WO2001075182A1

WO2001075182A1 - Rolled h-shaped steel having uniform microstructure and uniform mechanical properties and method for producing the same

Info

Publication number: WO2001075182A1
Application number: PCT/JP2001/002931
Authority: WO
Inventors: Suguru Yoshida; Hironori Satoh; Takeshi Yamamoto; Eiji Saiki; Masao Kurokawa
Original assignee: Nippon Steel Corporation
Priority date: 2000-04-04
Filing date: 2001-04-04
Publication date: 2001-10-11
Also published as: JP4231226B2; EP1281777B1; TW541342B; EP1281777A4; EP1281777A1

Abstract

A rolled wide flange beam to be used as a member for building structures which has a uniform microstructure and uniform mechanical properties, characterized in that the microstructure in the cross section thereof satisfies one or more of the following requirements , the following percentages being relative to respective values for a 1/4 flange portion : 1) a 1/2 flange portion and a fillet portion have an average ferrite grain diameter in the microstructure within ± 15 %, 2) a 1/2 web portion has an average ferrite grain diameter in the microstructure within ± 15 %, 3) a 1/2 flange portion and a fillet portion have an average pearlite percentage in the microstructure within ± 8 %, and 4) a 1/2 web portion has an average pearlite percentage in the microstructure within ± 8 %.

Description

Description Rolled H-section steel with uniform microstructure and uniform mechanical properties, and its manufacturing method

The present invention relates to an H-shaped steel used as a member for a building structure, and more particularly to a rolled H-shaped steel having a uniform microstructure and uniform mechanical properties in the H-shaped steel, and a method for producing the same. Background art

Cross-sectional dimensions of hot-rolled steel bars, such as H-beams, vary greatly depending on the product size, and the amount of reduction in each part during rolling and the temperature histories during and after rolling may differ significantly. . In particular, in the H-section steel, the 1/2 flange portion (hereinafter referred to as the “fillet portion”) where the flange and the web are joined in the flange portion is more deformed by rolling than the other flange portions. It has the characteristic that the amount is small and the processing in the high temperature range is forced. As a result, microstructural differences occur at each cross-section in the flange within the same member. This microstructural difference affects mechanical properties such as strength and toughness, and specifically, is a main cause of a decrease in strength and toughness of the fillet portion. The material difference in this cross section becomes remarkable in large size and thick wall size, and tends to be remarkable in heavy structure using such H-section steel.

In order to solve the above-mentioned problems, the strength and toughness of the fillet, which is conventionally the weakest part, is captured by methods such as increasing the amount of alloy added, so that the strength and toughness of the standard can be improved. Characteristic values are guaranteed. In this case, The mechanical properties of parts other than the fillet part are superior to those of the fillet part, and although they are distributed at a level that sufficiently satisfies the specified values, material differences occur within the flange cross section. However, it may not be suitable for components used for more strict steel structure design. That is, when a sudden large load is applied, there is a problem that a crack is generated from the fillet portion. For example, when a conventional H-shaped steel is used for members in a structure that has been subjected to seismic design, the collapse pattern that cannot be predicted at the design stage during a large earthquake occurs due to the material difference that occurs within the cross-sectional members. Risk of occurring.

On the other hand, in order to adopt manufacturing conditions such as alloys and processes that guarantee the mechanical properties of the fillet, which is the weakest part, the other cross-sectional parts must be over-guaranteed beyond the specified lower limit of mechanical properties. Is inefficient and uneconomical with unnecessary increases in steel prices. In addition, there is a problem that the microstructure is different between the flange portion and the web portion because the rolling reduction and the rolling temperature history are different from each other. Therefore, in order to more economically produce H-beams of the same standard, it is essential to reduce the material difference in this cross section.

Techniques for producing an H-section steel having more uniform mechanical properties in consideration of the above-described problems include, for example, controlled rolling and water cooling of the outer surface of the flange disclosed in Japanese Patent Application Laid-Open No. 6-22863. A method of manufacturing that combines accelerated cooling with the flange is considered, but with this technology, the amount of water in the width direction of the outer surface of the flange is adjusted, that is, water cooling is concentrated in the vicinity of the center of the flange width corresponding to the fillet. Therefore, it is possible to make the rolling temperature histories of the 1/4 flange and fillet closer and to make the mechanical properties of the flange section uniform, but before starting water cooling and during water cooling over the entire cross section including the web. It is difficult to control the temperature distribution by water cooling alone to homogenize the microstructure and sufficiently suppress the deviation in strength. At the rolling stage, a microstructural control method using the introduction of working strain by large rolling reduction, subsequent recovery and recrystallization phenomena is conceivable. And the microstructure could not be homogenized.

The production of H-section steel involves a breakdown process of rolling a heated slab to an H-shaped rough shape (hereinafter referred to as a coarse slab) and an intermediate process of forming the product to the dimensions such as thickness, width and height to the product size. And a finish rolling process. In the conventional manufacturing method, the ratio of the flange thickness to the web thickness of the rough slab to be finished in the breakdown process was formed to a value close to the ratio of the flange thickness to the web thickness of the product. This is due to the web waves that occur when the flange and web thickness reduction balance deviates significantly from 1 in the subsequent intermediate and finish rolling processes, especially in the simultaneous rolling process for flanges and webs called universal rolling. This is to prevent shape failure in the longitudinal direction of the steel material, such as buckling of the flange, tearing of the flange (difference in extension at the end), and dimensional defects such as thickness, width, and height.

Since the web thickness is thinner than the flange thickness in most of the sizes of the H-section steels, the above-mentioned rolling method tends to significantly reduce the temperature of the web during rolling and increase the temperature deviation in the H section. In this case, the temperature distribution is maximum at the fillet and minimum at the center of the web, and the temperature difference may reach 150 ° C or even 200 ° C in some cases.

In the presence of the temperature deviation in the H section, when rolling control using recovery recrystallization for the purpose of uniform micronization of the microstructure is performed, it is necessary to set separate times for each of the flange, fillet and web. Large rolling reduction is required. As described above, assuming that the rolling balance of the flange thickness and the web thickness is rolled at a value close to 1, large rolling reduction must be performed in a wide temperature range. To achieve this, it is necessary to increase the cross-sectional size of the rough slab to be finished in the breakdown process. New molding technology is required to manufacture the products. These were difficult to realize because they had economical problems such as a decrease in manufacturing work efficiency and technical problems such as the development of an unrealized method of manufacturing large-section coarse steel slabs.

Therefore, in the current process, universal rolling was performed between 950 and 110 ° C at a flange and web reduction rate of about 15 to 18% at most, per pass.

As a method of microstructure refining the mouth opening as an alternative to rolling and water cooling control, as disclosed in JP-A-4-279247 and JP-A-4-2792848, intragranular ferrite is used. There is a production method in which the transformation nuclei are dispersed in austenite to make the microstructure fine and uniform even under low-pressure conditions.This involves the amount of dissolved oxygen in the steelmaking stage and the formation of oxides that serve as intragranular ferrite transformation nuclei. In order to respond to mass production, additional cost factors such as enhancement of the secondary refining process capacity are added. Therefore, this production method is not suitable for the production of general-purpose steel that requires mass production.

Furthermore, techniques for manufacturing large-sized or thick-walled H-section steels in view of the above-mentioned problems include, for example, Japanese Patent Publication No. Sho 62-55048, Japanese Patent Publication No. Sho 62-54. In Japanese Patent Application Laid-Open No. 862/1994 and Japanese Patent Application Laid-Open No. H10-057676, there is proposed a technique for refining the microstructure of an orifice utilizing precipitation of VN. However, when H-shaped steels are manufactured using these technologies, the difference in the microstructure in the cross-section of the H-shape can be somewhat reduced, but a uniform microstructure and / or mechanical properties can be obtained. Not enough measures have been taken. In addition, there is concern that the production cost will increase due to the addition of V, and there will be problems from the economical viewpoint. There is the present situation.

Furthermore, in order to solve the above-mentioned problems, there is a so-called welded H-section steel, which is manufactured by welding steel sheets. Has low economic and market supply capacity in the H-beam market. Also, depending on the welding conditions, the mechanical properties of the weld may differ from those of the base metal, and it is not always possible to obtain a uniform microstructure and / or mechanical properties within the H-section. Disclosure of the invention

The present invention solves the above-mentioned various problems and reduces the microstructure deviation in each portion of H-shaped steels of various sizes manufactured by hot rolling, particularly large-sized and thick-walled H-shaped steels, An object of the present invention is to provide a rolled H-section steel having uniform mechanical properties in an H-section and a method for producing the same. The present invention has been made to achieve the above object, and the gist thereof is as follows.

(1) Carbon equivalent formula Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14: 0.15 to 0.40 mass% of chemical components An H-shaped steel manufactured from a billet having a uniform microstructure characterized in that the microstructure of the H-shaped steel cross section satisfies at least one of the following with respect to the 1Z4 flange portion: A rolled H-beam with microstructure and uniform mechanical properties.

1) The average ferrite particle size in the microstructure should be within ± 15% at 1/2 flange and fillet.

2) The average ferrite particle size in the microstructure should be within 15% in the 1/2 web part.

3) The average value of the pearlite fraction in the microstructure must be within ± 8% at the 1Z2 flange and fillet. . 4) The average pearlite fraction in the mouth tissue shall be ± 8% or less in the 1Z2 web part.

(2) Carbon equivalent equation Ceq. = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 Rolling finish temperature, which is indicated by the surface temperature at the time of rolling finish, in a section of an H-section steel manufactured from a billet having a temperature of 50 ° C or less between the three points of the 1/4 flange, fillet and 1/2 web A uniform microstructure and a uniform machine characterized in that the microstructure satisfies one or more of the following with respect to the 1/4 flange part in the H-section steel section by applying the finish rolling of A method for producing a rolled H-section steel having characteristics.

1) The average ferrite particle size in the microstructure is within ± 15% at the 12 flange and fillet.

2) The average ferrite particle size in the microstructure is within ± 15% in the 1/2 web part.

3) The average pearlite fraction in the mouth opening is within ± 8% at the 1/2 flange and fillet.

4) The average value of the pearlite fraction in the microstructure is within ± 8% in the 1/2 web part.

(3) In addition to the chemical composition described in (2) above, a steel slab containing 0.05 to 0.05% by mass of Nb is subjected to total pressure reduction at a steel material surface temperature of 9500C or less. The method for producing a rolled H-section steel having a uniform microstructure and uniform mechanical properties according to the above (2), wherein finish rolling is performed in which both the flange portion and the web portion have a ratio of 60% or more.

(4) In the method for producing a rolled H-section steel according to the above (2) or (3),

1) Rolling is started after heating the billet to a temperature range of 110 to 130 ° C, and the average thickness of the flange and the web at each part is 950 to 1 Rolling the flange and web reduction rate per pass at 100 ° C at least 20% or more at least once each,

2) The finish rolling in which the rolling finish temperature of the three points of the four flanges, the fillet part, and the 1Z2 web part is between 650 ° C and 860 ° C

A method for producing a rolled H-section steel having a uniform microstructure and uniform mechanical properties, characterized by rolling by any one of rolling methods or a combination of both.

(5) In the production method according to any of (3) or (4) above,

1) The process of cooling the flange between the passes of the repurse rolling in the intermediate rolling process, cooling the surface layer temperature to below 75 ° C, and rolling in the recuperation process between the passes of the reverse rolling. Perform at least twice.

2) The average cooling rate up to 500 ° C after the rolling in the finishing rolling process

Perform accelerated cooling by water cooling at 0.5 to 10 ° C / s.

Or a method for producing a rolled H-section steel having a uniform microstructure and uniform mechanical properties, characterized by being produced by combining any one of the above processes or a plurality of processes. (However, if 2) is not included, allow to cool naturally to 500 ° C after the end of rolling.)

Figure 1 is a diagram showing the location of the H-section steel and the position where the test piece was collected.

Figure 2 shows the change in the average austenite grain size after recrystallization according to the rolling temperature history. BEST MODE FOR CARRYING OUT THE INVENTION

As described above, in the case of H-section steel, the flange The 1/2 flange portion (fillet portion) where the web and the web are joined has a smaller amount of distortion due to rolling compared to other flange portions and has to be applied in a high temperature range, so that it is in the same member. As a result, a microstructural difference occurs in each section of the flange portion, and the microstructural difference causes a reduction in strength and toughness of the fillet portion. In other words, when an H-section steel, which is thinner than the flange portion, is manufactured by the conventional hot rolling process, the web portion is subjected to a relatively low temperature and large pressure manufacturing condition. The microstructure tends to be finer than the flange portion. At the same time, the hardenability of the web portion is lower than that of the flange portion, and the pearlite fraction tends to decrease.

This microstructure difference has a great effect on strength and toughness, and specifically causes an increase in the yield ratio of the web. In addition, the microstructure difference and the material difference are remarkable in the size in which the thickness ratio between the web and the flange is large, and in the thin portion of the web portion. Conventionally, the method of reducing the low-temperature large-pressing condition of the web part and shortening the time required for rolling production in order to approximate the rolling temperature history of the flange part, specifically, limiting the elongation length of the steel material, that is, the weight of the slab Although reductions in weight and rolling speed have been attempted, sufficient measures have not yet been taken to obtain a uniform mouth opening structure at each section. As described above, the H-section steel manufactured by the conventional manufacturing process has a material difference between the web and the flange, and depending on the conditions, it may not be suitable for the members used for strict steel structure design. is there. For example, when a conventional H-beam is used for a member of a structure that has been subjected to seismic design, a collapse pattern that cannot be predicted at the design stage occurs during a large earthquake due to the material difference occurring within the cross section. There is a danger.

Therefore, in the present invention, it is necessary to solve the above-mentioned disparity in Miku mouth organization. As a result of various studies, the average ferrite grain size or the average pearlite fraction in the mouth structure of the H-section was controlled on the basis of the 1/4 flange, and / or 1/2 It has been found that controlling the mechanical properties such as the yield strength and tensile strength at the flange, ridge and fillet is an important factor. This will be described in detail.

The mechanical properties of steel composed mainly of ferrite and pearlite microstructures can be predicted from ferrite grain size and pearlite fraction. When this steel material is deformed, it yields when plastic deformation of the ferrite phase, which is softer than the pearlite phase, starts. It is generally known that mechanical properties of polycrystals found in general steel materials depend on the grain size of this ferrite. In other words, it has been shown theoretically and experimentally that the yield strength has a dependence on the ferrite grain size, and more specifically, it has a linear relationship with the first-half power of the ferrite grain size. I have. In particular, in the case of steel materials of the same composition, the first square of the ferrite grain size and the yield strength are connected by a single linear relationship. This indicates that if the average particle size of the fine particles in the microstructure of steel with the same composition is almost uniform, the yield strength will be almost the same.

On the other hand, the tensile strength depends not only on the strength of ferrite, which is a soft phase, but also on the strength of pearlite, which is a hard phase. This is because the fracture limit in the tensile test indicating the tensile strength is caused by plastic deformation of both ferrite and pearlite. Since the tensile strength of a composite structure is generally considered to be the weighted average of the tensile strength of each constituent phase, the sum of the product of the strength and the structural fraction in each constituent phase is established as a predictive formula for tensile strength. In steels mainly composed of the frit phase and the pearlite phase, the product of the strength of the ferrite phase and the fraction of the fraction is the product of the strength of the pearlite phase and the proportion of the pearlite phase. The value obtained by adding the product is related to the tensile strength and the linearity. At this time, the main constituent phase is

Since it is two-phase, the ferrite fraction is equal to the value obtained by subtracting the pearlite fraction from 1 and the plastic deformation of pearlite is extremely small compared to the plastic deformation of ferrite. For two reasons, the dependence on the grain size is negligible, the tensile strength is an amount dependent on the ferrite grain size and the particle fraction. For example, according to Pic kering, the tensile strength of steel is shown by the following experimental formula (1), and the strength level of rolled steel is almost the same as the chemical composition value, perlite fraction, and ferrite grain size designed for the alloy. It is determined.

Tensile strength (MPa) = 15.4 (19.1 + 1.8 [Mn]

+5.4 [S i] +0.25 [%

Perlite] + 0.5 d- ¹ (1) where d: ferrite particle size (mm)

This indicates that if the average ferrite particle size and the average pearlite fraction in the microstructure of the steel material with the same composition are almost uniform, the tensile strengths are almost the same. Therefore, in order to maintain uniform strength in the cross section of the H-beam, it is essential to control the rolling and cooling processes in each part of the cross section.

The ferrite crystal grain size is determined by the number of ferrite transformation sites and the growth rate of the ferrite crystal in the transformation from austenite to ferrite.1) Austenite grain size immediately before ferrite transformation, 2) It is mainly governed by conditions such as heating temperature and strain amount of thermomechanical treatment represented by accelerated cooling controlled rolling (TMC P), cooling rate of transformation zone, and so on. The perlite ratio is mainly determined by the perlite transformation temperature. The present invention is based on the above principle, and reduces the microstructure difference between the web, flange and fillet of the H-shaped steel formed by rolling by the method described below, thereby obtaining the microstructure in the cross section of the H-shaped steel. And mechanical properties It realizes unification. The following countermeasures can be taken as a method to eliminate the difference in the mouth opening structure between the 1/4 flange portion and the 1/2 flange portion and the fillet portion and to make the mechanical characteristics uniform.

(1) For example, by performing a large rolling reduction of 20% or more at a reduction ratio, the austenite structure after recrystallization of not only the 1/4 flange portion but also the 1/2 flange portion and the fillet portion can be sufficiently reduced. The final microstructure is refined by granulation.

(2) By rolling at a relatively low temperature within the recrystallization temperature range (for example, at more than 950 ° C), recrystallization is performed not only at the 1/4 flange, but also at the 1/2 flange and fillet. The final austenite structure is refined sufficiently to make the final microstructure fine. In order to realize rolling in this relatively low temperature range, a method of cooling the flange between rolling passes with water is conceivable.

(3) After rolling, accelerated cooling by water cooling suppresses ferrite grain growth and increases the pearlite structure ratio.

The following countermeasures can be taken to resolve the microstructural difference between the 1Z4 flange portion and the 12 web portion.

1) A single rolling pass of the web using a hole type called flat pass rolling in the breakdown process is abolished and the temperature drop of the web during rolling is suppressed. In order to realize this process, a single rolling pass of the web is performed in the universal rolling process following the breakdown process. The so-called universal break-down rolling process is essential.

2) Reduce the time required for rolling and suppress the expansion of temperature differences between H-sections.

3) By performing large rolling, the austenite structure after recrystallization of not only the 1/4 flange part but also the fillet part is sufficiently refined to refine the final microstructure. I do. 4) By rolling in a relatively low temperature range within the recrystallization temperature range (for example, at more than 950 ° C), the austenite after recrystallization is not only in the 1/4 flange portion but also in the fillet portion. Fine-grain the tissue and make the final microstructure fine. In order to realize rolling in this relatively low temperature range, a method of cooling the steel material between rolling passes is conceivable.

5) Make the rolling temperature history in the non-recrystallization temperature range close to the three points of the flange, fillet and web. The following items should be controlled as specific methods.

• Suppresses the difference in the total draft in the unrecrystallized temperature range

If the total rolling reduction from the sheet thickness to the product thickness at the upper limit of the non-recrystallization temperature range (for example, about 950 ° C at the steel material surface temperature in the case of the Nb-containing steel of the present invention) is 60% or more, However, the difference in the amount of introduced strain due to rolling is reduced.

• Suppress differences in finishing temperature between parts

If the surface temperature of the copper material (hereinafter referred to as the finishing temperature) in finish rolling between the three points of the flange, fillet and web is below 860 ° C, the microstructure is sufficiently refined. However, when the temperature is lower than 65 ° C., a part of the microstructure is transformed into ferrite to produce processed ferrite by rolling, and the mechanical properties, particularly toughness, are reduced. The lower limit is set at 650 ° C. Furthermore, if the difference between the three finishing temperatures can be controlled within 50 ° C, the difference between the microstructures will decrease.

6) After completion of rolling, cooling rate: 0.5 to: L0.0. Accelerated cooling at a rate of 1 / s suppresses ferrite grain growth and increases the percentage of perlite and bainite structures.

In the present invention, the average ferrite particle diameter or the average percentage of pearlite described above is determined based on the 1Z4 flange portion as a reference. The average value of the errite particle size is within ± 15% at the 1/2 flange and the fillet, or the average pearlite fraction in the microstructure is 1Z2 at the flange and the fillet. Must be within ± 8%. The reason why the range of uniform microstructure was limited to ± 15% in average ferrite particle size and ± 8% in average pearlite fraction was that strength, toughness, etc. were within this range. The variation of the mechanical properties of the alloy can be controlled within about ± 5%, that is, when the average value of the fly particle diameter and the average value of the pearlite fraction are within the above-mentioned ranges, almost uniform mechanical properties can be obtained. It was clarified from the results of the experiment that this was done.

However, industrial production requires some tolerance. Tensile strength * Regarding the yield strength, if the range of the variation is within 5% for the variation in yield strength and tensile strength and within 3% for the variation in the yield ratio, it can be judged that it is uniform.For example, If at least one of the conditions is satisfied, it is determined that the mechanical properties are uniform within the cross section of the H-shaped steel. However, by adopting the manufacturing method of the present invention, the H Shaped steel can be obtained.

Based on 1/4 flange

1) 1 2 Rolled H-section steel with uniform mechanical properties with a yield strength of ± 5% or less at the flange and fillet

2) Yield ratio (yield strength / tensile strength) at the flange and fillet is within ± 3%.

3) Yield strength is within ± 5% and tensile strength is within ± 5% at 1Z2 flange and fillet.

4) 1 Z 2 Yield ratio (yield strength / tensile strength) within flange and fillet within ± 3% and tensile strength within ± 5% 5) Yield strength in the 1 Z 2 web part is within ± 5%.

6) The yield ratio is within ± 3% at the 1 Z 2 ゥヱ section.

7) The yield strength at the web section is within ± 5% and the tensile strength is within ± 5%.

8) Yield ratio is within 3% and tensile strength is within ± 5% at 1/2 web part.

Next, the reason why the carbon equivalent range of the steel of the present invention is limited to 0.15 to 0.40% by mass will be described. The carbon equivalent in the present invention is obtained by the carbon equivalent formula C eq. = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Μο / 4 + V / l4, The range is 0.15 to 0.40% by mass. This component range is specified as JIS standard SN400, SS400, SM400, SN490, SM490, etc. for rolled steel for general structures, rolled steel for welded structures, and for building structures This corresponds to the chemical composition of rolled steel materials. It has a tensile strength of 400 MPa and a strength of 600 MPa, and is a component range that achieves high toughness and high welding performance. When the carbon equivalent is in this range, the microstructure of the component steel is mainly composed of a ferrite phase and a pearlite phase, and the mechanism of the effect of the microstructure on the mechanical properties is established as described above. Note that the carbon equivalent equation described in the claims is also described in the JIS standard, and the lower the value, the better the welding performance. It is empirically known that the lower the value of toughness in the carbon equivalent equation, the better the value.

Further, in the present invention, in addition to the above-mentioned limited range of the carbon equivalent formula, the Nb content is added in the range of 0.05 to 0.035% by mass in order to improve the strength and toughness. It is known that the addition of Nb acts to suppress the recrystallization of steel. For example, even when the addition amount of Nb is 0.05% by mass, the carbon equivalent is within the range of the present invention. Then, it is possible to raise the non-recrystallization temperature range to a temperature range of about 950 ° C, for example. Ma If the Nb addition concentration exceeds 0.035% by mass, coarse Nb-based carbides may disperse and impair the base metal toughness and weldability. % By mass.

Next, the reasons for limiting the control rolling and control cooling conditions, which are features of the present invention, will be described.

When rolling the H-section steel, the reheating temperature of the slab was limited to the temperature range of 110 to 130 ° C, because plastic rolling is not suitable for hot-rolled production of section steel. Heating at 110 ° C or higher is required to facilitate deformation, and the upper limit is set at 130 ° C for the performance and economy of the heating furnace.

Next, the heated steel material is roll-formed by each of the rough rolling, intermediate rolling, and finish rolling. One of the characteristics of the rolling process of the present invention is that the reduction rate per pass in the intermediate rolling process is reduced. Large rolling under 20% or more is mentioned. The reason that rolling reduction at a rolling reduction of 20% or more per pass was limited to a temperature range of 950 to 110 ° C was austenite by recrystallization in this temperature range. This is to maximize the effect of grain refinement of the tissue. The larger the strain applied by rolling, the finer the austenite structure after recrystallization. Conventional rolling reduction 20. /. In the rolling process of less than, the recrystallized structure of the web and the flange was sufficiently fine-grained, but the recrystallized structure was sufficiently fine-grained in the fillet part due to the relatively small processing strain introduced. Did not. However, by rolling at a rolling reduction of 20% or more in the above temperature range, the recrystallization structure of the fillet is sufficiently refined, and a fine-grained austenite structure almost equivalent to that of the web and flange is obtained. In addition, as shown in Fig. 2, the more the number of times of large rolling reduction is 20% or more, the more austenite structure becomes finer, Since the average austenite grain size after recrystallization converges to a value that depends on the processing conditions, the effect of recrystallization tends to gradually reduce the grain refinement effect per pass when the frequency is large. Some of this is accumulated in the austenite grains and acts as ferrite transformation nuclei in the austenite grains, ultimately functioning in microstructural refinement.

In addition, by adding large rolling reduction to the manufacturing process, the number of rolling passes is reduced, and the time required for re-heating the slab to rolling to a predetermined H-section size is shortened. Partial temperature differences are reduced. That is, since the temperature difference between each part during the rolling pass is reduced, the variation in the temperature history of each part is reduced.

In addition to the rolling conditions under the large pressure, by performing water cooling between the rolling passes and after the end of the rolling, uniformity of the microstructure and uniformity of the mechanical properties in each section of the cross section are further promoted.

By performing water cooling on the flange between rolling passes, the fillet temperature is asymptotic to the web temperature or flange temperature, and the microstructure deviation within the cross section is further reduced. The flange water cooling performed between rolling passes is performed by cooling the flange to a temperature of 75 ° C or less immediately after water cooling, and rolling the steel surface in the process of reheating. This method is effective not only at least once but also several times to achieve a more fine graining effect. In addition, the water cooling gives a temperature gradient from the surface layer to the inside of the flange, which increases the penetration of processing into the inside by rolling compared to the case without water cooling, and also has the effect of assisting grain refinement inside the sheet thickness. Granted.

The number of repetitions of the water cooling and recuperation rolling depends on the thickness of the material to be rolled, for example, the flange thickness. The reason for limiting the surface temperature of the flange to below 75 ° C and cooling is not only to lower the temperature of the material to be rolled, but also to suppress the quench hardening of the surface. This is performed to incorporate the effect of exhibiting the effect of In other words, the ferrite is transformed by water cooling to austenite → ferrite transformation temperature (Ar ₃ temperature) or lower, and reheated by the two-phase rolling process of austenite + ferrite and the next rolling pass. The ferrite, which has been transformed by heating, undergoes a reverse transformation process to austenite again, resulting in a finer microstructure in the surface layer, significantly reducing hardenability and quenching and hardening of the surface layer even after accelerated cooling after rolling. Can be prevented.

Further, the reason that the flange portion was cooled at a cooling rate of 0.5 to 10 ° C / s after the rolling was completed and the rolling was terminated was that the grain growth of ferrite was suppressed by accelerated cooling and the The purpose is to make the structure fine and uniform and to increase the perlite ratio and obtain the desired strength with a low alloy. Example

Hereinafter, the present invention will be described based on examples.

The prototype steel was melted in a converter, and the steel slab formed into a 240-300 mm-thick slab by a continuous manufacturing method was heated and then rolled into an H-shaped steel.

The hot rolling conditions are basically a breakdown process by groove rolling, an intermediate rolling process by an intermediate universal rolling mill group consisting of an edger rolling mill and a universal rolling mill, and a finishing rolling process by a universal rolling mill. An H-beam manufacturing method is adopted. Note that this method includes the case where a skew rolling process for controlling the web height of the H-section steel was added.

In this rolling manufacturing method, in the breakdown step, a protrusion is formed at the center of the bottom of the hole, and rolling is performed in the width direction of the slab by a rolling roll in which a plurality of dies having different bottom widths are arranged so that the proper flange width and Web height Mold until finished. Subsequently, in the intermediate rolling process, the flange width is formed by an edger rolling mill and the web thickness and the flange thickness are formed by a universal rolling mill. Furthermore, it is formed into a specified H-section steel size by a finishing mill.

On the other hand, conventionally, in the breakdown process, after the above-mentioned rolling process, a single pass rolling process of the web using a hole type called flat pass rolling was performed.However, the web thickness was reduced at an early stage due to the single rolling process of the web. As a result, the temperature of the web decreased significantly in the subsequent steps, and it was necessary to perform rolling at a lower temperature than in other parts. Also, in the intermediate rolling process, the rolling reduction time per roll in the universal rolling mill is relatively small, which increases the time required for rolling production, and the temperature deviations depending on the location increase by that much, resulting in a difference in rolling temperature history. Was caused.

In this example, the flat pass rolling in the breakdown process was abolished, and the time required for rolling production by the large rolling reduction in the intermediate rolling process was shortened, whereby the microstructure of the mouth opening was homogenized and the mechanical properties such as tensile strength and yield strength were reduced. Uniformity has been achieved. For example, web thickness: 9 mm, flange thickness: 12 mm, web height: 500 mm, flange width: 200 mm H-shaped steel, web thickness: 40 mm, flange thickness: 60 mm When a large H-section steel having a web height of 500 mm and a flange width of 500 mm was manufactured by the above-described process, the microstructure shown in Table 1 was obtained. The mechanical properties of the present invention that make the strength uniform within the cross section include not only the sizes described above, but also, for example, a web thickness: 40 mm, a flange thickness: 60 mm, a web height: 500 mm, and a flange. Thick H-section steel with a width of 500 mm, etc., large web with a thickness of 19 mm, flange thickness of 37 mm, web height of 300 mm, flange width of 900 mm, etc. The same applies to H-section steel.

The mechanical properties of the H-section steel manufactured in this way are shown in Fig. 1. At the center of the thickness 2 of the flange 2 (1/2 t ₂ ), the width of the flange width (B) is 1/4, 1Z2 width (1/4 B, 1/2 B) and the center of the thickness of the web 3 The test piece was sampled from 1/2 H of the web height and determined. 1Z4B corresponds to a portion called a 14 flange portion, 1 / 2B corresponds to a fillet portion or a 1/2 flange portion, and 1Z2H corresponds to a portion called a 1/2 web portion. The properties of each of these parts were determined because the 1/4 flange (1 / 4B) and the fillet (1 / 2B) could represent the characteristics of the H-section flange. Table 1 shows the average ferrite grain size and the perlite fraction in the microstructure of the 1/4 flange, fillet, and 1Z2 web of the prototype steel. The measurement results of the average values and the ratios between the 1/4 part of the flange, the two parts of the fillet part, and the four parts of the flange 1 part and two parts of the 1/2 web part are shown. In the manufacturing stage, the average ferrite grain size and average perlite fraction of the steel of the present invention are distributed within the range specified by the present invention, while the conventional steel (comparative steel) has the range specified by the steel of the present invention. Unsatisfactory, therefore, did not reach the desired strength and toughness. The method of measuring the average particle size of the fine particles and the average value of the pearlite fraction from microstructure observation is not particularly limited, but at least it can be observed with an optical microscope. In which the local variation is judged to be sufficiently small Field of view: about 0.4111111 It is desirable to measure from an area of about 0.4 mm or more. [Table 1] Measurement results of microstructure in flange area of inventive steel and conventional steel (comparative steel)

'1: ((Foot part 1/4 flange part)-1) * 100 (%) or ((1/2 ゥ: Bull part Z1 / 4 flange part)-υ * ιοο (%) [Continued from Table 1] Microstructure measurement results of flanges of inventive steel and conventional steel (comparative steel)

'1: ((Fit part Z1 / 4 flange part) -1) * 100 (%) or ((1/2 ゥ part part 1/4 flange part) -1 100 (%) Example 2>

In the rolling method described in Example 1, the rolling reduction of the large reduction rolling in the intermediate rolling step was set to 20% or more, and the following rolling temperature conditions, rolling pass conditions, and cooling conditions after rolling are shown in Table 2. Produce H-section steel with uniform microstructure at three points: 1/4 flange, fillet, and 1Z2 ゥ It became clear that this was possible.

• Rolling finish temperature within 50 ° C between 3 points of 1 Z4 flange, fillet and 1 Z2 ゥ

• Rolling finishing temperature of 3 points of 1Z4F part, fillet part and 1Z2W part is more than 650 ° C and less than 860 ° C;

The total rolling reduction below 950 ° C is 60% or more for both the flange and the web (only when Nb is added)

-Water cooling of the flange between passes to cool the surface temperature to below 75 ° C and rolling in the process of reheating between passes

• After rolling, the average cooling rate is 0.5 ~ by accelerated cooling with water cooling to 500 ° C: L 0 ° C / s

Table 2 shows the combinations of the manufacturing conditions for the steel of the present invention in Table 1.

Table 2

Fig. 1 Medium pressure pass Water-cooling pass Rolling Finish difference 950 C or less Carbon equivalent after rolling Ferrite * 5 Pearlite * 5 Major category 10.10 l DiHiS.

Parts Number of times (times) * 1 Number of times (times) * 2 Finishing maximum value Total reduction rate Boat (° C) * 3 (%) * 4 Binchen diameter Maximum fraction ¹ Maximum deviation Invention steel 1 1/4 flange 1 / 4F flange: 0 0 879 37 (less than 60%) (automatic cooling) 0.36 0.000% 10.5 12.4% 18.8% 1.6% Fillet 1 / 2F 900 (less than 60%) 11.8 -2.9% 17.6% -6.4%

1/2 web 1 / 2W web: 0 863 (less than 60%) 10.2 19.1%

2 1/4 flange 1 / 4F flange: 3 0 910 31 (less than 60%) (own fiber cooled) 0.30 0.000% 11.8 4.2% 14.8% 2.0% Fillet 1 / 2F 922 (less than 60%) 12.3-5.1% 15.1% -3.4%

1/2 web 1 / 2W web: 3 891 (less than 60%) 11.2 14.3%

3 1/4 Flange 1 / 4F Flange: 3 0 886 25 84.6 (self-cooled) 0.36 0.014% 6.3 8.6% 20.1% 5.0% Fillet 1 / 2F 911 62.6 6.8 -1.% 21.1% 0.0%

1/2 web 1 / 2W web: 3 889 68.5 6.2 20.5%

4 1/4 flange 1 / 4F flange: 3 0 845 20 80.0 (self cooling) 0.38 0.010% 8.7 11.5% 19.6% 1.5% Bullet 1 / 2F 853 59.8 9.7-10.3% 19.9%-2.0%

1/2 web 1 / 2W ep: 4 833 66.1 7.8 19.2%

5 1/4 flange 1 / 4F flange: 2 0 799 22 76.0 (Baiyo cold) 0.38 0.009% 6.4 3.1% 19.9% 1.0% t

00 Fillet 1 / 2F 812 63.4 6.6-1.6% 19.5% -2.0%

1/2 web 1 / 2W web: 2 790 70.4 6.3 20.1%

6 1/4 flange 1 / 4F flange: 3 2 884 17 (less than 60%) (cool by starvation) 0.29 0.000% 8.8 11.% 15.1% 1.3% Fillet 1 / 2F 901 (less than 60%) 9.8 0.0 % 15.3% -3.3%

1/2 web 1 / 2W web: 2 887 (less than 60%) 8.8 14.6%

7 1/4 flange 1 / 4F run, 5 _{: 3} 2 862 28 84.6 (self-fiber cooled) 0.38 0.014% 6.5 0.0% 20.0% 4.5% Fillet 1 / 2F 887 62.6 6.5 -3.1% 20.9% -1.0 %

1/2 web 1 / 2W web: 3 859 68.5 6.3 19.8%

8 1/4 flange 1 / 4F 0 834 35 (less than 60%) (self-cooled) 0.29 0.000% 8.3 9.6% 15.1% 2.6% Fillet 1 / 2F 852 (less than 60%) 9.1-4.8% 15.5% -1.3%

1/2 web 1 / 2W web: 3 817 (less than 60%) 7.9 14.9%

9 1/4 flange 1 / 4F 4 807 27 (less than 60%) (autonomous cold) 0.32 0.000% 8.6 3.5% 15.2% 1.3% Fillet 1 / 2F 820 (less than 60%) 8.9 -5.8% 15.%- 1.3%

1/2 web 1 / 2W web: 1 793 (less than 60%) 8.1 15.0%

10 1/4 Flange 1 / 4F 4 796 33 80.0 (self cooled) 0.36 0.010% 6.3 8.6% 18.6% 1.1% Fillet 1 / 2F 807 61.0 6.8 -1.% 18.8% -3.8%

1/2 web 1 / 2W web: 4 774 66.1 6.2 17.9%

Continuation of 2

* l ir Fig. 1 Medium large rolling pass Water cooling pass Rolling Finish SS¾ 950 ° C or less Control after rolling Carbon equivalent ferrite * 5 Pearlite * 5 Number of times (times) * 1 times (times) * 2 Finishing value Max. C / sT 3 (%) * 4 Average particle size Maximum deviation Fraction Maximum deviation Invention copper 11 1/4 flange 1 / 4F flange: 3 0 901 36 (less than 60%) 1.8 0.36 0.000% 10.1 6.9% 16.1% 6.8% Fillet 1 / 2F 934 (less than 60%) 1.6 10.8 -4.0% 17.2% -1.9%

1/2 web 1 / 2W web: 3 898 (less than 60%) 1.8 9.7 15.8%

12 1/4 flange 1 / F flange: 3 0 887 33 84.6 0.9 0.38 0.01% 9.9 9.1% 18.4% 6.0% Fillet 1 / 2F 902 62.6 0.8 10.8 -1.0% 19.5% -4.9%

1 / 2W ^: P 1 / 2W Web: 3 869 68.5 0.9 9.8 17.5%

13 1/4 flange 1 / 4F flange: 3 0 842 24 (less than 60%) 1.8 0.28 0.000% 8.9 3.% 15.1% 2.6% Bullet 1 / 2F 855 (less than 60%) 1.6 9.2 -2.2% 15.5% -5.3%

1/2 web 1/2 web: 3 831 (less than 60%) 1.8 8.7 14.3%

14 1/4 flange 1 / 4F flange: 3 0 831 11 80.0 1.5 0.36 0.010% 6.3 8.6% 19.0% 1.6% Bullet 1 / 2F 842 61.0 1.2 6.8 -1.4% 19.3% -3.7%

1/2 web 1 / 2W web: 4 841 66.1 1.6 6.2 18.3%

15 1/4 flange 1 / 4F franc,: 2 2 863 38 (less than 60%) 1.6 0.29 0.000% & 2 4.9% 15.3% 5.9%

D

Fillet 1 / 2F 872 (less than 60%) 1.4 8.6 -3.7% 16.2% -5.2%

1/2 web 1 / 2W web: 2 834 (less than 60%) 1.7 7.9 14.5%

16 1/4 Flange 1 / 4F Malang, 5: 2 1 877 24 84.6 1.4 0.38 0.014% 9.1 3.3% 17.8% 6.7% Fillet 1 / 2F 889 62.6 1.3 9.4 -3.3% 19.0% -7.9%

1/2 web 1 / 2W web: 3 865 68.5 1.6 8.8 16.%

17 1/4 flange 1 / 4F flange 4 796 41 (less than 60%) 3.1 0.30 0.000% 7.7 0.0% 14.6% 0.7% Fillet 1 / 2F 815 (less than 60%) 2.7 7.6 -2.6% 14.7%- 3.4%

1/2 web 1 / 2W web: 1 774 (less than 60%) 3.2 7.5 14.1%

18 1/4 flange 1 / 4F 2 804 23 78.0 0.9 0.38 0.010% 8.7 11.5% 18.2% 3.3% Fillet 1 / 2F 820 (less than 60%) 0.8 9.7 -10.3% 18.8%-1.1%

1/2 web 1 / 2W web: 4 797 64.0 0.9 7.8 1 & 0%

19 1/4 flange 1 / 4F 4 796 27 84.6 3.4 0.36 0.014% 6.3 8.6% 18.5% 0.0% Fillet 1 / 2F 801 62.6 3.2 6.8 -1.4% 18.5% -2.2%

1/2 web 1/2 web: 3 774 68.5 3.6 6.2 18.1%

20 1/4 flange 1 / 4F 0 807 37 80.0 (self-cool) 0.34 0.010% 8.7 11.5% 18.9% 5.9% Fillet 1 / 2F 820 (less than 60%) 9.7 -10.3% 18.7%-1 . 1%

1/2 web 1 / 2W web: 0 783 66.1 7.8 20.0%

Table 2 continued

Fig. 1 Medium large rolling pass Water cooling pass Rolling Finish?

WO. As¾ 950. C or less after rolling; ^] Carbon equivalent Ferrite * 5 Pearlite * 5 Number of parts (times) * 1 times (times) * 2 Finish? £ g Maximum value Total rolling reduction itS (° C / s) * 3 (%) * 4 Average particle size Maximum fraction Maximum deviation Invention steel 21 1/4 flange 1 / 4F flange: 0 0 796 41 84.6 (automatic cooling) 0.36 0.010% 6.3 8.6% 20.1% 0.0% Fillet 1 / 2F 815 62.6 6.8 -1.% 18.9% -6.0%

1/2 web 1 / 2W web: 0 774 68.5 6.2 20.0%

22 1/4 flange 1 / 4F flange: 0 1 866 44 84.6 (natural fiber cooled) 0.35 0.011% 8.4 8.3% 18.1% 7.2% Fillet 1 / 2F 876 62.6 9.1 -11.9% 19.4% -3.3%

1/2 web 1 / 2W web: 0 832 68.5 7.4 17.5%

23 1/4 flange 1 / 4F flange: 0 1 874 39 84.6 (self-cooled) 0.35 0.011% 8.4 9.5% 18.% 4.9% Fillet 1 / 2F 886 62.6 9.2 -6.0% 19.3% -2.7%

1/2 web 1 / 2W web: 0 847 68.5 7.9 17.9%

24 1/4 flange 1 / 4F flange: 0 0 881 38 84.6 0.9 0.36 0.014% 8.8 9.1% 17.9% 5.6% Fillet 1 / 2F 895 62.6 0.8 9.6 -5.7% 18.9%-45%

1/2 web 1 / 2W web: 0 857 68.5 0.9 8.3 17.1%

25 1/4 Flange 1 / 4F: 7 Lange: 0 0 880 30 80.0 1.5 0.36 0.025% 8.5 0.0% 17.6% 5.7% Fillet 1 / 2F 891 61.0 1.3 8.2 -7.1% 18.6% -3.%

1/2 web 1 / 2W web: 0 861 € 6.1 1.7 7.9 17.0%

26 1/4 flange 1 / 4F flange: 0 4 841 29 80.0 1.4 0.32 0.020% 8.4 1.2% 14.1% 7.8% Fillet 1 / 2F 849 61.0 1.3 8.5 -11.9% 15.2% -2.1%

1/2 web 1 / 2W web: 0 812 66. 1 1.6 7. 4 13.8%

27 1/4 Flange 1 / 4F: 7 Range: 0 4 822 27 80.0 3.3 0.32 0.020% 7.8 5.1% 12.9% 2.3% Fillet 1 / 2F 829 61.0 3.2 8.2 -6.% 13.2% -2.3%

1/2 web l / 2ff web: 0 802 66. 1 3.5 7.3 12.6%

28 1/4 flange 1 / 4F 0 830 42 (less than 60%) (cool by self-starvation) 0.38 0.000% 8.1 9.9% 20.6% 3.9% Fillet 1 / 2F 854 (less than 60%) & 9-3.7% 19.9 %-3.4%

1/2 web 1 / 2W Gap: 0 812 (less than 60%) 7.8 21.%

29 1/4 flange 1 / 4F 0 795 14 (less than 60%) (self-cooled) 0.39 0.000% 6.5 0.0% 21.1% 0.5% Fillet 1 / 2F 800 (less than 60%) 6.5 -3.1% 20.5% -2.8%

1/2 web 1 / 2W web: 0 786 (less than 60%) 6.3 21.2%

30 1/4 flange 1 / 4F 2 829 29 (less than 60%) (self-cooled) 0.32 0.000% 6.8 4.4% 13.1% 7.6% Fillet 1 / 2F 838 (less than 60%) 7.1 1 -10.3% 14.1% -3.8%

1/2 web 1 / 2W web: 0 809 (less than 60%) 6.1 12.6%

Continuation of 2

Table 2 continued

Major Divisions

Comparative

C

1: The number of rolling passes in which the rolling reduction per pass between 950 and 1100 ° C is 20% or more.

2: Number of passes to cool surface layer temperature to 750 ° C or less by flange water cooling

3: 800 Average cooling rate up to 500 ° C (only for accelerated cooling by water cooling.)

4: Carbon equivalent = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14

5: Deviation = ((fillet part / 1/4 flange part)-1) X100 (%) or = ((fillet part / 1/2 ゥ part)-1) Χ 100 (%)

Table 3 shows the mechanical properties of the H-section steel manufactured by the same method as in Example 1.

Table 3 shows the measurement results of the yield strength and tensile strength of the 1/4 flange, fillet, and 1/2 web of the prototype steel, and the flange 1Z 4 And the ratio between the flange 1/4 part and the 1/2 web part is shown. In the production stage, the yield strength and tensile strength of the steel of the present invention are distributed within the range specified in the present invention, whereas the conventional steel (comparative steel) does not satisfy the range specified in the steel of the present invention, and therefore has the desired strength and strength. Not tough. The size of the tensile test piece for measuring the tensile strength and the yield strength is not particularly limited, but it is preferable that the test be performed at least in accordance with the JIS standard and the JIS standard.

[Table 3] Haze characteristics of various sections of section steel of invention steel and ¾έ¾ | (comparative steel)

"1: Carbon equivalent = C + Si / 24 + n / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14

* 2: ((fillet part / 1/4 flange part) -1 100 (%) or ((1/2 web part / 1/4 flange part H 00W) Note) Data with a yield of 5% or less and a yield ratio of ± 3% or less are shaded in gray. [Continued in Table 3] Mechanical production of each section of section steel of invention steel and (comparative steel)

Equivalent = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / U

* 2: ((7-bit part / 1/47 flange part H) * 100) or ((1/2 tube part / 1/4 flange part) -1) '100 (%)

Note) Data with a yield ratio and tensile ratio within ± 5% and a yield itfc siding ratio within ± 3% are shaded in gray. Industrial applicability

As described above, according to the present invention, the microstructure difference is small in each part of the H-section steel, and the H-section steel having a uniform mechanical property in the cross section of the H-section steel. Can be provided

Claims

The scope of the claims

1. Carbon equivalent formula Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14, steel with a chemical composition of 0.15 to 0.40 mass% A uniform microstructure and uniform H-section steel manufactured from a piece, characterized in that the microstructure of the H-section cross section satisfies at least one of the following with respect to the 1Z4 flange part: H-beam with excellent mechanical properties.

1) The average particle size of the fine particles in the microstructure of the mouth should be within ± 15% at the 1st and 2nd flanges and fillets.

2) The average particle size of the ferrite particles in the mouth structure of the mouth should be within 15% in the No.2 web part.

3) The average value of the pearlite fraction in the microstructure shall be within ± 8% at 1Z2 flange and fillet.

4) The average pearlite fraction in the mouth opening structure should be within 8% of the soil in the 1-to-2 web section.

2. Ceq. = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 from a slab having a chemical composition of 0.15 to 0.40 mass% Finish rolling in which the rolling finish temperature, which is indicated by the surface temperature during rolling finish, on the cross section of the H-beam to be manufactured is within 50 ° C between the three points of the 1/4 flange, fillet and 12 web As a result, the H-section has a uniform microstructure and uniform mechanical properties characterized by satisfying one or more of the following microstructures based on the 1Z4 flange in the H-section Manufacturing method of rolled H-section steel.

1) The average ferrite particle size in the microstructure is within ± 15% at the 12 flange and fillet portions.

2) The average ferrite particle size in the mouth opening structure is within 15% in the 1Z2 web section. 3) The average value of the pearlite fraction in the microstructure is within ± 8% at the 1/2 flange portion and the fillet portion.

4) The average pearlite fraction in the microstructure is within 8% for the 1/2 web section.

3. The chemical component according to claim 2, wherein Nb is 0.05-0.5.

A slab containing 035% by mass is subjected to finish rolling in which the total rolling reduction is 60% or more for both the flange portion and the web portion at a steel material surface temperature of 950 ° C or less. Item 4. The method for producing a rolled H-section steel having a uniform microstructure and uniform mechanical properties according to Item 2.

4. The method for producing a rolled H-section steel according to claim 2 or 3,

1) Rolling is started after heating the slab to a temperature range of 110 to 130 ° C, and the average thickness of the flange and the web at each site is 950 to 1,100 ° C. Rolling the flange and web reduction rate per pass between the rolls is more than 20% at least once,

2) Finish rolling, where the rolling finish temperature of all three points of the 1/4 flange, fillet and 1Z2 web is between 650 ° C and 860 ° C,

5. The method according to claim 3 or 4, further comprising:

1) The flange is water-cooled between the reverse rolling passes in the intermediate rolling process, the surface layer temperature is cooled to 75 ° C or lower, and the rolling is performed in the reheating process between the repurse rolling passes. Perform at least twice.

2) After the rolling in the finish rolling step, accelerated cooling by water cooling is performed at an average cooling rate of 0.5 to 10 ° CZs up to 500 ° C. Or a method for producing a rolled H-section steel having a uniform microstructure and uniform mechanical properties, characterized by being produced by combining any one of the above processes or a plurality of processes. (However, if 2) is not included, allow to cool naturally to 500 ° C after rolling.)