JP6819830B2 - H-shaped steel with protrusions and its manufacturing method - Google Patents

Description

The present invention relates to H-section steel with protrusions and a method for manufacturing the same, in addition to having excellent mechanical properties such as tensile strength and elongation, which are alternatives to reinforcing bars used as reinforcing materials for large structures such as piers, and toughness. Also excellent, with respect to H-beams with protrusions and their manufacturing methods.

In large structures such as piers, reinforced concrete using reinforcing bars is widely used as a reinforcing material. Generally, the construction of a reinforced concrete structure is carried out by installing a formwork after assembling the reinforcing bars and placing concrete in the formwork. Here, when it is necessary to overcrowd the reinforcing bars in terms of strength, not only the filling property of the concrete is lowered and the construction quality is deteriorated, but also the construction is prolonged, which is a big problem. In addition, the number of skilled workers engaged in the construction is decreasing year by year, and the development of structural steel that contributes to labor saving and shortening of construction period is further required.

In response to such a request, various studies have been conducted on H-section steels with protrusions, which have a larger cross-sectional rigidity than reinforcing bars and can reduce the number of members required in the same structure. It is known that this H-section steel with protrusions has protrusions on the outer surface of the flange and has high concrete adhesion performance equal to or higher than that of reinforcing bars. For H-beams with protrusions used for large structures as a substitute for reinforcing bars, in order to guarantee the performance as a structure, guarantee of toughness is required in addition to mechanical properties such as tensile strength and elongation.

In order to satisfy these requirements, for example, Patent Document 1 discloses an H-shaped steel with protrusions in which the tensile strength and toughness are improved in a well-balanced manner by adjusting the addition amounts of Nb, V and Ni in the steel. There is. Further, Patent Document 2 describes a technique for setting an optimum cooling stop temperature according to a flange thickness 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 protrusions. It is disclosed.

Japanese Patent No. 4045977 Japanese Unexamined Patent Publication No. 2006-75883

However, the H-section steel with protrusions described in Patent Documents 1 and 2 described above is a rolled material by continuous casting, although Nb and V forming carbon nitride are added to achieve both high tensile strength and toughness. There is a problem that defects on the surface of the slab, which are called continuous casting cracks, are likely to occur during the production of the steel, which lowers the manufacturability. The present invention has been made to advantageously solve the above-mentioned problems, and can dramatically improve manufacturability while ensuring tensile strength equal to or higher than that of conventional H-beams with protrusions. It is an object of the present invention to provide shaped steel together with its manufacturing method.

The present inventors prepared H-section steels with protrusions in which the contents of C, Si, Mn, P, S, Nb, V, Ti and N were changed, and investigated the tensile properties and toughness. As a result, it was found that when Nb or V is contained in the steel, the rate of continuous casting cracks is high. Furthermore, by optimizing the amounts of S, Ti, and N contained in the steel, continuous casting cracks can be stabilized and suppressed even when Nb and V are contained, and further, in the grain having TiN as the core. It was found that excellent toughness can be obtained by promoting ferrite transformation.

It is based on the above findings of the present invention, and its gist structure is as follows.
1. 1. C: 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 to 0.050 mass%, V: 0.005 to It contains 0.050% by mass, Ti: 0.005 to 0.030% by mass and N: 0.0020 to 0.0100% by mass in a range satisfying the following equation (1), and the balance has a steel composition of Fe and unavoidable impurities, and has tensile strength. H-shaped steel with protrusions having a mass of 490 MPa or more, a yield strength of 355 MPa or more, and a shock absorption energy vE0 at 0 ° C of 27 J or more.
Record
([% 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. 2. The steel composition further includes Cr: 1.0% by mass or less, Cu: 1.0% by mass or less, Ni: 1.0% by mass or less, Mo: 1.0% by mass or less, Al: 0.10% by mass or less, B: 0.010% by mass or less, Ca. The H-shaped steel with protrusions according to 1 above, which contains one or more selected from: 0.10% by mass or less, Mg: 0.10% by mass or less, and REM: 0.10% by mass or less.

3. 3. The H-shaped steel with protrusions according to 1 or 2 above, wherein the protrusions have a height of 1.5 mm or more.

4. A method for producing an H-section steel with protrusions, wherein the steel material having the steel composition according to any one of 1 or 2 above is hot-rolled to form an H-section steel with protrusions.
Protrusions are formed on the outer surface of the flange of the H-section steel by the finish rolling of the hot rolling, and after the finish rolling, the average cooling rate: 0.1 to 30 ° C / s from the cooling start temperature of 750 ° C. or higher to 500 ° C. A method for manufacturing an H-section steel with protrusions that is cooled under the conditions of.

5. The method for producing an H-section steel with protrusions according to 4 above, wherein the finish rolling is performed at a temperature of 800 ° C. or higher.

According to the present invention, it is possible to stably manufacture H-shaped steel with protrusions having excellent toughness, which contributes to the realization of rapid construction of large structures and the improvement of quality of concrete construction products, which is an industrially beneficial effect. Is brought.

A cross-sectional view of an H-section steel with protrusions is shown. It is a figure which shows the H-section steel with protrusions, (a) is a side view seen from the facing direction of the web, (b) is a plan view seen from the facing direction of the flange outer surface, (c) is the upper surface of the flange outer surface. The figures are shown respectively.

Hereinafter, the present invention will be specifically described. First, in the present invention, the reason why the steel composition is limited to the above range will be described. In addition, "%" in the following description shall represent "mass%" unless otherwise specified.

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

Si: 0.05-0.60%
Si must be contained in an amount of 0.05% or more as a base metal strength and a deoxidizing agent, but when the Si content exceeds 0.60%, in addition to a decrease in toughness, Si has a high binding force with oxygen. Therefore, the weldability deteriorates. 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 to 1.70%
Like Si, Mn 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. However, when the Mn content is less than 1.20%, the effect of addition is small, while when it exceeds 1.70%, the upper bainite transformation is promoted and the toughness is lowered, 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: 0.035% or less When the content of P exceeds 0.035%, the ductility of steel deteriorates. Therefore, in the present invention, the amount of P in steel is set to 0.035% or less. It is preferably 0.020% or less. On the other hand, the smaller the amount of P, the more preferable it is. Therefore, the lower limit of the P content is not particularly limited and may be 0%. However, normally, P is an element that is unavoidably contained in steel as an impurity, and excessive reduction of P causes an increase in refining time and an increase in cost. Therefore, the P content may be 0.005% or more. preferable.

S: 0.035% or less
When S is contained in steel, it is mainly present in the steel material in the form of A-based inclusions. When the S content exceeds 0.035%, the amount of inclusions increases remarkably, and at the same time, coarse inclusions are formed, which greatly reduces the toughness of the steel. Therefore, in the present invention, the S content in the steel is set to 0.035% or less. It is preferably 0.020% or less. On the other hand, the smaller the amount of S, the more preferable it is. Therefore, the lower limit of the S content is not particularly limited and may be 0%. Normally, S is an element that is inevitably contained in steel as an impurity, and excessive reduction in S causes an increase in refining time and cost, so the S content may be 0.002% or more. preferable.

Nb: 0.005 to 0.050%
Nb is an element that has the effect of improving tensile strength and yield point by precipitating as a carbonitride. In order to obtain this effect, the Nb content must be 0.005% or more. On the other hand, when the Nb content exceeds 0.050%, not only the precipitation embrittlement is promoted but also the upper bainite transformation is promoted, so that continuous casting cracks are likely to occur and the toughness is further lowered. Therefore, in the present invention, the Nb content is 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 to 0.050%
V is an element having an effect of improving the tensile strength and 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%, precipitation embrittlement is promoted, so that 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. The V content is preferably 0.030% or less.

Ti: 0.005 to 0.030%
Ti is a useful element effective in preventing surface cracking during bending-bending back during continuous casting, and is positively added in the range of 0.005% or more. Further, Ti is an element effective for improving toughness by forming TiN in steel to make austenite grains finer, and further making the microstructure finer by promoting intragranular ferrite transformation centered on TiN. 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 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 a useful element that forms a carbonitride in the steel and improves the strength of the steel, and its content needs to be 0.0020% or more. However, when the N content exceeds 0.0100%, the carbonitride formed becomes coarse and the toughness of the steel is lowered. Further, if the N content exceeds 0.0100%, surface cracks of the slab occur and the quality of the slab deteriorates, which is not preferable. 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 for each element to simply satisfy the above range, and for S, Ti and N, [% S], [% Ti] and [% N] are respectively contained in the steel. When the contents of S, Ti and N (% by mass) are taken, it is important to satisfy the relationship of the following equation (1).
([% S] / 32) / ([% Ti] / 48) + 4 × ([% N] / 14) / ([% Ti] / 48) ≦ 15.0 ・ ・ ・ (1)

The inventors investigated the cause of cracks in steel during continuous casting, and the precipitation of coarse MnS and V and Nb carbonitrides on the ferrite generated at the austenite grain boundaries during continuous casting caused cracks. We obtained the finding that it is the cause. Therefore, when a study was conducted to suppress the precipitation of MnS and V and Nb-based carbonitrides on the ferrite, the content of S, Ti and N in the steel was adjusted to obtain the grain boundary ferrite. It was found that the precipitation of MnS and V and Nb-based carbonitrides can be suppressed to suppress cracking during continuous casting. That is, by making the value calculated on the left side of the above equation (1), which is a parameter based on the contents of S, Ti and N, not exceed 15.0, S is precipitated as Ti carbon sulfide and N is TiN. It is possible to suppress the precipitation of coarse MnS and V and Nb-based carbonitrides on the ferrite generated at the austenite grain boundaries during continuous casting, and to stably suppress continuous casting cracks. It is more preferable that the right side of the above equation (1) is 10.0 or less, that is, the following equation (1)'is satisfied.
([% S] / 32) / ([% Ti] / 48) + 4 × ([% N] / 14) / ([% Ti] / 48) ≤ 10.0 ・ ・ ・ (1)'

In the steel composition of the H-section steel with protrusions used in the present invention, the balance other than the components described above is Fe and unavoidable impurities.
Further, in the H-shaped steel with protrusions of the present invention, in addition to the components described above, Cr: 1.0% or less, Cu: 1.0% or less, Ni: 1.0 for the purpose of improving strength, ductility, toughness, and weld characteristics. % 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. It may be contained arbitrarily.
Hereinafter, the reason for specifying the content of the above elements will be described.

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

Cu: 1.0% or less
Cu is an element that can further increase the strength of steel by solid solution strengthening. However, if the content exceeds 1.0%, Cu cracking is likely to occur. Therefore, when the component composition of steel contains Cu, the Cu content is 1.0% or less. More preferably, it is 0.005% or more and 0.5% or less.

Ni: 1.0% or less
Ni is an element that can increase the strength of steel without deteriorating ductility. Further, since Cu cracking can be suppressed by compound addition with Cu, it is desirable that Ni is also contained when the steel composition contains Cu. However, when the Ni content exceeds 1.0%, the hardenability of steel tends to increase and the toughness tends to decrease. Therefore, when the steel composition contains Ni, the amount of Ni is 1.0% or less. More preferably, it is 0.005% or more and 0.5% or less.

Mo: 1.0% or less
Mo is an element that can further increase the 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 component composition contains Mo, the Mo content is 1.0% or less. More preferably, it is 0.005% or more and 0.5% or less.

Al: 0.10% or less
Al is an element that can be added as an antacid. However, when the Al content exceeds 0.10%, a large amount of oxide-based inclusions are formed in the steel due to the high binding force of Al with oxygen, and as a result, the ductility of the steel is lowered. Therefore, when the steel composition contains Al, the Al content is preferably 0.10% or less. On the other hand, the lower limit of the Al content is not particularly limited, but it is preferably 0.001% or more for deoxidation. More preferably, it is 0.001% or more and 0.03% or less.

B: 0.010% or less B is an element having an effect of segregating at grain boundaries in steel and improving grain boundary strength. In addition, it is an element effective for improving toughness by forming a composite precipitate with TiN, which is a nucleation site of intragranular ferrite, and refining the microstructure. On the other hand, when the content exceeds 0.010%, the toughness is lowered due to the grain boundary precipitation of coarse carbonitride. Therefore, when the steel composition contains B, the B content is 0.010% or less. More preferably, it is 0.001% or more and 0.003% or less.

Ca: 0.10% or less
Ca has the effect of granulating the sulfide-based inclusions by altering the oxides and sulfides in the sulfide-based inclusions to those with high stability at high temperatures. Then, the toughness and ductility of the steel can be improved by the morphological control effect of the inclusions by Ca. However, if the Ca content exceeds 0.10%, the cleanliness tends to decrease and the toughness tends to decrease. Therefore, when the steel composition contains Ca, the Ca content is 0.10% or less. More preferably, it is 0.0010% or more and 0.0050% or less.

Mg: 0.10% or less
Mg has the effect of transforming oxides and sulfides in sulfide-based inclusions into those with high stability at high temperatures and granulating them. Then, the toughness and ductility of the steel can be improved by the morphological control effect of the inclusions by this Mg. However, if the Mg content exceeds 0.10%, the cleanliness tends to decrease and the toughness tends to decrease. Therefore, when the steel composition contains Mg, the Mg content should be 0.10% or less. More preferably, it is 0.0010% or more and 0.0050% or less.

REM: 0.10% or less
REM (rare earth metal) has the effect of transforming oxides and sulfides in sulfide-based inclusions into those with high stability at high temperatures to granulate the sulfide-based inclusions. Then, the toughness and ductility of the steel can be improved by the morphological control effect of the inclusions by this REM. However, if the REM content exceeds 0.10%, the cleanliness tends to decrease and the toughness tends to decrease. Therefore, when the steel composition contains REM, the REM content is 0.10% or less. More preferably, it is 0.0010% or more and 0.0050% or less.
The rest other than the elements described above are Fe and unavoidable impurities.

The H-section steel with protrusions of the present invention will be described in detail. That is, as shown in FIG. 1, the H-shaped steel with protrusions is formed by connecting a pair of flanges 2 with a web 3 in the same manner as a general H-shaped steel. The H-shaped steel with protrusions has protrusions 4 on the outer surface of the flange 2. The protrusion 4 is provided to impart concrete adhesion performance. In the H-shaped steel 1 with protrusions provided with the protrusions 4 for this purpose, the portion where the protrusions 4 are provided is the outer surface of the flange 2 as shown in FIG. 2A. In the illustrated example, the entire outer surface of the flange 2 is an enlarged view of a portion surrounded by a square in FIG. 2A, as a ridge extending in the width direction of the flange 2 in the cross-sectional shape shown in FIG. 2B. The protrusions 4 are formed so as to be arranged in the longitudinal direction of the flange 2.

The shape, dimensions, number, etc. of the protrusions can be arbitrarily set according to the specifications required for the H-shaped steel with protrusions. Therefore, although not limited to the illustrated example, for example, the height h of the protrusion 4 is preferably 1.5 mm or more in consideration of the concrete adhesion performance. On the other hand, the upper limit of the height h is preferably 6 mm from the viewpoint of preventing roll breakage. Further, the distance d between the protrusions 4 preferably satisfies the relationship of h / d ≧ 0.05 with the height h in consideration of the concrete adhesion performance.

Next, a method for manufacturing the H-shaped steel with protrusions of 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. Further, the hot rolling conditions for forming the H-shaped steel are not particularly limited, and may be performed according to a conventional method. In the finish rolling of hot rolling, protrusions can be formed by using a roll in which a groove corresponding to the protrusion to be formed is formed on the roll surface as a roll for reducing the portion (flange outer surface) on which the protrusion is formed. After finish rolling, it is necessary to perform cooling that satisfies the following conditions.

Flange temperature at the start of cooling: 750 ° C or higher In the present invention, the flange temperature at the start of cooling is 750 ° C or higher in order to prevent a decrease in production efficiency by starting cooling of the steel material immediately after finish rolling. To do. On the other hand, if the flange temperature at the start of cooling is less than the Ar ₃ temperature, it becomes difficult to obtain sufficient strength. Therefore, it is preferable that the flange temperature at the start of cooling is Ar ₃ or higher. The Ar ₃ transformation temperature is simply shown by the following equation (2), for example, in relation to the steel component.
Ar ₃ = 910-310 x [% C] +25 x ([% Si] +2 x [% Al])-80 x [Mneq] ・ ・ ・ (2)
Here, [Mneq] is a value calculated by the following equation (3).
[Mneq] = [% Mn] + [% Cr] + [% Cu] + [% Mo] + [% Ni] / 2 + 10 × ([% Nb] -0.02) ・ ・ ・ (3)
In the above equations (2) and (3), [% M] means the content (mass%) of the element M in the steel. Here, in calculating Ar ₃ by the above equations (2) and (3), regarding the content of the element M that is not positively contained, the content of the element M contained as an unavoidable impurity ( It shall be calculated using the analytical value).

Average cooling rate from cooling start temperature to 500 ° C: 0.1-30 ° C / s
If the average cooling rate from the cooling start temperature to 500 ° C. is less than 0.1 ° C./s, it is difficult to secure the predetermined tensile characteristics and toughness, so the cooling rate is set to 0.1 ° C./s or more. On the other hand, if the cooling rate exceeds 30 ° C./s, the formation of bainite or martensite causes adverse effects such as a decrease in toughness and an excessive increase in tensile strength. Therefore, the average from the cooling start temperature to 500 ° C. The cooling rate shall be in the range of 0.1 to 30 ° C / s. The preferred average cooling rate is in the range of 0.5-10 ° C / s.

By adjusting to the above-mentioned composition and rolling and cooling according to the above-mentioned conditions, the tensile strength of the H-section steel with protrusions is 490 MPa or more, the yield strength is 355 MPa or more, and the shock absorption energy vE0 at 0 ° C is 27 J. The above-mentioned excellent mechanical performance can be obtained. It is not necessary to specify the upper limit for any of the characteristics, but practically, the tensile strength is 640 MPa, the yield strength is 475 MPa, and the shock absorption energy vE0 at 0 ° C. is about 350 J.

Here, the flange thickness of the protruding H-section steel targeted by 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 process. That is, in order to give a desired protrusion height, it is necessary to increase the amount of reduction of the flange portion as much as possible. Therefore, protruding H-section steels with thick flanges require greater reduction. In the present invention, as described later, by controlling the rolling temperature within an appropriate range, it is said that the efficiency of forming the protrusion height is lowered, and even in a thick H-section steel having a flange thickness of 16 mm or more, a sufficient protrusion height is provided. Can be granted.

In finish rolling in which protrusions are formed during hot rolling, the finish rolling temperature is preferably 800 ° C. or higher from the viewpoint of forming protrusions having a sufficient protrusion height. If the finish rolling temperature is less than 800 ° C, it is difficult to stably form protrusions of sufficient height. On the other hand, the upper limit of the finishing temperature is not particularly limited, but if it exceeds 1050 ° C., the austenite particle size becomes coarse and the toughness tends to decrease. Therefore, it is preferable that the finishing temperature is 1050 ° C. or lower.

Hereinafter, the constitution and the action and effect of the present invention will be described more specifically according to Examples. However, the present invention is not limited by the following examples, and can be appropriately modified within a range that can be adapted to the gist of the present invention, all of which are included in the technical scope of the present invention. Is done.

The steel material having the composition shown in Table 1 was made into a beam blank having a cross section of 400 mm × 560 mm × a length of 8000 mm by a continuous casting machine, and the presence or absence of cracks on the surface was investigated. 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 10 mm or more was investigated. Surface cracks obtains the number of cracks per 1 m ^2, A: no cracks, B: 1 to 4 pieces ^/ m 2, C: evaluated using an index of 5 or more / ^{m 2,} A or B in the index The one judged was passed. Table 1 also shows the determination results of surface cracks. A steel having a steel composition satisfying the above formula (1) had a surface crack determination result of A or B.

Next, among these beam blanks, those having a surface crack determination result of A or B are heated at 1250 ° C. for 2 hours, then hot-rolled and cooled under the conditions shown in Table 2, and are shown in FIG. A cross-sectional shape, i.e., an H-section steel 1 with protrusions having a web 3 and a pair of flanges 2 arranged at both ends of the web was manufactured. Here, the cross-sectional dimensions (web height x flange width x web thickness x flange thickness) are H-shaped with protrusions as either of 320 x 323 x 25 x 25 mm and 350 x 333 x 35 x 40 mm. Manufactured steel. In finish rolling, a rolling roll for rolling down the outer surface of the flange is provided with a groove corresponding to the shape of a protrusion formed on the outer surface of the flange, and is rolled on the outer surface of the flange in the width direction of the flange 2 as shown in FIG. The existing protrusion 6 was formed. Here, the finish rolling roll that reduces the outer surface of the flange is provided with a groove capable of forming a protrusion having a protrusion width w: 15 mm and a protrusion height h: 1.5 mm or more. The cooling rate after finish rolling is the cooling rate (° C / ℃) by measuring the temperature of the outer surface of the flange with a radiation thermometer and converting the temperature change from the start of cooling to the stop of cooling per unit time (seconds). s) was calculated.

The obtained H-section steel with protrusions was subjected to protrusion height evaluation, tensile test and toughness test. Each evaluation content will be described in detail below.

<Protrusion height evaluation>
With respect to the obtained H-section steel with protrusions, the protrusion height h on the outer surface of the flange shown in FIG. 2 was measured. Such a value was measured at three points in the rolling direction of the H-section steel with protrusions after finish rolling, and the average value was adopted. The required performance lower limit of the protrusion height was set to 1.5 mm, and a value equal to or higher than this value was set as a suitable range for the protrusion height h. Further, the manufacturing conditions for obtaining the H-shaped steel with protrusions having the protrusion height h equal to or higher than this value can be evaluated as particularly preferable conditions from the viewpoint of ease of forming protrusions.

<Tensile test>
JIS1A test specified in JIS Z2201 so that the tensile direction is the flange longitudinal direction of the H-shaped steel from the flange 1 / 6B portion (length 60 mm in the flange width direction sandwiching 1 / 6B) shown by reference numeral 5 in FIG. A piece (flange full thickness test piece) was sampled and subjected to a tensile test according to JIS Z2241, and the yield strength (yield stress YS or 0.2% proof stress) and tensile strength were measured.

<Toughness test>
A 2 mm V notch Charpy impact test piece specified in JIS Z2202 was collected from the back surface of the flange 1 / 6B portion 5 shown in FIG. 1 at a position of 1 / 4t (t is the flange thickness), and according to JIS Z2242. A Charpy impact test was performed and the absorbed energy at 0 ° C. was measured.

Table 2 also shows the results of the above survey. Test results of H-shaped steel with protrusions produced by the manufacturing method within the scope of the present invention (the average cooling rate of the outer surface of the flange is within the range of the present invention) using compatible steel satisfying the steel composition of the present invention (test No. in Table 2) All of .1 to 19 and 31) satisfied the desired characteristics (tensile strength: 490 MPa or more, yield strength: 355 MPa or more, and impact absorption energy vE0: 27 J or more at 0 ° C.). In Test No. 33, the desired characteristics were satisfied with respect to the tensile strength, yield strength, and impact absorption energy at 0 ° C., but the finish rolling temperature was below the preferable lower limit of 800 ° C. The size was 1.4 mm, which was less than the preferable range (1.5 mm or more).

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

1 H-shaped steel with protrusions (rolled H-shaped steel)
2 Flange 3 Web 4 Protrusion 5 Flange 1 / 6B part (test piece collection position)

Claims (5)

C: 0.05 to 0.20% by mass, Si: 0.05 to 0.60% by mass, Mn: 1.20 to 1.70% by mass, P: 0.035% by mass or less, S: 0.035% by mass or less, Nb: 0.005 to 0.050% by mass, V: 0.005 to It contains 0.050% by mass, Ti: 0.005 to 0.030% by mass and N: 0.0020 to 0.0100% by mass in a range satisfying the following equation (1), and the balance has a steel composition of Fe and unavoidable impurities, and has tensile strength. H-shaped steel with protrusions on the outer surface of the flange , which has a mass of 490 MPa or more, a yield strength of 355 MPa or more, and a shock absorption energy vE0 at 0 ° C of 27 J or more.
Record
([% 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. The steel composition further includes Cr: 1.0% by mass or less, Cu: 1.0% by mass or less, Ni: 1.0% by mass or less, Mo: 1.0% by mass or less, Al: 0.10% by mass or less, B: 0.010% by mass or less, Ca. The H-shaped steel with protrusions according to claim 1, which contains one or more selected from: 0.10% by mass or less, Mg: 0.10% by mass or less, and REM: 0.10% by mass or less. The H-section steel with protrusions according to claim 1 or 2, wherein the protrusions have a height of 1.5 mm or more. A method for producing an H-shaped steel with protrusions, wherein the steel material having the steel composition according to claim 1 or 2 is hot-rolled to form an H-shaped steel with protrusions, which is obtained by the finish rolling of the hot rolling. forming a protrusion on the flange outer surface of the H-shaped steel, after on the partition rolling average until 500 ° C. from the cooling starting temperature above 750 ° C. cooling rate: cooling under the condition of 0.1 to 30 ° C. / s, tensile strength A method for producing H-shaped steel with protrusions , which has a height of 490 MPa or more, a yield strength of 355 MPa or more, and an impact absorption energy vE0 at 0 ° C of 27 J or more . The method for producing an H-section steel with protrusions according to claim 4, wherein the finish rolling is performed at a temperature of 800 ° C. or higher.

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