0001]CROSS REFERENCE TO RELATED APPLICATIONS
This application is based on Japanese Patent Application No. 2016-166535, filed in Japanese on August 29, 2016, and claims priority, the contents of which are incorporated herein.
[0002]The present invention relates to rolled H-section steel and a method of manufacturing the steel strip is produced by hot rolling.
BACKGROUND
[0003]H-shaped steel is widely used as a material, such as construction and civil engineering, offshore structures conventionally, those of various cross-section is used. In particular a rectangular cross-section of the slab obtained by a high continuous casting productive and steel material, H-section steel produced by hot rolling is low in manufacturing cost, are used in many fields. Conventionally, H-section steel produced from a slab has been produced by edging process shown in FIG. 1 (a). Edging method first slotted for guiding the steel to grooved central role in the slab end, it rolled in the width direction of the slab, to form the flange portion by extending the slab end portion in the thickness direction of the slab a rolling method. Alloying elements in the center segregation area was including Mn, which is formed when the cast slab is concentrated. Center segregation area by rolling in edging method further aggregate in a portion where the web and flange portions intermingled, so called "fillet", may adversely affect the toughness.
[0004]
　In view of such a problem, to eliminate macro segregation (aggregation of the center segregation area), it is effective to diffuse Mn or the like by a fixed time heating at high temperature, the slab before hot rolling how the heat treatment has been proposed (e.g., see Patent Document 1). Further, after addition of strain by rolling in order to promote diffusion, it is effective to retain a high temperature, after rough rolling the steel slab, a method of re-heated prior to intermediate rolling has been proposed ( For example, see Patent documents 2 and 3).
[0005]
　Further, a method of eliminating the macrosegregation besides heat treatment has been proposed (e.g., Patent Documents 4 and 5, reference). Patent Document 4 discloses a method of adding a reduction before completely solidified by a continuous casting. On the other hand, Patent Document 5, the edging caliber of slab width of the roughing mill, caliber bottom discloses a method of forming a flat box caliber, are referred to as wedge method.
CITATION
Patent Document
[0006]
Patent Document 1: JP 2012-180584 Patent Publication
Patent Document 2: JP-A 6-122921 Patent Publication
Patent Document 3: JP-A-6-122922
Patent Document 4: JP-A 5-305395 Patent Publication
Patent Document 5: JP 7-88502 JP
Summary of the Invention
Problems that the Invention is to Solve
[0007]
　As described above, conventionally, in order to suppress the decrease in toughness of a fillet portion of the rolled H-shape steel caused by the macro segregation, there have been proposed various countermeasures. However, that impair the productivity becomes a problem for edging method which is one of the measures against the prior art.
[0008]
　SUMMARY OF THE INVENTION In view of such circumstances, without impairing the productivity relative to the edging method is prior art, to provide rolled H-section steel macrosegregation of the fillet portion has been reduced and the manufacturing method thereof It lies in the fact.
Means for Solving the Problems
[0009]
　The present invention is, with respect to the width direction of the rolled material, an interrupt is formed by shaping the caliber of protrusions are formed to put a vertically interrupts, and having a sequentially folding step to this starting point. According to this process, the center segregation area in forming the flange from the slab is dispersed throughout the flanges, without impairing the productivity, it is possible to suppress aggregation of the center segregation area at the fillet portion.
　The gist of the present invention is as follows.
[0010]
[1]でby
mass%,
C: 0.01 ~
0.25%, Si: 0.05% ~ 0.50%, Mn: 0.40
~ 2.50%, P: 0.050% or
less, S : 0.050% or
less, N: 0.020% or
less, a Cu: 0.70% or
less, of Ni: 0.70% or
less, of Cr: 0.50% or less,
V: 0.12% or
less, of Mo: 0 .30% or
less of Nb: 0.08% or
less of Ti: 0.05% or
less of Al: 0.07% or
less, the REM: 0.010% or
less of Ca: 0.0050% or less,
remnants: Fe and unavoidableびimpurities,
A rolled H-shaped steel having the chemical composition is, the top 5% average value of Mn concentration in the outermost embrittlement portion of the flange is, the position of 1/6 from the end face of the flange width to the flange width direction, and, or less 1.6 times the Mn concentration at the position of 1/4 from the surface of the flange located on the opposite side of the web to the flange thickness direction, toward the center of the flange width on one end face or both end faces of the flange width 15mm or more and the upper 5% average value of Mn concentration in the center segregation area to be distributed to an area within the flange surface 2mm in thickness direction, the position of 1/6 from the end face of the flange width to the flange width, and and equal to or less than 1.6 times 1.1 times the Mn concentration at the position of 1/4 from the surface of the flange located on the opposite side of the web to the flange thickness direction, rolled H-section steel.
[2] The steel strip of rectangular cross-section and heated to 1100 ~ 1350 ° C., in order rough rolling step, a method of manufacturing the rolled H-shaped steel according to the intermediate rolling step performs finish rolling step [1], wherein the rolling mill to perform the rough rolling process, three or more grooved to shape the material to be rolled is provided at least one of said plurality of grooved is vertically interrupt to the width direction of the material to be rolled an interrupt forming hole type disposed pair of upper and lower rolls projecting portion is formed to put in a subsequent stage of the interrupt forming caliber, sequentially folding the cleavage site formed by the interruption forming caliber wherein the shaping hole type is provided, the production method of the rolled H-shaped steel.
[3] characterized in that said tip angle of the protrusion formed on the interruption forming caliber is 40 ° or less, the production method of the rolled H-shaped steel according to [2].
[4] and the length H of the interrupt formed by the protrusions, the the thickness T of the steel strip with a rectangular section, the width F of the flange of rolled H-shaped steel which is formed by the finish rolling step, the following and satisfies the equation (1), [2] or [3] the method for producing a rolled H-shaped steel according to.
H ≧ 0.5F-0.5T ··· (1 )
Effect of the invention
[0011]
　According to the present invention, without performing a special heat treatment of the re-heating or temperature maintenance or the like after the preheating and rolling, it is possible to obtain an excellent H-shaped steel toughness of a fillet part in a simple process. Thus, without impairing the economic efficiency, or the like becomes possible to further improve the reliability of steel structures for the rolled H-section steel with a member, the present invention is the contribution of the industry is extremely remarkable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012]
And [Figure 1] "edging method", it is a schematic illustration of the comparison between the "split method".
FIG. 2 is a diagram showing the correlation between segregation ratio and the Charpy transition temperature difference DerutavTrs.
3 is a schematic explanatory view showing a position of observation of the mechanical tests and metallographic.
4 is a schematic diagram showing a manufacturing process of the H-shaped steel according to the embodiment of the present invention.
It is a schematic explanatory view showing the shape of a roll and the rolled material used in [5] rough rolling.
DESCRIPTION OF THE INVENTION
[0013]
　It will be described below with reference to the drawings, embodiments of the present invention. In the specification and drawings, components having substantially the same function and structure are a repeated explanation thereof by referring to the figures.
[0014]
　The present inventors have put the interruption when forming the flange portion, by producing bending the flange portion, segregation is dispersed throughout the flanges to give the finding that aggregation of segregation in the fillet portion can be improved . First, briefly describing the present findings.
　Incidentally, a method of manufacturing the H-beams as is rolling shaping by bending the flange portion according to the present embodiment herein referred to as "split method".
[0015]
　First, briefly described with reference to FIG. 1 for an overview of the "split method". Figure 1 is to be one of the rough rolling process in the conventional manufacturing method of the H-shaped steel so-called "edging" method, the so-called "split method is a rough rolling process in the manufacturing method of the H-shaped steel according to this embodiment it is a schematic illustration of comparison with ".
[0016]
　As shown in FIG. 1 (a), edging method, during rough rolling in the production of the H-beams from the slab, to impart grooves for guiding the slab Anagata center the slab ends, rough rolling a method of performing hot rolling by the attached grooved rolls in the machine. The heated slab in a heating furnace and rolled in the width direction, a flange portion is formed by extending the slab end portion in the thickness direction of the slab. Thus with respect to the flange portion is the material to be rolled which is formed, in order to further adjust the shape and size of the product precisely, such as rolling finish by intermediate rolling mill by the intermediate rolling and the finish rolling mill is performed, the final H form steel products are manufactured.
[0017]
　On the other hand, as shown in FIG. 1 (b), the split method, during rough rolling in the production of the H-beams from the slab, the interrupt forming a deep groove depths (interrupt) as compared to the edging method the slab end faces It is imparted by use hole type. Then, the granted groove, rolling molding line like widening divide slab end that is the separation portion using the grooved rolls of the shaped hole type protrusions are formed to widen the groove divide. A method of forming a flange portion by performing such split spread rolled shaped for example by changing a plurality of times the angle is split method. Thus to the rolled material and the flange portion formed further conducted intermediate rolling and finish rolling and the like, the final H-shaped steel products are produced.
[0018]
　The present inventors, when compared edging method and Split method shown in FIG. 1, focusing on the center segregation area is high mainly Mn concentration present in the slab region, and rough rolling by edging method, by splitting method the rough rolling was found that there is a large difference in the aggregation or dispersion state of the center segregation area of the slab.
　That is, as shown in FIG. 1 (a), the edging process when rolling the slab in the width direction by the grooved roll, the center segregation area is known to aggregate to the fillet portion. On the other hand, as shown in FIG. 1 (b), little rolling the slab in the width direction of the split method, taking a method such widening split flange portion, the center segregation area is distributed across the flange, the fillet rough rolling is conducted without aggregation. In particular, the protrusion tip angle of the caliber of an interrupt by an acute angle of 40 ° or less, it has been found that the aggregation of the center segregation area it is possible to suppress.
[0019]
　The present inventors have found that by splitting method, vTrs in F / 6 showing the average mechanical properties of H-beams (Charpy transition temperature) is at 0 ℃ below, as center segregation area shown in FIG. 2 most toughness was knowledge that differences can be suppressed within 40 ° C. of vTrs of the most fragile portion to deteriorate. This is mainly island martensite is MnS and hard phase present in a higher center segregation area of ​​the Mn concentration (MA), is presumed to be due to suppressed embrittlement by the upper bainite.
[0020]
　Hereinafter, due to the findings as described above, the rolled H-section steel and a manufacturing method thereof according to the present embodiment will be described in detail. In the following description, the description "%" for component, in particular means "% by mass" unless otherwise specified.
[0021]
　First, the component composition of the H-beams for (chemical composition) will be described.
[0022]
(C: 0.01 ~ 0.25%)
　C promotes MA generation in the fillet part, lowers the toughness. However, C is possible to inexpensively improve the strength, to completely remove the step on the C steelmaking from lead to increased costs, the amount of C 0.01% or more. On the other hand, MA is increased at a position where the center segregation area are aggregated in the fillet when the C content exceeds 0.25%, the toughness is lowered, to limit the C content to 0.25% or less. Preferably 0.20% or less C content, more preferably less than 0.17%.
[0023]
(Si: 0.05 ~ 0.50% or
　less) Si is a deoxidizing element, contributes to the improvement of strength, similar and C, and is an element to produce MA. When Si amount exceeds 0.50%, to lower the toughness of the base metal and weld heat affected zone by the formation of the hard phase, to limit the amount of Si in 0.50% or less. Si content is preferably 0.30% or less, more preferably 0.20% or less, further preferably 0.10% or less. However, since the process cost of deoxidation when not containing Si is increased, the inclusion of Si 0.05% or more.
[0024]
(Mn: 0.40 ~ 2.50%)
　H-shaped steel produced by edging method center segregation area of the slab to aggregate the fillet. Mn is easily aggregated in particular the center segregation area, by locally forming the MA concentration of Mn which is an embrittlement phase by increasing, the increase in upper bainite is coarse tissue, increase in MnS, increase in hardenability increase of the hardness is promoted. As a result, the toughness is remarkably lowered. In particular, the inclusion of Mn in excess of 2.50%, the fillet portion, impairing the toughness of the base metal and weld heat affected zone by an increase in inclusions. Therefore, to limit the amount of Mn below 2.50%. Mn content is preferably not more than 2.00%, more preferably at most 1.80%. Meanwhile, Mn can be effective element for refining the grain size, the inclusion of 0.40% or more.
[0025]
(P: 0.050% or less)
　P is weld cracking due to solidification segregation, so causing decrease in toughness, it should be reduced as much as possible. P content is preferably limited to 0.050% or less, more preferably 0.010% or less. Incidentally, the lower limit, since the steelmaking cost and removed to less than 0.001% increases greatly, and may be 0.001% or more.
[0026]
(S: 0.050% or less)
　S is solidification segregation forms MnS at the center segregation area formed by welding cracks, so causing hydrogen cracking, etc. not only decrease in toughness, it should be reduced as much as possible . S content is preferably limited to 0.050% or less, more preferably 0.010% or less. Incidentally, the lower limit, since the steelmaking cost and removed to less than 0.001% increases greatly, and may be 0.001% or more.
[0027]
　Further, for the purpose of improving the strength and toughness, Cu, Ni, Cr, V, Mo, Nb, Ti, Al, 1 or two or more may be contained as an optional additive element of N. Arbitrary additive element, because it is not necessarily added, the lower limit of the content of each optional additive elements is 0%.
[0028]
(Cu: 0.70% or
　less) Cu is an element contributing to the improvement of strength. However, Cu content exceeds 0.70%, the strength is excessively increased, the toughness is lowered, to limit the amount of Cu to 0.70%. The Cu content is preferably not more than 0.50%, more preferably 0.30% is less, further preferably 0.10% or less. The lower limit of the Cu content is preferably 0.01%.
[0029]
(Ni: 0.70% or
　less) Ni is to enhance the strength and toughness, a very effective element. However, Ni is an expensive element, to suppress the increase of the alloy cost, limiting the Ni amount to 0.70%, preferably 0.50% or less, more preferably 0.30% or less, more preferably It is not more than 0.10%. Ni content is preferably 0.01% or more, more preferably 0.02% or more.
[0030]
(Cr: 0.50% or
　less) Cr is also an element which contributes to improvement in strength. However, it generates carbides Cr is added exceeding 0.50%, because it may impair the toughness, to limit the Cr content to 0.50% or less, preferably not more than 0.30%. Cr content lower limit is preferably 0.01%.
[0031]
(V: 0.12% or less)
　V is an element which forms nitride (VN), it may be contained 0.01% or more in order to increase the strength of the base material. Preferably 0.02% or more weight V, more preferably 0.03% or more. On the other hand, V is an expensive element, the upper limit of the V amount is limited to 0.12%, preferably limited to 0.08%.
[0032]
(Mo: 0.30% or
　less) Mo increases the hardenability, an element which contributes to improvement in strength. However, the addition of Mo in excess of 0.30%, Mo carbide (Mo 2 for promoting the production of MA in precipitation or fillets of C), Mo amount of the lower limit is preferably 0.01%.
[0033]
(Nb: 0.08% or
　less) Nb is an element which ferrite is miniaturized, improving the toughness. However, if adding over 0.08% excessively inhibit ferrite transformation, to promote the formation of MA, to limit the amount of Nb to 0.08% or less, preferably 0.05% or less, more preferably 0.03% or less.
[0034]
(Ti: 0.05% or
　less) Ti is an element which forms TiN, TiN becomes coarse when the Ti content exceeds 0.05%, it becomes a starting point of brittle fracture, Ti content 0.05% limited to the following. Preferably 0.03% or less of Ti amount, and more preferably 0.02% or less. Although the amount of Ti lower limit may be 0% fine TiN is to contribute to refinement of the structure, may contain more than 0.005%.
[0035]
(Al: 0.07% or
　less) Al is a deoxidizing element, when the Al content exceeds 0.07%, to lower the toughness of the base metal and weld heat affected zone by inclusions, the Al amount It is limited to 0.07% or less. Al content is preferably 0.05% or less, more preferably 0.04% or less, more preferably 0.03% or less. The lower limit of the Al content is not specified, but may be 0%, Al is a useful deoxidizing element, it may be contained 0.01% or more.
[0036]
(N: 0.020% or less)
　N is an element which lowers the toughness of the base metal and weld heat affected zone. When N content exceeds 0.020%, the impairing low temperature toughness by the formation of solid solution N and coarse precipitates, limiting the amount of N to 0.020% or less. N content less preferably 0.010%, more preferably 0.007% or less. Meanwhile, since the steelmaking costs when attempting to reduce the N content to less than 0.002% increases, the amount of N may be 0.002% or more. N content in terms of cost may be 0.003% or more.
[0037]
　Further, for the purpose of controlling the form of inclusions, REM, one or two of Ca may be contained as an optional additive element.
[0038]
(REM: 0.010% or less, Ca: 0.0050% or
　less) REM and Ca is a deoxidizing element, to contribute to control the form of sulfide, it may be added. However, REM, because oxides of Ca is easily floated in the molten steel, 0.010% of REM content contained in the steel below limits the amount of Ca to 0.0050%. The lower limit of the REM content and the Ca content is preferably 0.0005%, respectively.
[0039]
　It will now be described metallographic and properties of rolled H-shaped steel according to the present invention. Figure 3 is a schematic explanatory view showing a position of observation of the mechanical tests and metallographic. Hereinafter, primarily in the position shown in FIG. 3, illustrating the results of verification tests metallographic and characteristics.
[0040]
　As shown in FIG. 3, the position of 1/6 from the end face of the flange width direction of the flange to the flange width direction, and the surface of the flange located on the opposite side of the web (i.e., the outer surface) from the flange thickness direction 1/4 position of, and the temperature is lowered easily flange end during hot rolling, the temperature is intermediate between hard flange central lowered. Further, there is no possibility that the center segregation area is observed at this site. Therefore, this position is considered to indicate an average chemical composition and mechanical properties of the H-beam from the temperature distribution.
　In this specification, the position, with the flange width F and the flange thickness t is denoted as "F / 6-t / 4".
[0041]
　H-beam according to this embodiment, suppresses the material variation within the flange. Therefore, measurement of observation and mechanical properties of the metal structure of the H-beam (intensity and Charpy absorbed energy) is most fragile part and in the vicinity F / 2-3t / 4 of H-shaped steel shown in Fig. 3, F / performed 6-t / 4 each sample piece from the position taken in.
[0042]
　Position of the most fragile portions, the right and left directions in the figure by circumstances at the time of flange rough rolling, i.e. not constant relative to the flange width direction. Therefore, in terms of center segregation area it was made to appear by nital corrosion solution portions are agglomerated, showing the position of 3/4 from the surface of the flange located on the opposite side of the web in the flange thickness direction (3t / 4) and the straight line, the center segregation area was determined with the intersection portions which are agglomerated with the position of the most fragile part. Position the sample pieces were taken from the most fragile part specified, measurements were performed observations and mechanical properties of the metal structure.
[0043]
　Evaluation of metal structure of the rolled H-shaped steel of the present invention is carried out by optical microscopy, scanning electron microscopy (SEM) and electron microprobe (EPMA). By light microscopy, most fragile portion shown in FIG. 3 to identify the field of view of 10 mm × 10 mm as the center. In identified field, accelerating voltage 20kV after electrolytic polishing, belt-like beam shape length 20 [mu] m, the condition of step 20 [mu] m, was measured Mn concentration at the position of the most fragile portion defined. Of 500 points × 500 points in the visual field, the average value of 12500 points as the top 5% or more values determined (this is referred to as "top 5% average"), Mn concentration in the outermost embrittlement unit ( CMn-max)
and the.
　On the other hand, samples were taken from the position of the F / 6-t / 4, according to JIS G0404 (2014 year edition), the position of the value of Mn concentration determined by analyzing the chemical composition of the sample F / 6-t / 4 It was the Mn concentration (CMn) in. Furthermore, it was evaluated as segregation ratio by dividing the value (CMn-max) to (CMn) (CMn-max) / (CMn).
[0044]
　Target value of the intensity of rolled H-shaped steel according to the present invention were set on the basis of the steel standard EN10225 adopted in Europe area. With F / 6-t / 4 specimens taken from the position that the measured yield point at room temperature (YP) or 0.2% yield strength above 325 MPa, a tensile strength (TS) is not less than 450MPa It is desirable The target value of the toughness and ΔvTrs ≦ 40 ℃.
[0045]
　Figure 2 is a diagram showing the correlation between segregation ratio and the Charpy transition temperature difference ΔvTrs the definitive H-beams. The segregation ratio in FIG. 2, the concentration ratio of Mn in reference to the position of the most fragile portions and F / 6-t / 4 as described above to FIG.
　As shown in FIG. 2, in the case of manufactured in conventional edging techniques rolled H-shaped steel, the segregation ratio is greater than 1.6, and most brittle portions, the position of the F / 6-t / 4 Charpy transition temperature difference ΔvTrs is over 40 ° C. with. MnS by Mn is more segregated in the outermost embrittlement portion in this state, island martensite is a hard phase (MA), upper bainite or the like is formed, embrittlement can not be suppressed.
　On the other hand, it rolled H-section steel produced by a split method, and the most fragile part, the Charpy transition temperature difference ΔvTrs between the position of the F / 6-t / 4 is 40 ° C. or less. That is, in the state where the segregation ratio becomes 1.6 or less, aggregation of the center segregation area is suppressed, it rolled H-shaped steel excellent in uniformity in the cross-section is obtained in the flange than conventional products.
　Incidentally, when the steel structure building to be used in a general temperature condition is subjected to seismic force, etc., in order to H-section steel members satisfies a predetermined mechanical properties without brittle fracture, F / 6-t / it is desirable 4 position of vTrs is 0 ℃ or less.
[0046]
　As described above, in the rolled H-shaped steel according to the present invention, it is preferable segregation ratio shown in FIG. 2 is 1.6 or less. Furthermore, as the segregation ratio is low, it is suppressed aggregation of the center segregation area, since it is excellent embrittlement, and more preferably 1.5 or less. Also, segregation ratio, it is not less than the characteristic on a 1.0 numerical is preferably, for example, 1.0 or more, or 1.1 or more.
[0047]
　Next, a method for manufacturing the H-shaped steel according to the present embodiment. In this embodiment, in the step shown in FIG. 4, heating a rectangular billet having excellent productivity, rough rolling step, performed an intermediate rolling process, finishing rolling process, hot rolling consisting, accelerated cooling by water cooling device was carried out, the production of H-shaped steel. Of hot rolling, rough rolling is performed by a split method shown in FIG. 1 (b).
[0048]
　In steel making process (Fig. 4 upstream of the furnace in), after adjusting the chemical composition of the molten steel, cast to obtain a rectangular billet (also called "slab" is referred). Casting, from the viewpoint of productivity, preferred is continuous casting. 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 heating temperature in hot rolling is preferably not more than 350 mm.
[0049]
　Then heated steel strip, performing hot rolling using a heating furnace. Subsequently, the rough rolling by a split method shown in FIG. 1 (b) using the rough rolling mill. Thereafter, the intermediate rolling with intermediate universal rolling mill and (intermediate rolling mill) and a water cooling device. Then, to terminate the hot rolling was finished rolling using a finish rolling mill. At this time, it may be water-cooled to H-beams at a timing as needed. The following describes conditions in each process.
[0050]
(Heating temperature of the steel strip: 1100 ~ 1350 ℃)
　heating temperature of the steel slab, and 1100 ~ 1350 ° C.. Since deformation resistance heating temperature is low is increased, and 1100 ° C. or higher in order to ensure the shaping of the hot rolling. On the other hand, if the heating temperature of the steel strip exceeds 1350 ° C., there is the oxide of the surface of the steel strip which is a material to damage by melting furnace. Nb, etc., in order to sufficiently solid solution element that forms a precipitate, it is preferable that the lower limit of the heating temperature of the steel slab and 1150 ° C. or higher. In particular, the plate thickness of the product is thin, since the cumulative rolling reduction is increased, it is preferable to set the heating temperature of the steel slab to 1200 ° C. or higher. To fine tissue, it is preferable that the upper limit of the heating temperature of the steel slab to 1300 ° C. or less.
[0051]
(Interrupt length provisions of H in the rough rolling step)
　In the rough rolling by splitting method, and the thickness T of the steel strip with a rectangular section, the width F of the flange of the finish rolling process rolled H-shaped steel which is formed by the FIG. 5 may be set interrupt length H so as to satisfy a predetermined grooved tip angle (grooved inner periphery of the protrusion tip angle) of the grooved by the interrupt length H and the following formula (1) in the.
　H ≧ 0.5F-0.5T ··· (1 )
[0052]
　As the above formula (1), the lower limit of the interrupt length H is the thickness T of the steel strip having a rectangular cross section, 0.5F-0 with respect to the width F of the flange of rolled H-shaped steel which is formed by a finish rolling process and more than .5T. This can be achieved by performing the rolling shaping by splitting method to the flange width after rough rolling is equal to the flange width of the product, center segregation area is a to suppress the reduction amount of at obtuse grooved and easy aggregation . The upper limit of the interruption length H is not particularly provided, exceeds 0.8f-0.5 T requires excessive edging rolling during intermediate rolling, since the productivity drops, less desirable 0.8f-0.5 T.
[0053]
(Protruding tip angle at the interruption time of the caliber)
　FIG. 1 (b), the for Anagata tip angles shown in FIG. 5 (protruding tip angle in the grooved circumference) sufficient acute in forming an interruption may be an angle, for example, the upper limit may be set to 40 °. Type tip angle exceeds 40 ° when the slab in the center segregation area is not dispersed in the flange, in order to aggregate the edging rolling Similarly fillet portion shown in FIG. 1 (a). The center segregation area during rolling in the interrupt forming caliber as indicated by the split method shown in FIG. 1 (b) the Anagata tip angle by a 40 ° or less is dispersed without agglomeration in the flange, the fillet it is possible to suppress a decrease in toughness.
　The lower limit of Anagata tip angle is not particularly provided, due to the possibility of breakage roll during rolling and below 25 °, preferably more than 25 °.
　At this time, the center segregation area of the slab rather than divided into right and left flanges of the I position, as shown in FIG. 1 (b), may be distributed to the left or right flange.
[0054]
　Split method shown in FIG. 1 (b), for example, the case of producing the flange width 150mm or more rolled H-beams, the center segregation area is distributed in the flange portion, the flange, from the vicinity of the center of the flange width of the flange width 15mm or more toward the one end face or both end faces, and the flange surface in the thickness direction (from the flange surface located on the opposite side of the web in the flange thickness direction) remaining in the region within 2 mm. Figure 1 (b) in the case of producing a rolled H-section steel by a split method shown, the center segregation area dispersed in the flange portion would remain over a predetermined length during the region. The center segregation area to be distributed in the vicinity of the surface layer can be revealing in identification by nital corrosion solution described above.
　The top 5% average concentration of Mn in the center segregation area to be dispersed in the vicinity of the surface layer and (CMn-surface), polarized at this position析度(CMn-surface) / (CMn ) is 1.1 to 1.6 it is desirable that. Split method compared to edging method, there is a tendency that the flange surface of the segregation ratio is higher. When segregation ratio is 1.1 or more, there is a merit that the inspection can confirm the crack surface visually is facilitated, also based on the crack surface, also to trace the product to be more prepared as each individual possible it is. On the other hand, if the segregation ratio exceeds 1.6, it becomes easy to enter a large number of cracks on the flange surface, it is desirable that segregation ratio is 1.1 to 1.6. Incidentally, (CMn-surface) the upper 5% average concentration of Determination in shall conform to Determination of the top 5% average concentration in the (CMn-max). That is, a sample of the sampling position is different only, method of obtaining the numerical value is basically the same.
[0055]
(Intermediate rolling step)
　In the intermediate rolling step of hot rolling may be controlled rolling by the intermediate universal rolling mill. Controlled rolling is a manufacturing method of controlling the rolling temperature and reduction ratio. The intermediate rolling of the hot rolling, is preferably subjected to water-cooling rolling between passes 1 pass or more. The path between the water-cooled rolling, by performing water cooling between rolling passes, the temperature difference is given to and the internal surface of the flange and rolling. Water cooling rolling between passes, for example, by water cooling between rolling passes, after the flange surface temperature was cooled to 700 ° C. or less, a manufacturing method of rolling with recuperator process.
[0056]
　When performing water cooling rolling between passes, with a water cooling device provided before and after the intermediate universal rolling mill, it is preferable to perform water cooling between rolling passes, repeating the spray cooling and reverse rolling of the flange outer surface by the water-cooling unit it is preferable to perform. The path between the water-cooled rolling, even if the rolling reduction is small, it is possible to introduce the working strain to the inside of the plate thickness. Moreover, by reducing the rolling temperature in a short time by water cooling is also improved productivity.
[0057]
　Incidentally, after the end of hot rolling as the intermediate rolling step and the finish rolling process, as it is, the water cooling apparatus provided on the exit side of the finishing mill, may be subjected to accelerated cooling on the inner and outer surfaces of the flanges. The cooling rate of the inner and outer surfaces of the flange becomes uniform, thereby improving the material and shape accuracy. Web top surface after the rough rolling process by cooling water injected into the inner surface of the flange, the upper surface side is cooled. To suppress warpage of the web it may be cooled from the lower surface of the web.
[0058]
　In rolled H-section steel produced by the manufacturing method of the H-shaped steel according to the present embodiment described, the center segregation area present in the slab prior to rolling shaping dispersed without aggregating in fillet rolling over it is possible to complete the modeling. Specifically, in the flanges after rolling shaping, DerutavTrs is rolled H-section steel is manufactured such that 40 ° C. or less, the segregation ratio becomes 1.6 or less (see FIG. 2).
[0059]
　In such rolled H-shaped steel, that such center segregation area to the fillet portion of the flange aggregated adversely affect the toughness and embrittlement is avoided. That is, the production of H-section steel products excellent in toughness and embrittlement can be achieved. The center segregation area dispersed in flanges, the flanges, towards the center of the flange width on one end face or both end faces of the flange width 15mm or more, and the flange thickness direction from the surface located on the opposite side of the web While remaining in the region within 2mm in, for non-aggregated, effects on toughness and embrittlement it is estimated that almost no. Furthermore, conventionally, such as various inspection and experiments to examine the internal state of the flanges is determined, in the H-shaped steel product according to the present embodiment is examined visually flange surface located on the opposite side of the web be able to.
[0060]
　Having described an example of an embodiment of the present invention, the present invention is not limited to the illustrated form. Within the scope of the spirit as set forth in the appended claims, various can employ modifications included also be understood that such modifications and changes belong to the technical scope of the present invention.
Example
[0061]
　As an example of the present invention, samples were taken from the rolled H-shaped steel produced meets the chemical composition and manufacturing conditions described in the above embodiment, the chemical analysis was conducted for the sample. On the other hand, as a comparative example, samples were taken from the rolled H-section steel that does not satisfy any of the component compositions and the manufacturing conditions described in the above embodiment was subjected to the same chemical analysis. Hereinafter, detailed examples, comparison of Comparative Example will be described.
[0062]
　(Example)
　First, No. of Example As 1-13 and 28, the component composition shown in Table 1: Steels having (% by mass) by continuous casting, the thickness was produced steel slabs of 250 ~ 300 mm. Melting of steel is carried out in a converter furnace, primary deoxidation to adjust the component by addition of the alloy, if necessary, subjected to vacuum degassing treatment. Then, the resulting steel slab was subjected to hot rolling in the manufacturing conditions shown in Table 2. In hot rolling, subsequent to rough rolling, intermediate universal rolling mill, by using the water-cooling device provided on the front and back, was water cooled after spray cooling and reverse rolling and rolling of the flange outer surface as required .
[0063]
[Table 1]

[Table 2]

[0064]
　Then, from the position of the most fragile portions and F / 6-t / 4 (see FIG. 3), were taken test pieces the rolling direction to the length direction, mechanical properties were measured. As mechanical properties, yield point (YP), tensile strength (TS), to measure the vTrs. The tensile test was carried out in conformity with JIS Z 2241 (2011 year edition), Charpy impact test was carried out in accordance with JIS Z 2242 (2005 2011 Edition). Further, the area within the square samples were taken from each position of the most fragile part and F / 6-t / 4, 10mm of the center segregation area is aggregated (longitudinal direction) × 10 mm (flange thickness direction), by EPMA and (CMn-max), measured and calculated by the method described (CMn) respectively JIS G0404 (2014 year edition).
　Further, over 15mm towards at least one end face of the flange width direction from the center of the flange width, which remained in center segregation within the surface layer 2 mm, as the Mn concentration in the surface layer portion, parallel to center segregation and the flange thickness direction excluding, and the region of the flange surface under 10mm in the thickness direction (see FIG. 3), it was measured and calculated (CMn-surface) by EPMA.
　It shows the measured and calculated results are shown in Table 3 below.
[0065]
[table 3]

[0066]
　The target values ​​of the characteristics of the H-beam to be produced, room temperature yield point (YP), or 0.2% proof stress than 335MPa, a tensile strength (TS) is more than 450 MPa, DerutavTrs is 40 ° C. or less.
[0067]
　As shown in Table 3, No. of Example 1 to 13 and 28, the normal temperature strength is the target range, and, DerutavTrs satisfies the following 40 ° C. of the target value. Also, segregation ratio of Mn was 1.6 or less both. Segregation ratio of Mn is preferably 1.5 or less, more preferably 1.4 or less.
[0068]
　(Comparative example)
　No. of Comparative Example As 14-27, and Steels having the compositions shown in Table 4, were thick in the same manner as in the above embodiments is produced a steel strip of 250 ~ 300 mm. Then, the resulting steel slab was subjected to hot rolling in the manufacturing conditions shown in Table 5.
　In the following Tables 4 and point underlined in Table 5 is the portion that does not satisfy the component composition and production conditions according to the present invention described in the above embodiment.
[0069]
[Table 4]

[Table 5]

[0070]
　Then, from the most fragile part and F / 6-t / 4 position (see FIG. 3), were taken test pieces the rolling direction to the length direction, as in the above embodiments, mechanical properties were measured. As mechanical properties, yield point (YP), tensile strength (TS), to measure the vTrs. Further, samples were taken from each position of the outermost brittle portion surface layer portion and the F / 6-t / 4, similarly to the above embodiment, by EPMA and (CMn-max) (CMn- surface), JIS G0404 ( was measured and calculated by the method described (CMn), respectively in 2014 edition).
　It shows the measured and calculated results in Table 6 below. Incidentally, portions underlined in Table 6 below is a value deviated from the target value of the individual properties of the H-beam to be produced.
[0071]
[Table 6]

[0072]
　As shown in Table 6, No. 14, 16 and 18 C, Mn, the strength because the amount of Si is less missing. No. 15 Many C content, No. 17 Many Si amount, an increase of the hard phase and vTrs in F / 6-t / 4 by coarsening is not less 0 ℃ higher toughness even at most fragile portion is decreased. No. 19 Many weight Mn, vTrs in F / 6-t / 4 is not less 0 ℃ above, the center segregation ratio is deteriorated at the most fragile part, toughness is deteriorated by the MnS and MA. No. 20 Many P content, No. 21 are often amount S, toughness is lowered. No. 22 is beyond the 40 ° grooved tip angle of rough rolling because the slab center segregation area are aggregated without dispersion, the toughness of the lowest embrittlement portion is decreased. No. 23 and 24 is insufficient length of the interruption, for the slab center segregation area are aggregated without dispersion, the toughness of the lowest embrittlement portion is decreased. No. 25 Many weight Nb, No. 26 Many weight Mo, No. 27 are often amount REM, toughness of the most fragile portion is decreased.
Industrial Applicability
[0073]
　The present invention is applicable to steel strip in the rolling H-section steel and a manufacturing method thereof are produced by hot rolling.

WE CLAIM

By
mass%,
C: 0.01 ~
0.25%, Si: 0.05% ~ 0.50%, Mn: 0.40
~ 2.50%, P: 0.050% or
less, S: 0. 050% or
less, N: 0.020% or
less, Cu: 0.70% or
less, Ni: 0.70% or
less, Cr: 0.50% or less,
V: 0.12% or
less, Mo: 0.30%
hereinafter, Nb: 0.08% or
less, Ti: 0.05% or
less, Al: 0.07% or
less, REM: 0.010% or
less, Ca: 0.0050% or less,
the balance: Fe and inevitable impurities,
in a rolled H-section steel having a certain chemical composition,
the top 5% average value of Mn concentration in the outermost embrittlement portion of the flange is, the position of 1/6 from the end face of the flange width to the flange width direction, and the web Mn concentration at a position of 1/4 from the surface of the flange located opposite the flange thickness direction It is 1.6 times or less of,
From the center of the flange width toward the one end face or both end faces of the flange width 15mm or more, and, the top 5% average value of Mn concentration in the center segregation area to be distributed to an area within the flange surface 2mm in thickness direction , the position of 1/6 from the end face of the flange width to the flange width direction and 1.1 times or more of the Mn concentration at the position of 1/4 from the surface of the flange located on the opposite side of the web to the flange thickness direction 1. wherein the 6-fold or less, rolled H-section steel.
[Requested item 2]
The steel strip having a rectangular cross section were heated to 1100 ~ 1350 ° C., in order rough rolling step, an intermediate rolling step, a method of manufacturing the rolled H-shaped steel according to claim 1 carried out finish rolling step,
said rough rolling the rolling mill to perform the process, three or more of the caliber is provided for shaping the material to be rolled,
at least one of said plurality of grooved places the vertically interrupt to the width direction of the rolled material projections parts are interrupt forming hole type disposed pair of upper and lower rolls that are formed,
in a subsequent stage of the interrupt forming caliber, shaping holes successively bending the cleavage site formed by the interruption forming caliber wherein the mold is provided, the production method of the rolled H-shaped steel.
[Requested item 3]
Characterized in that the tip angle of the protrusion formed on the interruption forming caliber is 40 ° or less, the production method of the rolled H-shaped steel according to claim 2.
[Requested item 4]
The length H of the interrupt formed by the protrusions, and the thickness T of the steel strip of the rectangular cross-section, the width F of the finish rolling process rolled H-shaped steel formed by flanges, the following equation (1 ) and satisfies the method for producing a rolled H-shaped steel according to claim 2 or 3.
H ≧ 0.5F-0.5T ··· (1 )