Technical field
[0001]The present disclosure, H-section steel and a method for producing the same.
BACKGROUND
[0002]In recent years, the building of high-rise buildings are large-sized, high-rise and the like is progressing. Therefore, as the primary strength members 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 and further toughness of ensuring also difficult trend.
[0003]With respect to such problems, for the production of H-shaped steel, while ensuring the strength by applying accelerated cooling, a technique for obtaining a steel material to ensure good toughness is proposed (Patent Document 1).
[0004]Further, by applying the accelerated cooling, to ensure high strength of 590MPa class, a technique for ensuring the toughness is proposed at 0 ° C. (Patent Document 2).
[0005]Similarly, by applying the accelerated cooling, to ensure high strength, a technique for ensuring the toughness is proposed at 0 ° C. (Patent Document 3).
[0006]Further, the oxide containing Mg by finely dispersed in the steel, the old γ grain size finer, by applying the accelerated cooling, to ensure high strength, to ensure the toughness at 21 ° C. At the same time the steel the obtained technology has been proposed (Patent Document 4).
[0007]
　Cu, Ni, Cr, Mo, and after hot rolling the slab with added B, and allowed to cool, and a method to ensure uniform mechanical properties have been proposed (Patent Document 5).
[0008]
　After heating a steel material having a predetermined chemical composition, after rolling the flanges and the web under certain conditions, the flange heats recovery after accelerated cooling at a cooling rate 1 ° C. / s or more, the web is allowed to cool to techniques have been proposed (Patent Document 6).
[0009]
　In the cross section of the H-section steel produced from a steel strip having a chemical composition which is a specific carbon equivalent, 1/4 flange portion microstructure referenced to the satisfaction technology specific conditions has been proposed (Patent Documents 7 ).
CITATION
Patent Document
[0010]
　Patent Document 1: Japanese Patent 2003-328070 JP
　Patent Document 2: Japanese Patent 2006-322019 JP
　Patent Document 3: Japanese Patent Laid-Open 11-335735 discloses
　Patent Document 4: Japanese Patent 2016-141834 JP
　Patent Document 5: Japanese Patent Laid-Open 8-197103 discloses
　Patent Document 6: Japanese Patent 2006-249475 JP
　Patent Document 7: International Publication No. 2001-075182
Summary of the Invention
Problems that the Invention is to Solve
[0011]
　When producing thick steel plate, applying accelerated cooling after hot rolling, cooling rate of the internal steel sheet is slower than the surface. Therefore, in the surface and interior of the steel sheet, a large difference occurs in the temperature history during the cooling, the strength by the site of the steel sheet, the ductility, and the difference in mechanical properties such as toughness occur.
[0012]
　In addition, the large buildings, the thickness of the flange is 25mm or more H-beams use (hereinafter also referred to as heavy gauge H-shaped steel.) Is desired. However, H-section steel shape is specific, rolling conditions in universal rolling (temperature, rolling reduction) is limited. Therefore, particularly, when producing the heavy gauge H-shaped steel, compared to the thick steel plate, the web, flange, there is a difference in mechanical properties at each part of the fillet, etc. increases.
[0013]
　With respect to such problems, the technique disclosed in Patent Document 5 has been proposed.
[0014]
　Conventionally, a heavy gauge H-shaped steel thickness of the flange is 25mm or more, or at room temperature, which had been at best toughness requirements at 0 ° C., by considering the use in cold districts or the like, more toughness at low temperatures but there is a case that is required. Further, in order to weight reduction of steel (specifically, the yield strength or 0.2% proof stress, more 385MPa) yield strength is high and increasing demand for steel.
　However, Patent Documents 1-5, strength and excellent low-temperature toughness, and since the configuration and manufacturing method for obtaining the H-beams of very thick is not listed, H-beams is obtained having such properties It is did not. Also, H-section steel disclosed in Patent Document 6, the low temperature toughness is not sufficient. Furthermore, H-section steel disclosed in Patent Document 7, since it is mainly formed of a ferrite phase and a pearlite phase, toughness is found that no stable.
[0015]
　The present disclosure has been made in view of such circumstances, H-shaped steel excellent in strength and low-temperature toughness, as well, and to provide its manufacturing method.
Means for Solving the Problems
[0016]
　The means for solving the above problems includes the following aspects.
(1)
　in
mass%,
C:
0.040 ~ 0.100%, Mn: 0.50 ~ 1.70%,
Cu: 0.01 ~ 0.50%, Ni: 0.01 ~ 0.50% ,
Cr:
0.01
~ 0.50%, Nb: 0.001
~ 0.050%, V: 0.010 ~ 0.120%, Al: 0.005
~ 0.100%, Ti: 0.001
0.025% ~, B: 0.0005 ultra
0.0020% ~,
N: 0.0001 ~
0.0120%, Si: 0 ~ 0.08%, Mo: 0 ~
0.20%, W: 0
0.50%
~,
Ca: 0 ~ 0.0050% Zr: 0 ~ 0.0050%
Mg: 0 ~ 0.0050% REM: 0 ~ 0.005%, and,
the balance Fe and impurities,
　the following carbon equivalent Ceq obtained by the equation (1) is the 0.300 to 0.480,
　the thickness of the flange 25 It is a ~ 140mm,
　The widthwise length of the flange F, the thickness t 2 When,
　in the width direction of the flange, the widthwise end face of the flange (1/6) a position of the F, and, in a thickness direction of the flange, the flange from the thickness direction outer surface (1/4) t of 2 the position is the center of the measurement position, the average crystal grain size in the plane perpendicular to the width direction of the flange is less than or equal to 38 [mu] m,
　centered on the measuring position martensitic steel tissue in a plane perpendicular to the width direction of the flange - area fraction of austenite mixed structure (MA) is not more than 1.2%,
　in the width direction of the flange, the widthwise end surface of the flange (1 / 6) the position of F, and was measured for total thickness of the thickness direction of the flange, the rolling direction of the yield strength or 0.2% proof stress of the flange is at least 385MPa, a tensile strength of more than 490MPa It is in,
　It absorbed energy Charpy test at -20 ° C. in serial measurement position is above 200 J, H-section steel.
　Equation (1) Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15
　where, represents C, Mn, Cr, Mo, V, Ni, and Cu contents of the elements (% by mass). If not contained is set to 0.
(2)
　A method of producing a H-shaped steel according to
　(1), heating the steel slab to 1100 ~ 1350 ° C. having a composition as set forth in (1),
　Starts rolling after the heating, in the width direction of the flange at the position in the width direction end face from (1/6) F of the flange, the surface temperature of 900 ° C. or higher, the cumulative reduction rate A at 1100 ° C. or less than 10% by and pressure less than 900 ° C., subjected to rolling for rolling in the cumulative reduction rate B at 750 ° C. or higher than 10%, a step of terminating the rolling as 25 ~ 140 mm flange thickness at a surface temperature of 750 ° C. or higher,
　the after rolling, the widthwise length of the flange F, the thickness t 2 When, in the width direction of the flange, the widthwise end face of the flange (1/6) a position of F, and the thickness direction of the flange in, from the thickness direction outer surface of the flange (1/4) t 2 at the position of the acceleration average cooling rate is 0.4 ° C. / s or higher cooling, across the air continuously or during intermittent a step, performed manner
producing side of the H-shaped steel having Law.
(3)
　the accelerated cooling is in the width direction of the flange, in the width from the end face of the (1/6) F position of the flange, recuperation temperature after cooling stop to accelerated cooling until 600 ° C. or less, (2 method of manufacturing H-shaped steel according to).
The invention's effect
[0017]
　According to the present disclosure, H-shaped steel excellent in strength and low temperature toughness, and its manufacturing method are provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018]
FIG. 1 is a diagram for explaining a position of collecting a test piece of heavy gauge H-shaped steel.
The [2] Charpy test is a perspective view showing a test piece for evaluating the toughness.
3 is a diagram showing an example of an apparatus for producing extremely thick H-section steel of the present disclosure.
DESCRIPTION OF THE INVENTION
[0019]
　In the present disclosure, numerical ranges expressed using "to" means a range including numerical values described before and after "to" as the lower and upper limits. Further, numerical ranges when the numerical values set forth are "super" or "less than" are assigned before and after "to" means a range that does not include the lower limit or the upper limit value of these values.
　In this disclosure, "%" indicating the content of the component (element) means "% by mass".
　In this disclosure, the term "process" not only separate steps, if even that can not be clearly distinguished from other processes intended purpose of the process is achieved, in this term included.
[0020]
　H-shaped steel of the present disclosure includes a component composition described below, having a carbon equivalent below.
　In addition, the thickness of the flange is 25 ~ 140mm.
　Further, the widthwise length of the flange F, the thickness t 2 When, in the width direction of the flange, the widthwise end face of the flange (1/6) a position of the F, and, in a thickness direction of the flange , from the thickness direction outer surface of the flange (1/4) t 2 the position is the center of the measurement position, the ferrite average crystal grain size in the plane perpendicular to the width direction of the flange is less than 38 [mu] m.
　Around the said measuring position, martensitic steel tissue in a plane perpendicular to the width direction of the flange - area fraction of austenite mixed structure (MA) is not more than 1.2%.
　Then, in the width direction of the flange, a position of the widthwise end face from (1/6) F of the flange, and was measured for total thickness of the thickness direction of the flange, the yield strength in the rolling direction of the flange or 0.2% proof stress of not less than 385MPa, a tensile strength of not less than 490 MPa.
　Absorbed energy Charpy test at -20 ° C. in the measurement position is equal to or more than 200 J.
[0021]
　First, a description will be given circumstances that led to the creation of the H-section steel of the present disclosure.
　As described above, the extremely thick H-section steel thickness of the flange is 25mm or more, room temperature or had been most required toughness at 0 ° C.. However, at present there is a case where considering the use in cold districts or the like, is more required toughness at low temperatures (about -20 ° C.). Further, in order to weight reduction of heavy gauge H-shaped steel, (specifically, the yield strength or 0.2% proof stress is higher 385MPa) high yield strength is increasing demand for steel.
[0022]
　Accordingly, the present inventors have extremely thick H-section steel (hereinafter, may be referred to as steel.) On strength and toughness in the interior of the flange, performed investigated the effect of chemical composition and metal structure, the following findings were obtained.
[0023]
　First, the inclusion of indiscriminately various alloy elements aiming to secure high strength due to the increase in hardenability, the martensite in steel - austenite mixed structure (hereinafter, MA also described) by the increase of the low temperature toughness It was found that there is a case in which results in a decrease. In order to suppress the reduction in toughness at the area fraction in the steel to the amount of MA, it is important to 1.2% or less. For this purpose, it was found that reducing the Si content is effective. Specifically, it is effective to reduce the Si content to 0.08% or less, and finding a more preferable that it be reduced to less than 0.05%.
[0024]
　Further, the present inventors found that high yield strength or 0.2% proof stress, and in order to achieve a good toughness at -20 ° C. is, Cu, Ni, Cr, effective the inclusion of Nb and V It was found that there is. Cu, Ni, Cr, and Nb, achieves high strength by improving hardenability, Nb and V increases the strength of steel through precipitation strengthening. Further, by containing Nb, through an increase in strain in the steel material by rolling in the pre-recrystallization temperature region, contributing to miniaturization of the steel structure after the accelerated cooling, to improve the toughness.
[0025]
　By appropriate selection of these alloying elements, it has become possible to ensure the toughness at high yield strength or 0.2% proof stress, and -20 ° C..
[0026]
　Furthermore, in order to realize the above such metal structure stably it was also revealed that only selection of alloying elements is insufficient. More specifically, when performing the hot rolling, at a recrystallization temperature region and non-recrystallization temperature zone of austenite, by adding a sufficient rolling strain, respectively, as measured by EBSD (electron backscatter diffraction method) the average crystal grain size, revealed that it is important to not more than 38 [mu] m.
[0027]
　Then, 900 ° C. or higher, at a temperature range of 1100 ° C. or less, the cumulative rolling reduction subjected to hot rolling (cumulative reduction ratio A) is more than 10%, less than 900 ° C., a temperature range of above 750 ° C., the cumulative rolling reduction ( cumulative rolling reduction B) performs rolling of 10% or more of heat. By performing these hot rolling was also apparent that can achieve an average crystal grain size of the. This is because in the temperature range of not lower than 900 ° C., since austenite grains are fine grains of, because that can achieve improved toughness due to miniaturization of the steel structure after the accelerated cooling. Further, in the temperature range below 900 ° C., in many imparts that the strain in the steel material, it can be realized to improve the toughness due to miniaturization of the steel structure after the accelerated cooling.
[0028]
　In general, the more the production of heavy gauge H-shaped steel by performing a strong accelerated cooling, the cooling rate in the steel cross-section varies greatly depending on the position. The flange width F, the flange thickness t 2 When, in the steel section (in particular, in the flange width direction, the widthwise end face of the flange (1/6) a position of F, and the flange thickness direction in, from the thickness direction outer surface of the flange (1/4) t 2 and position of, (1/2) t 2 in the section between the position of) the difference of the cooling rate is decreased, a large mechanical properties the difference does not occur. Therefore, the cooling rate of the accelerated cooling is also 2.0 ° C. / s or less and it is preferable to be in average, the present inventors have revealed. However, the average of the upper limit of the cooling rate of the accelerated cooling is not particularly limited. It is an example of preferred conditions that the cooling rate of the accelerated cooling average 2.0 ° C. / s or less.
[0029]
　To ensure strength of the steel, the accelerated cooling is preferably carried out as much as possible for a long time. Specifically, recuperation temperature after stopping the accelerated cooling is preferably performed until 600 ° C. or less. Accelerated cooling, to may be carried out to continuously target temperature, with a time of one or more air cooling during the accelerated cooling may be intermittent cooling. However, in order to ensure strength of steel, the widthwise length of the flange F, the thickness t 2 When, in the width direction of the flange, the widthwise end face of the flange (1/6) a position of F, and, in the thickness direction of the flange, the thickness direction outer surface of the flange (1/4) t 2 at the location of, it is effective to average cooling rate 0.4 ° C. / s or higher.
　The above is the events that led to the creation of the H-section steel of the present disclosure.
[0030]
　The following describes H-shaped steel of the present disclosure.
　First, a description will be given reasons for limiting the chemical composition (chemical composition).
[0031]
(C: 0.040 ~ 0.100%)
　C is an element effective in strengthening steel, the H-shaped steel of the present disclosure to 0.040% of the lower limit of the C content. Preferred lower limit of the C content is 0.050%. On the other hand, when the C content exceeds 0.100%, the excessive amount of generated cementite and MA, it leads to a decrease in toughness. Therefore, 0.100% of the upper limit of the C content. The preferable upper limit of the C content is 0.080%.
[0032]
(Mn: 0.50 ~
　1.70%) Mn, in order to contribute to the improvement of the strength, the H-shaped steel of the present disclosure to 0.50% the lower limit of the Mn content. To enhance the strength, it is preferable to 1.00% the lower limit of the Mn content. On the other hand, when the Mn content exceeds 1.70% hardenability excessively increases, impairing toughness conducive to the production of MA. Therefore, to 1.70% of the upper limit of the Mn content. The preferable upper limit of the Mn content is 1.60%.
[0033]
(Cu: 0.01 ~
　0.50%) Cu improves the hardenability, which contributes to the improvement of the tensile strength. To obtain this effect, the Cu content is 0.01% or more. The preferable lower limit of Cu content is 0.10%. However, when the Cu content is excessive, resulting in deterioration of the toughness. Therefore, the upper limit of the Cu content is 0.50%. The preferable upper limit of Cu content is 0.30%.
[0034]
(Ni: 0.01 ~
　0.50%) Ni is an element in solid solution in the steel enhancing the hardenability, which contributes to the improvement of the tensile strength. In order to improve the tensile strength, the Ni content is 0.01% or more. Preferred lower limit of the Ni content is 0.10%. However, the Ni content of 0.50 percent by excessively enhancing the hardenability lowers the toughness promotes the formation of MA. Thus, 0.50% of the upper limit of the Ni content. The preferable upper limit of the Ni content is 0.30%.
[0035]
(Cr: 0.01 ~
　0.50%) Cr is an element contributing to the improvement of the tensile strength by increasing hardenability. In order to improve the tensile strength, the Cr content is 0.01% or more. A preferable lower limit of Cr content is 0.05%. However, the Cr content is 0.50% greater, excessively enhance the hardenability, lowers the toughness promotes the formation of MA. Thus, 0.50% of the upper limit of the Cr content. The preferable upper limit of the Cr content is 0.30%.
[0036]
(Nb: 0.001 ~
　0.050%) Nb, when performing the hot rolling, inhibiting the recrystallization of austenite, contributes to grain refinement of ferrite and bainite by to accumulate work strain in the steel material and, further, it contributes to the improvement of strength by precipitation strengthening. To obtain these effects, the Nb content is 0.001% or more. The preferable lower limit of Nb content is 0.010%. However, when excessively containing Nb, promotes the formation of MA, it can lead to significant degradation of toughness. Therefore, 0.050% of the upper limit of Nb content. The preferable upper limit of Nb content is 0.040%.
[0037]
(V: 0.010 ~ 0.120%)
　V contributes to precipitation strengthening by forming carbonitride. Additionally, carbonitrides of V precipitated in the grains of the austenite acts as transformation nuclei for ferrite and bainite, also has the effect of refining the crystal grains of ferrite and bainite. To obtain these effects, the V content is 0.010% or more. The preferable lower limit of V content is 0.030%, more preferable lower limit is 0.050%. However, if excessively containing V, the toughness is sometimes impaired due to coarsening of the precipitates. Therefore, the upper limit of the V content is 0.120%. The preferable upper limit of the V content is 0.100%.
[0038]
(Al: 0.005 ~
　0.100%) Al is a H-shaped steel of the present disclosure act as a deoxidizing element. To obtain the deoxidizing effect, the Al content is 0.005% or more. On the other hand, if excessively containing Al, becomes the base point of brittle fracture Al oxide is coarsened, toughness is reduced. Therefore, 0.100% of the upper limit of the Al content.
[0039]
(Ti: 0.001 ~
　0.025%) Ti is to form TiN, which is an element for fixing N in the steel. To obtain this effect, the H-shaped steel of the present disclosure, and 0.001% the lower limit of the Ti content. Further, TiN is the pinning effect, has the effect of fine austenite. Therefore, a preferred lower limit of the Ti content is 0.007%. On the other hand, if the Ti content exceeds 0.025%, coarse TiN is formed and impairs the toughness. Therefore, 0.025% of the upper limit of the Ti content. The preferable upper limit of the Ti content is 0.020%.
[0040]
(B: 0.0005 super ~ 0.0020%)
　B is an element that enhances the hardenability results in increase in strength of the steel material. To obtain this effect, the H-shaped steel of the present disclosure, the lower limit of the B content is 0.0005 percent. The preferable lower limit of the B content is 0.0006%. On the other hand, when the B content is excessive, to promote the formation of MA, to reduce the toughness, the upper limit of B content is 0.0020%. The preferable upper limit of the B content is 0.0015%.
[0041]
(N: 0.0001 ~ 0.0120%)
　N forms TiN and VN, which is an element contributing to the grain refinement and precipitation strengthening of tissues. Therefore, the lower limit of the N content is set to 0.0001%, it may limit 0.0010%. However, when N content becomes excessive, it reduces the toughness of the base material, the surface cracks and cause material failure due to strain aging of the produced steel when performing casting. Therefore, the upper limit of the N content to 0.0120%. Preferably, the preferred upper limit of the N content is 0.0080%.
[0042]
(P: 0.03% or less, S: 0.02% or less, O (oxygen): 0.005% or
　less) P, S, and O are impurities, the content thereof is not particularly limited. However, P and S, so causing weld cracking and toughness decrease due to solidification segregation, the content of P and S are preferably reduced. The upper limit of the P content is preferably limited to 0.03%. More preferable upper limit of the P content is 0.01%. The upper limit of the S content is preferably limited to 0.02%. The lower limit of the P content and the S content is not particularly limited, and may be 0 percent. For example, in terms of dephosphorization cost reduction and desulfurization cost, it may be respectively 0.0001% or more. Further, O is the excessive content, toughness is reduced by coarsening effects and oxide particles of dissolved O (solid solution oxygen). Therefore, it is preferable that the upper limit of the O content 0.0050%. More preferable upper limit of the O content is 0.0030%. The lower limit of O content is not particularly limited, may be 0 percent, it may be 0.0001% or more.
[0043]
　It may also contain Si. Furthermore, in order to increase the strength and toughness, Mo, W, Ca, Zr, Mg, and may contain one or more of REM. These elements may be contained or may not be contained. Therefore, the lower limit of these elements is 0%.
[0044]
(Si: 0 ~
　0.08%) Si is a deoxidizing element, which contributes to the improvement of strength. The H-shaped steel of the present disclosure, when a large amount of Si, to provide a deterioration of toughness by promoting the production of MA, and 0.08% the upper limit of the Si content. The preferable upper limit of the Si content is 0.05%. Si content in terms of suppressing the generation of MA, the less preferred. When containing Si, the lower limit of the Si content is not particularly limited. For example, the lower limit of the Si content in the case of containing Si may be 0%, and may be 0.01%.
[0045]
(Mo: 0 ～ 0.20
　Pasento) Mo is an element that enhances the hardenability in solid solution in the steel. To obtain this effect, it is preferable that the Mo content is 0.01% or more, and more preferably 0.05% or more. However, it may cause the inclusion 0.20% of Mo, a deterioration in toughness and promotes the formation of MA. Therefore, 0.20% of the upper limit of the Mo content.
[0046]
(W: 0 ～ 0.50 Pasento)
　W is an element to improve the hardenability in solid solution in the steel. To obtain this effect, it is preferable that the W content is 0.01% or more, and more preferably 0.10% or more. However, it may cause the inclusion 0.50% of is W, the decrease in toughness conducive to the production of MA. Therefore, the upper limit of the W content is set to 0.50%.
[0047]
(Ca: 0 ~
　0.0050%) Ca is an element effective for morphology control of sulfides to suppress the formation of coarse MnS, which contributes to the improvement of toughness. To obtain this effect, it is preferable that the Ca content is 0.0001% or more, and more preferably 0.0010% or more. On the other hand, the inclusion of Ca of more than 0.0050%, the toughness is reduced. Therefore, the upper limit of the Ca content is 0.0050%. More preferable upper limit of the Ca content is 0.0030%.
[0048]
(Zr: 0 ~
　0.0050%) Zr is precipitated as carbides and nitrides and contributes to precipitation strengthening of the steel. To obtain this effect, it is preferable that the Zr content is 0.0001% or more, and more preferably 0.0010% or more. On the other hand, may the inclusion of Zr exceeding 0.0050% toughness leads to coarsening of carbides and nitrides of Zr is reduced. Therefore, the upper limit of the Zr content is 0.0050%.
[0049]
(Mg: 0 ~ 0.0050%, REM: 0 ~ 0.005%)
　Others In the H-shaped steel of the present disclosure, for the purpose of improving the base material toughness and weld HAZ toughness, Mg and REM (rare earth elements; that refers Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and at least one element selected from the group consisting of Lu. it may contain one or more of elements). The lower limit of these elements is 0%. However, when containing these elements too, no effect of improving the base material toughness and weld HAZ toughness is obtained. Therefore, when containing Mg, the lower limit of the Mg content may be 0.0001%. The upper limit of the Mg content is 0.0050%. The preferable upper limit of the Mg content is 0.0032%. Further, when containing REM, the lower limit of the REM content may be 0.001%. The upper limit of the REM content is 0.005% or less. The preferable upper limit of the REM content is 0.003%.
[0050]
(Balance: Fe and impurities)
　Further, in the chemical composition of the H-shaped steel of the present disclosure, the balance Fe and impurities. Here, the impurity components contained in the raw material, or a component mixed in the manufacturing process, intentionally refer to a component not intended to be contained in the steel.
[0051]
　In H-shaped steel of the present disclosure, from the viewpoint of ensuring the tensile strength, to define the carbon equivalent Ceq obtained by the following formula (1) in the range of 0.300 to 0.480. Ceq is insufficient hardenability is less than 0.300, the tensile strength is insufficient. Preferably, the lower limit of the Ceq and 0.350. On the other hand, if Ceq exceeds 0.480, hardenability is excessively increased, the strength becomes excessive, toughness is reduced. Preferably, the upper limit of the Ceq and 0.450.
[0052]
　Ceq is a hardenability index (carbon equivalent), obtained by known equation (1). Here, C, Mn, Cr, Mo , V, Ni, and Cu represents the content of each element in the steel (mass%). Elements that are not contained is set to 0.
　Equation (1) Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15
　where, represents C, Mn, Cr, Mo, V, Ni, and Cu contents of the elements (% by mass). If not contained is set to 0. That is, in equation (1), H-shaped steel is, C, Mn, Cr, Mo, V, when containing an element of Ni, and Cu substitutes content of each element contained (mass%). In addition, if there is an element that does not contain substitutes 0.
[0053]
　In extremely thick H-section steel of the present disclosure, as a position at which the average toughness is obtained, collected portion including a measurement position 7 shown in FIG. 1 as a specimen, the average grain size, an area fraction of MA, and toughness to evaluate the.
[0054]
　Here, description will be given of a measurement position 7 in Fig. Figure 1 is a schematic cross-sectional view perpendicular to the rolling direction of the H-beams 4.
　H-beam 4 has a pair of plate-shaped flanges 5 which face each other, so as to be perpendicular to the flange 5, and is provided so as to connect the center in the lateral direction of the facing surface of the flange 5, a plate-shaped web 6 equipped with a.
　In Figure 1, the X-axis direction is defined as the width direction of the flange 5, the Y-axis direction is defined as the thickness direction of the flange 5 defines the Z-axis direction to the rolling direction (length direction of the flange 5).
[0055]
　As shown in FIG. 1, the widthwise length of the flange 5 and F, the thickness of the flange 5 t 2 when the, from the widthwise end surface 5a of the flange 5 (1/6) position of F (in Figure 1, a F / 6 hereinafter), and the thickness direction outer surface 5b of the flange 5 (1/4) t 2 position of (in FIG. 1, t 2 as a measurement position 7/4 the drawing) . Then, around the measuring position 7, the width direction perpendicular to the plane of the flange 5 is a plane to measure the area fraction of the average grain size and MA. Four measurement positions 7 (F / 6 and t which in the horizontal and vertical directions of the flanges 5 of the H-shaped steel 4 2 of the intersections of / 4), the flange 5 along either one place of the measurement position 7 the cross section perpendicular to the width direction (X direction) and the measurement surface. Then, the average crystal grain size 1mm square area measuring position 7 along the rolling direction and the center line of the cross section, the area fraction of MA in 500μm square area, measured respectively. Here, the average crystal grain size, for any one position of the upper, lower, left and right four measurement positions 7 of the flange 5, cross section taken along the 1/4 from the tip in the rolling direction of the H-beam (Z-direction) in performing the measurement. Note that the thickness direction outer surface 5b of the flange 5, a one surface in the thickness direction of the flange 5, a surface of a direction which does not contact the web 6, the end face indicated by the reference numeral 5b shown in FIG. 1 it is. Further, the widthwise end face 5a of the flange 5 is an end showing the code 5a shown in FIG.
[0056]
　Crystal grain size in the steel structure can be determined by observation with EBSD (electron backscatter diffraction method). Crystal grain size, here a circle equivalent diameter. EBSD allows the measurement position 7 as the center, in 1mm square area orthogonal to the width direction of the flange 5, to observe the crystal orientation of the metal structure at 0.2μm intervals. Then, the difference in inclination is a 5 ° or more as the grain boundary, the grain boundary to calculate the average crystal grain size of all the metal structure containing the (hereinafter, simply referred to as the mean grain size). The average crystal grain size referred to herein is a weighted average calculated by weighting by multiplying the area of ​​the grain on the grain size of each crystal.
[0057]
　To ensure the toughness measurement position 7, the average crystal grain size of the steel structure in the following 38 [mu] m. If the average crystal grain size exceeds 38 [mu] m, the toughness falls. Conditions of the average crystal grain size, the tensile strength 490MPa or more steel of interest in H-shaped steel of the present disclosure, is an important element to ensure the toughness at -20 ° C.. This is obtained by revealed by experiments. The lower limit of the average grain size is not particularly limited. The lower limit of the average crystal grain size, in terms of manufacturability, for example, may be 5 [mu] m.
[0058]
　Area fraction of MA in the steel structure is an observation sample taken from steel in terms of corroded by repeller reagent, and observed by optical microscopy, by extracting the MA by known image analysis software can be measured . Specifically, in observation samples etched with repeller reagent, around the measuring position 7 of the steel, the 500μm square plane perpendicular to the width direction of the flange 5 is taken at 200 times by an optical microscope. And, for the captured image, to extract the MA by the image analysis software "Image-Pro", measuring the area fraction of MA. The area fraction of the MA, for any one position of the upper, lower, left and right four measurement positions 7 of the flange 5, cross section taken along the 1/4 from the tip in the rolling direction of the H-beam (Z-direction) in performing the measurement.
[0059]
　In H-shaped steel of the present disclosure, in order to ensure the toughness measurement position 7, the area fraction of MA steel tissue to 1.2% or less. When MA area fraction of more than 1.2%, toughness is reduced. Area fraction of MA is subject in H-shaped steel of the present disclosure, in the above tensile strength 490MPa steel is an important factor to ensure the toughness at -20 ° C.. This is obtained by revealed by experiments. In terms of suppressing the deterioration of toughness, the area fraction of MA is preferably smaller. Area fraction of MA is preferably 1.0% or less, more preferably 0.8% or less. Area fraction of the MA, may be 0%.
[0060]
　In H-shaped steel of the present disclosure, the steel material of the metal structure, in terms of ensuring the toughness at the measurement position 7, perlite 0-10%, a MA0 ~ 1.2% Other balance, ferrite (polygonal ferrite), bainite may be made of at least one of acicular ferrite. In terms of ensuring the strength and low temperature toughness, the balance, ferrite (polygonal ferrite), and it is preferably made of at least one of bainite and acicular ferrite. Of the remainder, if it contains ferrite (polygonal ferrite), the area fraction of ferrite (polygonal ferrite) in the balance is not particularly limited, for example, may be 10-90%.
[0061]
　As shown in FIG. 2, the test piece 9 in evaluating the toughness by Charpy test, the measurement position 7 and the center of the cross section of the rolling direction, can be exemplified cuboid longitudinal direction is taken to be parallel to the rolling direction. The surface of molding a notch in the test piece 9, and the width direction end surface 5a parallel to either side of the flange 5 (the surface 11 and 13 shown in FIG. 2). Further, the test piece 9, the measurement position 7 if the widthwise center of the test piece (the center of the X-axis direction shown in FIG. 2), may be taken from any position in the rolling direction. Notch direction is the width direction of the flange 5 (X-axis direction shown in FIG. 2).
[0062]
　Next, the tensile test, described test pieces for evaluating the yield strength or 0.2% proof stress.
　By a tensile test, the test piece in the evaluation of yield strength or 0.2% proof stress, in FIG. 1, the widthwise end face 5a of the flange 5, toward the width direction of the flange 5 (X-axis direction shown in FIG. 1) Te, a test piece cut as the center in the lateral direction of the (1/6) the position of F, the test piece. Using this test piece, carried out a tensile test. Specimen, the longitudinal direction of the test piece parallel to the rolling direction (Z-axis direction shown in FIG. 1), also in the direction of the thickness of the flange 5 (Y-axis direction shown in FIG. 1) of the total (total thickness) it suffices to cut. The thickness of the width direction of the specimen, in the range specified in JIS Z 2241 (2011). The above test piece, from the widthwise end surface 5a of the flange 5, toward the width direction of the flange 5, (1/6) position of F is, if the widthwise center of the test piece, which position in the rolling direction it may be taken from.
[0063]
　Then, H-shaped steel of the present disclosure describes the shape and mechanical properties of the H-beam 4 very thick of interest.
　The thickness t of the flange 5 of the H-shaped steel 4 of the present disclosure 2 is a 25 ~ 140 mm. The thickness t 2 of the lower limit of the 25mm, for example, the H-beams 4 for use in high-rise building structure, the thickness t of the flange 5 2 is because there is a demand that more strength members 25mm. The thickness t of the flange 5 2 preferred lower limit is 40 mm. On the other hand, the thickness t of the flange 5 2 The upper limit of the 140mm, the thickness t of the flange 5 2 If exceeds 140mm, because processing amount to achieve both insufficient strength and toughness of the hot working is difficult. The thickness t of the flange 5 of the H-shaped steel 4 2 preferred upper limit is 125 mm. Therefore, the thickness t of the flange 5 2 may be 25 ~ 125 mm, it may be 40 ~ 125 mm. The thickness t of the web 6 of H-beams 4 1 are not particularly specified, is preferably 15 ~ 125 mm.
[0064]
　The ratio of the thicknesses of / web 6 of the flange 5 (t 2 / t 1 Regarding), on the assumption that the production of H-beams 4 by hot rolling, it is preferable to 0.5-2.0 . The ratio of the thicknesses of / web 6 of the flange 5 (t 2 / t 1 when) exceeds 2.0, there is that the web 6 is deformed wavy shape. On the other hand, the ratio of the thicknesses of / web 6 of the flange 5 (t 2 / t 1 If) is less than 0.5, there is the flange 5 is deformed wavy shape.
[0065]
　Target value of the mechanical properties of the H-beam 4 according to the H-shaped steel of the present disclosure, the test piece in the evaluation of yield strength or 0.2% proof stress mentioned above, the yield strength or 0.2% proof stress at room temperature There 385MPa or more, the tensile strength is greater than or equal to 490MPa.
　Here, the yield strength or 0.2% proof stress, stress - in strain curve, if the breakdown phenomenon appears obtains a yield strength, if the breakdown phenomenon does not appear indicating the determination of the 0.2% proof stress. That is, if the breakdown phenomenon appears in yield strength is at least 385MPa, 0.2% proof stress if breakdown phenomenon does not appear it means that at least 385MPa.
[0066]
　The target value of the Charpy absorbed energy at -20 ° C. in H-section steel 4 of the present disclosure, the test pieces 9 described above, is at least 200 J. Since the intensity is too high the toughness is sometimes impaired, yield strength or 0.2% proof stress at room temperature is preferably at most 530 MPa, tensile strength is preferably not more than 690 MPa. Note that the ambient temperature in the present disclosure refers to a range of 20 ℃ ± 5 ℃.
[0067]
　It will now be described preferred manufacturing method of the H-shaped steel 4 of the present disclosure.
　A preferred method of manufacturing H-shaped steel 4 of the present disclosure has the following steps.
　Heating the steel slab to 1100 ~ 1350 ° C. with 1) the aforementioned component composition (chemical composition).
　2) starts rolling after heating, in the width direction of the flange at the position in the width direction end face from (1/6) F of the flange, the cumulative rolling reduction A at the surface temperature of 900 ° C. ~ 1100 ° C. or less exceeds 10% pressure, and subjected to rolling the cumulative reduction ratio B of lower than 750 ° C. ~ 900 ° C. rolling at 10% or more, the step of terminating the rolling flange thickness at a surface temperature of 750 ° C. or higher as 25 ~ 140 mm.
　3) after rolling, the widthwise length of the flange F, the thickness t 2 When, in the width direction of the flange, the widthwise end face of the flange (1/6) a position of the F, and flange thickness in the direction from the thickness direction outer surface of the flange (1/4) t 2 at the position of the average cooling rate is 0.4 ° C. / s or higher accelerated cooling, across the air continuously or during in intermittently carry out the process.
　Hereinafter, each step will be specifically described.
[0068]
　First, in the step of steel before heating the steel slab, so that the component composition described above, after adjusting the chemical components of molten steel, cast to obtain a slab. Casting is not particularly limited, but may be a beam blank having a shape close to the H-beams 4 to be manufactured. From the viewpoint of productivity, preferred is continuous casting. The thickness of the steel strip, from the viewpoint of productivity, it is preferably not less than 200 mm. Reduction of segregation, when considering the homogeneity of the pre-heating temperature at which the hot rolling, the thickness of the steel slab is preferably less 350 mm.
[0069]
　Then, heating the resulting steel slab. The heating temperature of the steel slab, the lower limit and 1100 ° C.. When the heating temperature of the steel piece is lower than 1100 ° C., deformation resistance when performing the finish rolling is high. Moreover, Nb, etc., in order to sufficiently solid solution an element forming carbides and nitrides, the lower limit of the heating temperature of the steel slab is preferably set to 1150 ° C.. The upper limit of the heating temperature of the billet to 1350 ° C.. When the heating temperature of the steel strip is hotter than 1350 ° C., the scale of the surface of the steel strip is material detrimental to the production and liquefied.
[0070]
　Then, after heating the steel slab, starts rolling (hot rolling). The H-shaped steel of the present disclosure, the grain refinement of austenite grains, ferrite, bainite or the like is comminuted, the average crystal grain diameter is less 38 [mu] m. Therefore, the rolling reduction when performing hot rolling, from the widthwise end surface 5a of the flange 5 in FIG. 1, toward the width direction of the flange 5, (1/6) at the position of F, the surface temperature of 900 ° C. ~ 1100 10% super cities cumulative reduction rate a at ° C., the cumulative reduction rate B at less than 750 ° C. ~ 900 ° C. and 10% or more. Here, the hot rolling, for example, as shown in FIG. 3, after the intermediate rolling at a cumulative rolling reduction A, it is sufficient to finish rolling at a cumulative rolling reduction B. The cumulative reduction ratio A and B here, the difference between the flange thickness after the flange thickness before rolling and rolling, divided by the flange thickness before rolling. Incidentally, Ar 3 Doing rolling at temperatures below point, there is a case where the hardenability decreases. In addition, before the accelerated cooling begins the start of the ferrite transformation, there is a case in which YS or TS is reduced. Therefore, the lower limit of the finish rolling temperature is set to 750 ° C. at a surface temperature. Rolling process, the surface temperature is completed rolling the thickness of the flange 5 as 25 ~ 140 mm (may be 25 ~ 125 mm) at 750 ° C. or higher. That's the lower limit is less than 750 ° C. rolling finishing temperature, sufficient strength can not be obtained. The upper limit of the finish rolling temperature is preferably 850 ° C.. Incidentally, is that the yield strength or 0.2% proof stress and YS here. TS is that of tensile strength.
[0071]
　After the completion of rolling (hot rolling) applies accelerated cooling. Accelerated cooling in applying the may be subjected to cooling in continuous, or may be performed intermittently across the air. At that time, the average cooling rate at the measurement position 7 shown in FIG. 1, and 0.4 ° C. / s or higher. Cooling rate, the shape of the steel after rolling, the starting temperature of the accelerated cooling, and based on the recuperation temperature after accelerated cooling termination, derived by calculation. No strength to target obtained at an average cooling rate of less than 0.4 ° C. / s. Exceeds 2.0 ° C. / s, in the width direction of the steel section (in particular the flange 5, from the widthwise end surface 5a of the flange 5 (1/6) a position of F, and the flange in the thickness direction , from the thickness direction outer surface 5b of the flange 5 (1/4) t 2 and position of, (1/2) t 2 the difference of the cooling rate in the section) of the position of the increases, large mechanical properties there is a case in which the difference occurs. Therefore, the average cooling rate is preferably not more than 2.0 ° C. / s. Here, making the average cooling rate 2.0 ° C. / s or less is an example of a preferred embodiment, the upper limit of the average cooling rate is not limited.
[0072]
　Incidentally, when applying accelerated cooling from the viewpoint of securing strength, the position from the widthwise end surface 5a of the (1/6) F of the flange 5 after stopping accelerated cooling, to a recuperation temperature of the surface is 600 ° C. or less it is more preferable to perform accelerated cooling.
[0073]
　Further, after cooling to 500 ° C. or less and rolling primary, again, heated to 1100 ~ 1350 ° C., may be employed a process of performing secondary rolling (so-called 2 Heat 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. The hot rolling may pass between the water-cooled roll. Note that the path between the water-cooled rolling, than the temperature at which austenite is transformed phase are those for the purpose of temperature drop at high temperature range.
[0074]
　Hot rolling is performed under the above conditions, H-section steel 4 produced is superior in strength and low temperature toughness. By including the Nb and V, ferrite, bainite or the like is fine granules of, the H-beams 4 with excellent strength and low temperature toughness. More specifically, H-shaped steel 4, the thickness of the flange 5 is 25 ~ 140 mm (may be 25 ~ 125 mm). Also, H-section steel 4, the aforementioned tensile yield strength in the test or 0.2% proof stress than 385MPa, a tensile strength of at least 490 MPa, and the Charpy absorbed energy at -20 ° C. in the test piece 9 the aforementioned more than 200J show. Thus, H-beams 4 produced becomes H-beams 4 extra-thick high-strength superior in low temperature toughness. A method of manufacturing H-shaped steel 4 of the present disclosure do not require a high degree of steelmaking techniques and accelerated cooling, it is possible to manufacture burden, construction period of the shortening. Thus, without impairing the economical efficiency, etc. can improve the reliability of large buildings, the contribution of the industry is extremely remarkable.
Example
[0075]
　Hereinafter, a detailed explanation of the H-section steel of the present disclosure based on examples, H-section steel of the present disclosure is not limited to the examples.
[0076]
　Table 1 and smelted steel having the compositions shown in Table 2, 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. Thus heating the resulting steel pieces, subjected to hot rolling to produce a H-beams 4. Components shown in Table 1 and Table 2 are those obtained for samples taken from each H-beam 4 after production by chemical analysis.
[0077]
[Table 1]

[0078]
[Table 2]

[0079]
　In Table 1 and Table 2, and the blank means that no intentional addition of an element. Numerical Underlined means outside the scope of the H-shaped steel of the present disclosure. Incidentally, P, S, and the content of each element of the O (oxygen), respectively, P: 0.03% or less, S: 0.02% or less, O: was 0.005% or less.
[0080]
　The manufacturing process of the H-shaped steel 4 shown in FIG. The steel slab heated by a heating furnace 1, was carried out in the roughing mill 2a, universal rolling device column containing intermediate mill 2b, and a finishing mill 2c. After the end of hot rolling was applied intermittently accelerated cooling across the continuous or air. If the hot rolling and inter-pass water-cooled rolling, the water cooling between rolling passes, with a water-cooling apparatus 3 provided before and after the intermediate universal rolling mill (intermediate rolling mill 2b), spray cooling of the flange outer surface and the reverse rolling It was carried out.
[0081]
　Taken for H-beams 4 produced, as described above, around the measurement position 7 shown in FIG. 1, to include a surface orthogonal to the width direction of the flange 5, from H-beams 4 Microscopy test piece did. It collected using a microscope for observation specimen, performed EBSD observation of the surface was measured average grain size. Further, also a measurement position 7 as the center, to include a surface orthogonal to the width direction of the flange 5, by using a microscopic observation test pieces taken from the H-shaped steel 4, measure the area fraction of MA in the surface did. Furthermore, like around the measurement position 7, with the Charpy test piece longitudinal direction is taken to be parallel to the rolling direction (see FIG. 2), the Charpy test at -20 ° C., was evaluated low temperature toughness. As described above, when the widthwise length of the flange 5 and F, from the widthwise end surface 5a of the flange 5, toward the width direction of the flange 5 (X-axis direction shown in FIG. 1), (1 / as the thickness direction around the position of 6) F, test piece was cut out from the H-section steel 4 was subjected to a tensile test in the rolling direction of the flange 5 by using the test piece.
[0082]
　Tensile test was performed in conformity with JIS Z 2241 (2011), may exhibit breakdown behavior yield point, determine the 0.2% yield strength may not exhibit a yield behavior, and the YS. The test piece of the tensile test, and No. JIS1A, measurement temperature was carried out at 20 ℃ ± 5 ℃. Charpy impact test conforms to JIS Z 2242 (2005), it was carried out at -20 ° C..
[0083]
　Target value of the mechanical properties, yield strength or 0.2% proof stress at room temperature (YS) more than 385MPa, a tensile strength (TS) is not less than 490 MPa. Further, Charpy absorbed energy (vE at -20 ° C. -20 target value) is greater than or equal to 200 J. Incidentally, the notch shape of the Charpy test V notch, notch depth was set to 2 mm.
[0084]
　The heating temperature of the steel strip during fabrication, manufacturing conditions such as hot rolling, the average crystal grain size, an area fraction of MA, the yield strength or 0.2% proof stress (YS), tensile strength (TS) and -20 ° C. absorbed energy Charpy test (vE in -20 to), are shown in tables 3 to 6. Incidentally, the rolling reduction when performing the hot rolling in Tables 3 and 5, from the widthwise end surface 5a of the flange 5 in FIG. 1, toward the width direction of the flange 5 (X-axis direction shown in FIG. 1), ( 1/6) a rolling reduction at the position of F. The average cooling rate of the measurement position 7, the flange thickness t of the H-shaped steel 4 2 , water cooling start temperature, from the measured value of the recuperation temperature, and is calculated by computer simulation.
[0085]
[table 3]

[0086]
[Table 4]

[0087]
[table 5]

[0088]
[Table 6]

[0089]
　In Tables 3 through 6, the numerical values ​​underlined are meant to be outside the scope of the H-shaped steel of the present disclosure.
[0090]
　Production No. 1 to 4 and 6 to 7, 9 to 13, and 16-17 (Tables 3 and 4), as well as production No. 20-23 (Tables 5 and 6), the chemical composition, carbon equivalent Ceq, cumulative rolling reduction A, the cumulative rolling reduction B, rolling finishing temperature, average cooling rate, an average crystal grain size, and MA area fraction of, It was in the range of H-section steel of the present disclosure. These samples YS and TS are satisfied the 385MPa and 490MPa, which is the lower limit value of each target. Furthermore, the Charpy absorbed energy at -20 ° C., not less than 200 J, satisfied the goal.
[0091]
　On the other hand, production No. 5,8,14,15,18, and 19 (Tables 3 and 4), as well as, No. 24-39 (Tables 5 and 6), the chemical composition, Ceq, cumulative rolling reduction A, the cumulative rolling reduction B, rolling finishing temperature, average cooling rate, one of the average grain size, and MA area fraction of 1 One or more outside the scope of H-section steel of the present disclosure. Therefore, YS, TS, and of the Charpy absorbed energy at -20 ° C., any one or more does not satisfy the target value of the.
[0092]
　Specifically, in Table 3 and Table 4, production No. 5, since the rolling finishing temperature is less than 750 ° C., YS and TS did not satisfy the target.
　Production No. 8, since the average cooling rate in the measurement position 7 of Figure 1 during the accelerated cooling is less than 0.4 ° C. / s, YS and TS did not satisfy the target.
　Production No. 14 and No. 18, the rolling reduction at 900 ℃ ~ 1100 ℃ (cumulative reduction ratio A) was insufficient. Therefore, the average crystal grain size becomes outside the range of H-section steel of the present disclosure, the Charpy absorbed energy at -20 ° C. was reached the target value.
　Production No. 15 and No. 19, the rolling reduction at 900 ° C. of less than ~ 750 ° C. or higher (cumulative reduction ratio B) is insufficient. Therefore, the average crystal grain size becomes outside the range of H-section steel of the present disclosure, the Charpy absorbed energy at -20 ° C. was reached the target value.
[0093]
　In Tables 5 and 6, manufactured No. 24, C content and MA area fraction was out of range limit. Production No. 26, Si content was outside the range limit. Production No. 27, Mn content and the MA area fraction was out of range limit. Production No. 29, Cu content was out of range limit. Production No. 30, Ni content and the MA area fraction was out of range limit. Production No. 31, Cr content and the MA area fraction was out of range limit. Production No. 32, Nb content and the MA area fraction was out of range limit. Production No. 33, V content was outside the range limit. Production No. 34, Ti content was outside the range limit. Production No. 36, B content and the MA area fraction was out of range limit. Production No. 37, N content was the upper limit, however. Production No. 39, Ceq was outside the range of the upper limit. Therefore, these samples, Charpy absorbed energy at -20 ° C. was reached the target value.
[0094]
　In Tables 5 and 6, manufactured No. 25, C content was outside the range of the lower limit. Production No. 28, Mn content was outside the range of the lower limit. Production No. 35 B content was outside the range of the lower limit. Production No. 38 were out of the range Ceq is lower. Therefore, these samples, YS and TS did not reach the target value.
[0095]
　The metal structure of each embodiment, 10% perlite or less is MA1.2%, other than these balance, ferrite (polygonal ferrite), it consisted of at least one of bainite and acicular ferrite.
[0096]
　Incidentally, reference numerals affixed to the respective figures are as follows.
　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
　5a widthwise end face of the flange
　of 5b flange thickness direction outer surface
　6 web
　7 toughness and steel measurement position of the tissue
　9 specimens
[0097]
　Japanese disclosure of patent application 2017-049844 its entirety is incorporated herein by reference.
　All documents described herein, patent applications, and technical standards, each individual publication, patent application, and that the technical specification is incorporated by reference to the same extent as if marked specifically and individually, It incorporated by reference herein.

The scope of the claims
[Requested item 1]
　Component composition, by
mass%,
C:
0.040 ~ 0.100%, Mn: 0.50 ~ 1.70%,
Cu: 0.01 ~ 0.50%, Ni: 0.01 ~ 0.50
%,
Cr:
0.01 ~ 0.50%, Nb: 0.001 ~
0.050%, V: 0.010 ~ 0.120%, Al: 0.005 ~
0.100%, Ti: 0.
~ 0.025% 001, B: 0.0005 ultra
0.0020% ~,
N: 0.0001 ~
0.0120%, Si: 0 ~ 0.08%, Mo: 0 ~
0.20%, W:
~
0.50% 0,
Ca: 0 ~ 0.0050%, Zr: 0 ~ 0.0050%,
Mg: 0 ~ 0.0050% REM: 0 ~ 0.005%, and,
the balance: Fe and impurities becomes,
　a carbon equivalent Ceq is from 0.300 to 0.480 as determined by the following formula (1),
　the flange A thickness of 25 ~ 140 mm,
　the widthwise length of the flange F, the thickness t 2When,
　in the width direction of the flange, the widthwise end face of the flange (1/6) a position of the F, and, in the thickness direction of the flange, the thickness direction outer surface of the flange (1/4) t 2 the position is the center of the measurement position, the average crystal grain size in the plane perpendicular to the width direction of the flange is less than or equal to 38 [mu] m,
　centered on the measurement position, the steel structure in the plane perpendicular to the width direction of the flange martensite - area fraction of austenite mixed structure (MA) is not more than 1.2%,
　in the width direction of the flange, the widthwise end face of the flange (1/6) a position of the F, and flange of the measured relative to the total thickness of the thickness direction, the rolling direction of the yield strength or 0.2% proof stress of the flange is at least 385MPa, a tensile strength of not less than 490 MPa,
　Shah at -20 ° C. in the measurement position Absorbed energy Rs test is greater than or equal to 200 J, H-section steel.
　Equation (1) Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15
　where, represents C, Mn, Cr, Mo, V, Ni, and Cu contents of the elements (% by mass). If not contained is set to 0.
[Requested item 2]
　A method of manufacturing a H-shaped steel according to claim 1,
　heating the steel slab having a composition as set forth in claim 1 to 1100 ~ 1350 ° C.,
　starts rolling after said heating, the flange in the width direction, at the position of (1/6) F from the widthwise end surface of the flange, the surface temperature of 900 ° C. or higher, 1100 ° C. and pressure of 10 percent cumulative reduction rate a is below than 900 ° C., 750 ° C. or higher cumulative rolling reduction in B performs a rolling of rolling at 10% or more, a step of terminating the rolling and the thickness of the flange as 25 ~ 140 mm at a surface temperature of 750 ° C. or higher,
　after the rolling, the widthwise length of the flange F, the thickness t 2 When, in the width direction of the flange, the widthwise end face of the flange (1/6) a position of the F, and, in the thickness direction of the flange, the thickness direction outer surface of the flange from (1/4) t 2 at the location of The average cooling rate is 0.4 ° C. / s or higher accelerated cooling, and performing intermittently across the air continuously or during
manufacturing method of H-beams with.
[Requested item 3]
　The accelerated cooling is in the width direction of the flange, the widthwise end face of the flange (1/6) at the position of F, according to claim 2, recuperation temperature after cooling stop to accelerated cooling until 600 ° C. or less method of manufacturing the H-shaped steel.