Technical field
[0001]
　The present invention, thick H-section steel having excellent strength and low temperature toughness, and a method for producing the same. This application, on December 21, 2016, claiming priority on Japanese Patent Application No. 2016-248181 filed in Japan, the contents of which are incorporated herein.
BACKGROUND
[0002]
　In recent years, advances have larger and taller, such as building high-rise buildings, as the strength member required in the structure, thick steel are utilized. However, in general, steel materials, as the thickness of the product is increased, securing the strength becomes difficult, it becomes difficult more secure toughness.
[0003]
　Such contrast problems, Patent Document 1 while securing the toughness by utilizing the effect of refining prior austenite grain by Ca-Al-based oxide, to obtain a steel material that ensures high strength by applying accelerated cooling techniques have been proposed.
[0004]
　In Patent Document 2, while ensuring the toughness by utilizing the effect of refining prior austenite grain by Mg-S inclusions, it has been proposed a technique for obtaining a steel material that ensures high strength by applying accelerated cooling there.
[0005]
　However, when producing thick steel plate, applying accelerated cooling after hot rolling, the cooling rate is slower than the surface within the steel sheet, a large difference in temperature history during the cooling occurs at the surface and the interior, strength by site of steel, ductile, is a difference in mechanical properties such as toughness occur.
[0006]
　In addition, the large buildings, the use of thick H-section steel is desired, the H-beam has a specific shape. Although in shaping the billet into H shape like universal rolling is applied, the rolling conditions are universal rolling (temperature, rolling reduction) is limited. Therefore, when manufacturing H-shaped steel, in particular when the thickness of the flange to produce a thick H-section steel is 20mm or more, compared to the general thick steel plate (steel plate), to control the mechanical properties it is not easy.
[0007]
　Such contrast problems, Patent Documents 3 and 4, to reduce the amount of C, after hot rolling a slab of adding B, and allowed to cool, and a method to ensure uniform mechanical properties have been proposed there.
　In Patent Document 5-8, high strength, a manufacturing method of the thick H-section steel or H-shaped steel and high toughness for the purpose is disclosed.
CITATION
Patent Document
[0008]
Patent Document 1: Japanese Patent No. 5655984 discloses
Patent Document 2: Japanese Japanese Patent No. 5867651
Patent Document 3: Japanese Patent 2003-328070 JP
Patent Document 4: Japanese Patent 2011-106006 JP
Patent Literature 5: Japanese Unexamined Japanese Patent Application Laid-Open No. 11-158543
Patent Document 6: Japanese Patent Laid-Open 11-335735 discloses
Patent Document 7: Japanese Patent 2016-84524 JP
Patent Document 8: Japanese Patent Laid-Open 10-68016 discloses
Summary of the Invention
Problems that the Invention is to Solve
[0009]
　Conventionally, in the thick H-section steel, such as the thickness of the flange is more than 20 mm, since it is not easy to control the mechanical properties, in such a thick H-section steel, at room temperature or, at best toughness at 0 ℃ only to satisfy has been required. However, in recent years, in consideration of the use in cold districts or the like, with respect to thick H-section steel is more required to be excellent in toughness at low temperatures. In addition, in view of the strength per unit weight of a structural material for thick H-section steel, also yield stress (specifically yield strength or 0.2% proof stress in) is greater than or equal to 385MPa request It is.
[0010]
　The present invention has been made in view of such circumstances, and an object thereof is to provide a thick H-section steel and a manufacturing method thereof excellent in strength and low temperature toughness.
Means for Solving the Problems
[0011]
The gist of the present invention is as follows.
(1) H-shaped steel according to one embodiment of the present invention, steel, as chemical components, by mass%, C: 0.05 ~ 0.160% , Si: 0.01 ~ 0.60%, Mn: 0.80 ~ 1.70%, Nb: 0.005 ~ 0.050%, V: 0.05 ~ 0.120%, Ti: 0.001 ~ 0.025%, N: 0.0001 ~ 0. 0120%, Cr: 0 ~ 0.30 %, Mo: 0 ~ 0.20%, Ni: 0 ~ 0.50%, Cu: 0 ~ 0.35%, W: 0 ~ 0.50%, Ca: 0 ~ 0.0050%, Zr: 0 contained ~ 0.0050%, Al: 0.10% or less, B: limit 0.0003% or less, the balance being Fe and impurities, Ceq = C + Mn / 6+ (Cr + Mo + V) / 5 + when the (Ni + Cu) / 15, C in the chemical components, Mn, Cr, Mo, V , Ni, Cu is, Satisfy .30 ≦ Ceq ≦ 0.48, the steel, as a metal structure, in an area fraction, the ferrite hints less than 60 to 100%, the mixed structure MA of martensite and austenite 3.0% below restrict the ferrite and tissues other than the MA was limited to less than 37%, an average particle size of the ferrite is the 1 ~ 30 [mu] m, when viewed in cutting plane perpendicular to the steel to the rolling direction, shape H in the form, the thickness of the flange is 20 ~ 140 mm, when the width direction length of the flange and the F, at a width from end face of the (1/6) F position of the flange, the tensile yield stress 385 in ~ 530 MPa, maximum tensile strength is 490 ~ 690 MPa, the thickness of the flange t 2 when the above (1/6) position and the F, from the thickness direction outer surface of the flange (1/4 ) 2 at the position, the absorbed energy of the Charpy test at -20 ° C. is at least 100 J.
The H-shaped steel according to (2) above (1), the steel, as the chemical components, by mass%, Nb: 0.02 may contain super to 0.050%.
(3) In the above (1) or H-shaped steel according to (2), the steel, as the chemical components, by mass%, N: 0.005 may contain ultra-0.0120%.
(4) In the above (1) ~ (3) H-shaped steel according to any one of the steel, as the chemical components, by mass%, Cu: may be limited to less than 0.03% .
(5) In the above (1) ~ (4) H-shaped steel according to any one of the steel, as the chemical components, by mass%, Al: may be limited to less than 0.003% .
(6) In the above (1) ~ (5) H-shaped steel according to any one of the thickness of the flange may be a 25 ~ 140 mm.
(7) The method of producing H-shaped steel according to one embodiment of the present invention, the above (1) to a method of manufacturing H-shaped steel according to any one of (6), (1) to ( 5) a steelmaking process to obtain a molten steel having a chemical composition according to any one of the casting process to obtain a steel slab by casting the molten steel after the steel making process, the steel strip after the casting step 1100 a heating step of heating to ~ 1350 ° C., with respect to the steel strip after the heating step, so that the shape when viewed in cutting plane perpendicular to the rolling direction becomes H-shaped, the widthwise end face of the flange ( 1/6) and the cumulative rolling reduction at the position of F is 900 ° C. ultra ~ 1100 ° C. at 20% or more, cumulative rolling reduction at the position 730 ~ 900 ° C. at least 15%, rolled at 730 ° C. or higher a hot rolling step of performing rolling under conditions to terminate, allowed to cool hot-rolled material after the hot rolling step cooling Includes a degree, the.
Effect of the invention
[0012]
　According to this aspect of the present invention, it is possible to provide a thick H-section steel and a manufacturing method thereof excellent in strength and low temperature toughness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013]
FIG. 1 is a schematic cross-sectional view illustrating the position of collecting a test piece of H-beam according to an embodiment of the present invention.
FIG. 2 is a flowchart of a method of manufacturing H-shaped steel according to an embodiment of the present invention.
DESCRIPTION OF THE INVENTION
[0014]
　It will be described below in detail preferred embodiments of the present invention. However, the present invention is not limited only to the configuration disclosed in this embodiment, and various modifications are possible without departing from the scope of the present invention. In addition, the numerical limitation range below the lower limit value and the upper limit value is included in the range. A number indicating the "super" or "less than", the value is not included in the numerical range. "%" For the content of each element means "mass%".
[0015]
　As described above, heretofore, the thick H-section steel thickness of the flange is 20mm or more, room temperature or had been most required toughness at 0 ° C.. However, at present, taking into account the use in cold districts or the like, with respect to thick H-section steel is required to be excellent in toughness at lower temperature of about -20 ° C.. In addition, in view of the strength per unit weight of a structural material for thick H-section steel, also yield stress (specifically yield strength or 0.2% proof stress in) is greater than or equal to 385MPa request It is.
[0016]
　The inventors have therefore, thick H-section steel (hereinafter, may be referred to as steel) with respect to, in particular with respect to the flanges is an important site in the structure of the H-shaped steel, steel composition on the strength and low temperature toughness ( Effect of chemical composition) and the steel structure of the steel (steel metal structure) performed studies, the following findings were obtained. In the present embodiment, the intensity means that the tensile yield stress and tensile maximum strength, low temperature toughness is meant that the absorption energy Charpy test at -20 ° C..
[0017]
　First, an increase in excess hardenability by the addition of alloying elements, martensite in steel - austenite mixed structure (hereinafter referred to as MA) to facilitate the generation of results in a decrease in low-temperature toughness. In particular, B of the alloying elements so remarkable tendency to promote MA generation, it is effective to limit the following impurity levels without positively adding B.
[0018]
　Further, to achieve high yield stress (yield strength or 0.2% proof stress), in order to improve the toughness at -20 ° C. At the same time, the addition of Nb is effective. Nb is to increase the strength of steel through precipitation strengthening, excessively it is not necessary to increase the hardenability, it is possible to increase the strength of steel without promoting the formation of MA. Further, Nb suppresses the recrystallization of austenite during hot rolling, the strain in the steel material by rolling accumulated, the effect of resulting in grain refining of ferrite after transformation.
[0019]
In order to improve the toughness at -20 ° C., the addition of V is effective. V is carbonitride (VC, VN, or composite) precipitated as to function as nucleation sites for ferrite, has the effect of resulting in grain refining of ferrite.
[0020]
　Further, the addition of Mn, and the strength and low temperature toughness is further improved. In addition, after controlling the steel components, as the steel structure, the area fraction of ferrite, the area fraction of MA, will be controlling the average crystal grain size of the ferrite, on which both the high strength and low temperature toughness in is important.
[0021]
　To stably control the steel structure, the steel strip having a controlled steel components when hot rolling, at a recrystallization temperature region and non-recrystallization temperature zone of austenite, to provide sufficient rolling strain, respectively is necessary. Specifically, in a temperature range of 900 ° C. ultra ~ 1100 ° C., the cumulative rolling reduction is performed rolling of 20% or more of heat, further in a temperature range of 900 ° C. or less, the cumulative rolling reduction between 15% or more heat rolling I do. By rolling at 900 ° C. greater than and fine austenite grains reduces the hardenability kept low and the amount of MA, by rolling at 900 ° C. or less, most imparted to the ferrite strain in the steel material increase the nucleation frequency to fine the ferrite.
[0022]
　Further, in order to stably control the steel structure, the time of cooling after hot rolling, it is preferable that the difference in cooling rate between the surface and the interior of the steel material is small. If allowed to cool without accelerated cooling the steel after hot rolling, the surface and interior of the steel, the cooling rate becomes both smaller, the difference also decreases. For example, a flange thickness of a 20 mm H-shaped steel, and when cool the steel after hot rolling, the surface and inside of the average cooling rate of the steel from 800 ° C. to 500 ° C. or less both 1 ° C. / sec.
[0023]
　When the cooling rate after hot rolling is slow, generally, it is not easy to secure yield stress and low temperature toughness at the same time. However, by optimally controlling the steel components and production conditions, it is possible to achieve both the yield stress and low temperature toughness. For example, as a steel component, the C content is 0.05% to 0.160%, to limit B was not below the impurity level added, was added actively Nb and V, Mn, Ti, such as N suitably controlling the content of alloying elements, to control the carbon equivalent Ceq in the range of 0.30 to 0.48. In addition, by optimally controlling the manufacturing conditions, as the steel structure, the area fraction of ferrite, the area fraction of MA, fabricate and average crystal grain size of the ferrite. As a result, it becomes possible to obtain a thick H-section steel having excellent strength and low temperature toughness.
[0024]
　The following describes H-shaped steel according to the present embodiment. First, it will be described in detail the steel composition and reasons for limiting its.
[0025]
　H-beam according to the present embodiment, as chemical components, containing the basic element comprises a selection element as required, the balance being Fe and impurities.
[0026]
　Of the chemical components of the H-shaped steel according to the present embodiment, C, Si, Mn, Nb, V, Ti, N is the basic element (main alloying elements).
[0027]
(C: 0.05 ~
　0.160%) C (carbon) is an element effective in strengthening steel. Therefore, to 0.05% the lower limit of the C content. Preferably, the lower limit of the C content 0.060% 0.070%, or 0.080%. On the other hand, when the C content exceeds 0.160% leads to a decrease in low-temperature toughness. Therefore, to 0.160% the upper limit of C content. In order to further improve the low temperature toughness, preferably, the upper limit of the C content, and 0.140% 0.130% or 0.120%.
[0028]
(Si: 0.01 ~
　0.60%) Si (Silicon) is a deoxidizing element, is an element contributing to the improvement of strength. Therefore, the lower limit of the Si content is set to 0.01%. Preferably, the lower limit of the Si content, 0.05%, 0.10%, or 0.15%. On the other hand, when the Si content exceeds 0.60% promotes generation of MA, lowering the low temperature toughness. Therefore, 0.60% of the upper limit of the Si content. In order to further improve the low temperature toughness, preferably, the upper limit of Si content is 0.40%, or 0.30%.
[0029]
(Mn: 0.80 ~
　1.70%) Mn (manganese) is an element contributing to the improvement of strength. Therefore, 0.80% of the lower limit of the Mn content. To enhance the strength, preferably, the lower limit of the Mn content, 1.0%, 1.1%, or 1.2%. On the other hand, when the Mn content exceeds 1.70% hardenability excessively increases, it promotes the formation of MA, impairing low temperature toughness. Therefore, to 1.70% of the upper limit of the Mn content. Preferably, the upper limit of the Mn content is 1.60%, or 1.50%.
[0030]
(Nb: 0.005 ~
　0.050%) Nb (Niobium) suppresses recrystallization of austenite during hot rolling, and contributes to grain refinement of the ferrite be accumulated processing strain in the steel material, further , an element which contributes to the improvement of strength by precipitation strengthening. Therefore, to 0.005% the lower limit of the Nb content. Preferably, the lower limit of the Nb content, 0.010%, 0.020% or greater, 0.025%, or 0.030%. However, when the Nb content exceeds 0.050% it can lead to significant degradation of low-temperature toughness. Therefore, 0.050% of the upper limit of Nb content. Preferably, the upper limit of the Nb content 0.045% 0.043%, or 0.040%. Incidentally, if not intentionally added Nb, Nb content as impurity is less than 0.005%. The Nb content to 0.005% or more is deliberately to contain Nb to the steel.
[0031]
(V: 0.05 ~ 0.120%) V
　(Vanadium) is precipitated as carbonitrides in the grains of austenite, act as transformation nuclei for ferrite, the ferrite grains with an element having an effect of refining is there. Therefore, to 0.05% the lower limit of the V content. Preferably, the lower limit of the V content of 0.05 percent, 0.06%, or 0.07%. However, when the V content exceeds 0.120%, the impairing low-temperature toughness due to coarsening of the precipitates. Therefore, the upper limit of the V content is 0.120%. Preferably, the upper limit of the V content, and 0.110% or 0.100%.
[0032]
(Ti: 0.001 ~
　0.025%) Ti (Titanium) is to form a TiN, an element for fixing the N in the steel. Therefore, to 0.001% the lower limit of the Ti content. To further fine austenite by pinning effect of TiN, preferably, the lower limit of the Ti content 0.005% 0.007% or 0.010%. On the other hand, if the Ti content exceeds 0.025%, coarse TiN is formed and impairs the low temperature toughness. Therefore, 0.025% of the upper limit of the Ti content. Preferably, the upper limit of the Ti content, 0.020% or 0.015%, or 0.012%.
　Also, if not positively added Al, because Ti acts as a deoxidizing element, N is generated that does not bind to Ti. However, this N is a Ti oxide precipitate as V carbonitrides as nuclei. That, Ti is by Ti oxide acting as a deoxidizing element is deposited, precipitation of V carbonitride is promoted, thereby improving the low temperature toughness.
[0033]
(N: 0.0001 ~
　0.0120%) N (nitrogen) form a TiN and VN, which is an element contributing to the grain refining and precipitation strengthening of tissues. Therefore, the lower limit of the N content to 0.0001%. Preferably, the lower limit of the N content 0.0020% 0.0035% to 0.0050 percent, or 0.0060%. However, N content exceeds 0.0120%, reduced low-temperature toughness, causing material failure due to strain aging of surface cracks and fabricated steel during casting. Therefore, the upper limit of the N content to 0.0120%. Preferably, the upper limit of the N content, and 0.0110%, 0.0100%, or 0.0090%.
[0034]
　H-beam according to the present embodiment, as chemical components, it contains impurities. Note that the "impurities", in manufacturing the steel industrially, refers to those mixed from the ore and scrap as a raw material, or manufacturing environment and the like. For example, it means Al, B, P, S, an element O and the like. Of these impurities, Al and B, in order to sufficiently exhibit the effect of the present embodiment, it is preferable to limit as follows. Further, since the content of impurities is preferably less, it is not necessary to limit the lower limit, the lower limit of the impurity may be 0%.
[0035]
(Al: 0.10% or
　less) Al (aluminum) is an element used as a deoxidizing element, when the Al content exceeds 0.10%, the oxide is coarsened become a starting point of brittle fracture, low temperature toughness is lowered. Therefore, to limit the upper limit of the Al content to 0.10%. When it is not used as a positively deoxidizing element Al as, Ti acts as a deoxidizing element, Ti oxide is precipitated in the steel. The Ti oxide functions as a nucleation site for V carbonitride, a ferrite grain size finer, contributing to the improvement of low temperature toughness. Therefore, without using Al as a deoxidizing element, Al as an impurity, the upper limit of the Al content, less than 0.003%, may be limited 0.002%, or 0.001%. In general, the Al content to more than 0.003% is deliberately to contain Al to the steel.
[0036]
(B: 0.0003% or
　less) B (boron) increases the hardenability, promotes the formation of MA, reducing the low-temperature toughness. Therefore, in this embodiment, to limit B of the following impurity levels without positively added. Limiting the upper limit of B content 0.0003%. Preferably, the upper limit of the B content is less than 0.0003% 0.0002%, or 0.0001%. In general, B content and to 0.0003 percent is deliberately to contain B to the steel.
[0037]
(P: 0.03% or less, S: 0.02% or less, O: 0.005% or
　less) P (phosphorus), S (sulfur), and O (oxygen) is an impurity. P and S, solidification segregation to facilitate the weld cracking and reduces the low temperature toughness. Preferably, the upper limit of the P content, 0.03%, 0.02%, or 0.01%. Also, preferably, the upper limit of the S content is limited to 0.02% or 0.01%. O reduces the low temperature toughness in solid solution in the steel, also reduces the low temperature toughness by coarsening of the oxide particles. Preferably, the upper limit of the O content is limited to 0.005% 0.004% or 0.003%.
[0038]
　H-beam according to the present embodiment, in addition to the basic elements and impurities as described above, it may contain a selection element. For example, instead of a part of Fe is a balance mentioned above, as a selective element, Cr, Mo, Ni, Cu, W, Ca, Zr, may contain Mg, and / or REM. These optional elements may be contained according to the purpose. Therefore, it is not necessary to limit the lower limit of these selected elements, the lower limit may be 0%. Moreover, even if these optional elements is contained as an impurity, the effect is not impaired.
[0039]
(Cr: 0 ~
　0.30%) Cr (chromium) is an element contributing to the improvement of strength. If necessary, the Cr content may be from 0 to 0.30%. For further improvement of the strength, preferably, the lower limit of the Cr content is 0.01% 0.05%, or 0.10%. On the other hand, when the Cr content exceeds 0.30%, to promote the formation of MA, which may reduce low-temperature toughness. Therefore, preferably, the upper limit of the Cr content, 0.30%, 0.25%, or 0.20%.
[0040]
(Mo: 0 ~
　0.20%) Mo (molybdenum) is an element contributing to the improvement of strength by solid solution in the steel. If necessary, the Mo content may be from 0 to 0.20%. For further improvement of the strength, preferably, the lower limit of the Mo content is 0.01% 0.05%, or 0.10%. However, when the Mo content exceeds 0.20%, to promote the formation of MA, resulting in deterioration of low-temperature toughness. Therefore, preferably, the upper limit of Mo content, 0.20%, 0.17%, or 0.15%.
[0041]
(Ni: 0 ~
　0.50%) Ni (nickel) is an element contributing to the improvement of strength by solid solution in the steel. If necessary, the Ni content may be from 0 to 0.50%. For further improvement of the strength, preferably, the lower limit of the Ni content is 0.01% 0.05%, or 0.10%. However, when the Ni content exceeds 0.50%, increasing the hardenability, it promotes the formation of MA, which may reduce low-temperature toughness. Therefore, preferably, the upper limit of the Ni content, 0.50%, 0.30%, or 0.20%.
[0042]
(Cu: 0 ~
　0.35%) Cu (copper) is an element contributing to the improvement of strength. If necessary, the Cu content may be from 0 to 0.35 percent. However, the addition of Cu is to facilitate the production of MA, sometimes the low temperature toughness is reduced. Therefore, preferably, the Cu content, 0.30% or less, 0.20% or less, 0.10% or less, or be limited less than 0.03% the impurity levels or below 0.01% good.
[0043]
(W: 0 ~
　0.50%) W (tungsten) is an element contributing to the improvement of strength by solid solution in the steel. If necessary, the W content may be from 0 to 0.50%. Preferably, the lower limit of the W content, 0.001%, 0.01%, or 0.10%. However, when the W content exceeds 0.50%, to promote the formation of MA, which may reduce low-temperature toughness. Therefore, preferably, the upper limit of the W content, 0.50% 0.40%, or 0.30%. Incidentally, if not intentionally added W, W content as impurity is less than 0.001%. The W content to more than 0.001% is intentionally incorporating the W to the steel.
[0044]
(Ca: 0 ~
　0.0050%) Ca (calcium) is effective in morphological control of sulfides to suppress the formation of coarse MnS, which is an element contributing to the improvement of low temperature toughness. If necessary, the Ca content may be 0 to 0.0050 percent. Preferably, the lower limit of the Ca content, 0.0001%, 0.0005%, or 0.0010%. On the other hand, when the Ca content exceeds 0.0050%, the low temperature toughness is reduced. Therefore, preferably, the upper limit of the Ca content is 0.0050% 0.0040%, or 0.0030% or.
[0045]
(Zr: 0 ~
　0.0050%) Zr (zirconium) are carbides, nitrides, or precipitated as a composite, an element which contributes to precipitation strengthening. If necessary, the Zr content may be 0 to 0.0050 percent. Preferably, the lower limit of the Zr content, 0.0001%, 0.0005%, or 0.0010%. On the other hand, when the Zr content exceeds 0.0050% leads to coarsening of such carbides and nitrides of Zr, sometimes the low temperature toughness is reduced. Therefore, preferably, the upper limit of the Zr content is 0.0050% 0.0040%, or 0.0030% or. Incidentally, if not intentionally added Zr, Zr content as impurity is less than 0.0001%. The Zr content in order to 0.0001% or more is deliberately to contain Zr to the steel.
[0046]
(Mg: 0 ~ 0.0050%, REM: 0 ~
　0.0050%) Mg (magnesium) and REM (rare earth element) is an element contributing to the improvement of the toughness of the base material toughness and weld heat affected zone (HAZ) it is. If necessary, the Mg content from 0 to 0.0050%, the REM content may be 0 to 0.0050 percent. Preferably, the lower limit of the Mg content, 0.0005%, and 0.0010% or 0.0020%, the lower limit of the REM content, 0.0005%, and 0.0010%, or 0.0020% to. Meanwhile, preferably, the upper limit of the Mg content, 0.0040% 0.0030% or 0.0025% to the upper limit of the REM content 0.0040% 0.0030%, or 0.0025 % to.
[0047]
: (Ceq 0.30 ~ 0.48)
　in H-shaped steel according to the present embodiment, from the viewpoint of securing the strength, to control the carbon equivalent Ceq. Specifically, when the Ceq Equation 1 below, C in the chemical components of the H-shaped steel, Mn, Cr, Mo, V , Ni, Cu are, in mass%, 0.30 ≦ Ceq ≦ 0. to satisfy the 48. If Ceq is less than 0.30, the strength is insufficient. Therefore, the 0.30 lower limit of Ceq. Preferably, the lower limit of the Ceq, 0.32%, 0.34%, or 0.35%. On the other hand, if Ceq exceeds 0.48, low temperature toughness is reduced. Therefore, a 0.48 upper limit of Ceq. Preferably, the upper limit of the Ceq, 0.45%, 0.43%, or 0.40%. Incidentally, when calculating the Ceq by Equation 1 below, elements content below the limit of detection in the steel, the 0 as the value may be calculated a Ceq into Equation 1.
[0048]
　Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 · · · (式 1)
[0049]
　Steel components described above may be measured by general analytical methods of steel. For example, the steel component may be measured by using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Incidentally, C and S combustion - using infrared absorption method, N is the inert gas fusion - using a thermal conductivity method, O inert gas fusion - can be measured using a non-dispersive infrared absorption method.
[0050]
　It will now be described in detail the steel structure and limiting reasons of H-shaped steel according to the present embodiment.
[0051]
　The H-shaped steel according to the present embodiment, the steel structure is in area fraction, ferrite containing 60 to less than 100% to limit the mixed structure MA of martensite and austenite to 3.0% or less, ferrite and MA limiting the tissues other than below 37%. Further, the average particle size of the ferrite 1μm or more and 30μm or less
[0052]
(Ferrite area fraction of 60 to less than 100%)
　ferrite, it is a major constituent phases of the steel structure in the H-shaped steel according to the present embodiment. When the area fraction of ferrite is less than 60%, low-temperature toughness is lowered. Therefore, the 60% lower limit of the ferrite fraction. Preferably, the lower limit of the ferrite fraction, 65%, 70%, or 75%. Meanwhile, by controlling the area fraction of ferrite to 100%, to accompany formation of pearlite or bainite, which is physically difficult. Therefore, the upper limit of the ferrite fraction is less than 100%. To control preferably the strength and low temperature toughness, preferably, the upper limit of the ferrite fraction is 90%, 85%, or 80%.
[0053]
(MA area fraction of: 3.0% or
　less) when the MA generation of is promoted, the low temperature toughness is reduced. The H-shaped steel according to the present embodiment, the strength of the steel is increased without promoting the formation of MA. Therefore, to limit the MA fraction to 3.0% or less. Preferably, the upper limit of the MA fraction, 2.5%, 2.0%, or 1.5%. Since MA fraction is preferably as small as the lower limit of the MA fraction may be 0%.
[0054]
(Area fraction of tissues other than the ferrite and MA 37% or less)
　in the steel structure of the H-shaped steel according to the present embodiment, as a tissue other than the ferrite and MA as described above, and the like bainite and pearlite. When tissues other than ferrite and MA are included in excess, the low temperature toughness is lowered. Therefore, to limit the area fraction of tissues other than the ferrite and MA (the remainder of the ferrite and MA) below 37%. Preferably, the fraction of tissues other than the ferrite and MA, 35% or less, 30% or less, or 25% or less. Since the fraction of tissues other than the ferrite and MA is preferably smaller, the lower limit may be 0%.
[0055]
: (1 ~ 30 [mu] m average particle size of the ferrite)
　preferably has an average particle size of the ferrite is fine. When the ferrite grain diameter exceeds 30 [mu] m, low-temperature toughness is lowered. Therefore, to 30μm the upper limit of the ferrite grain size. Preferably, the upper limit of the ferrite grain size, and 25 [mu] m, 22 .mu.m or 18 [mu] m,. Meanwhile, controlling the ferrite grain size to less than 1μm is industrially difficult. Therefore, the lower limit of the ferrite grain size and 1 [mu] m. Preferably, the lower limit of the ferrite grain size, and 3 [mu] m, 5 [mu] m or 10 [mu] m,.
[0056]
　Steel structure described above may be determined by observation with an optical microscope. For example, Figure 1 is a schematic cross-sectional view perpendicular to the rolling direction of the H-shaped steel, steel structure is observed as an observation surface evaluation site 7 vicinity shown in FIG. Specifically, in FIG. 1, the widthwise end surface 5a of the flange (1/6) F position and of the thickness direction outer surface 5b of the flange (1/4) t 2 Evaluation site is the position of the as the viewing surface 7 near to observe steel structure. Incidentally, the observation plane is the width direction end surface 5a parallel to the plane of the flange.
[0057]
　Observing the steel structure is polished and corroded the viewing surface as described above. Polishing was performed to the observation surface is a mirror surface, corrosion, using etchant suitable for identifying constituent phases. For example, it corroded the observation surface mirror finished by nital liquid to out revealing steel structure, since pearlite and bainite is colored, can be identified ferrite, martensite, and austenite. Further, identified the corroded the observation surface mirror finished by repeller solution to out revealing the steel structure, the constituent phases other than martensite and austenite is colored black, a mixed structure MA of martensite and austenite be able to.
[0058]
　The H-shaped steel according to the present embodiment, determined the fraction of ferrite and MA from the observation surface that is nital corrosion, the remainder was a fraction of a tissue of pearlite and bainite, obtaining the MA fraction from the observation surface that is repeller corrosion. Specifically, on nital corrosion was 200 times the optical photomicrographs taken at the observation plane (multiple field-of-view if necessary), one side places the measurement point on 25μm grid, the measurement point of at least 1000 determines whether ferritic or MA, the number of measurement points is determined that ferrite or MA, the value obtained by dividing the number of all the measurement points and the fraction of ferrite or MA.
[0059]
　Similarly, on the repeller corroded 200-power optical microscope photograph taken at the observation plane (multiple field-of-view if necessary), one side places the measurement point on 25μm grid, or MA at the measurement point of at least 1000 determines whether the number of measurement points is determined that MA, a value obtained by dividing the number of all the measurement points and MA fraction. The fraction of ferrite, pearlite obtained above, bainite, and the total fraction of MA fraction determined by subtracting from 100%.
[0060]
　Further, the H-shaped steel according to the present embodiment, by using a 200-fold optical micrograph of taken at observation surface was nital corrosion described above, the average particle size of the ferrite from cutting method conforming to JIS G0551 (2013) Ask.
[0061]
　It will now be described in detail the mechanical properties of the H-shaped steel according to the present embodiment.
[0062]
　The H-shaped steel according to the present embodiment, as a position where the average mechanical properties (strength and low temperature toughness) is obtained, to evaluate the mechanical properties were taken test specimens from the region including the evaluation portion 7 shown in FIG.
[0063]
　First described evaluation portion 7 in FIG. Figure 1 is a schematic cross-sectional view perpendicular to the rolling direction of the H-shaped steel. In Figure 1, the X-axis direction is defined as the width direction of the flange, the Y-axis is defined as the thickness direction of the flange, define a Z-axis direction to the rolling direction.
[0064]
　As shown in FIG. 1, the center of the evaluation site 7, the widthwise length of the flange and F, the thickness of the flange t 2 when the, from the widthwise end surface of the flange (1/6) F position and the, from the thickness direction outer surface of the flange (1/4) t 2 is the position of the. Note that the thickness direction outer surface of the flange, a one surface in the thickness direction of the flange, a surface of a direction which does not contact the web 6, is a surface 5b shown in FIG. Further, the widthwise end surface of the flange is an end 5a shown in FIG.
[0065]
　Specimens in evaluating low temperature toughness by Charpy test, the position of the evaluation region 7, the longitudinal direction of the test piece is taken to be parallel to the rolling direction. The surface of molding a notch in the test piece, and the width direction end surface 5a parallel to either side of the flange. Further, the test piece, from the widthwise end surface 5a of the flange (1/6) F position and of the thickness direction outer surface 5b of the flange (1/4) t 2 taken from any position if the position of it may be.
[0066]
　Tensile yield stress (yield strength or 0.2% proof stress) by the test and the tensile strength (maximum tensile strength) test pieces for evaluating the, in FIG. 1, the widthwise end surface 5a of the flange (1/6) of F position is taken so that the thickness direction center of the test piece. Specimen, the longitudinal direction of the test piece are parallel to the rolling direction, it is sufficient to cut the entire thickness direction of the flange. Incidentally, the test strip may be taken from any position as long as the position in the width direction end surface 5a of the flange (1/6) F.
[0067]
　The H-shaped steel according to the present embodiment, as mechanical properties, the yield stress at room temperature becomes higher 385MPa, a tensile strength becomes higher 490 MPa, the Charpy absorbed energy at -20 ° C. greater than or equal to 100 J. Since the intensity is too high there may impair the low-temperature toughness, preferably, the upper limit of the yield stress 530 MPa, the upper limit of the tensile strength and 690 MPa. Moreover, since making the Charpy absorbed energy at -20 ° C. and 500J greater is industrially difficult, the upper limit of the Charpy absorbed energy at -20 ° C. may 500J. Here, the normal temperature refers to 20 ° C..
[0068]
　When evaluating the mechanical properties of the H-shaped steel according to the present embodiment, the tensile test was performed in conformity with JIS Z2241 (2011), Charpy test is conducted in conformity with JIS Z2242 (2005). Incidentally, it obtained from a tensile test stress - when the breakdown phenomenon is observed in the strain curve of the yield strength determined as yield stress, the stress - obtaining 0.2% proof stress as the yield stress when the breakdown phenomenon strain curve is not observed.
[0069]
　It will now be described in detail the shape of the H-shaped steel according to the present embodiment.
[0070]
　The H-shaped steel according to the present embodiment, the flange thickness t 2 of the 20 ~ 140 mm. For example, in a high-rise building construction, thick H-section steel is determined as the strength member. Therefore, the lower limit of the flange thickness and 20 mm. Preferably, the lower limit of the flange thickness to 25 mm, 40 mm or a 56 mm,. On the other hand, the thickness t of the flange 2 when exceeds 140 mm, it is difficult achieve both the hot working volume during processing is insufficient strength and low temperature toughness. Therefore, the upper limit of the flange thickness and 140 mm. Preferably, the upper limit of the flange thickness, and 125 mm, 89 mm or 77 mm,. For example, the thickness t of the flange 2 is preferably from 25 ~ 140 mm. Incidentally, the web thickness t of the H-shaped steel 1 is not particularly defined, preferably from 20 ~ 140 mm, and more preferably 25 ~ 140 mm.
[0071]
　In the production of the H-shaped steel in hot rolling, the ratio of the flange thickness / web thickness (t 2 / t 1 ) is preferably 0.5 to 2.0. The ratio of the flange thickness / web thickness (t 2 / t 1 when) exceeds 2.0, it may be deformed into a shape like waving web. On the other hand, the ratio of the flange thickness / web thickness (t 2 / t 1 If) is less than 0.5, there is the flange is deformed wavy shape.
[0072]
　In the prior art, the thickness of the flange is a thick H-section steel as above 20 mm, it is difficult to achieve both strength and toughness. However, the H-shaped steel according to the present embodiment, even though the flange thickness is 20mm or more thick H-section steel, so to optimally control the steel composition and the steel structure, compatibility between strength and low temperature toughness It can become.
[0073]
　It will now be described in detail preferred method of H-shaped steel according to the present embodiment.
[0074]
　Method of manufacturing H-shaped steel according to the present embodiment includes a steel making process, a casting step, a heating step, a hot rolling step and a cooling step.
[0075]
　The steel making process, so that the steel composition described above, to adjust the chemical composition of the molten steel. In steelmaking, may be used molten steel produced by performing a converter refining and secondary refining, may be used molten steel was melted in an electric furnace as a raw material. The steelmaking process, if necessary, may be subjected to deoxidation treatment, a vacuum degassing treatment.
[0076]
　The casting process, casting the molten steel after the steel-making process to obtain a billet. Casting is carried out continuous casting method, or ingot method. From the viewpoint of productivity, preferred is continuous casting. The shape of the steel piece, the beam blank near the H-section steel produced shape is preferred, not particularly limited. The thickness of the steel strip, from the viewpoint of productivity, it is preferable to be at least 200 mm, reduction and segregation, when considering the homogeneity of the pre-heating temperature at which the hot rolling is preferably not more than 350 mm.
[0077]
　In the heating step, heating the steel piece after the casting process to 1100 ~ 1350 ° C.. Deformation resistance heating temperature during the finish rolling is less than 1100 ° C. billet increases. Therefore, the lower limit of the heating temperature and 1100 ° C.. Such as Nb, in order to sufficiently solid solution forming elements such as carbides and nitrides, preferably, the lower limit of the heating temperature and 1150 ° C.. On the other hand, if the heating temperature exceeds 1350 ° C., they affect production scale of the steel strip surface is liquefied. Therefore, the upper limit of the heating temperature and 1350 ° C.. In the heating step, it may be used a steel strip which is not cooled to room temperature after the casting process.
[0078]
　The hot rolling process is performed on the steel piece after the heating step, rough rolling, intermediate rolling, the finish rolling. In rough rolling, performing molding so that the shape when viewed in cutting plane perpendicular to the rolling direction becomes substantially H shape. Against billet of substantially H-shaped, in a temperature range of the surface temperature of the steel 900 ° C. ultra ~ 1100 ° C., the cumulative rolling reduction is performed rolling of 20% or more of heat, further surface temperature of the steel 730 ° C. ~ in a temperature range of 900 ° C., the cumulative rolling reduction perform hot rolling of 15% or more. In this hot rolling, performing molding so that the shape when viewed in the above cut surface is finally H shape.
[0079]
　900 ° C. in a temperature range of ultra ~ 1100 ° C., in order to reduce the amount of bainite and MA by fine austenite grains, the cumulative rolling reduction of 20% or more. Preferably, the lower limit of the cumulative reduction rate at a temperature region of 900 ° C. ultra ~ 1100 ° C., and 25%, 30%, or 35%. If necessary, the upper limit of the cumulative reduction rate at a temperature region of 900 ° C. ultra ~ 1100 ° C. may be 60%.
[0080]
　730 The ° C. ~ temperature range of 900 ° C., for grain refining of ferrite, the cumulative rolling reduction is 15% or more. Preferably, the lower limit of the cumulative reduction rate in the temperature range of 730 ℃ ~ 900 ℃, 20%, and 25%, or 30%. If necessary, the upper limit of the cumulative reduction rate in the temperature range of 730 ° C. ~ 900 ° C. may be 50%.
[0081]
　Incidentally, resulting in deterioration of low-temperature toughness is rolling at temperatures below 730 ° C.. Therefore, the rolling end temperature (finishing rolling temperature), and 730 ° C. or higher at a surface temperature of the steel. Preferably, the upper limit of the finish rolling temperature, and 750 ° C..
[0082]
　The hot rolling step, rough rolling, intermediate rolling, performs the finish rolling, for example, 900 ° C. rolling in the temperature range of ultra ~ 1100 ° C. is rough rolling may be performed in any intermediate rolling or finish rolling . Similarly, rolling in the temperature range of 730 ° C. ~ 900 ° C. is rough rolling may be performed in any intermediate rolling or finish rolling. In the method of manufacturing H-shaped steel according to the present embodiment, the cumulative rolling reduction in the temperature range described above may be employed to control.
[0083]
　Further, the cumulative rolling reduction at the temperature range is determined based on the flange thickness at a position corresponding to (1/6) F from the widthwise end surface 5a of the flange shown in Figure 1. For example, the cumulative rolling reduction in the temperature range of 900 ° C. ultra ~ 1100 ° C. has a reduction ratio of the surface temperature of the steel is calculated from the difference of the flange thickness Metropolitan immediately before reaching the flange thickness and 900 ° C. at the time 1100 ° C. to. Similarly, the cumulative rolling reduction in the temperature range of 730 ° C. ~ 900 ° C. is a reduction ratio of the surface temperature of the steel is calculated from the difference of the flange thickness Metropolitan in flange thickness and 730 ° C. the time at the point 900 ° C..
[0084]
　In the hot rolling step, rough rolling, intermediate rolling, a method of finish rolling is not particularly limited. For example, performs breakdown rolling as a crude rolling, subjected to universal rolling or edging rolling as intermediate rolling, by performing the universal rolling as the finish rolling, the shape is the H-shaped when viewed in cutting plane perpendicular to the rolling direction It can be shaped to.
[0085]
　The hot rolling process may be carried out water-cooling between rolling passes. Water cooling between rolling passes is a cooling austenite is performed for the purpose of temperature control in the temperature range higher than the temperature at which transformation phase. Bainite and MA will not be generated in the steel material by water cooling between rolling passes.
[0086]
　Further, in the hot rolling step may be carried out 2 heat rolling. The 2 heat rolling, after cooling after the primary rolling a steel piece 500 ° C. or less, it is again rolling method by heating the steel slab to 1100 ~ 1350 ° C. performing secondary rolling. The 2 heat rolling, little plastic deformation in the hot rolling, because the drop in temperature is also reduced in the rolling process, it is possible to lower the second time heating temperature.
[0087]
　In the cooling step, cooling the hot-rolled material after hot rolling step. In the method of manufacturing H-shaped steel according to the present embodiment is allowed to cool as it is hot-rolled material in the atmosphere after the completion of hot rolling. If allowed to cool hot-rolled material in the atmosphere, the surface and inside of the average cooling rate of the steel from 800 ° C. to 500 ° C. is as follows 1 ° C. / sec. By allowing it to cool in air to Netsunobezai, because the cooling rate at the surface and inside of the steel becomes uniform, variation in the mechanical properties due to the site of the steel it is suppressed. Incidentally, in the manufacturing method of the H-shaped steel according to the present embodiment, cooling is immediately after hot rolling to steel temperature is 400 ° C. or less, the cooling in the air without performing forced cooling means.
[0088]
　In the prior art, since the hot-rolled material was accelerated cooling to achieve both strength and toughness, the variation of the surface and the inside at the mechanical properties of the steel material has occurred. On the other hand, in the manufacturing method of the H-shaped steel according to the present embodiment, even though allowed to cool in air to Netsunobezai, so to optimally control the steel composition and the steel structure, the surface and inside of the steel product it is possible to achieve both strength and low temperature toughness without variations in mechanical characteristics.
[0089]
　Method of manufacturing H-shaped steel according to the present embodiment does not require advanced steelmaking technology and accelerated cooling, it is possible to achieve production load reduction, shortening of the construction period. Thus, H-shaped steel according to the present embodiment, without impairing the economic efficiency, it is possible to improve the reliability of large buildings.
Example 1
[0090]
　Will be further specifically described in detail the effects of an embodiment of the present invention through examples, the conditions in the examples, in one example of conditions adopted for confirming the workability and effects of the present invention There, the present invention is not limited to this single example of conditions. The present invention does not depart from the gist of the present invention, as far as it achieves the object of the present invention may employ various conditions.
[0091]
　The steel having the chemical components shown in Table 1 to Table 3 were melted, by continuous casting, the thickness was produced steel slabs of 240 ~ 300 mm. Melting of steel is carried out in a converter furnace, primary deoxidation to adjust the component by addition of alloying elements, if necessary, subjected to vacuum degassing treatment. The resulting heated steel strip, subjected to hot rolling to produce a H-shaped steel. Component No. Steel components shown as 1 to 48 was determined to samples taken from each H-beam after production by chemical analysis. Although not shown in the table, any of the embodiments also, P is 0.03% or less, S is 0.02% or less, O was 0.005% or less. Note that blank chemical components in the table represents that did not positively added to the steel, or content was below the detection limit.
[0092]
　The manufacturing process of the H-shaped steel shown in Fig. Hot rolling a steel slab heated by a heating furnace 1, was carried out in the roughing mill 2a, intermediate rolling mill 2b, a universal rolling mill train comprising a finishing mill 2c. As it is hot-rolled material after the end of hot rolling was allowed to cool to 400 ° C. or less. Surface and inside of the average cooling rate of the hot rolled material from completion of hot rolling temperature to 500 ° C. was both at 1 ° C. / sec or less. When performing water cooling between passes of hot rolling, it was spray cooling of the flange outer surface by using a water-cooling apparatus 3 provided before and after the intermediate universal rolling mill (intermediate rolling mill) 2b. At this time, it was carried out a reverse rolling.
[0093]
　In Tables 4 to 6 show the production conditions and production results. Rolling reduction during hot rolling shown in Tables 4 to 6 are cumulative rolling reduction at each temperature region at a position corresponding to the widthwise end surface 5a from (1/6) F of the flange shown in Figure 1.
[0094]
　For H-shaped steel produced, as described above, it performs Charpy test at -20 ° C. using a specimen taken from the evaluation portion 7 shown in FIG. 1, to evaluate the low-temperature toughness. Moreover, subjected to tensile test at room temperature (20 ° C.) with the widthwise end surface 5a of the flange (1/6) position of F is the center of the thickness direction specimens were evaluated tensile properties. Also, perform structure observation using a sample to be observed surface evaluation site 7 vicinity shown in FIG. 1, to evaluate the steel microstructure.
[0095]
　The tensile test was carried out in accordance with JIS Z2241 (2005). Tensile test stress - if the strain curve exhibits a yield behavior and yield stress and yield point, if not exhibit a yield behavior was the yield stress of 0.2% proof stress. Charpy impact test was carried out in accordance with JIS Z2242 (2005). Charpy impact test was conducted at -20 ° C..
[0096]
　Tissue observation, by the method described above, using an optical microscope photograph, ferrite fraction, MA fraction, as well as to measure the fraction of tissues other than the ferrite and MA. In addition, tissues other than the ferrite and MA is a bainite or pearlite. Also, using an optical microscope photograph to determine the average particle size of the ferrite by a cutting method conforming to JIS G0551 (2013).
[0097]
　As the tensile properties, the yield stress at room temperature (YS) of not less than 385MPa, a tensile strength (TS) is determined as acceptable steel is at least 490 MPa. Further, as a low-temperature toughness, the Charpy absorbed energy at -20 ℃ (vE-20) was determined as acceptable steel is at least 100 J.
[0098]
　As shown in Tables 1-6, an invention sample preparation No. 1 to 8, manufacture No. 11-18, and manufacturing No. 34-43 are steel components, steel structure, and any of mechanical properties satisfied the scope of the present invention.
[0099]
　On the other hand, comparative examples manufactured No. 9-10, production No. 19-33, and manufacturing No. 44-50 are steel components, steel structure, and any of the mechanical properties did not satisfy the scope of the present invention.
[0100]
　Production No. 9, because the rolling reduction at 900 ° C. ultra ~ 1100 ° C. is insufficient, ferrite fraction of the steel tissue becomes insufficient, becomes excessive fraction of tissues other than the ferrite and MA, at -20 ° C. Charpy absorbed energy is an example that has become insufficient.
[0101]
　Production No. 10, since the reduction ratio at 730 ° C. ~ 900 ° C. is insufficient, ferrite grain size becomes coarse, which is an example of a insufficient Charpy absorbed energy at -20 ° C..
[0102]
　Production No. 19, since the rolling reduction at 900 ° C. ultra ~ 1100 ° C. is insufficient, ferrite fraction is insufficient, MA fraction becomes excessive, the fraction of tissues other than the ferrite and MA is excessive, -20 Charpy absorbed energy at ℃ is an example that has become insufficient.
[0103]
　Production No. 20 Many C content, production No. 25 Many Nb content, production No. 26 Many V content, production No. 28 Many Al content, production No. 29 Many Ti content, production No. 30 Many N content, production No. 31 because Ceq was excessive, an example in which a insufficient Charpy absorbed energy at -20 ° C..
[0104]
　Production No. 21 has low C content, production No. 24 has low Mn content, production No. 32 is insufficient Ceq, production No. 46 Since there were only the Si content, an example of YS and TS becomes insufficient.
[0105]
　Production No. 22 Many Si content, production No. 23 is often Mn content, because MA fraction was excessive, an example in which a insufficient Charpy absorbed energy at -20 ° C..
[0106]
　Production No. 27, since the V content was small, the ferrite grain size becomes coarse, which is an example of a insufficient Charpy absorbed energy at -20 ° C..
[0107]
　Production No. 33 is excessive B content and Ceq, production No. 49 because in many cases the B content, MA fraction becomes excessive, an example in which a insufficient Charpy absorbed energy at -20 ° C..
[0108]
　Production No. 44 and production No. 45, since the V content was small, the ferrite grain size becomes coarse, which is an example of a insufficient Charpy absorbed energy at -20 ° C..
[0109]
　Production No. 47 Since there were only the Nb content, ferrite grain size becomes coarse, YS and TS becomes insufficient, an example in which a insufficient Charpy absorbed energy at -20 ° C..
[0110]
　Production No. 48 Since there were only the Ti content, the ferrite grain size becomes coarse, which is an example of a insufficient Charpy absorbed energy at -20 ° C..
[0111]
　Production No. Since 50 was low rolling finishing temperature are examples became insufficient Charpy absorbed energy at -20 ° C..
[0112]
[Table 1]

[0113]
[Table 2]

[0114]
[table 3]

[0115]
[Table 4]

[0116]
[table 5]

[0117]
[Table 6]

Industrial Applicability
[0118]
　According to this aspect of the present invention, since the provision of thick H-section steel and a manufacturing method thereof excellent in strength and low temperature toughness becomes possible, has high industrial applicability.
DESCRIPTION OF SYMBOLS
[0119]
　1 furnace
　2a rough rolling mill
　2b intermediate mill
　2c finishing mill
　3 intermediate mill before and after the water-cooling unit
　4 H-section steel
　5 flange
　widthwise end face of 5a flange
　thickness direction outer surface of 5b flange
　6 web
　7 tensile properties, low temperature toughness, and evaluation sites of steel tissue
　widthwise length of the F flange
　H height
　t 1　the web thickness
　t 2　flange thickness

The scope of the claims
[Requested item 1]
　Steel, as chemical components, by
　　mass%, C:
　　0.05
　　~ 0.160%, Si: 0.01 ~ 0.60%, Mn: 0.80
　　~ 1.70%, Nb: 0.005 ~
　　% 0.050,
　　V:
　　0.05 ~ 0.120%, Ti: 0.001 ~ 0.025%, N:
　　0.0001 ~ 0.0120%, Cr: 0 ~
　　0.30%, Mo: 0 　　0.20%
~, 　　Ni: 0 ~ 　　0.50%, Cu: 0 ~ 0.35%, W: 0 ~ 0.50%, 　　Ca: 0 ~ 0.0050%, Zr: 0 ~ 0.0050% 　containing, 　　Al: 0.10% or 　　less, B: 0.0003% or less 　limited to, 　the balance being Fe and 　impurities, when the Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15, C in the chemical components, Mn, Cr, Mo, V , Ni, Cu is, 0.30 ≦ Ceq ≦ 0.4 Satisfy 8, 　wherein the steel is, as the metal structure, the area fraction, 　　ferrite containing 60 to less than 100% 　　to limit the mixed structure MA of martensite and austenite to 3.0% or less, 　the ferrite and the tissues other than MA was limited to less than 37%, 　an average particle size of the ferrite is the 1 ~ 30 [mu] m, 　when viewed in cutting plane perpendicular to the steel to the rolling direction, the shape is H-shaped, flange thickness There are 20 ~ 140 mm, 　when the width direction length of the flange and the F, at a width from end face of the (1/6) F position of the flange, a tensile yield stress of 385 ~ 530 MPa, tensile maximum intensity There is a 490 ~ 690 MPa, 　the thickness of the flange t 2 when the above (1/6) position and the F, (1/4) the thickness direction outer surface of the flange t 2 at the position , -20 ℃ Absorbed energy Charpy test is not less than 100J at H-beams, characterized in that.

[Requested item 2]
　The steel, as the chemical components, by
　　mass%, Nb: 0.02 super ~ 0.050%
　containing
H-shaped steel according to claim 1, characterized in that.
[Requested item 3]
　The steel, as the chemical components, by
　　mass%, N: 0.005 ultra ~ 0.0120%
　containing
H-shaped steel according to claim 1, characterized in that.
[Requested item 4]
　The steel, as the chemical components, by mass%,
　　Cu: less than 0.03%
　to limit the
H-shaped steel according to claim 1, characterized in that.
[Requested item 5]
　The steel, as the chemical components, by
　　mass%, Al: less than 0.003%
　is limited to
H-beam according to claim 1, characterized in that.
[Requested item 6]
　When the thickness of the flange is 25 ~ 140 mm
H-shaped steel according to claim 1, characterized in that.
[Requested item 7]
　A method of manufacturing a H-shaped steel according to any one of claims 1 to 6,
　　the steel making process to obtain a molten steel having the chemical composition according to any one of claims 1 to 5,
　　wherein the steel a casting step of obtaining a steel slab by casting the molten steel after the step,
　　a heating step of heating the steel piece after the casting process to 1100 ~ 1350 ° C.,
　　with respect to the steel strip after the heating step, rolling as the shape when viewed in cutting plane perpendicular to the direction to the H-shaped, the widthwise end face of the flange (1/6) cumulative rolling reduction at the position of F is 900 ° C. ultra ~ 1100 ° C. at 20% or more , and the said and the cumulative rolling reduction is 730 ~ 900 ° C. at 15% or higher at the position, and the hot rolling step of performing rolling under conditions to terminate the rolling at 730 ° C. or more,
　　hot rolling after the hot rolling step comprising a cooling step of cooling the timber, a
manufacturing method of H-beams, characterized in that.