that is excellent in terms ofthe hydrogen embrittlement resistance. In addition, · · according to the present invention, it becol-l)es p.o ssible.~o manufacture a high-strength - • ' ! -I galvarroealed steel sheet that is excellent in terms of the hydrogen embrittlement 20 resistance without degrading the productivity. Particularly, the present invention is expected to be used as a reinforcing member for automobiles, and has a large industrial· meaning. We claim 1. A method of manufacturing the galvanized steel sheet including a steel sheet portion containing, by mass%, C: 0.05% to 0.50%, Si: 0.005% to 2.5%, Mn: 0.01% to 3.0%, Al: 0% to 0.5%, Ni: 0% to 2.0%, Cu: 0% to 2.0%, Cr: 0% to 2.0%, Mo: 0% to 2.0%, B: 0% to 0.002%, Ti: 0% to 0.1%, Nb: 0% to 0.1%, V: 0% to 0.1%, REM: 0% to 0.1%, Ca: 0% to 0.1%, P: limited to 0.03% or less, S: limited to 0.02% or less, N: limited to 0.0060% or less, and a remainder of Fe and inevitable impurities and a plated layer formed on the surface of the steel sheet portion, the method comprising: a process in which a direct current magnetic field that traverses the thickness of a slab is applied so as to form a direct current electric field zone during continuous casting, and an upper pool that forms an upper area of the slab after the casting and a lower pool that forms a lower area are partitioned, and a process in which a steel material composed of Fe or an alloy mainly containing Fe is supplied to the upper pool, a process of hot-rolling the steel material to obtain a steel sheet, a process of cold-rolling the steel sheet, and a process of annealing the steel sheet ahead of a plating in a continuous galvanizing line, wherein, conditions for the annealing are: a peak sheet temperature is controlled to 650°C to 900°C; an annealing atmosphere at the peak sheet temperature is controlled to contain, by volume%, 1% to 10% of hydrogen and a remainder composed of nitrogen and inevitable impurities; and a dew point is controlled to be higher than 0°C and 50°C or lower.