TW202235637A - H-shaped steel - Google Patents

Abstract

Provided is an H-shaped steel having an excellent coating durability and strength-toughness balance. The H-shaped steel has: a composition containing, by mass, 0.05 to 0.20% of C, 0.05 to 1.00% of Si, 0.50 to 2.00% of Mn, 0.003 to 0.035% of P, 0.035% or below of S, 0.01 to 0.50% of Cu, and 0.01 to 0.50% of Ni, and further containing one or more substances selected from the group consisting of 0.005 to 0.30% of W and 0.005 to 0.50% of Mo, the following relationship being satisfied by Cu, P, W, and Mo; a tensile strength of 400 MPa or above; a yield strength of 235 MPa or above; and a vE0 of 27 J or above. 0.25 ≤ 2.6 * [%Cu] + 0.8 * [%P] + 4.2 * [%W] + 1.1 * [%Mo] ≤ 1.30 The [%Cu], [%P], [%W], and [%Mo] respectively represent the Cu, P, W, and Mo content (mass%), and the value is zero if the respective element is not contained.

Description

H-shaped steel

The present invention relates to a kind of H-shaped steel, and relates to a kind of steel that is mainly used in the atmospheric corrosion environment on land such as construction/civil engineering and bridges, etc., especially in severe corrosion such as sea and coast where there is a lot of flying salt. H-shaped steel used in the environment.

For steel structures such as bridges, anti-corrosion measures such as strict coating are usually taken. With regard to H-shaped steel, which is often used as a structural member, for example, weather-resistant steel is often used in an environment with a small amount of flying salt. Here, the weather-resistant steel is a steel whose surface is covered with a highly protective rust layer formed by concentrating alloying elements such as Cu, P, Cr, and Ni when used in an atmosphere exposed to the atmosphere, thereby reducing the corrosion rate. dramatically drop. It is known that bridges using such weather-resistant steel can withstand decades of service in an unpainted state in an environment with a small amount of flying salt.

On the other hand, it is difficult to form a highly protective rust layer in an environment with a large amount of flying salt such as the sea or near the coast, and it is difficult to use weather-resistant steel in an uncoated state. Therefore, in environments with a large amount of flying salt, such as at sea or near the coast, steel materials that have been treated with anti-corrosion treatment such as coating on ordinary steel materials are generally used. Coating is a very effective anti-corrosion method, but it requires regular repairs because it deteriorates significantly due to exposure to the atmosphere. When repairing, if the deteriorated coating and the rust generated on the base remain, the anti-corrosion effect brought by the coating will be significantly reduced. In order to avoid this problem, it is necessary to grind and remove the old paint and rust on the repaired part, and repaint it again. Since this operation requires visual confirmation, automation is extremely difficult, and manual operations by skilled workers are necessary. Therefore, when using a painted steel material, there exists a problem that the maintenance cost of a structure increases, and also life cycle cost increases.

Accordingly, it is desired to develop an H-shaped steel with excellent corrosion resistance, especially an H-shaped steel with excellent coating durability, which can reduce the frequency of painting and suppress the maintenance cost of the structure by prolonging the repainting cycle.

In view of this background, for example, in Patent Document 1, a method for manufacturing H-shaped steel is disclosed, which can also precisely control rolling and cooling conditions by adding Cr and Cu to ensure corrosion resistance. Suppresses red heat embrittlement caused by molten Cu. In addition, Patent Document 2 discloses an H-shaped steel, which has excellent corrosion resistance even in coastal areas where the amount of flying salt is 0.05 mdd or more by adjusting the addition amount of Mo and Ni, and is excellent in weather resistance. . Furthermore, Patent Document 3 to Patent Document 7 disclose a high weather resistance steel in which, in addition to the addition of the above-mentioned alloy elements, a predetermined amount of Sn or Sb is also added, thereby greatly improving the corrosion resistance of severe corrosion at sea or near the coast. Corrosion resistance in the environment. [Prior art literature] [Patent Document]

Patent Document 1: Japanese Patent Laid-Open No. 1996-199233 Patent Document 2: Japanese Patent No. 3314682 Patent Document 3: Japanese Patent No. 6658412 Patent Document 4: Japanese Patent Laid-Open No. 2006-118011 Patent Document 5: Japanese Patent Laid-Open No. 2010-7109 Patent Document 6: Japanese Patent Laid-Open No. 2012-255184 Patent Document 7: Japanese Patent Laid-Open No. 2013-166992

[Problem to be Solved by the Invention]

However, the H-shaped steels described in Patent Document 1 and Patent Document 2 have a problem of insufficient weather resistance in an environment with high flying salt content without taking into account the coating durability. In addition, from the viewpoint of formability, in H-shaped steel that must be heated at 1200°C or higher during hot working, the crystal grains tend to be coarsened more easily than thick steel plates. In Patent Document 7, if the corrosion-resistant element is excessively contained, there is also a problem that it is difficult to secure toughness.

The present invention is made in view of the above circumstances, and an object of the present invention is to provide an H-shaped steel excellent in coating durability and strength-toughness balance.

In addition, "excellent coating durability" means that a coating film is formed on the surface of steel and the expansion area of the coating film is 480 mm ² or less when the corrosion test under the following conditions is performed. <Corrosion Test Conditions> Initial defects applied to the coating film: 1 mm wide, 40 mm long straight cut Amount of artificial sea salt adhesion: 6.0 g/m ² Test time: 1200 cycles (9600 hours) Cycle conditions: (Conditions 1. Temperature: 60°C, relative humidity: 35%, holding time: 3 hours), (condition 2. temperature: 40°C, relative humidity: 95%, holding time: 3 hours), from condition 1 to condition 2 and A cycle of 8 hours in total with each transition time from condition 2 to condition 1 being 1 hour

In addition, "excellent strength-toughness balance" means that the tensile strength is 400 MPa or more, the yield strength is 235 MPa or more, and the impact absorption energy at 0°C is 27 J or more. [Means to solve the problem]

The inventors of the present invention produced H-shaped steel in which the contents of C, Si, Mn, P, S, Cu, Ni, W, and Mo were changed, and diligently investigated coating durability, tensile properties, and toughness. As a result, it was found that by setting the content of each element contained in the steel in a specific range, and controlling the parameters including the amount of Cu, P, W, and Mo in a specific range, it is possible to obtain not only excellent coating durability In addition, H-shaped steel with excellent strength-toughness balance.

The present invention is based on the above knowledge, and its gist structure is as follows. [1] An H-shaped steel having a steel composition having a tensile strength of 400 MPa or more, a yield strength of 235 MPa or more, and an impact absorption energy of 27 J or more at 0°C, wherein the steel composition contains C: 0.05% by mass ~0.20% by mass, Si: 0.05% by mass to 1.00% by mass, Mn: 0.50% by mass to 2.00% by mass, P: 0.003% by mass to 0.035% by mass, S: 0.035% by mass or less, Cu: 0.01% by mass to 0.50% by mass, and Ni: 0.01% by mass to 0.50% by mass, Further containing one or two selected from W: 0.005% by mass to 0.30% by mass, Mo: 0.005% by mass to 0.50% by mass, And it contains Cu, P, W, and Mo within the range satisfying the following formula (1), and the rest contains Fe and unavoidable impurities, 0.25≦2.6×[%Cu]+0.8×[%P]+4.2×[%W]+1.1×[%Mo]≦1.30 ･･･(1) Here, [%Cu], [%P], [%W] and [%Mo] in the formula (1) are the contents (mass %) of Cu, P, W and Mo in the steel, respectively. set to 0 in case of [2] The H-shaped steel as described in [1], wherein the steel composition further contains Cr: 1.00% by mass or less, Sn: 0.200% by mass or less, Sb: 0.200% by mass or less, Al: 0.100% by mass or less, Nb: 0.50% by mass or less, V: 0.50% by mass or less, Ti: 0.50% by mass or less, B: 0.0100% by mass or less, Zr: 0.100% by mass or less, Ca: 0.100% by mass or less, Mg: 0.100% by mass or less, and REM: one or more of 0.100% by mass or less. [3] The H-shaped steel according to [1] or [2], which has a coating film on the surface. [4] The H-shaped steel as described in [3], wherein the coating film has an anti-corrosion base layer, an undercoat layer, a middle coat layer, and an upper coat layer, and the anti-corrosion base layer is formed by using an inorganic zinc-rich paint. The undercoat layer is formed by using epoxy resin paint, the middle coat layer is formed by using a fluororesin topcoat paint, and the top coat layer is formed by using a fluororesin topcoat paint. [Effect of the invention]

According to the present invention, it is possible to provide an H-shaped steel excellent in coating durability and strength-toughness balance.

According to the present invention, it is possible to provide an H-shaped steel excellent in coating durability and strength-toughness balance, which can be used in outdoor atmospheric corrosion environments such as bridges, especially in severe environments such as the sea or the coast where there is a lot of flying salt. When used in a corrosive environment, it can also extend the period required for repainting and reduce the frequency of painting.

According to the present invention, it is possible to stably manufacture H-shaped steel having excellent coating durability and strength-toughness balance, and it is possible to obtain H-shaped steel excellent in coating durability at low cost as follows: Even if H-shaped steel is used in outdoor atmospheric corrosion environments such as bridges, especially in severe corrosion environments such as seas or coasts with a lot of flying salt, it can also extend the repainting cycle to reduce the frequency of painting . Furthermore, by using the H-shaped steel excellent in coating durability of the present invention, it is suitably used in outdoor atmospheric corrosion environments such as bridges, especially in severe corrosion environments such as the sea or near the coast where there is a lot of flying salt. The bridges and other structures used can reduce the maintenance cost of such structures, thereby reducing the life cycle cost.

Hereinafter, the present invention will be specifically described. First, in the present invention, the reason for limiting the steel composition to the above range will be described. In addition, "%" in the following description means "mass %" unless otherwise specified.

C: 0.05% to 0.20% C is an element required to ensure the strength of the base material, and at least 0.05% needs to be added. However, the addition of more than 0.20% of C not only reduces the toughness of the base metal but also reduces the weldability. Therefore, in the present invention, the C content is set to 0.05% to 0.20%. Furthermore, the C content is preferably at least 0.07%, more preferably at least 0.09%, and still more preferably at least 0.11%. In addition, the C content is preferably at most 0.18%, more preferably at most 0.15%.

Si: 0.05% to 1.00% Si not only ensures the strength of the base material, but also has the effect of forming a dense rust layer and improving the durability of the coating of the H-shaped steel. However, if the Si content is less than 0.05%, the effect of the addition is small. On the other hand, if it exceeds 1.00%, the toughness and weldability will deteriorate. Therefore, in the present invention, the Si content is set to 0.05% to 1.00%. Furthermore, the Si content is preferably at least 0.10%, more preferably at least 0.15%, and still more preferably at least 0.20%. In addition, the Si content is preferably at most 0.60%, more preferably at most 0.45%.

Mn: 0.50% to 2.00% Like Si, Mn is an element effective in improving hardenability and ensuring the strength of the base material. However, if the Mn content is less than 0.50%, the effect of the addition is small. On the other hand, the addition of more than 2.00% of Mn promotes the transformation of the upper bainite and lowers the toughness, which is not preferable. Therefore, in the present invention, the Mn content is set to 0.50% to 2.00%. Furthermore, the Mn content is preferably at least 0.60%, more preferably at least 0.80%, and still more preferably at least 1.20%. In addition, the Mn content is preferably at most 1.80%, more preferably at most 1.60%.

P: 0.003%～0.035% P is an element having high solid-solution strengthening ability, and toughness is lowered by hardening of ferrite, so in the present invention, the P content in steel is made 0.035% or less. On the other hand, P is an element that contributes to the improvement of coating durability, so at least 0.003% of P needs to be added. Therefore, in the present invention, the P content is set to 0.003% to 0.035%. Furthermore, the P content is preferably at least 0.005%, more preferably at least 0.008%, and still more preferably at least 0.010%. In addition, the P content is preferably at most 0.025%, more preferably at most 0.020%.

S: less than 0.035% S mainly exists in the steel in the form of A-type inclusions, but if the S content exceeds 0.035%, the amount of the inclusions will increase significantly, and coarse inclusions will be formed at the same time, so the toughness will be greatly reduced. Therefore, in the present invention, the S content is made 0.035% or less. The S content is preferably at most 0.020%, more preferably at most 0.010%, still more preferably at most 0.008%. On the other hand, the less S is, the better. Therefore, the lower limit of the S content is not particularly limited and may be 0%. However, S is usually an element inevitably contained in steel as an impurity, so it can exceed 0% industrially. Furthermore, excessive reduction of S leads to an increase in refining time and an increase in cost, so the S content is preferably 0.002% or more.

Cu: 0.01%～0.50% Cu is an important element in the H-shaped steel excellent in coating durability of the present invention, and has the effect of forming a dense rust layer by making the rust particles of the rust layer finer, and suppressing oxygen or Permeation of chloride ions to ground iron. In addition, Cu is added together with Ni, and further together with Ni and W, and utilizes the synergistic effect with these elements to greatly improve the coating durability of steel materials. This effect can be obtained when the Cu content is above 0.01%. On the other hand, if the Cu content exceeds 0.50%, not only will the cost of the alloy increase, but also Cu cracks will easily occur during hot working. Furthermore, since the hardenability of steel improves further, toughness also falls. Therefore, in the present invention, the Cu content is set to 0.01% to 0.50%. Furthermore, the Cu content is preferably at least 0.03%, more preferably at least 0.05%, and still more preferably at least 0.07%. In addition, the Cu content is preferably at most 0.30%, more preferably at most 0.20%.

Ni: 0.01% to 0.50% Ni also has the effect of forming a dense rust layer by making the rust particles of the rust layer finer, suppressing the penetration of oxygen or chloride ions, which are corrosion accelerating factors, into the base iron, and suppressing Cu cracks. Furthermore, Ni is added together with Cu, and then compounded together with Cu and W, and utilizes the synergistic effect with these elements to greatly improve the coating durability of steel materials. This effect can be obtained when the Ni content is above 0.01%. However, if the Ni content exceeds 0.50%, the hardenability of the steel will further increase and the toughness will decrease. Therefore, in the present invention, the Ni content is set to 0.01% to 0.50%. Furthermore, the Ni content is preferably at least 0.03%, more preferably at least 0.05%, and still more preferably at least 0.07%. In addition, the Ni content is preferably at most 0.30%, more preferably at most 0.20%.

One or two selected from W: 0.005%-0.30%, Mo: 0.005-0.50% W: 0.005%-0.30% W dissolves out with the anode reaction of steel, and distributes in the rust layer in the form of WO ₄ ^2- In this way, chloride ions, which are corrosion accelerating factors, are electrostatically prevented from penetrating through the rust layer and reaching the base iron. Furthermore, by precipitating a compound containing W on the surface of the steel, the anode reaction of the steel is suppressed. Furthermore, W is added in combination with Cu and Ni, and utilizes the synergistic effect with these elements to greatly improve the coating durability of steel materials. This effect can be obtained when the W content is above 0.005%. However, if the W content exceeds 0.30%, not only the cost of the alloy increases, but also the hardenability of the steel remarkably increases and the toughness decreases. Therefore, in the present invention, the W content when W is contained is set to 0.005% to 0.30%. Furthermore, the W content is preferably at least 0.01%, more preferably at least 0.03%, and still more preferably at least 0.05%. In addition, the W content is preferably at most 0.30%, more preferably at most 0.20%.

Mo: 0.005%～0.50% Mo dissolves with the anode reaction of steel, and is distributed in the rust layer in the form of MoO ₄ ^2- , thereby preventing chloride ions, which are corrosion-promoting factors, from penetrating the rust layer and reaching the base iron. In addition, the anode reaction of the steel is suppressed by depositing a compound containing Mo on the surface of the steel. This effect can be obtained when the Mo content is 0.005% or more. However, if its content exceeds 0.50%, the upper ductile iron transformation will be promoted, and the toughness will decrease. Therefore, in the present invention, the Mo content when Mo is contained is set to 0.005% to 0.50%. Furthermore, the Mo content is preferably at least 0.02%, more preferably at least 0.05%, and still more preferably at least 0.07%. In addition, the Mo content is preferably at most 0.40%, more preferably at most 0.30%. In the present invention, it is preferable to contain W in the above-mentioned W and Mo, and it is more preferable to contain W and Mo.

Furthermore, in the present invention, since it is a shaped steel, it is not sufficient for each element to satisfy the above-mentioned ranges, and it is important for Cu, P, W, and Mo to satisfy the relationship of the following formula (1).

0.25≦2.6×[%Cu]+0.8×[%P]+4.2×[%W]+1.1×[%Mo]≦1.30 ･･･(1) Here, [%Cu], [%P], [%W], and [%Mo] in the formula (1) are the contents (mass %) of Cu, P, W, and Mo in the steel, respectively. set to 0 in case of

The inventors evaluated the coating durability and the strength-toughness balance using various H-shaped steels having steel components in the above content ranges, and as a result obtained the following insight: In order to obtain desired characteristics for both, it is important to It is to control the content of Cu, P, W, and Mo in a specific range besides making the said each component into the said content range. Specifically, by taking the parameters based on the content of Cu, P, W and Mo, that is, the value calculated by the above formula (1) (from 2.6×[%Cu]+0.8×[%P]+4.2×[% W]+1.1×[%Mo] (calculated value) is 0.25 or more and 1.30 or less, and excellent coating durability and strength-toughness balance can be stably obtained. If the value calculated from the formula (1) is less than 0.25, it will be difficult to stably form a dense rust layer that suppresses the penetration of oxygen or chloride ions, which are corrosion accelerating factors, into the base iron, and the coating durability will decrease. On the other hand, when the value calculated by the formula (1) exceeds 1.30, the superposition of hardenability improvement by Cu, W, and Mo and ferrite hardening by P becomes remarkable, and toughness decreases. In addition, the range of the value calculated by the said (1) formula is more preferable to be 0.40-1.20, ie, content of Cu, P, W, and Mo satisfies the following (2) formula.

0.40≦2.6×[%Cu]+0.8×[%P]+4.2×[%W]+1.1×[%Mo]≦1.20 ･･･(2) Here, [%Cu], [%P], [%W], and [%Mo] in the formula (2) are the same as those in the formula (1).

The value calculated from the above formula (1) (the value calculated from 2.6×[%Cu]+0.8×[%P]+4.2×[%W]+1.1×[%Mo]) is preferably 0.40 or more, more preferably Preferably, it is 0.50 or more. In addition, the value calculated from the above formula (1) is preferably 1.20 or less, more preferably 1.10 or less.

The steel composition of the H-shaped steel of the present invention may optionally contain Cr: 1.00% or less, Sn: 0.200% or less for the purpose of improving coating durability, strength, ductility, and toughness in addition to the above-mentioned components. , Sb: 0.200% or less, Al: 0.100% or less, Nb: 0.50% or less, V: 0.50% or less, Ti: 0.50% or less, B: 0.0100% or less, Zr: 0.100% or less, Ca: 0.100% or less, Mg : 0.100% or less and REM: 0.100% or less, one or more.

Cr: less than 1.00% Cr is an element that can further increase the strength of steel by solid solution strengthening. In order to sufficiently obtain such an effect, it is preferable to contain 0.01% or more of Cr. However, if its content exceeds 1.00%, the upper ductile iron transformation will be promoted and the toughness will decrease. Therefore, when Cr is contained, the Cr content shall be 1.00% or less. The Cr content is more preferably at least 0.05%, and still more preferably at least 0.10%. In addition, the Cr content is preferably at most 0.50%, more preferably at most 0.30%.

Sn: 0.200% or less Sn exists in the rust layer near the surface of the base iron, and by making the rust particles finer, chloride ions, which are corrosion accelerating factors, are prevented from penetrating the rust layer and reaching the base iron. In addition, Sn suppresses anodic reaction on the surface of the steel material. Furthermore, Sn is added together with Cu and Ni, and further combined with Cu, Ni, and W, and utilizes the synergistic effect with these elements to greatly improve the coating durability of steel materials. In order to sufficiently obtain such an effect, it is preferable to contain 0.005% or more of Sn. However, if its content exceeds 0.200%, ductility or toughness will decrease. Therefore, when Sn is contained, the Sn content shall be 0.200% or less. The Sn content is more preferably at least 0.010%, further preferably at least 0.020%. In addition, the Sn content is preferably at most 0.100%, more preferably at most 0.080%.

Sb: less than 0.200% Sb exists in the rust layer near the surface of the base iron, and by making the rust particles finer, chloride ions, which are corrosion accelerating factors, are prevented from penetrating the rust layer and reaching the base iron. In addition, Sb suppresses anodic reaction on the steel surface. Furthermore, Sb is added together with Cu and Ni, and further combined with Cu, Ni, and W, and utilizes the synergistic effect with these elements to greatly improve the coating durability of steel materials. In order to sufficiently obtain such an effect, it is preferable to contain 0.005% or more of Sb. However, if its content exceeds 0.200%, ductility or toughness will decrease. Therefore, when Sb is contained, the Sb content shall be 0.200% or less. The Sb content is more preferably at least 0.010%, further preferably at least 0.020%. In addition, the Sb content is preferably at most 0.100%, more preferably at most 0.080%.

Al: less than 0.100% Al is an element that can be added as a deoxidizer. In order to sufficiently obtain such an effect, it is preferable to contain 0.001% or more of Al. However, if the Al content exceeds 0.100%, a large amount of oxide-based inclusions will be formed in the steel due to Al's high bonding force with oxygen, and as a result, the ductility of the steel will decrease. Therefore, when Al is contained, the Al content shall be 0.100% or less. The Al content is more preferably at least 0.010%, further preferably at least 0.020%. In addition, the Al content is preferably at most 0.080%, more preferably at most 0.050%.

Nb: less than 0.50% Nb is an element having an effect of increasing tensile strength or yield point by precipitation as carbonitrides. In order to sufficiently obtain such an effect, it is preferable to contain 0.005% or more of Nb. However, if its content exceeds 0.50%, in addition to promoting precipitation embrittlement, it will also promote the upper ductile iron transformation, so the toughness will decrease. Therefore, when Nb is contained, the Nb content is made 0.50% or less. The Nb content is more preferably at least 0.010%, further preferably at least 0.020%. In addition, the Nb content is preferably at most 0.20%, more preferably at most 0.10%.

V: less than 0.50% V is an element that precipitates in the form of VN in austenite during rolling or cooling after rolling to form ferrite transformation nuclei and has an effect of refining crystal grains. In addition, V also has a function of increasing the strength of the base material through precipitation strengthening, and is an element useful for securing tensile strength and toughness. In order to sufficiently obtain such an effect, it is preferable to contain V at 0.005% or more. However, if the content exceeds 0.50%, the toughness of the base material tends to decrease due to excessive precipitation strengthening. Therefore, when V is contained, the V content is made 0.50% or less. The V content is more preferably at least 0.010%, further preferably at least 0.020%. In addition, the V content is preferably at most 0.20%, more preferably at most 0.10%.

Ti: less than 0.50% Ti is an element that not only forms TiN and refines Worthfield iron grains, but also refines the microstructure by promoting the transformation of intragranular ferrite with TiN as the core, which is also effective for improving toughness. In order to sufficiently obtain such an effect, it is preferable to contain 0.005% or more of Ti. However, if the content thereof exceeds 0.50%, coarse TiN will be generated and the toughness will decrease. Therefore, when Ti is contained, the Ti content is made 0.50% or less. The Ti content is more preferably at least 0.010%, further preferably at least 0.020%. In addition, the Ti content is preferably at most 0.20%, more preferably at most 0.10%.

B: less than 0.0100% B is an element having the effect of segregating at grain boundaries in steel and increasing the strength of grain boundaries. In addition, it is an element that forms composite precipitates with TiN that become nucleation sites of intragranular ferrite, and is also effective for improving toughness by refining the microstructure. In order to sufficiently obtain such an effect, it is preferable to contain 0.0001% or more of B. On the other hand, if the content exceeds 0.0100%, the toughness will decrease due to the precipitation of grain boundaries of coarse carbonitrides. Therefore, when B is contained, the B content shall be 0.0100% or less. The B content is more preferably at least 0.0010%, further preferably at least 0.0020%. In addition, the B content is preferably at most 0.0050%, more preferably at most 0.0040%.

Zr: 0.100% or less Zr is an element that can further increase the strength of steel. In order to sufficiently obtain this effect, it is preferable to contain 0.005% or more of Zr. However, if the content exceeds 0.100%, the effect of increasing strength will be saturated, and the toughness will also decrease. Therefore, when Zr is contained, the Zr content shall be 0.100% or less. The Zr content is more preferably at least 0.010%, further preferably at least 0.015%. In addition, the Zr content is preferably at most 0.050%, more preferably at most 0.040%.

Ca: 0.100% or less Ca has the effect of modifying the oxides and sulfides in the sulfide-based inclusions into ones with high stability at high temperatures, and granulating the sulfide-based inclusions. And, the toughness and ductility of steel can be improved by the effect of Ca on the shape control of inclusions. In order to sufficiently obtain such an effect, it is preferable to contain 0.0001% or more of Ca. However, if the Ca content exceeds 0.100%, the cleanliness and toughness will decrease. Therefore, when Ca is contained, the Ca content shall be 0.100% or less. The Ca content is more preferably at least 0.0010%, further preferably at least 0.0020%. In addition, the Ca content is preferably at most 0.0100%, more preferably at most 0.0050%.

Mg: less than 0.100% Mg has the effect of modifying the oxides and sulfides in the sulfide-based inclusions into those with high stability at high temperatures, and granulating the sulfide-based inclusions. Furthermore, the toughness and ductility of steel can be improved by the shape control effect of Mg on inclusions. In order to sufficiently obtain such an effect, it is preferable to contain 0.0001% or more of Mg. However, if the Mg content exceeds 0.100%, the cleanliness and toughness will decrease. Therefore, when Mg is contained, the Mg content shall be 0.100% or less. The Mg content is more preferably at least 0.0010%, further preferably at least 0.0020%. In addition, the Mg content is preferably at most 0.0100%, more preferably at most 0.0050%.

REM: less than 0.100% REM (rare earth metal) has the function of changing the oxides and sulfides in the sulfide-based inclusions to those with high stability at high temperatures, and granulating the sulfide-based inclusions. Furthermore, the toughness and ductility of the steel can be improved by the effect of the REM on the shape control of the inclusions. In order to sufficiently obtain such an effect, it is preferable to contain 0.0001% or more of REM. However, if the REM content exceeds 0.100%, the cleanliness and toughness will decrease. Therefore, when REM is contained, the REM content shall be 0.100% or less. The REM content is more preferably at least 0.0010%, further preferably at least 0.0020%. In addition, the REM content is preferably at most 0.0100%, more preferably at most 0.0050%. Furthermore, REM is a general term for Sc, Y, and 15 elements ranging from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71, and the REM content mentioned here is the total content of these elements.

Furthermore, the remainder of the steel composition contains Fe and unavoidable impurities. The so-called unavoidable impurities refer to the following impurities: substances that exist in raw materials or are inevitably mixed in during the manufacturing process. They are originally unnecessary substances, but they are allowed to be contained because they are trace amounts and do not affect the characteristics. . Examples of unavoidable impurities include N, O, and the like. N can be contained up to 0.0150% and O can be contained up to 0.005%.

In addition, the H-shaped steel of the present invention is usually used by coating the steel surface, and in this case, has a coating film on the surface. Here, the coating film on the steel surface includes, for example, a coating film having an anti-corrosion base layer, an undercoat layer, an intermediate coat layer, and a top coat layer in this order from the steel surface. Furthermore, it is preferable that the anti-corrosion base layer is formed using an inorganic zinc-rich paint (for example, manufactured by Kansai Paint Co., Ltd.: SD zinc (zinc) 1500), and the undercoat layer is formed using an epoxy resin paint (for example, Kansai Paint Co., Ltd. Co., Ltd. manufacturing: Epomarine (Epomarine) HB (K)), the intermediate coating uses the intermediate coating for fluororesin top coating (for example, Kansai Paint Co., Ltd. manufacturing: Celatect (Celatect) intermediate coating ), and the top coat is formed using a fluororesin top coat (for example, manufactured by Kansai Paint Co., Ltd.: Celatect (K) top coat).

Next, the manufacturing method of the H-shaped steel of this invention is demonstrated. The melting method and casting method of the steel material (slab or beam blank) are not particularly limited, and any conventionally known methods are suitable. In addition, as an example of hot rolling conditions for forming H-shaped steel from the above-mentioned steel material, there may be mentioned hot rolling in which a steel material having a predetermined composition is heated to a predetermined heating temperature, and a predetermined finish rolling After rolling at high temperature, it is cooled at a prescribed cooling rate.

From the viewpoint of ensuring sufficient formability, the heating temperature of the steel material during hot rolling is preferably set at 1150°C to 1350°C. If the heating temperature is lower than 1150° C., the deformation resistance of hot rolling increases, and the load on rolling rolls increases, resulting in difficulty in hot rolling. On the other hand, if the heating temperature exceeds 1350° C., in addition to the partial melting of the steel material to generate internal defects, the grain size of the waustian iron will become coarse, so that the upper part will be easily toughened during cooling after finish rolling. Iron, resulting in a decrease in toughness. Therefore, it is preferable to set the said heating temperature to 1150 degreeC - 1350 degreeC.

In addition, in the finish rolling, it is preferable to set the finish rolling temperature (finish rolling finish temperature) to 720° C. or higher from the viewpoint of ensuring toughness. If the finish rolling temperature is lower than 720° C., the rolling reduction in the ferrite+Worth field iron two-phase region increases, and the toughness decreases due to the influence of rolling strain. On the other hand, the upper limit of the finish-rolling temperature is not particularly limited, but if it exceeds 1050°C, the grain size of the ferrite grains will become coarse, resulting in a decrease in toughness. Therefore, it is preferable to set the finish-rolling temperature to 1050°C. below ℃.

Furthermore, if the average cooling rate from the cooling start temperature after finishing rolling to 500° C. is less than 0.1° C./sec, it is difficult to ensure predetermined tensile properties and toughness, so the average cooling rate is preferably 0.1° C./sec. ℃/sec or more. On the other hand, when the average cooling rate exceeds 30° C./sec, toughness decreases due to formation of ductile iron or martensite. Therefore, the average cooling rate is preferably in the range of 0.1°C/sec to 30°C/sec. The average cooling rate is more preferably 30.0° C./sec or less, further preferably 20.0° C./sec or less. In addition, as an example, the said cooling start temperature is finish rolling finish temperature. In addition, the said temperature means the surface temperature of steel materials.

By performing hot rolling as described above on the steel material whose composition is adjusted as described above, an H-shaped steel excellent in coating durability can be obtained, which has a tensile strength TS of 400 MPa or more and a yield strength ( Mechanical properties where the yield point YP (or 0.2% endurance) is 235 MPa or more and the impact absorption energy (Charpy impact absorption energy) vE0 at 0°C is 27 J or more. Furthermore, vE0 is preferably 47 J or more. In addition, in the present invention, tensile strength, yield strength, and impact absorption energy at 0° C. can be obtained by the methods described in Examples.

Furthermore, the tensile strength TS is preferably at least 490 MPa, more preferably at least 520 MPa. In addition, the upper limit of the tensile strength TS is not particularly limited, but is preferably 640 MPa or less. The yield strength is preferably at least 325 MPa, more preferably at least 355 MPa. In addition, the upper limit of the yield strength is not particularly limited, but is preferably 475 MPa or less. vE0 is more preferably 100 J or more. [Example]

Hereinafter, the structure and effects of the present invention will be described in more detail according to the embodiments. However, the present invention is not limited to the following examples, and can be appropriately modified within the scope of the scope of the present invention, and all of these are included in the technical scope of the present invention.

Using a continuous casting machine, the steel with the composition shown in Table 1 was made into a beam blank with a cross-section of 400 mm×560 mm×8000 mm in length, and it was hot-rolled under the hot-rolling conditions shown in Table 2 to manufacture the steel shown in Figure 1. The cross-sectional shape shown is an H-shaped steel having a web 3 and a pair of flanges 2 arranged at both ends of the web. Here, the cross-sectional dimensions (web height×flange width×web thickness×flange thickness) were set to 900 mm×300 mm×18 mm×34 mm to manufacture H-shaped steel. The average cooling rate after finish rolling is calculated by measuring the temperature of the flange surface with a radiation thermometer and converting the temperature change from the cooling start temperature (finish rolling finish temperature) to 500°C per unit time (seconds). Average cooling rate (°C/sec).

The obtained H-shaped steel was subjected to coating durability evaluation, tensile test and Charpy impact test. Hereinafter, each evaluation content is demonstrated in detail.

<Evaluation of coating durability> From the 1/4t part (t/4 part) from the back of flange 1/6B part (B/6 part) 4 shown in Fig. 1 (t is flange thickness), Collect test pieces of 70 mm × 50 mm × 5 mm. The surface of the test piece was shot blasted so that the surface roughness became International Organization for Standardization (ISO) Sa 2.5, ultrasonically degreased in acetone for 5 minutes, and air-dried. Then, one side of the test piece was used as the painted surface, and an inorganic zinc-rich paint (thickness: 75 μm) was applied as an anti-corrosion base, and then epoxy resin paint (thickness: 120 μm) was applied as an undercoat, and then, coated with The intermediate coating (thickness: 30 μm) for the fluororesin coating is used as the intermediate coating, and then the fluororesin coating (thickness: 25 μm) is applied as the top coating to form an anti-corrosion base layer, an undercoat layer, and an intermediate coat and coating film on top. In addition, the other one surface and the end surface of the test piece were sealed with a solvent-based epoxy resin coating, and then covered with a silicon-based sealant. After painting, a linear incision (incision defect) with a width of 1 mm and a length of 40 mm was made in the center of the coating film formed on the test piece so as to reach the base iron, and an initial defect was provided. Next, a corrosion test was implemented under the conditions shown below. That is, a solution obtained by diluting the artificial sea salt to a predetermined concentration with pure water was sprayed so that the adhesion amount of the artificial sea salt on the surface of the test piece was 6.0 g/m ² , and the artificial sea salt was attached to the test piece. Then, using this test piece, a corrosion test was carried out in which (condition 1. temperature: 60° C., relative humidity: 35%, retention time: 3 hours), (condition 2. temperature: 40° C., relative humidity: 95%, retention time: 3 hours), a cycle of 8 hours in total with each transition time from condition 1 to condition 2 and from condition 2 to condition 1 as 1 hour is set as one cycle, and this is repeated for 1200 cycles . Furthermore, the attachment of artificial sea salt was set once a week. Then, after the corrosion test was completed, the expansion area from the initial defect portion in the coating (painting expansion area) was measured to evaluate the coating durability. In this evaluation, it was judged that the coating swelling area was 480 mm ² or less as having excellent coating durability.

＜Tensile test＞ From the flange 1/6B portion 4 shown in FIG. 1 , a JIS No. 1A full-thickness tensile test piece specified in Japanese Industrial Standards (JIS) Z2201 with the tensile direction as the longitudinal direction of the H-shaped steel was collected. , according to JIS Z2241 tensile test to measure yield strength (yield point YP or 0.2% endurance), tensile strength TS.

＜Toughness Test＞ From the 1/4t part from the back of the flange 1/6B part 4 shown in Figure 1, a 2 mmV notch Charpy impact test piece specified in JIS Z2202 was collected, and the Charpy impact test was performed in accordance with JIS Z2242 to measure 0 Charpy impact absorption energy at °C.

As a result of the tensile test and the toughness test, those satisfying all the tensile strength: 400 MPa or more, yield strength: 235 MPa or more, and impact absorption energy at 0° C.: 27 J or more were judged to be excellent in strength-toughness balance.

Table 2 shows the results of the investigation. H-shaped steels (tests No.1 to No.18, No.41, No.42, No.44, No.45 in Table 2) manufactured using suitable steels satisfying the steel composition of the present invention have excellent coating properties. Durability, meet the desired mechanical properties (tensile strength TS: 400 MPa or more, yield strength: 235 MPa or more, impact absorbed energy vE0 at 0°C: 27 J or more), excellent strength-toughness balance.

On the other hand, the comparative examples (Tests No.19 to No.36, No.43, and No.46 in Table 2) in which the steel composition of the H-shaped steel did not satisfy the conditions of the present invention, or the suitable ones that did not satisfy the conditions of the present invention In the comparative examples of the hot rolling conditions (Tests No. 37 to No. 40 in Table 2), any of the coating durability, tensile strength, yield strength, and impact absorption energy did not satisfy the required characteristics.

[Table 1] Steel No. Composition (mass%) ⑴Formula ^*2 exam preparation C Si mn P S Cu Ni W Mo Cr sn Sb al Nb V Ti B Zr Ca Mg REM 1 0.11 0.07 0.53 0.009 0.006 0.46 0.45 0.005 0.005 - - - - - - - - - - - - 1.23 suitable for steel 2 0.10 0.25 0.90 0.033 0.004 0.07 0.03 0.09 - - - - - - - - - - - - - 0.59 3 0.09 0.32 0.73 0.018 0.003 0.06 0.11 - 0.25 - - - - - - - - - - - - 0.45 4 0.14 0.15 0.61 0.010 0.002 0.02 0.05 0.29 - - - - - - - - - - - - - 1.28 5 0.05 0.79 1.06 0.004 0.034 0.18 0.08 0.03 0.01 - - - - - - - - - - - - 0.61 6 0.06 0.25 1.82 0.015 0.005 0.04 0.18 0.11 - - - - - - - - - - - - - 0.58 7 0.18 0.40 1.38 0.013 0.005 0.15 0.07 0.04 0.03 - - - - - - - - - - - - 0.60 8 0.15 0.43 1.40 0.020 0.009 0.04 0.09 0.03 - 0.23 - - - - - - - - - - - 0.25 9 0.10 0.31 0.66 0.022 0.003 0.12 0.14 0.12 0.15 - - - - - - - - - - - - 1.00 10 0.08 0.29 1.50 0.014 0.004 0.09 0.05 0.09 - - 0.052 0.024 - - - - - - - - - 0.62 11 0.12 0.36 1.29 0.019 0.006 0.21 0.04 0.10 0.02 - - - 0.033 - - - - - - - - 1.00 12 0.13 0.20 0.70 0.014 0.003 0.10 0.13 0.05 - - - - - 0.024 - - - - - - - 0.48 13 0.17 0.33 1.18 0.013 0.014 0.06 0.32 0.08 0.03 - - - - - 0.073 - - - - - - 0.54 14 0.14 0.17 0.62 0.016 0.002 0.17 0.10 0.20 - - - - - - - 0.016 0.0025 - - - - 1.29 15 0.09 0.42 1.43 0.028 0.003 0.11 0.06 0.15 - - - - - - - - - 0.019 - - - 0.94 16 0.07 0.51 1.10 0.017 0.004 0.24 0.20 - 0.04 - - - - - - - - - 0.0045 - - 0.68 17 0.11 0.13 0.75 0.016 0.002 0.06 0.16 0.04 - - - - - - - - - - - 0.0027 - 0.34 18 0.13 0.25 1.36 0.015 0.002 0.20 0.05 0.01 0.02 - - - - - - - - - - - 0.0071 0.60 19 0.04 0.13 0.59 0.011 0.007 0.13 0.08 0.04 - - - - - - - - - - - - - 0.51 compare steel 20 0.21 0.51 1.52 0.016 0.003 0.25 0.21 0.13 0.13 - - - - - - - - - - - - 1.35 twenty one 0.06 0.04 0.80 0.013 0.010 0.09 0.05 0.11 - - - - - - - - - - - - - 0.71 twenty two 0.17 1.02 1.45 0.015 0.009 0.15 0.09 0.06 0.05 - - - - - - - - - - - - 0.71 twenty three 0.05 0.08 0.48 0.022 0.006 0.05 0.02 0.09 - - - - - - - - - - - - - 0.53 twenty four 0.19 0.36 2.02 0.010 0.005 0.20 0.10 0.19 0.09 - - - - - - - - - - - - 1.43 25 0.11 0.45 0.70 0.002 0.005 0.01 0.28 0.05 - - - - - - - - - - - - - 0.24 26 0.13 0.24 1.15 0.037 0.004 0.34 0.17 0.14 0.03 - - - - - - - - - - - - 1.53 27 0.14 0.18 0.73 0.018 0.040 0.11 0.03 0.07 - - - - - - - - - - - - - 0.59 28 0.12 0.40 1.56 0.017 0.004 - 0.18 - 0.09 - - - - - - - - - - - - 0.11 29 0.15 0.37 1.47 0.021 0.003 0.51 0.14 0.03 - - - - - - - - - - - - - 1.47 30 0.09 0.59 0.52 0.015 0.005 0.02 - 0.04 0.01 - - - - - - - - - - - - 0.24 31 0.16 0.45 1.39 0.016 0.009 0.24 0.52 0.17 - - - - - - - - - - - - - 1.35 32 0.14 0.32 0.70 0.019 0.015 0.08 0.05 0.003 0.007 - - - - - - - - - - - - 0.24 33 0.17 0.17 0.53 0.020 0.006 0.06 0.10 0.31 - - - - - - - - - - - - - 1.47 34 0.14 0.45 1.59 0.010 0.004 0.02 0.06 0.01 0.01 - - - - - - - - - - - - 0.11 35 0.13 0.31 1.51 0.015 0.002 0.16 0.22 0.25 - - 0.086 - 0.020 - - - - - - - - 1.46 36 0.13 0.38 0.55 0.031 0.006 0.35 0.18 0.24 0.06 - - - - - - - - - - - - 2.01 37 0.12 0.27 1.05 0.012 0.005 0.14 0.15 0.08 - - 0.006 - - - - - - - - - - 0.71 suitable for steel 38 0.11 0.38 1.29 0.015 0.003 0.11 0.10 0.11 - - 0.198 - - - - - - - - - - 0.76 39 0.16 0.46 1.52 0.018 0.009 0.22 0.13 0.13 - - 0.201 - - - - - - - - - - 1.13 compare steel 40 0.10 0.45 0.82 0.013 0.005 0.19 0.12 0.09 - - - 0.005 - - - - - - - - - 0.88 suitable for steel 41 0.06 0.37 1.35 0.015 0.003 0.08 0.14 0.10 - - - 0.196 - - - - - - - - - 0.64 42 0.15 0.55 1.64 0.017 0.012 0.24 0.16 0.14 - - - 0.203 - - - - - - - - - 1.23 compare steel ※1 The underline indicates that it is out of the scope of the present invention. ※2 2.6×[%Cu]+0.8×[%P]+4.2×[%W]+1.1×[%Mo]

[Table 2] Test No. Steel No. Hot rolling condition steel properties exam preparation Heating temperature [°C] Finishing temperature ^{※ 1} [℃] Average cooling rate ^{※ 2} [℃/sec] Film expansion area [mm ² ] Tensile strength [MPa] Yield strength [MPa] Impact absorbed energy vE0[J] 1 1 1250 772 0.4 395 420 290 186 Invention example 2 2 1300 796 0.6 462 485 335 159 3 3 1160 741 0.9 468 499 344 197 4 4 1280 769 1.1 359 431 297 141 5 5 1260 763 15.6 442 604 429 165 6 6 1200 745 7.8 451 598 425 89 7 7 1180 771 3.2 466 553 393 236 8 8 1340 827 4.5 470 579 411 250 9 9 1320 794 0.6 410 430 297 213 10 10 1280 781 9.9 435 569 404 152 11 11 1260 769 11.5 412 588 417 179 12 12 1250 760 1.2 478 446 308 201 13 13 1260 776 2.1 444 525 373 243 14 14 1200 755 0.6 367 420 290 142 15 15 1300 794 3.7 410 546 388 219 16 16 1270 786 6.9 461 514 365 313 17 17 1250 780 0.5 478 432 298 324 18 18 1230 770 4.6 464 540 383 162 19 19 1200 767 1.2 460 375 259 310 comparative example 20 20 1310 800 5.3 402 641 455 9 twenty one twenty one 1290 786 0.9 467 397 274 271 twenty two twenty two 1170 729 4.1 459 632 449 12 twenty three twenty three 1200 774 0.6 470 361 249 327 twenty four twenty four 1160 768 3.7 368 650 462 twenty one 25 25 1250 792 0.3 502 458 316 185 26 26 1230 780 5.5 389 515 366 25 27 27 1190 770 0.4 429 440 304 16 28 28 1210 785 2.5 566 582 413 39 29 29 1200 783 6.9 402 612 435 twenty three 30 30 1250 787 0.5 512 424 293 214 31 31 1280 796 4.1 421 628 446 17 32 32 1200 771 0.4 482 445 307 172 33 33 1250 790 0.8 371 429 296 20 34 34 1300 812 5.0 591 586 416 113 35 35 1240 780 6.2 395 595 422 16 36 36 1280 797 0.5 336 436 301 8 37 2 1360 797 2.3 458 624 406 20 38 3 1240 1061 1.5 470 556 373 twenty four 39 3 1260 714 0.6 478 469 342 19 40 4 1250 758 30.4 370 835 585 8 41 37 1280 780 6.3 432 501 356 224 Invention example 42 38 1260 772 0.7 348 538 382 129 43 39 1300 798 7.5 320 636 439 10 comparative example 44 40 1250 769 4.6 403 506 359 210 Invention example 45 41 1280 780 1.2 398 549 390 135 46 42 1320 797 5.9 353 661 456 9 comparative example *1 Finish rolling finish temperature *2 The underlined average cooling rate from the cooling start temperature (rolling finish temperature) to 500°C indicates that it is out of the scope of the present invention.

1: H-shaped steel 2: Flange 3: web 4: Flange 1/6B part (test piece collection position)

FIG. 1 is a cross-sectional view of an H-shaped steel and a diagram showing collection positions of test pieces.

Claims (4)

An H-shaped steel having the following steel composition with a tensile strength of 400 MPa or more, a yield strength of 235 MPa or more, and an impact absorption energy of 27 J or more at 0°C, the steel composition containing C: 0.05% by mass to 0.20% by mass, Si: 0.05% by mass to 1.00% by mass, Mn: 0.50% by mass to 2.00% by mass, P: 0.003% by mass to 0.035% by mass, S: 0.035% by mass or less, Cu: 0.01% by mass to 0.50% by mass, and Ni: 0.01% by mass to 0.50% by mass, Further containing one or two selected from W: 0.005% by mass to 0.30% by mass, Mo: 0.005% by mass to 0.50% by mass, And it contains Cu, P, W, and Mo within the range satisfying the following formula (1), and the rest contains Fe and unavoidable impurities, 0.25≦2.6×[%Cu]+0.8×[%P]+4.2×[%W]+1.1×[%Mo]≦1.30･･･（1） Here, [%Cu], [%P], [%W], and [%Mo] in the formula (1) are the contents (mass %) of Cu, P, W, and Mo in the steel, respectively. set to 0 in case of The H-shaped steel as claimed in item 1, wherein the steel composition further contains selected from Cr: 1.00% by mass or less, Sn: 0.200% by mass or less, Sb: 0.200% by mass or less, Al: 0.100% by mass or less, Nb: 0.50% by mass or less, V: 0.50% by mass or less, Ti: 0.50% by mass or less, B: 0.0100% by mass or less, Zr: 0.100% by mass or less, Ca: 0.100% by mass or less, Mg: 0.100% by mass or less, and REM: one or more of 0.100% by mass or less. The H-shaped steel according to Claim 1 or Claim 2, which has a coating film on its surface. The H-shaped steel as described in claim item 3, wherein the coating film has an anti-corrosion base layer, an undercoat, a middle coat and a top coat, and the anti-corrosion base layer is formed by using an inorganic zinc-rich paint, so The undercoat layer is formed using epoxy resin paint, the middle coat layer is formed using a fluororesin top coat paint, and the top coat layer is formed using a fluororesin top coat paint.

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