CN113396236A

CN113396236A - H-shaped steel with protrusions and manufacturing method thereof

Info

Publication number: CN113396236A
Application number: CN202080011533.3A
Authority: CN
Inventors: 安藤佳祐; 木村达己; 伊木聪
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2019-01-31
Filing date: 2020-01-29
Publication date: 2021-09-14
Anticipated expiration: 2040-01-29
Also published as: SG11202108195WA; WO2020158823A1; JPWO2020158823A1; JP6819830B2; CN113396236B; KR20210118925A; KR102602081B1

Abstract

The invention provides a H-shaped steel with a protrusion and a manufacturing method thereof, wherein the H-shaped steel with the protrusion can ensure tensile strength, inhibit surface cracks during continuous casting and greatly improve manufacturability. The following steel composition is formed: c is contained in a range satisfying ([% S ]/32)/([% Ti ]/48) +4 × ([% N ]/14)/([% Ti ]/48) ≦ 15.0: 0.05 to 0.20 mass%, Si: 0.05 to 0.60 mass%, Mn: 1.20 to 1.70 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, Nb: 0.005-0.050 mass%, V: 0.005-0.050% by mass, Ti: 0.005-0.030 mass% and N: 0.0020 to 0.0100% by mass, the balance being Fe and unavoidable impurities, the tensile strength being 490MPa or more, the yield strength being 355MPa or more, and the impact absorption energy vE0 at 0 ℃ being 27J or more.

Description

H-shaped steel with protrusions and manufacturing method thereof

Technical Field

The present invention relates to a H-shaped steel with a projection and a method for manufacturing the same, and more particularly, to a H-shaped steel with a projection and a method for manufacturing the same, which is used as a substitute for a reinforcing bar used as a reinforcing material for a large structure such as a pier, and which has excellent mechanical properties such as tensile strength and elongation, and also has excellent toughness.

Background

Reinforced concrete using reinforcing steel bars as reinforcing materials is widely used in large structures such as piers. In general, a reinforced concrete structure is constructed by installing a mold after assembling reinforcing bars and casting concrete in the mold. Here, when the excessive arrangement of the reinforcing bars is required in terms of strength, there is a great problem that the filling property of the concrete is lowered, not only the construction quality is deteriorated, but also the construction time is long. Further, the number of skilled workers who work in such construction tends to decrease year by year, and there is a further need for development of structural steel that contributes to saving labor and shortening the construction period of the current work.

In response to such a demand, various studies have been made on H-shaped steels with projections which have greater section rigidity than reinforcing bars and which can reduce the number of parts required for the same structure. It is known that the H-beam with projections has a high concrete adhesion performance equal to or higher than that of a steel bar by providing projections on the outer surface of a flange. In order to ensure the performance as a structure of H-shaped steel with projections which is used as a substitute for reinforcing steel for a large structure, it is required to ensure toughness in addition to mechanical properties such as tensile strength and elongation.

In order to satisfy these requirements, for example, patent document 1 discloses a H-shaped steel with projections which can improve tensile strength and toughness in a well-balanced manner by adjusting the amounts of Nb, V and Ni added to the steel. Patent document 2 discloses a technique of setting an optimum cooling stop temperature in accordance with the thickness of a flange and appropriately adjusting the amount of cooling water on the inner and outer surfaces of the flange for the purpose of improving the toughness of the H-shaped steel with projections.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 4045977

Patent document 2: japanese patent laid-open No. 2006 and 75883.

Disclosure of Invention

However, the H-shaped steel with projections described in the

above patent documents

1 and 2 achieves both high tensile strength and toughness by adding Nb and V which form carbonitrides, but when a rolled material is produced by continuous casting, defects on the surface of the cast piece called continuous casting cracks are likely to occur, and there is a problem that the productivity is lowered. The present invention has been made to solve the above problems, and an object of the present invention is to provide a H-shaped steel with projections and a method for manufacturing the same, which can ensure tensile strength equal to or higher than that of conventional H-shaped steel with projections and can significantly improve manufacturability.

The present inventors have conducted extensive investigations on the tensile properties and toughness of H-shaped steels with projections having varied contents of C, Si, Mn, P, S, Nb, V, Ti and N. As a result, it was found that when Nb and V were contained in the steel, the occurrence rate of continuous casting cracks was high. Further, by optimizing the amounts of S, Ti, and N contained in the steel, it is possible to stably suppress continuous casting cracks even when Nb and V are contained, and to obtain excellent toughness by promoting the transformation of intragranular ferrite with TiN as a nucleus.

The present invention is based on the above findings, and mainly comprises the following configurations.

1. A H-shaped steel with protrusions has a steel composition containing C in a range satisfying the following formula (1): 0.05 to 0.20 mass%, Si: 0.05 to 0.60 mass%, Mn: 1.20 to 1.70 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, Nb: 0.005-0.050 mass%, V: 0.005-0.050% by mass, Ti: 0.005-0.030 mass% and N: 0.0020 to 0.0100% by mass, the balance being Fe and unavoidable impurities, the tensile strength being 490MPa or more, the yield strength being 355MPa or more, and the impact absorption energy vE0 at 0 ℃ being 27J or more.

([％S]/32)/([％Ti]/48)+4×([％N]/14)/([％Ti]/48)≤15.0···(1)

Here, [% S ], [% Ti ] and [% N ] are the contents (mass%) of S, Ti and N in the steel, respectively.

2. The H-shaped steel with projections according to the above 1, wherein the steel composition further contains a metal selected from the group consisting of Cr: 1.0 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Mo: 1.0 mass% or less, Al: 0.10 mass% or less, B: 0.010 mass% or less, Ca: 0.10 mass% or less, Mg: 0.10 mass% or less and REM: 0.10 mass% or less of 1 or 2 or more.

3. The H-beam with projections according to the above 1 or 2, wherein the height of the projections is 1.5mm or more.

4. A method for producing a H-shaped steel with projections, comprising hot rolling a steel slab having the steel composition according to any one of the above 1 or 2 to form a H-shaped steel with projections,

forming protrusions on the outer surface of the flange of the H-shaped steel by the finish rolling of the hot rolling, and after the finish rolling, cooling the steel at an average cooling rate between a cooling start temperature of 750 ℃ or higher and 500 ℃: cooling at a temperature of 0.1-30 ℃/s.

5. The method for producing a H-shaped steel with projections according to the above 4, wherein the finish rolling is performed at a temperature of 800 ℃ or higher.

According to the present invention, H-shaped steel with projections having excellent toughness can be stably manufactured, which contributes to rapid construction of large structures and improvement in quality of concrete products, and brings industrially advantageous effects.

Description of the symbols

FIG. 1 is a cross-sectional view of a H-shaped steel with projections.

Fig. 2 is a view showing a H-shaped steel with a protrusion, (a) is a side view seen from a direction in which webs face each other, (b) is a plan view seen from a direction in which flange outer surfaces face each other, and (c) is a plan view showing the flange outer surfaces.

Detailed Description

The present invention will be specifically described below. First, the reason why the steel composition is limited to the above range in the present invention will be described. In the following description, "%" means "% by mass" unless otherwise specified.

C：0.05～0.20％

C is an element necessary for securing the strength of the base material, and is required to be contained at least 0.05%. However, if the C content exceeds 0.20%, not only the toughness of the base metal is lowered, but also the weldability is lowered. Therefore, the C content is set to 0.05 to 0.20% in the present invention. The C content is preferably 0.10% or more. The C content is preferably 0.15% or less.

Si：0.05～0.60％

Si is required to be contained in an amount of 0.05% or more for securing the base material strength and as a deoxidizer, and if the Si content exceeds 0.60%, not only toughness is lowered, but also weldability is deteriorated because Si has a high binding force with oxygen. Therefore, in the present invention, the Si content is set to 0.05 to 0.60%. The Si content is preferably 0.20% or more. The Si content is preferably 0.40% or less.

Mn：1.20～1.70％

Mn is a relatively inexpensive element that increases the strength of steel, similarly to Si, and is therefore an element important for increasing the strength. However, if the Mn content is less than 1.20%, the effect of addition is small, while if it exceeds 1.70%, transformation of upper bainite is promoted to lower toughness, which is not preferable. Therefore, in the present invention, the Mn content is set to 1.20 to 1.70%. The Mn content is preferably 1.40% or more. The Mn content is preferably 1.60% or less.

P: less than 0.035%

If the content of P exceeds 0.035%, the ductility of the steel deteriorates. Therefore, in the present invention, the P content in the steel is set to 0.035% or less. Preferably 0.020% or less. On the other hand, the smaller the amount of P, the more preferable, and therefore the lower limit of the P content is not particularly limited, and may be 0%. However, P is an element that is inevitably contained in steel as an impurity, and since excessive reduction of P leads to increase in refining time and increase in cost, the P content is preferably 0.005% or more.

S: less than 0.035%

When S is contained in steel, S is mainly present in the steel in the form of A-type inclusions. If the S content exceeds 0.035%, the amount of the inclusions is remarkably increased and coarse inclusions are generated, thereby greatly lowering the toughness of the steel. Therefore, in the present invention, the S content in the steel is set to 0.035% or less. Preferably 0.020% or less. On the other hand, the smaller the amount of S, the more preferable, and therefore the lower limit of the S content is not particularly limited, and may be 0%. It should be noted that S is an element that is inevitably contained in steel as an impurity, and since excessive reduction of S leads to increase in refining time and increase in cost, the S content is preferably 0.002% or more.

Nb：0.005～0.050％

Nb is an element that increases the tensile strength and the effect of increasing the yield point by precipitating as carbonitride. In order to obtain this effect, the Nb content needs to be 0.005% or more. On the other hand, if the Nb content exceeds 0.050%, precipitation embrittlement is facilitated, and upper bainite transformation is promoted, so that continuous casting cracks are likely to occur, and toughness is also lowered. Therefore, in the present invention, the Nb content is set to 0.005 to 0.050%. The Nb content is preferably 0.010% or more. The Nb content is preferably 0.030% or less.

V：0.005～0.050％

V is an element that increases the tensile strength and the effect of increasing the yield point by precipitating as a carbonitride. In order to obtain this effect, the V content needs to be 0.005% or more. On the other hand, if the V content exceeds 0.050%, it contributes to precipitation embrittlement, and therefore, continuous casting cracks are likely to occur. Therefore, in the present invention, the V content is set to 0.005 to 0.050%. The V content is preferably 0.010% or more. Further, the V content is preferably 0.030% or less.

Ti：0.005～0.030％

Ti is an element effective for preventing surface cracking during bending-bending in continuous casting, and is positively added in a range of 0.005% or more. Ti is an element effective for forming TiN in steel to refine austenite grains, promoting intragranular ferrite transformation with TiN as a nucleus to refine a microstructure, and improving toughness. On the other hand, if the Ti content exceeds 0.030%, coarse TiN is generated, and the toughness of the steel is lowered, which is not preferable. Therefore, in the present invention, the Ti content is set to 0.005 to 0.030%. The Ti content is preferably 0.010% or more. The Ti content is preferably 0.020% or less.

N：0.0020～0.0100％

N is an element useful for forming carbonitrides in the steel to improve the strength of the steel, and the content thereof needs to be 0.0020% or more. However, if the N content exceeds 0.0100%, the formed carbonitride coarsens and the toughness of the steel decreases. Further, if the N content exceeds 0.0100%, cracks are formed on the surface of the cast piece, and the quality of the cast piece is undesirably reduced. Therefore, in the present invention, the N content is set to 0.0020 to 0.0100%. The N content is preferably 0.0030% or more. The N content is preferably 0.0070% or less.

Further, in the present invention, it is not sufficient to simply satisfy the above ranges for each element, and it is important to satisfy the relationship of the following formula (1) when [ S ], [% Ti ], and [ N ] are respectively defined as the contents (mass%) of S, Ti and N in the steel for S, Ti and N.

([％S]/32)/([％Ti]/48)+4×([％N]/14)/([％Ti]/48)≤15.0···(1)

The inventors investigated the cause of cracking in steel during continuous casting, and found that precipitation of coarse MnS and carbonitride of V and Nb on ferrite formed by austenite grains during continuous casting is a cause of cracking. Therefore, as a result of studies to suppress the precipitation of MnS and V and Nb-based carbonitrides on the ferrite, it was found that the precipitation of MnS and V and Nb-based carbonitrides on the grain boundary ferrite can be suppressed and cracks during continuous casting can be suppressed by adjusting the contents of S, Ti and N in the steel. That is, by setting the value calculated from the left side of the above formula (1) based on the parameters of S, Ti and N content to not more than 15.0, it is possible to precipitate S as Ti carbosulfide and N as TiN, and to precipitate coarse MnS and V and Nb-based carbonitrides on ferrite formed of austenite grains during continuous casting, thereby stably suppressing continuous casting cracks. The right side of the above formula (1) is more preferably 10.0 or less, that is, the following formula (1)' is satisfied.

([％S]/32)/([％Ti]/48)+4×([％N]/14)/([％Ti]/48)≤10.0…(1)’

The steel composition of the H-shaped steel with projections used in the present invention is such that the balance other than the above-described components is Fe and unavoidable impurities.

In addition, in the H-shaped steel with projections according to the present invention, in addition to the above-described components, for the purpose of improving the strength, ductility, toughness, and weld characteristics, any one selected from Cr: 1.0% or less, Cu: 1.0% or less, Ni: 1.0% or less, Mo: 1.0% or less, Al: 0.10% or less, B: 0.010% or less, Ca: 0.10% or less, Mg: 0.10% or less, REM: 0.10% or less of 1 or 2 or more.

The reason for determining the content of the above-mentioned elements will be described below.

Cr: 1.0% or less

Cr is an element that can achieve further high strength of steel by solid solution strengthening. However, if the content exceeds 1.0%, transformation of upper bainite is promoted to lower toughness, which is not preferable. Therefore, when the steel contains Cr in the composition, the Cr content is preferably 1.0% or less. More preferably 0.005% or more and 0.5% or less.

Cu: 1.0% or less

Cu is an element that can achieve further enhancement of the strength of steel by solid solution strengthening. However, if the content exceeds 1.0%, Cu cracks are likely to occur. Therefore, when the composition of the steel contains Cu, the Cu content is 1.0% or less. More preferably 0.005% to 0.5%.

Ni: 1.0% or less

Ni is an element that can achieve high strength of steel without deteriorating ductility. Further, since Cu cracks can be suppressed by the composite addition with Cu, Ni is preferably contained also when the steel composition contains Cu. However, if the Ni content exceeds 1.0%, the hardenability of the steel tends to be further improved, and the toughness tends to be lowered. Therefore, when the steel composition contains Ni, the Ni content is 1.0% or less. More preferably 0.005% to 0.5%.

Mo: 1.0% or less

Mo is an element that can achieve further high strength of steel by solid solution strengthening. However, if the content exceeds 1.0%, a large amount of upper bainite is formed in the steel, and the toughness tends to decrease. Therefore, when the composition contains Mo, the Mo content is 1.0% or less. More preferably 0.005% to 0.5%.

Al: less than 0.10%

Al is an element that can be added as a deoxidizer. However, if the Al content exceeds 0.10%, Al has a high bonding force with oxygen, and therefore, oxide inclusions are formed in a large amount in the steel, resulting in a reduction in ductility of the steel. Therefore, when the steel composition contains Al, the amount of Al is preferably 0.10% or less. On the other hand, the lower limit of the Al content is not particularly limited, but is preferably 0.001% or more for deoxidation. More preferably 0.001% to 0.03%.

B: 0.010% or less

B is an element which segregates in the steel at grain boundaries to improve the grain boundary strength. Further, it is an element effective for improving toughness by forming composite precipitates with TiN which becomes nucleation sites of intragranular ferrite to refine the microstructure. On the other hand, if the content exceeds 0.010%, coarse carbonitride grain boundaries precipitate, and the toughness decreases. Therefore, when the steel composition contains B, the B content is 0.010% or less. More preferably 0.001% to 0.003%.

Ca: less than 0.10%

Ca has an effect of converting oxides and sulfides in sulfide-based inclusions into substances having high stability at high temperatures, thereby making the sulfide-based inclusions into particles. Further, the morphology control effect of the inclusions by the Ca can improve the toughness and ductility of the steel. In particular, if the Ca content exceeds 0.10%, the cleanliness tends to be low and the toughness tends to be low. Therefore, when the steel composition contains Ca, the Ca content is preferably 0.10% or less. More preferably 0.0010% to 0.0050%.

Mg: less than 0.10%

Mg has an effect of converting oxides and sulfides in sulfide-based inclusions into substances having high stability at high temperatures and thus making them into particles. Further, the toughness and ductility of the steel can be improved by the morphology control effect of the inclusions caused by the Mg. In particular, if the Mg content exceeds 0.10%, the cleanliness tends to be low and the toughness tends to be low. Therefore, when the steel composition contains Mg, the Mg content is 0.10% or less. More preferably 0.0010% to 0.0050%.

REM: less than 0.10%

REM (rare earth metal) has a function of converting oxides and sulfides in sulfide-based inclusions into substances having high stability at high temperatures, thereby making the sulfide-based inclusions into particles. Further, the effect of controlling the morphology of inclusions by REM is improved, and the toughness and ductility of steel can be improved. In particular, if the REM content exceeds 0.10%, the cleanliness tends to be low and the toughness tends to be low. Therefore, when REM is contained in the steel composition, the REM content is 0.10% or less. More preferably 0.0010% to 0.0050%.

The balance other than the above-described elements is Fe and inevitable impurities.

The H-shaped steel with projections of the present invention will be explained in detail. That is, the H-section with projections is formed by connecting a pair of flanges 2 by a web 3, as shown in fig. 1, similarly to a general H-section. Further, the H-shaped steel with projections has projections 4 on the outer surface of the flange 2. The protrusions 4 are provided to impart adhesive properties to the concrete. In the H-section steel 1 with projections 4 provided for this purpose, the portions where the projections 4 are provided are on the outer surface of the flange 2 as shown in fig. 2 (a). In the illustrated example, the projections 4 are formed on the entire outer surface of the flange 2 so as to be aligned in the longitudinal direction of the flange 2, the projections 4 are ribs extending in the width direction of the flange 2 in the cross-sectional shape shown in fig. (b), which is an enlarged view of a portion surrounded by four corners in fig. 2 (a).

The shape, size, number, and the like of the projections may be arbitrarily set according to the specification required for the H-section steel with projections. Therefore, not limited to the illustrated example, the height h of the protrusion 4 is preferably 1.5mm or more in consideration of the concrete adhesion performance. On the other hand, the upper limit of the height h is preferably 6mm from the viewpoint of preventing roll breakage. The distance d between the projections 4 preferably satisfies a relationship of h/d ≧ 0.05 with respect to the height h in consideration of the concrete adhesion property.

Next, a method for producing the H-shaped steel with projections according to the present invention will be described. The melting method and casting method of steel (slab or beam blank) are not particularly limited, and any conventionally known method is suitable. In addition, the hot rolling conditions for forming into H-shaped steel are also not particularly limited, and may be performed according to a conventional method. In the finish rolling of the hot rolling, the projections may be formed by using a roll having grooves formed on the surface thereof corresponding to the projections formed as a roll for rolling down the portions where the projections are formed (the outer surface of the flange). After finish rolling, cooling is required to satisfy the following conditions.

Flange temperature at the start of cooling: above 750 deg.C

In the present invention, it is desirable to prevent a decrease in production efficiency by starting cooling of the steel material immediately after finish rolling, and the flange temperature at the start of cooling is 750 ℃ or higher. On the other hand, if the flange temperature at the start of cooling is less than Ar₃Since it is difficult to obtain sufficient strength at the temperature, it is preferable to further set the flange temperature at the start of cooling to Ar₃Above the temperature. In addition, Ar₃The transformation temperature is simply shown in relation to the steel composition by, for example, the following formula (2).

Ar₃＝910-310×[％C]+25×([％Si]+2×[％Al])-80×[Mneq]…

(2)

Here, [ Mneq ] is a value calculated from the following formula (3).

[Mneq]＝[％Mn]+[％Cr]+[％Cu]+[％Mo]+[％Ni]/2+10×([％Nb]-0.02)…(3)

In the above formulas (2) and (3), [% M]The content (mass%) of the element M in the steel). Here, Ar is calculated by the above-mentioned formulas (2) and (3)₃In the case of the above, the content of the element M which is not positively contained is calculated by using the content (analysis value) of the element M which is contained as an inevitable impurity.

Average cooling rate from cooling start temperature to 500 ℃: 0.1-30 ℃/s

When the average cooling rate from the cooling start temperature to 500 ℃ is less than 0.1 ℃/s, it is difficult to ensure predetermined tensile properties and toughness, and therefore the cooling rate is 0.1 ℃/s or more. On the other hand, if the cooling rate is increased to more than 30 ℃/s, bainite or martensite is formed, which causes adverse effects such as reduction in toughness and excessive increase in tensile strength, and therefore the average cooling rate from the cooling start temperature to 500 ℃ is set to a range of 0.1 to 30 ℃/s. The average cooling rate is preferably set to 0.5 to 10 ℃/s.

By adjusting the above composition and performing rolling and cooling under the above conditions, excellent mechanical properties such as a tensile strength of 490MPa or more, a yield strength of 355MPa or more, and an impact absorption energy vE0 at 0 ℃ of 27J or more can be obtained in the H-shaped steel with projections. Although there is no need to limit the upper limit of any of the properties, the tensile strength is 640MPa, the yield strength is 475MPa, and the impact absorption energy vE0 at 0 ℃ is about 350J in practice.

Here, the flange thickness of the H-shaped steel with projections to be targeted in the present invention is not particularly limited. The protrusions on the outer surface of the flange are formed by using a grooved roll in the finish rolling step. That is, in order to provide a desired projection height, it is necessary to increase the amount of depression of the flange portion as much as possible. Therefore, the H-section steel with the projections having the thick flange requires a larger reduction amount. In the present invention, as will be described later, by controlling the rolling temperature within an appropriate range, it is possible to provide a sufficient protrusion height also in a thick H-shaped steel having a flange thickness of 16mm or more, which is considered to be low in the formation efficiency of the protrusion height.

In the finish rolling in which the forming for forming the projections is performed during the hot rolling, it is preferable that the finish rolling temperature is 800 ℃ or higher from the viewpoint of forming the projections having a sufficient projection height. If the finish rolling temperature is less than 800 ℃, it is difficult to stably form projections of a sufficient height. On the other hand, the upper limit of the finish rolling temperature is not particularly limited, and when it exceeds 1050 ℃, the austenite grain size tends to be coarse, and the toughness tends to be lowered. Therefore, the finish rolling temperature is preferably 1050 ℃ or lower.

Examples

Hereinafter, the constitution and the operation and effects of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and can be modified as appropriate within a range that can be adapted to the gist of the present invention, and these are included in the technical scope of the present invention.

Steel materials having the composition shown in Table 1 were cast into beam blanks having a cross section of 400 mm. times.560 mm. times.8000 mm in length by a continuous casting machine, and the presence or absence of surface cracks was examined. That is, the surface of the beam blank was observed in the longitudinal direction, and the presence or absence of cracks having a length of 10mm or more was examined. Surface cracking was determined by finding cracks per 1m²The number of cracks of (2) was determined using a: no crack, B: 1 to 4 pieces/m²C, C: more than 5/m²The index (2) is evaluated, and the index is qualified in the case of judgment A or judgment B. Table 1 also shows the results of the determination of surface cracks. In the steel having a steel composition satisfying the above formula (1), the result of determination of surface cracking is a or B.

Next, the beam blanks having surface cracks a or B as a result of determination of the surface cracks were heated at 1250 ℃ for 2 hours, and then hot-rolled and cooled under the conditions shown in table 2, to produce H-section steel 1 with projections having the cross-sectional shape shown in fig. 1, that is, the shape having a web 3 and a pair of flanges 2 disposed at both ends of the web. Here, the cross-sectional dimensions (web height. times. flange width. times. web thickness. times. flange thickness) were set to either 2 of 320X 323X 25mm and 350X 333X 35X 40mm, and H-shaped steel with projections was produced. In the finish rolling, as a roll for pressing the outer surface of the flange, a roll provided with grooves corresponding to the shape of the projections formed on the outer surface of the flange is used, and the projections 6 extending in the width direction of the flange 2 shown in fig. 2 are formed on the outer surface of the flange. Here, the provision of the finishing roll for depressing the outer surface of the flange enables formation of a projection width w: 15mm and protrusion height h: 1.5mm or more. The cooling rate after finish rolling was calculated by measuring the temperature of the outer surface of the flange with a radiation thermometer and converting the temperature change per unit time from the start of cooling to the stop of cooling (in degrees centigrade/s).

[ Table 1]

The obtained H-shaped steel with projections was subjected to projection height evaluation, tensile test and toughness test. The details of each evaluation will be described below.

< evaluation of protrusion height >

The height H of the projections on the outer surface of the flange shown in FIG. 2 was measured for the H-section steel with projections obtained. The values were measured at 3 positions, i.e., the leading end, the center and the trailing end in the rolling direction of the H-section with projections after finish rolling, and the average value was used. The lower limit of the required performance of the protrusion height is set to 1.5mm, and a value equal to or larger than this is defined as a preferable range of the protrusion height h. In addition, from the viewpoint of easy formation of the projections, the production conditions under which the H-shaped steel with projections having the projection height H of not less than this value is obtained can be evaluated as particularly preferable conditions.

< tensile test >

From a portion 1/6B (the length in the flange width direction of 1/6B is 60mm) indicated as 5 in FIG. 1, a JIS1A test piece (total thickness of flange test piece) prescribed in JIS Z2201 was sampled so that the tensile direction was the longitudinal direction of the flange of the H-shaped steel, and a tensile test was performed in accordance with JIS Z2241 to measure the yield strength (yield stress YS or 0.2% proof stress) and the tensile strength.

< toughness test >

A2 mmV notched Charpy impact test piece specified in JIS Z2202 was sampled from the flange rear surface of the flange 1/6B part 5 shown in FIG. 1 at a position 1/4t (t is the flange thickness), and the Charpy impact test was carried out in accordance with JIS Z2242 to measure the absorption energy at 0 ℃.

The results of the above investigation are shown in table 2. The test results (test Nos. 1 to 19, 31 in Table 2) of the H-shaped steel with projections produced by the production method within the range of the present invention (the average cooling rate of the outer surface of the flange is within the range of the present invention) using an appropriate steel satisfying the steel composition of the present invention all satisfy the desired characteristics (tensile strength: 490MPa or more, yield strength: 355MPa or more, and impact absorption energy at 0 ℃ vE 0: 27J or more). In test No.33, the tensile strength, yield strength, and impact absorption energy at 0 ℃ satisfy the desired characteristics, but the finish rolling temperature is less than 800 ℃ which is the preferred lower limit, and therefore the projection height is 1.4mm, which is less than the preferred range (1.5mm or more).

On the other hand, the steel composition of the H-section steel does not satisfy the conditions of the present invention, or any of the tensile strength, yield strength and toughness of the comparative examples (test Nos. 20 to 30, 32 to 34 in Table 2) to which the production method within the scope of the present invention is not applied does not satisfy the required characteristics.

[ Table 2]

In addition, the method is as follows: underline indicates outside the scope of the invention

In addition, 2: cross-sectional dimensions: any one of 320 × 323 × 25 × 25mm and 350 × 333 × 35 × 40mm

Description of the symbols

H-shaped steel with bulge (Rolling H-shaped steel)

2 Flange

3 web plate

4 protrusion

5 Flange 1/6B part (test piece sampling position)

Claims

1. A H-shaped steel with protrusions has a steel composition containing C in a range satisfying the following formula (1): 0.05 to 0.20 mass%, Si: 0.05 to 0.60 mass%, Mn: 1.20 to 1.70 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, Nb: 0.005-0.050 mass%, V: 0.005-0.050% by mass, Ti: 0.005-0.030 mass% and N: 0.0020 to 0.0100% by mass, the balance being Fe and unavoidable impurities, the tensile strength being 490MPa or more, the yield strength being 355MPa or more, and the impact absorption energy vE0 at 0 ℃ being 27J or more,

([％S]/32)/([％Ti]/48)+4×([％N]/14)/([％Ti]/48)≤15.0…(1)，

here, [% S ], [% Ti ] and [% N ] are the contents of S, Ti and N in the steel, respectively, in mass%.

2. The embossed H-beam of claim 1, wherein the steel composition further comprises a material selected from the group consisting of Cr: 1.0 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Mo: 1.0 mass% or less, Al: 0.10 mass% or less, B: 0.010 mass% or less, Ca: 0.10 mass% or less, Mg: 0.10 mass% or less and REM: 0.10 mass% or less of 1 or 2 or more.

3. The H-beam with projections according to claim 1 or 2, wherein the height of the projections is 1.5mm or more.

4. A method for producing a H-shaped steel with projections, comprising subjecting a steel slab having the steel composition according to any one of claims 1 and 2 to hot rolling to form a H-shaped steel with projections,

5. The method for producing a projected H-shaped steel according to claim 4, wherein the finish rolling is performed at a temperature of 800 ℃ or higher.