JP5760519B2 - Rolled H-section steel with excellent toughness and method for producing the same - Google Patents

Description

  The present invention relates to a rolled H-section steel widely used as a material for welded steel structures in the fields of architecture, civil engineering, offshore structures, bridges, and the like. It relates to the manufacturing method.

  Rolled H-section steel manufactured by hot rolling has a lower toughness at a portion (reference numeral 4 in FIG. 1) called a “fillet portion” where the web and the flange cross each other than the web and the flange. This is because the processing amount of the fillet part when hot-rolling into H-shaped steel is lower than other webs and flanges, and the rolling temperature is also high, so that austenite grains can be sufficiently refined by recrystallization. In addition, the cooling rate after rolling is slower than that of the web and the flange, so that the microstructure is likely to be coarsened.

  However, in order to efficiently perform the welding work when manufacturing the steel structure, the fillet part is often formed with a welding through hole (scallop) around its periphery, and there is a welded part nearby. Exists. Therefore, from the viewpoint of suppressing brittle fracture of the steel structure, it is extremely important to improve the toughness of the fillet portion.

  Moreover, in high-strength H-section steel of YP 325 MPa or more used for construction of high-rise buildings, super-high-rise buildings, large-scale factories, etc., a relatively large amount of alloying elements are added to achieve high strength. However, the web thin-wall outer constant constant H-section steel, which has been widely used in recent years, is caused by the temperature difference caused by the difference in the plate thickness between the web and the flange, and the web buckling caused by the cooling unevenness during rolling and subsequent cooling (web In order to prevent the occurrence of waves), a thick flange having a high temperature is forcibly cooled. Therefore, the second phase of the fillet part tends to have an upper bainite structure, and the toughness is further lowered.

Many proposals have been made for techniques for improving the toughness of the fillet portion. For example, in Patent Document 1, hot rolling is performed so that the cumulative reduction ratio in the fillet portion is 1100 ° C. or less and 20% or more, hot rolling is finished at 800 to 1000 ° C., and the inner and outer surfaces of the flange are controlled and cooled. In addition, Patent Document 2 discloses a technique for miniaturizing the fillet structure by setting the cooling stop temperature to the Ms point or higher and Ar _{3 to} 200 ° C. or lower. Patent Document 2 discloses rolling using oxide, MnS, etc. dispersed in a slab as a core. A technique for refining the ferrite structure by precipitating VN during and after cooling and using this as a ferrite transformation nucleus to produce ferrite from within the austenite grains is disclosed in Patent Document 3. A technology that refines the microstructure by controlling the dissolved oxygen concentration of molten steel and adding a deoxidizing element to the mold just before solidification to disperse many fine oxides. In item 4, there is a technology that forcibly cools the flange of an H-shaped steel obtained by hot-rolling steel with a combined addition of V and N, and uses the precipitation of VN to refine the microstructure of the fillet. Further, Patent Document 5 discloses a technique for improving the toughness of the fillet portion by adding appropriate amounts of Ti and N and reducing the carbon equivalent.

JP 2003-155520 A Japanese Patent Laid-Open No. 04-131356 Japanese Patent Laid-Open No. 04-279248 JP 2003-268498 A JP 2004-269905 A

  However, even if the techniques disclosed in Patent Documents 1 to 5 are applied, in order to increase the strength, it is necessary to add a relatively large amount of alloy elements and to increase the carbon equivalent. Therefore, the toughness of the fillet portion is not yet at a sufficient level, and the actual situation is that further improvement is required.

  The present invention has been developed to solve the above-mentioned problems of the prior art, and its purpose is to provide a rolled H-section steel of YP 325 MPa or higher that has excellent fillet toughness and to propose an advantageous production method thereof. There is.

  Inventors repeated earnest examination in order to aim at the toughness improvement of the fillet part of rolled H-section steel. As a result, the fillet part of the rolled H-shaped steel corresponds to the final solidified part of the cast steel material, so that the segregation is large in the steel added with a large amount of alloy elements, and the second phase is the upper bainite in the positive segregation part. It has been found that island-like martensite is easily generated inside, while in the negative segregation part having a small segregation component, the ferrite of the main phase is coarsened and the toughness is greatly reduced.

  Therefore, further investigation was performed by paying attention to the segregation degree of Mn, which is a typical segregation element in the ferret part, and the ferrite grain size. As a result, before hot rolling the steel material, by performing a preliminary heat treatment, by reducing the degree of segregation of Mn in the ferret part, it is possible to suppress the formation of the upper bainite structure, and to refine the ferrite grain size, It has been found that the toughness of the fillet portion can be improved.

  Further, the inventors have found that when the inclusions present in the fillet part contain a large amount of rod-like MnS, the upper shelf energy of the fillet part decreases, and in order to improve this, It has been found that it is effective to control the form of inclusions by adding REM.

The present invention developed based on the above findings is C: 0.01-0.20 mass%, Si: 0.01-1.0 mass%, Mn: 0.5-2.0 mass%, P: 0.030 mass% or less. , S: 0.030 mass% or less, Al: 0.003-0.1 mass%, Ca: 0.0001-0.01 mass% and REM: 0.001-0.03 mass% containing species or two, it has a component composition and the balance being Fe and unavoidable impurities, the carbon equivalent Ceq defined by JIS G3136 is 0.36～0.46Mass%, and the fillet This is a rolled H-section steel having an average ferrite grain size of 30 μm or less and a Mn segregation degree of 1.7 or less.

  In addition to the above component composition, the rolled H-section steel of the present invention further includes Cu: 0.01 to 1.0 mass%, Ni: 0.01 to 1.0 mass%, Cr: 0.05 to 1.0 mass%, Mo: 0.01-1.0 mass%, V: 0.001-0.2 mass%, Nb: 0.001-0.03 mass%, Ti: 0.001-0.020 mass%, and B: 0.0001- One type or two or more types of 0.003 mass% are contained.

  The rolled H-section steel of the present invention is characterized in that the number ratio of Ca (O, S) and REM (O, S) in the inclusions of 1 μm or more present in the fillet portion is 50% or more. .

The present invention also possess the above component composition, after 1~50hr heating the carbon equivalent Ceq defined by JIS G3136 is a steel material Ru 0.36～0.46Mass% der at a temperature of 1200 to 1350 ° C. , (Ar ₃ transformation point−100) after pre-heat treatment to cool to below, reheated to 1200-1350 ° C. and hot-rolled to H-shaped steel, the ferrite average particle size of fillet part is 30 μm Hereinafter, a method for producing a rolled H-section steel, characterized in that the degree of segregation of Mn is 1.7 or less, is proposed.

  According to the present invention, before hot-rolling a steel material into an H-shaped steel, it is heated to a predetermined temperature and then subjected to a preliminary heat treatment for cooling, so that a high-strength rolled H-form of YP 325 MPa or more that is excellent in toughness of the fillet portion. It becomes possible to provide steel industrially stably. Therefore, according to this invention, it can contribute greatly to the improvement of the safety | security of a welded steel structure.

It is a figure explaining the specimen collection position in the fillet part of a rolled H-section steel, and an example.

First, the reason for limiting the component composition of the rolled H-section steel of the present invention will be described.
C: 0.01-0.20 mass%
C is an element necessary for ensuring the strength of the H-section steel as a welded structural steel, and requires addition of at least 0.01 mass%. However, since addition exceeding 0.20 mass% reduces weldability, the upper limit is made 0.20 mass%. Preferably it is the range of 0.03-0.18 mass%.

Si: 0.01-1.0 mass%
Si is an element effective for increasing the strength of steel, but in order to obtain the effect, addition of 0.01 mass% or more is necessary. On the other hand, addition exceeding 1.0 mass% lowers the toughness of the fillet portion and the weld heat affected zone (HAZ), so the upper limit is made 1.0 mass%. Preferably it is the range of 0.05-0.6 mass%.

Mn: 0.5 to 2.0 mass%
Mn, like Si, is a relatively inexpensive element that has the effect of increasing the strength of steel, and is therefore an important element for increasing the strength of welded structural steel. However, if it is less than 0.5 mass%, the effect of addition is small, while addition over 2.0 mass% is not preferable because it promotes the upper bainite transformation and lowers the toughness of the fillet portion. Therefore, Mn is set to a range of 0.5 to 2.0 mass%. Preferably it is the range of 0.6-1.6 mass%.

P: 0.030 mass% or less P is an impurity inevitably mixed in steel, and is a harmful element that greatly reduces the toughness of the base material, particularly the fillet portion and the toughness of the welded portion. Therefore, P is preferably as low as possible, but mixing up to 0.030 mass% can be tolerated. Therefore, the upper limit of P is 0.030 mass%. Preferably it is 0.025 mass% or less.

S: 0.030 mass% or less S, like P, is an impurity that is inevitably mixed in steel, and is a harmful element that promotes embrittlement. In particular, S forms Mn and MnS and greatly reduces the upper shelf energy of the fillet portion. For this reason, the smaller the amount of S, the better. However, 0.030 mass% or less is acceptable. Therefore, the upper limit of S is 0.030 mass%. Preferably it is 0.025 mass% or less.

Al: 0.003-0.1 mass%
Al is an element added as a deoxidizing material for steel, and it is necessary to add 0.003 mass% or more. However, even if it exceeds 0.1 mass%, the deoxidation effect is saturated. Therefore, Al is set to a range of 0.003 to 0.1 mass%.

Ca: 0.0001 to 0.01 mass%, REM: One or two selected from 0.001 to 0.03 mass% Ca and REM are sulfide inclusions MnS, oxysulfide of Ca and REM It has a form control effect of being transformed into (sulfur oxide) and granulated, and is an element particularly effective for improving the toughness and ductility of the fillet part. In order to develop the effect, Ca needs to be added in an amount of 0.0001 mass% or more, and REM needs to be added in an amount of 0.001 mass% or more. On the other hand, when Ca exceeds 0.01 mass% and REM exceeds 0.03 mass%, the cleanliness of the steel decreases. Therefore, Ca is in the range of 0.0001 to 0.01 mass%, and REM is in the range of 0.001 to 0.03 mass%. Preferably, Ca is in the range of 0.0010 to 0.005 mass%, and REM is in the range of 0.003 to 0.02 mass%.

Carbon equivalent Ceq: 0.36-0.46 mass%
The carbon equivalent Ceq needs to be 0.36 mass% or more in order to ensure the strength of the base material, particularly the fillet portion and the web. However, if it exceeds 0.46 mass%, the weldability and the toughness of the HAZ part are lowered, so the upper limit is made 0.46 mass%. Preferably it is the range of 0.36-0.44 mass%.
Here, in this invention, the said carbon equivalent Ceq is the following formula prescribed | regulated to JIS G3136 "rolled steel materials for building structures";
Carbon equivalent Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
However, in said formula, each element symbol is content (mass%) of each element.
Calculating using

In addition to the essential component composition, the rolled H-section steel of the present invention further includes one or more selected from Cu, Ni, Cr, Mo, V, Nb, Ti, and B within the following ranges. Can be added.
Cu: 0.01-1.0 mass%, Ni: 0.01-1.0 mass%, Cr: 0.05-1.0 mass%, Mo: 0.01-1.0 mass%, V: 0.001- 0.2 mass%, Nb: 0.001 to 0.03 mass%
Cu, Ni, Cr, Mo, V, and Nb all lower the ferrite transformation start temperature (Ar ₃ transformation point) during cooling after hot rolling, and contribute to refinement of ferrite grains. It is also effective as an element for increasing the strength. On the other hand, if added excessively, the hardenability of the fillet portion is excessively increased, so that upper bainite is formed and the toughness is lowered. In consideration of these effects, Cu, Ni, Cr, Mo, V, and Nb are preferably added within the above range.

Ti: 0.001 to 0.020 mass%
Ti is an element that forms TiN, refines austenite grains, and is effective in improving toughness by refining the microstructure. In order to obtain this effect, 0.001 mass% or more is preferably added. On the other hand, even if added over 0.020 mass%, TiN becomes coarse and the effect of refining austenite grains cannot be obtained. Therefore, the upper limit is preferably 0.020 mass%. More preferably, it is the range of 0.003-0.017 mass%.

B: 0.0001 to 0.003 mass%
B is an element effective in increasing the strength of thick H-section steel because it has the effect of improving hardenability. In order to acquire this effect, it is preferable to add 0.0001 mass% or more. However, addition exceeding 0.003 mass% forms borocarbide and lowers toughness. Therefore, B is preferably added in the range of 0.0001 to 0.003 mass%.

Next, the characteristics of the fillet part of the rolled H-section steel of the present invention will be described.
Mn segregation degree of fillet part: 1.7 or less, ferrite grain size: 30 μm or less As described above, as a result of the inventors' investigation, the cause of the decrease in the toughness of the fillet part is that the ferret part is the final solidified part of the steel material. It is greatly related to the large segregation. That is, in the fillet portion corresponding to the final solidified portion, a positive segregation portion and a negative segregation portion are mixed, and the positive segregation portion in which a large amount of alloy elements such as Mn is present is easily transformed into upper bainite. Fragile island-like martensite is generated, and the toughness is reduced. On the other hand, the negative segregation part has a low amount of alloy elements such as Mn and preferentially undergoes ferrite transformation at a high temperature. It becomes coarse and also reduces toughness. Furthermore, the sulfide inclusion MnS present in the fillet portion mainly becomes rod-like MnS, and when it is present in a large amount, the upper shelf energy is reduced. And it became clear that these effects overlapped and the toughness fall of the fillet part was caused.

Therefore, in the present invention, the degree of segregation of Mn is defined as an index representing the level of segregation in the fillet portion, the value is restricted to 1.7 or less, and the average grain size of ferrite is restricted to 30 μm or less. Here, the Mn segregation degree is defined as a ratio (C _max / C ₀ ) of the Mn maximum concentration C _max of the ferret portion to the average concentration C ₀ of Mn in the 1/4 t portion from the back surface of the flange 1 / 6B portion. .
When the segregation degree of Mn exceeds 1.7, in the positive segregation part where the concentration of alloy elements such as Mn is high, the formation of island martensite due to the upper bainite transformation becomes significant, and the concentration of alloy elements such as Mn This is because, in a negative segregation portion having a low value, ferrite transformation occurs from a high temperature and coarse ferrite is generated, so that the toughness of the fillet portion is greatly reduced. Note that the Mn segregation degree is preferably 1.55 or less.

  Moreover, the reason for prescribing the average particle size of ferrite in the fillet portion to be 30 μm or less is that when the average particle size of ferrite exceeds 30 μm, the toughness is significantly reduced, and the Charpy absorbed energy at 0 ° C. is less than 100 J. It is. The average particle diameter of the ferrite is preferably 25 μm or less. In addition, the average particle diameter of the ferrite in the present invention refers to the average particle diameter of the equivalent circle diameter obtained by observing the microstructure with an optical microscope, tracing the ferrite grains, and performing image analysis.

The number ratio of Ca (O, S) and REM (O, S) in inclusions of 1 μm or more present in the fillet part is 50% or more. The rolled H-section steel of the present invention is 1 μm or more present in the fillet part. The total number ratio of Ca (O, S) and REM (O, S) in the inclusions is preferably 50% or more. According to the investigation by the inventors, the fillet part of the rolled H-section steel produced using a steel material not added with Ca or REM has a large amount of rod-like MnS extending particularly in the rolling direction. Reduce Charpy upper shelf energy. Therefore, in the present invention, Ca and REM are added as essential components as steel components, and the inclusions generated in the fillet part are controlled in form to granular Ca (O, S) or REM (O, S). , Preventing a decrease in shelf energy.
However, in order to more surely obtain the effect of adding Ca and REM, the total number ratio of granular Ca (O, S) or REM (O, S) in inclusions of 1 μm or more existing in the ferret part. Is preferably 50% or more. Here, the size of the inclusion is a size obtained from a secondary electron image observed by SEM or EPMA, and in the case of a rod-like shape, the size of the long side.

Next, the manufacturing method of the rolled H-section steel of this invention is demonstrated.
The method for producing a rolled H-section steel according to the present invention comprises melting steel that conforms to the component composition described above to form a steel material, heating the steel material to a predetermined temperature, then performing breakdown rolling, Although it is a manufacturing method consisting of a series of steps of rolling, intermediate rolling, and finish rolling to make H-shaped steel, as described below, the steel material before hot rolling is pre-heat treated. To reduce the segregation of the final solidified part.
Therefore, the melting of the steel may be performed by a generally known smelting process through a converter, vacuum degassing treatment, etc., and the production of the steel material is also performed by a continuous casting method or an ingot-bundling rolling method, etc. It may be produced by a generally known method and is not particularly limited.

Pre-heat treatment: After heating at 1200 to 1350 ° C. × 1 to 50 hr, cooling to (Ar ₃ transformation point−100) ° C. or less As described above, the method for producing the rolled H-section steel of the present invention is to use a steel material as H Prior to hot rolling on the shape steel, preliminary heat treatment is performed in advance at a predetermined temperature and time to reduce segregation of the fillet portion and to refine the ferrite grain size. In order to obtain the segregation reducing effect, it is necessary to heat at 1200 to 1350 ° C. for 1 to 50 hours.
When the heating temperature is less than 1200 ° C. or the heating time is less than 1 hr, the reduction of segregation of Mn is insufficient. On the other hand, heating exceeding 1350 ° C. increases the scale loss and the surface wrinkles due to the scale. Moreover, when heating time exceeds 50 hr, the effect will be saturated and productivity will be inhibited.

The steel material subjected to the heat treatment needs to be cooled to a temperature of (Ar ₃ transformation point−100) ° C. or lower after that. This cooling is intended to refine the microstructure of the fillet portion by once cooling the coarsened austenite. That is, even when heat treatment for reducing segregation is performed, when reheating from a temperature exceeding (Ar ₃ transformation point−100) ° C. to a predetermined temperature required for hot rolling and hot rolling as it is Since coarse austenite is maintained as it is in the fillet portion, the microstructure is coarsened and a sufficient toughness improving effect cannot be obtained. On the other hand, after performing heat treatment for reducing segregation, cooling to a temperature of (Ar ₃ transformation point−100) ° C. or lower, and then reheating to a predetermined temperature required for hot rolling Since the transformation from austenite to ferrite during cooling and the transformation from ferrite to austenite during reheating occurs, the austenite becomes finer, so that the microstructure of the fillet part, especially ferrite can be made finer. It is. The cooling temperature after the heat treatment may be any (Ar ₃ transformation point -100) ° C. or less, may be at room temperature.

Here, the temperature of the Ar ₃ transformation point may be obtained by actual measurement, but can be obtained from the steel component using the following formula.
Ar ₃ (° C.) = 910-273C + 25Si-74Mn-5Cu-56Ni-16Cr-9Mo-1620Nb
However, each element symbol in the above formula indicates the content (mass%) of the component.

Hot Rolling The steel material that has been subjected to the preliminary heat treatment is then reheated to a temperature of 1200 to 1350 ° C. and then hot rolled to an H-section steel. When the reheating temperature is less than 1200 ° C., the deformation resistance is high and the rolling load becomes large. On the other hand, reheating above 1350 ° C. is not preferable because there is a possibility of increasing scale loss and generating surface defects due to scale.
The hot rolling after reheating the steel material is not particularly limited as long as the conventional hot rolling, which is breakdown rolling, rough rolling, intermediate rolling, and finish rolling, may be performed as in the prior art. The cooling after hot rolling may be either air cooling or water cooling.
Note that this hot rolling need not be performed after all the steps are preheated and then reheated. For example, some steps such as breakdown rolling may be performed before cooling of the preheat treatment.
Further, the H-shaped steel of the present invention is less susceptible to the deterioration of toughness due to strong cooling after hot rolling compared to the conventional rolled H-shaped steel, so that the flange requires strong cooling after hot rolling. It is suitable as an H-section steel whose thickness is twice or more the web thickness.

  After melting the steel having chemical composition of A to I shown in Table 1 by a normal refining process through a converter and vacuum degassing treatment, and making it a steel material (slab or beam blank) by continuous casting method The steel material is heat-treated at the heating temperature and time shown in Table 2 and subjected to a preliminary heat treatment for cooling, and then re-heated, and is generally known for hot rolling that performs breakdown rolling, rough rolling, intermediate rolling, and finish rolling. The H-shaped steel having the dimensions shown in Table 2 was produced.

Each rolled H-section obtained as described above was subjected to the following evaluation test.
<Tensile test>
From the flange 1 / 6B shown in FIG. 1, a JIS1A test piece defined in JIS Z2201 whose tensile direction is the length direction of the H-section steel is taken, a tensile test is performed according to JIS Z2241, and the yield stress YS (Or 0.2% yield strength), tensile strength TS, and yield ratio YR were measured.
<Toughness test>
A 2 mm V notch Charpy impact test piece defined in JIS Z2202 is sampled from the 1/4 t portion from the back surface of the flange 1 / 6B portion shown in FIG. The absorbed energy at 0 ° C. was measured.
<Measurement of Mn segregation degree>
A small test piece is collected from the fillet part, embedded in resin, buffed, and then subjected to an investigation using an EPMA under the conditions of an acceleration voltage of 20 kV, a beam diameter of 4 μm, and a step of 4 μm, 1 mm × 1 mm (250 steps × 250 Step) Mn surface analysis was performed, and the Mn segregation degree (C _max / C ₀ ) was determined by the ratio of the Mn peak value (maximum value) to the Mn average value in the 1/4 t part from the back surface of the flange 1 / 6B part. .
<Measurement of ferrite particle size>
After collecting a small test piece from the fillet part, embedding in resin, buffing, corroding with nital, and observing the microstructure at 200 times using an optical microscope, tracing 100 or more ferrite grains, Image analysis processing was performed to calculate the equivalent circle diameter, and the average particle diameter was obtained.
<Identification of inclusions>
Using the embedded and polished sample used for the measurement of the ferrite particle size, component analysis was performed on 10 or more inclusions having a size of 1 μm or more using EPMA, and the main inclusions were identified and the size was 1 μm or more. The ratio of Ca (O, S) and REM (O, S) in the inclusions was determined.

The measurement results are shown in Table 3.
From Table 3, all of the H-shaped steels of the inventive examples obtained by rolling steel materials satisfying the composition of the present invention under conditions suitable for the present invention have high strength of YP325 MPa or more, and Both the material and fillet have Charpy absorbed energy of 100 J or more. In particular, the toughness of the fillet portion of the invention example in which the ratio of Ca (O, S) and REM (O, S) in the inclusions having a size of 1 μm or more is 50% or more is excellent at 150 J or more.
On the other hand, in the H-section steel (No. 14) to which no Ca or REM is added, the MnS morphology control is insufficient, and the ratio of Ca (O, S) and REM (O, S) is low. , Charpy absorbed energy is low. Moreover, in the H-section steel (No. 2, 4, 8, 9) in which the heat treatment temperature of the steel material before hot rolling is less than 1200 ° C. and the holding time is less than 1 hr, the value of Mn segregation is large, and the fillet part Since the upper bainite is formed, the toughness of the fillet portion is reduced. Moreover, the be subjected to a heat treatment 1~50hr before hot rolling at a temperature of 1200 to 1350 ° C., the cooling temperature (Ar ₃ transformation point -100) higher than ° C. H-section steel (Nanba3,6), The microstructure of the fillet portion is rough, and the toughness of the fillet portion is reduced. Further, the H-section steel (No. 13) in which Ceq exceeds the upper limit value of the present invention has reduced toughness, and the H-section steel (No. 15) in which Ceq is lower than the lower limit value of the present invention has a target strength. (YP ≧ 325 MPa) is not obtained.

  The H-section steel of the present invention is not limited to the fields of architecture, civil engineering, offshore structures, bridges, etc., but can be applied to a wide range of fields where H-section steel is used.

1: Rolled H-section steel 2: Flange 3: Web 4: Fillet part 5: Test piece sampling position

Claims (4)

C: 0.01-0.20 mass%, Si: 0.01-1.0 mass%, Mn: 0.5-2.0 mass%, P: 0.030 mass% or less, S: 0.030 mass% or less, Al : 0.003-0.1 mass% is contained, Ca: 0.0001-0.01 mass% and REM: 1 type or 2 types chosen from 0.001-0.03 mass% are contained, and the remainder has composed of Fe and unavoidable impurities, the carbon equivalent Ceq defined by JIS G3136 is 0.36～0.46Mass%, and the average ferrite grain diameter of the fillet portion is 30μm or less, Mn segregation Rolled H-section steel having a degree of 1.7 or less. In addition to the above component composition, Cu: 0.01 to 1.0 mass%, Ni: 0.01 to 1.0 mass%, Cr: 0.05 to 1.0 mass%, Mo: 0.01 to 1.0 mass %, V: 0.001 to 0.2 mass%, Nb: 0.001 to 0.03 mass%, Ti: 0.001 to 0.020 mass%, and B: 0.0001 to 0.003 mass%, or 1 or 2 The rolled H-section steel according to claim 1, comprising a seed or more. The rolled H shape according to claim 1 or 2, wherein the number ratio of Ca (O, S) and REM (O, S) in inclusions of 1 µm or more present in the fillet portion is 50% or more. steel. Have a component composition according to claim 1 or 2, after 1~50hr heating the carbon equivalent Ceq defined by JIS G3136 is a steel material Ru 0.36～0.46Mass% der at a temperature of 1200 to 1350 ° C. , (Ar ₃ transformation point−100) after pre-heat treatment to cool to below, reheated to 1200-1350 ° C. and hot-rolled to H-shaped steel, the ferrite average particle size of fillet part is 30 μm Hereafter, the manufacturing method of the rolling H-section steel characterized by making Mn segregation degree 1.7 or less.

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