CN116802333A

CN116802333A - H-shaped steel

Info

Publication number: CN116802333A
Application number: CN202180092151.2A
Authority: CN
Inventors: 安藤佳祐; 大坪浩文; 三浦进一; 中村直人; 盐谷和彦
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2021-03-03
Filing date: 2021-11-26
Publication date: 2023-09-22
Also published as: KR20230125287A; WO2022185632A1; TWI808555B; JP7405246B2; JPWO2022185632A1; TW202235637A

Abstract

The invention provides an H-shaped steel with excellent coating durability and strength-toughness balance. An H-shaped steel comprising, in mass%, C:0.05 to 0.20 percent of Si:0.05 to 1.00 percent of Mn:0.50 to 2.00 percent of P:0.003 to 0.035 percent, S: less than 0.035%, cu:0.01 to 0.50 percent of Ni:0.01 to 0.50%, and further comprises W: 0.005-0.30%, mo:0.005 to 0.50% and Cu, P, W and Mo satisfy the following formula, wherein the tensile strength of the H-shaped steel is 400MPa or more, the yield strength is 235MPa or more, and the vE0 is 27J or more. 0.25.ltoreq.2.6 [%Cu ] +0.8 [%P ] +4.2 [%W ] +1.1 [%Mo ]. Ltoreq.1.30 [%Cu ], [%P ], [%W ] and [%Mo ] are contents (mass%) of Cu, P, W and Mo, respectively, and are not contained and set to 0.

Description

H-shaped steel

Technical Field

The present invention relates to an H-shaped steel used mainly in outdoor atmospheric corrosive environments on land such as buildings, civil engineering, and bridges, and particularly in severe corrosive environments such as offshore and coastal environments where flying salt content is large.

Background

For steel structures such as bridges, corrosion protection measures such as strict coating are generally adopted. As for H-type steel that is used as a structural member in many cases, for example, weather-resistant steel is used in environments with a small amount of flying salt. Here, the weather-resistant steel is the following steel material: when the corrosion inhibitor is used in an atmosphere-exposed environment, the corrosion rate is greatly reduced by covering the surface with a rust layer having high protection property and enriched with an alloy element such as Cu, P, cr, ni. It is known that bridges using such weather-resistant steels can withstand decades of use in a non-painted state in environments with low flying salt content.

On the other hand, in an environment with a large amount of flying salt such as at sea or near the coast, it is difficult to form a rust layer with high protection, and it is difficult to use weather-resistant steel in an uncoated state. Therefore, in an environment with a large amount of flying salt such as at sea or near the coast, steel materials having been subjected to corrosion-resistant treatment such as coating on ordinary steel materials are generally used. Coating is a very effective means of corrosion protection, but it requires periodic repair because of significant degradation in the atmosphere exposure environment. When repairing, if a deteriorated coating and rust generated on the substrate remain, the anticorrosive effect by the coating is significantly reduced. To avoid this problem, it is necessary to grind and remove old paint and rust at the repaired site, and recoating is performed again at the site. Since this operation needs to be visually confirmed, automation is extremely difficult, and a manual operation by a skilled operator is necessary. Therefore, when a coated steel material is used, there is a problem that maintenance costs of the structure are increased, and further life cycle costs are increased.

Accordingly, it is desired to develop an H-shaped steel excellent in corrosion resistance, particularly an H-shaped steel excellent in coating durability, which can reduce the coating frequency and suppress the maintenance cost of the structure by extending the period of recoating.

In view of such a background, for example, patent document 1 discloses a method for producing H-steel, which can suppress red-hot embrittlement due to molten Cu by precisely controlling rolling and cooling conditions while ensuring corrosion resistance by adding Cr and Cu. Patent document 2 discloses an H-shaped steel excellent in weather resistance, which has excellent corrosion resistance even in coastal regions having a flying salt content of 0.05mdd or more by adjusting the addition amounts of Mo and Ni. Patent documents 3 to 7 disclose high weather resistance steels in which predetermined amounts of Sn and Sb are added in addition to the above alloy elements, thereby greatly improving corrosion resistance in severe corrosive environments such as offshore and near coast.

Prior art literature

Patent literature

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 application laid-open No. 2010-7109

Patent document 6: japanese patent application laid-open No. 2012-255184

Patent document 7: japanese patent laid-open No. 2013-166992

Disclosure of Invention

Problems to be solved by the invention

However, the H-shaped steel described in patent documents 1 and 2 has a problem that the weather resistance in a high-flying salt environment is insufficient, because the coating durability is not considered. Further, since H-shaped steel, which requires heating at 1200 ℃ or higher at the time of hot working, tends to be coarsened in crystal grains as compared with thick steel plates from the viewpoint of formability, if corrosion resistant elements are excessively contained as in patent documents 3 to 7, there is also a problem that it is difficult to secure toughness.

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

The term "excellent in coating durability" means that the expansion area of the coating film when the coating film is formed on the surface of the steel and the corrosion test under the following conditions is performed is 480mm ² The following is given.

< Corrosion test Condition >)

Initial defects imparted to the coating film: linear incision with width of 1mm and length of 40mm

Attachment amount of artificial sea salt: 6.0g/m ²

Test time: 1200 cycles (9600 hours)

Circulation conditions: (condition 1. Temperature: 60 ℃ C., relative humidity: 35%, holding time: 3 hours), (condition 2. Temperature: 40 ℃ C., relative humidity: 95%, holding time: 3 hours), and a total of 8 hours of circulation in which each transition time from condition 1 to condition 2 and from condition 2 to condition 1 is set to 1 hour

The term "excellent in balance between strength and toughness" means that the tensile strength is 400MPa or more, the yield strength is 235MPa or more, and the impact absorption energy at 0℃is 27J or more.

Means for solving the problems

The inventors produced H-steel with varying contents of C, si, mn, P, S, cu, ni, W and M omicrongroup, and conducted deep examination of coating durability, tensile properties, and toughness. As a result, it was found that H-shaped steel having excellent strength-toughness balance in addition to excellent coating durability can be obtained by setting the content of each element contained in the steel to a specific range and controlling parameters including Cu, P, W, and M omicrongroup amounts to specific ranges.

The present invention is based on the above-described findings, and its gist is as follows.

[1] An H-section steel having a steel structure containing C:0.05 to 0.20 mass% of Si:0.05 to 1.00 mass percent of Mn:0.50 to 2.00 mass percent, P:0.003 to 0.035 mass%, S:0.035 mass% or less, cu:0.01 to 0.50 mass% and Ni:0.01 to 0.50 mass% and further comprises W:0.005 to 0.30 mass% of Mo:0.005 to 0.50 mass% and contains Cu, P, W and Mo in a range satisfying the following formula (1), the balance being Fe and unavoidable impurities,

the H-shaped steel has a tensile strength of 400MPa or more, a yield strength of 235MPa or more, and an impact absorption energy at 0 ℃ of 27J or more.

0.25≤2.6×[％Cu]+0.8×[％P]+4.2×[％W]+1.1×[％Mo]≤1.30…(1)

Here, in the formula (1) [%cu ], [%p ], [%w ], and [%mo ] are contents (mass%) of Cu, P, W, and Mo in the steel, respectively, and are not contained, and sometimes 0.

[2] The H-shaped steel according to [1], wherein the steel composition further comprises a steel composition selected from the group consisting of Cr:1.00 mass% or less, sn:0.200 mass% or less, sb:0.200 mass% or less, al:0.100 mass% or less, nb:0.50 mass% or less, V:0.50 mass% or less, ti:0.50 mass% or less, B:0.0100 mass% or less, zr:0.100 mass% or less, ca:0.100 mass% or less, mg:0.100 mass% or less and REM:0.100 mass% or less of one or two or more kinds.

[3] The H-shaped steel according to [1] or [2], which has a coating film on the surface.

[4] The H-shaped steel according to [3], wherein the coating film has an anticorrosive base layer, an undercoat layer and a top coat layer, the anticorrosive base layer is formed by using an inorganic zinc-rich paint, the undercoat layer is formed by using an epoxy resin paint, the top coat layer is formed by using a top coat paint for a fluororesin top coat paint, and the top coat layer is formed by using a fluororesin top coat paint.

Effects of the invention

According to the present invention, an H-shaped steel excellent in coating durability and strength-toughness balance can be provided.

According to the present invention, it is possible to provide an H-shaped steel excellent in coating durability and strength-toughness balance, which can lengthen the repainting period and reduce the coating frequency even when used in an outdoor atmospheric corrosive environment such as a bridge, particularly in a severe corrosive environment such as the sea or the vicinity of the coast where flying salt content is large.

According to the present invention, an H-shaped steel having excellent coating durability and a balance of strength and toughness can be stably produced, and an H-shaped steel having excellent coating durability can be obtained at low cost, which can lengthen a recoating cycle and reduce a coating frequency even when used in an outdoor atmosphere corrosive environment such as a bridge, particularly in a severe corrosive environment such as a sea or the vicinity of a coast where flying salt content is large. Further, by suitably using the H-shaped steel excellent in coating durability of the present invention for a structure such as a bridge or the like which is used in an outdoor atmosphere corrosive environment such as a bridge or the like, particularly in a severe corrosive environment such as a sea or the vicinity of a coast where flying salt content is large, maintenance costs of such a structure and further life cycle costs can be reduced.

Drawings

Fig. 1 is a view showing a sectional view of an H-shaped steel and a cutting position of a test piece.

Detailed Description

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

C：0.05～0.20％

C is an essential element for securing the strength of the base material, and is required to be added at least 0.05%. However, when C is added in excess of 0.20%, not only the toughness of the base material but also the weldability is lowered. Accordingly, the C content is set to 0.05 to 0.20% in the present invention. The C content is preferably 0.07% or more, more preferably 0.09% or more, and still more preferably 0.11% or more. The C content is preferably 0.18% or less, more preferably 0.15% or less.

Si：0.05～1.00％

Si has an effect of improving the coating durability of the H-steel by forming a dense rust layer in addition to ensuring the strength of the base material. However, if the Si content is less than 0.05%, the effect of addition is small, while if it exceeds 1.00%, toughness and weldability are deteriorated. Accordingly, in the present invention, the Si content is set to 0.05 to 1.00%. The Si content is preferably 0.10% or more, more preferably 0.15% or more, and still more preferably 0.20% or more. The Si content is preferably 0.60% or less, more preferably 0.45% or less.

Mn：0.50～2.00％

Like Si, mn is an element effective for improving hardenability and ensuring strength of the base material. However, when the Mn content is less than 0.50%, the effect of addition is small, whereas when Mn is added in excess of 2.00%, transformation of upper bainite is promoted, and toughness is lowered, which is not preferable. Therefore, the Mn content is set to 0.50 to 2.00% in the present invention. The Mn content is preferably 0.60% or more, more preferably 0.80% or more, and still more preferably 1.20% or more. The Mn content is preferably 1.80% or less, more preferably 1.60% or less.

P：0.003～0.035％

Since P is an element having high solid solution strengthening ability and decreases toughness by hardening of ferrite, the P content in the steel is set to 0.035% or less in the present invention. On the other hand, since P is an element contributing to improvement of coating durability, it is necessary to add at least 0.003% of P. Therefore, in the present invention, the P content is set to 0.003 to 0.035%. The P content is preferably 0.005% or more, more preferably 0.008% or more, and still more preferably 0.010% or more. The P content is preferably 0.025% or less, more preferably 0.020% or less.

S: less than 0.035%

S exists mainly in the form of a-type inclusions in steel, but when the S content exceeds 0.035%, the inclusion content increases significantly and coarse inclusions are produced, so that the toughness decreases significantly. Therefore, in the present invention, the S content is set to 0.035% or less. The S content is preferably 0.020% or less, more preferably 0.010% or less, and still more preferably 0.008% or less. On the other hand, the lower limit of the S content is not particularly limited and may be 0% since the smaller S is more preferable, but S is an element inevitably contained in steel as an impurity in general and may be more than 0% industrially. Since excessive reduction of S leads to an increase in refining time and cost, 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 following effects: the rust particles of the rust layer are refined to form a dense rust layer, thereby inhibiting the permeation of oxygen and chloride ions, which are corrosion promoters, into the steel base. Further, cu is added in combination with Ni, and further with Ni and W, whereby the coating durability of the steel material is greatly improved by the synergistic effect of these elements. Such an effect can be obtained by setting the Cu content to 0.01% or more. On the other hand, when the Cu content exceeds 0.50%, not only the alloy cost increases but also Cu cracks are easily generated at the time of hot working. Further, the hardenability of the steel is further improved, and therefore, the toughness is also reduced. Therefore, in the present invention, the Cu content is set to 0.01 to 0.50%. The Cu content is preferably 0.03% or more, more preferably 0.05% or more, and still more preferably 0.07% or more. The Cu content is preferably 0.30% or less, more preferably 0.20% or less.

Ni：0.01～0.50％

Ni also has the following effects: the rust particles of the rust layer are refined to form a dense rust layer, whereby penetration of oxygen and chloride ions as corrosion promoters into the steel base is suppressed, and Cu cracking is suppressed. Further, ni is added in combination with Cu, and further with Cu and W, whereby the coating durability of the steel material is greatly improved by the synergistic effect of these elements. Such an effect can be obtained by making the Ni content 0.01% or more. However, when the Ni content exceeds 0.50%, the hardenability of the steel further increases and the toughness decreases. Therefore, in the present invention, the Ni content is set to 0.01 to 0.50%. The Ni content is preferably 0.03% or more, more preferably 0.05% or more, and still more preferably 0.07% or more. The Ni content is preferably 0.30% or less, more preferably 0.20% or less.

Selected from the group consisting of W: 0.005-0.30%, mo: 0.005-0.50% of one or two kinds of

W：0.005～0.30％

W is eluted with anodic reaction of steel material, WO ₄ ^2- Is distributed in the rust layer, thereby electrostatically preventing the corrosion-promoting factor chloride ions from penetrating the rust layer to reach the steel base. Further, by depositing a compound containing W on the surface of the steel material, the anode reaction of the steel material is suppressed. Further, W is added in combination with Cu and Ni, and the synergistic effect of these elements greatly improves the coating durability of the steel material. Such an effect can be obtained by setting the W content to 0.005% or more. However, when the W content exceeds 0.30%, not only the alloy cost increases, but also the hardenability of the steel significantly 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%. The W content is preferably 0.01% or more, more preferably 0.03% or more, and still more preferably 0.05% or more. The W content is preferably 0.30% or less, more preferably 0.20% or less.

Mo：0.005～0.50％

Mo is eluted with the anodic reaction of steel material in MoO ₄ ^2- Is distributed in the rust layer, thereby preventing chloride ions as corrosion promoters from penetrating the rust layer to reach the steel base. In addition, by depositing a compound containing Mo on the surface of the steel material, the anodic reaction of the steel material is suppressed. Such an effect can be obtained by making the Mo content 0.005% or more. However, when the content exceeds 0.50%, the transformation of upper bainite is promoted, and the toughness is lowered. Therefore, in the present invention, the Mo content when Mo is contained is set to 0.005 to 0.50%. The Mo content is preferably 0.02% or more, more preferably 0.05% or more, and still more preferably 0.07% or more. The Mo content is preferably 0.40% or less, more preferably 0.30% or less.

In the present invention, among the above-mentioned W and Mo, W is preferably contained, and W and Mo are more preferably contained.

In the present invention, since the steel is a section steel, it is not sufficient that each element satisfies only the above-described range, and it is important that the relationship of the following expression (1) is satisfied for Cu, P, W, and Mo.

0.25≤2.6×[％Cu]+0.8×[％P]+4.2×[％W]+1.1×[％Mo]≤1.30…(1)

The inventors evaluated the coating durability and strength-toughness balance using various H-steels having steel components in the above content ranges, and as a result, found the following findings: in order to obtain desired characteristics for both, it is important to control the contents of Cu, P, W and Mo to specific ranges in addition to the above-mentioned content ranges of the respective components. Specifically, by setting the parameters based on the contents of Cu, P, W, and Mo, that is, the values calculated by the above formula (1) (the values calculated by 2.6× [%cu ] +0.8× [%p ] +4.2× [%w ] +1.1× [%mo ]) to 0.25 or more and 1.30 or less, excellent coating durability and strength-toughness balance can be stably obtained. When the value calculated from the formula (1) is less than 0.25, it is difficult to stably form a dense rust layer that inhibits permeation of oxygen and chloride ions, which are corrosion promoters, into the steel base, and coating durability is reduced. On the other hand, when the value calculated from the formula (1) exceeds 1.30, the increase in hardenability by Cu, W, and Mo and the superposition of ferrite hardening by P become remarkable, and the toughness is lowered. The range of the values calculated from the above formula (1) is more preferably set to 0.40 to 1.20, that is, the contents of Cu, P, W and Mo are set to satisfy the following formula (2).

0.40≤2.6×[％Cu]+0.8×[％P]+4.2×[％W]+1.1×[％Mo]≤1.20…(2)

Here, in the formula (2) [% Cu ], [% P ], [% W ], and [% Mo ] 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 0.50 or more. The value calculated from the above formula (1) is preferably 1.20 or less, more preferably 1.10 or less.

In addition to the above components, the steel composition of the H-shaped steel of the present invention may optionally contain a composition selected from the group consisting of Cr: less than 1.00%, sn:0.200% or less, sb: less than 0.200%, al: less than 0.100%, nb: less than 0.50%, V: less than 0.50%, ti: less than 0.50%, B: less than 0.0100%, zr: less than 0.100%, ca: less than 0.100%, mg:0.100% below and REM:0.100% or less of one or two or more kinds of the above.

Cr: less than 1.00%

Cr is an element that can achieve further higher strength of steel by solid solution strengthening. In order to sufficiently obtain such an effect, cr is preferably contained in an amount of 0.01% or more. However, when the content exceeds 1.00%, the transformation of upper bainite is promoted, and the toughness is lowered. Therefore, when Cr is contained, the Cr content is set to 1.00% or less. The Cr content is more preferably 0.05% or more, and still more preferably 0.10% or more. The Cr content is preferably 0.50% or less, more preferably 0.30% or less.

Sn: less than 0.200%

Sn is present in the rust layer near the surface of the steel base, and by micronizing the rust particles, chlorine ions, which are corrosion promoters, are prevented from penetrating the rust layer and reaching the steel base. In addition, sn suppresses anode reaction on the steel surface. Further, sn is added in combination with Cu and Ni, and further with Cu, ni, and W, and the synergistic effect of these elements greatly improves the coating durability of the steel material. In order to sufficiently obtain such effects, it is preferable to contain 0.005% or more of Sn. However, when the content exceeds 0.200%, ductility and toughness are reduced. Therefore, when Sn is contained, the Sn content is set to 0.200% or less. The Sn content is more preferably 0.010% or more, and still more preferably 0.020% or more. The Sn content is preferably 0.100% or less, more preferably 0.080% or less.

Sb: less than 0.200%

Sb is present in the rust layer near the surface of the steel base, and by miniaturizing the rust particles, chloride ions as corrosion promoters are prevented from penetrating the rust layer to reach the steel base. In addition, sb suppresses anode reaction on the steel surface. Further, sb is added in combination with Cu and Ni, and further with Cu, ni, and W, and the synergistic effect of these elements greatly improves the coating durability of the steel material. In order to sufficiently obtain such effects, 0.005% or more of Sb is preferably contained. However, when the content exceeds 0.200%, ductility and toughness are reduced. Therefore, when Sb is contained, the Sb content is set to 0.200% or less. The Sb content is more preferably 0.010% or more, still more preferably 0.020% or more. The Sb content is preferably 0.100% or less, more preferably 0.080% or less.

Al: less than 0.100%

Al is an element that can be added as a deoxidizer. In order to sufficiently obtain such effects, it is preferable to contain 0.001% or more of Al. However, when the Al content exceeds 0.100%, a large amount of oxide inclusions are formed in the steel due to the high bonding force with oxygen possessed by Al, and as a result, the ductility of the steel is lowered. Therefore, when Al is contained, the Al content is set to 0.100% or less. The Al content is more preferably 0.010% or more, still more preferably 0.020% or more. The Al content is preferably 0.080% or less, more preferably 0.050% or less.

Nb: less than 0.50%

Nb is an element having an effect of increasing tensile strength and 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, when the content exceeds 0.50%, not only precipitation embrittlement but also upper bainite transformation is promoted, and toughness is lowered. Therefore, when Nb is contained, the Nb content is set to 0.50% or less. The Nb content is more preferably 0.010% or more, and still more preferably 0.020% or more. The Nb content is preferably 0.20% or less, more preferably 0.10% or less.

V: less than 0.50%

V is an element that precipitates in austenite as VN during rolling or during cooling after rolling to form ferrite transformation nuclei and has an effect of refining crystal grains. V also has an effect of improving the strength of the base material by precipitation strengthening, and is a useful element for securing tensile strength and toughness. In order to sufficiently obtain such effects, it is preferable to contain V at 0.005% or more. However, when the content exceeds 0.50%, the toughness of the base material tends to be lowered due to excessive precipitation strengthening. Therefore, when V is contained, the V content is set to 0.50% or less. The V content is more preferably 0.010% or more, still more preferably 0.020% or more. The V content is preferably 0.20% or less, more preferably 0.10% or less.

Ti: less than 0.50%

Ti is an element effective for improving toughness by not only forming TiN and refining austenite grains but also refining microstructure by promoting ferrite transformation in grains having TiN as a core. In order to sufficiently obtain such an effect, it is preferable to contain 0.005% or more of Ti. However, when the content exceeds 0.50%, coarse TiN is generated and toughness is lowered. Therefore, when Ti is contained, the Ti content is set to 0.50% or less. The Ti content is more preferably 0.010% or more, still more preferably 0.020% or more. The Ti content is preferably 0.20% or less, more preferably 0.10% or less.

B:0.0100% or less

B is an element that has an effect of segregating in grain boundaries in steel and improving grain boundary strength. In addition, the TiN is an element effective for improving toughness by forming a composite precipitate of TiN and nucleation sites of ferrite in the crystal grains and 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, when the content exceeds 0.0100%, the toughness is lowered due to grain boundary precipitation of coarse carbonitrides. Therefore, when B is contained, the B content is set to 0.0100% or less. The content of B is more preferably 0.0010% or more, and still more preferably 0.0020% or more. The B content is preferably 0.0050% or less, more preferably 0.0040% or less.

Zr: less than 0.100%

Zr is an element capable of further increasing the strength of steel. In order to sufficiently obtain this effect, zr is preferably contained in an amount of 0.005% or more. However, when the content exceeds 0.100%, not only the effect of increasing the strength is saturated, but also the toughness is lowered. Therefore, when Zr is contained, the Zr content is set to 0.100% or less. The Zr content is more preferably 0.010% or more, still more preferably 0.015% or more. The Zr content is preferably 0.050% or less, more preferably 0.040% or less.

Ca: less than 0.100%

Ca has a function of granulating the sulfide-based inclusion by changing oxides and sulfides in the sulfide-based inclusion to substances having high stability at high temperatures. Further, the toughness and ductility of the steel can be improved by the morphological control effect of the inclusions caused by the Ca. In order to sufficiently obtain such effects, ca is preferably contained at 0.0001% or more. However, if the Ca content exceeds 0.100%, the cleanliness is lowered and the toughness is lowered. Therefore, when Ca is contained, the Ca content is set to 0.100% or less. The Ca content is more preferably 0.0010% or more, and still more preferably 0.0020% or more. The Ca content is preferably 0.0100% or less, more preferably 0.0050% or less.

Mg: less than 0.100%

Mg has a function of granulating the sulfide-based inclusion by changing oxides and sulfides in the sulfide-based inclusion to substances having high stability at high temperatures. Further, the toughness and ductility of the steel can be improved by the morphological control effect of the inclusions by the Mg. In order to sufficiently obtain such effects, mg is preferably contained at 0.0001% or more. However, if the Mg content exceeds 0.100%, the cleanliness is lowered and the toughness is lowered. Therefore, in the case of Mg content, mg content is set to 0.100% or less. The Mg content is more preferably 0.0010% or more, and still more preferably 0.0020% or more. The Mg content is preferably 0.0100% or less, more preferably 0.0050% or less.

REM: less than 0.100%

REM (rare earth metal) has a function of granulating sulfide-based inclusions by changing oxides and sulfides in the sulfide-based inclusions to substances having high stability at high temperatures. Further, the toughness and ductility of the steel can be improved by the morphological control effect of the inclusions by the REM. In order to sufficiently obtain such effects, it is preferable to contain REM at 0.0001% or more. However, when the REM content exceeds 0.100%, the cleanliness is lowered and the toughness is lowered. Therefore, when REM is contained, the REM content is set to 0.100% or less. The REM content is more preferably 0.0010% or more, and still more preferably 0.0020% or more. The REM content is preferably 0.0100% or less, more preferably 0.0050% or less. REM is a generic term for Sc, Y, and 15 elements from lanthanum (La) having an atomic number 57 to lutetium (Lu) having an atomic number 71, and herein, the REM content is a total content of these elements.

The balance of the steel components is composed of Fe and unavoidable impurities. Unavoidable impurities refer to the following impurities: the substances which are present in the raw materials or inevitably mixed in the production process are not essential, but are contained in a small amount and do not affect the characteristics, and therefore are allowed to be contained. As the unavoidable impurities, for example, N, O and the like are cited, N may be allowed to be contained by 0.0150%, and O may be allowed to be contained by 0.005%.

The H-shaped steel of the present invention is usually used after coating the steel surface, and in this case, the surface has a coating film. Examples of the coating film on the steel surface include a coating film having an anticorrosive base layer, an undercoat layer, a middle coating layer, and a top coating layer in this order from the steel surface. It should be noted that, preferably: the anticorrosive base layer is formed using an inorganic Zinc-rich paint (for example, SD Zinc 1500, manufactured by Kaschin paint Co., ltd.), the undercoat layer is formed using an epoxy resin paint (for example, epomarine HB (K), manufactured by Kaschin paint Co., ltd.), the intermediate layer is formed using a fluororesin top coating material (for example, celatec F, manufactured by Kaschin paint Co., ltd.), and the top layer is formed using a fluororesin top coating material (for example, celatec F (K) top coat, manufactured by Kaschin paint Co., ltd.).

Next, a method for producing the H-shaped steel of the present invention will be described. The method of melting and casting a steel raw material (billet or beam blank) is not particularly limited, and any conventionally known method is suitable. As an example of hot rolling conditions for forming the H-shaped steel from the steel stock, the following hot rolling may be mentioned: a steel material having a predetermined composition is heated to a predetermined heating temperature, rolled at a predetermined finish rolling temperature, and then cooled at a predetermined cooling rate.

From the viewpoint of securing sufficient formability, the heating temperature of the steel stock at the time of hot rolling is preferably set to 1150 to 1350 ℃. When the heating temperature is lower than 1150 ℃, the deformation resistance of the hot rolling increases, and the load on the rolling rolls increases, and as a result, the hot rolling becomes difficult. On the other hand, when the heating temperature exceeds 1350 ℃, the steel material is partially melted, internal defects are generated, and besides, the austenite grain size becomes coarse, so that upper bainite is easily generated during cooling after finish rolling, and a decrease in toughness occurs. Therefore, the heating temperature is preferably 1150 to 1350 ℃.

In finish rolling, it is preferable to set the finish rolling temperature (finish rolling end temperature) to 720 ℃ or higher from the viewpoint of securing toughness. When the finish rolling temperature is lower than 720 ℃, the rolling reduction in the ferrite-austenite dual-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 ℃, the austenite grain diameter becomes coarse and the toughness decreases, so that it is preferable to set the finish rolling temperature to 1050 ℃ or less.

Further, if the average cooling rate from the cooling start temperature after finishing finish rolling to 500 ℃ is less than 0.1 ℃/sec, it is difficult to secure predetermined elongation characteristics and toughness, and therefore the average cooling rate is preferably set to 0.1 ℃/sec or more. On the other hand, when the average cooling rate exceeds 30 ℃/sec, the toughness is lowered due to the formation of bainite or martensite. Therefore, the average cooling rate is preferably set to a range of 0.1 to 30 ℃/sec. The average cooling rate is more preferably 30.0 ℃/sec or less, and still more preferably 20.0 ℃/sec or less. The cooling start temperature is, for example, a finish rolling end temperature. The above temperature refers to the surface temperature of the steel material.

By hot rolling the steel material having the above composition adjusted, an H-shaped steel excellent in coating durability can be obtained which has mechanical properties of a tensile strength TS of 400MPa or more, a yield strength (yield point YP or 0.2% yield strength) of 235MPa or more, and an impact absorption energy (charpy impact absorption energy) vE0 at 0 ℃ of 27J or more. It is preferable that vE0 is 47J or more. In the present invention, the tensile strength, the yield strength, and the impact absorption energy at 0℃can be obtained by the methods described in examples.

The tensile strength TS is preferably 490MPa or more, more preferably 520MPa or more. The upper limit of the tensile strength TS is not particularly limited, but is preferably 640MPa or less. The yield strength is preferably 325MPa or more, more preferably 355MPa or more. The upper limit of the yield strength is not particularly limited, but is preferably 475MPa or less. The vE0 is more preferably 100J or more.

Examples

Hereinafter, the constitution and the working 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 may be appropriately modified 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.

The steels having the compositions shown in Table 1 were produced into a parison having a cross section of 400mm X560 mm X8000 mm by a continuous casting machine, and hot-rolled under the hot-rolling conditions shown in Table 2 to produce H-shaped steel 1 having the cross section shown in FIG. 1, that is, having a web 3 and a pair of flanges 2 disposed at both ends of the web. Here, the cross-sectional dimensions (web height×flange width×web thickness×flange thickness) were 900mm×300mm×18mm×34mm, and H-section steel was produced. The average cooling rate after finish rolling was 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 end temperature) to 500 ℃ into a value per unit time (second).

The obtained H-steel was subjected to a coating durability evaluation, a tensile test, and a charpy impact test. The following describes each evaluation content in detail.

< evaluation of coating durability >)

A test piece of 70 mm. Times.50 mm. Times.5 mm was cut from a 1/4t portion (t/4 portion) (t is the flange thickness) from the back of the flange 1/6B portion (B/6 portion) 4 shown in FIG. 1.The surface of the test piece was subjected to shot blasting so that the surface roughness was ISO Sa 2.5, subjected to ultrasonic degreasing in acetone for 5 minutes, and air-dried. Next, a single surface of the test piece was used as a coating surface, an inorganic zinc-rich paint (thickness: 75 μm) was applied as an anticorrosive base, an epoxy resin paint (thickness: 120 μm) was applied as a primer, an intermediate paint for a fluororesin top paint (thickness: 30 μm) was applied as an intermediate paint, and a fluororesin top paint (thickness: 25 μm) was applied as a top paint, to form a coating film comprising an anticorrosive base layer, an undercoat layer, an intermediate paint, and a top coat. The other surface and the end face of the test piece were sealed with a solvent-based epoxy resin paint, and further covered with a silicon-based sealant. After the coating, the width of the coating film formed on the test piece was introduced so as to reach the steel base at the center: 1mm, length: a 40mm straight cut (kerf flaw) was set as an initial defect. Next, corrosion tests were conducted under the conditions shown below. That is, the amount of artificial sea salt adhering to the surface of the test piece was 6.0g/m ² In the above method, the artificial sea salt is diluted with pure water to a solution of a predetermined concentration by spraying, and the artificial sea salt is adhered to the test piece. Next, a corrosion test was performed using the test piece, wherein 1 cycle was set to a total of 8 hours (condition 1. Temperature: 60 ℃, relative humidity: 35%, holding time: 3 hours), (condition 2. Temperature: 40 ℃, relative humidity: 95%, holding time: 3 hours), and each transition time from condition 1 to condition 2 and from condition 2 to condition 1 was 1 hour, and 1200 cycles were repeated. The artificial sea salt was attached once a week. After the corrosion test, the expansion area (coating expansion area) from the initial defective portion during coating was measured, and the coating durability was evaluated. In this evaluation, the coating expansion area was 480mm ² The following test pieces were judged to be excellent in coating durability.

< tensile test >)

From the flange 1/6B portion 4 shown in fig. 1, a whole thickness tensile test piece of JIS1A No. defined in JIS Z2201 in which the tensile direction is the longitudinal direction of the H-shaped steel was cut, and a tensile test was performed in accordance with JIS Z2241 to measure a yield strength (yield point YP or 0.2% yield strength) and a tensile strength TS.

< toughness test >)

A2 mmV notched Charpy impact test piece defined in JIS Z2202 was cut from the 1/4t portion from the back of the flange 1/6B portion 4 shown in FIG. 1, and a Charpy impact test was performed in accordance with JIS Z2242 to measure the impact absorption energy at 0 ℃.

In the results of the tensile test and the toughness test, the test specimens satisfying all the requirements of a tensile strength of 400MPa or more, a yield strength of 235MPa or more, and an impact absorption energy of 27J or more at 0℃were judged to be excellent in the balance of strength and toughness.

Table 2 shows the test results. The H-shaped steel (test Nos. 1 to 18, 41, 42, 44, 45 in Table 2) suitable for steel production, which satisfies the steel composition of the present invention, has excellent coating durability, satisfies desired mechanical properties (tensile strength TS:400MPa or more, yield strength: 235MPa or more, impact absorption energy vE0 at 0 ℃ C.: 27J or more), and has excellent balance of strength and toughness.

On the other hand, in the comparative examples (test nos. 19 to 36, 43, 46 in table 2) in which the steel composition of the H-shaped steel does not satisfy the conditions of the present invention, or the comparative examples (test nos. 37 to 40 in table 2) in which the preferable hot rolling conditions of the present invention are not satisfied, any one of the coating durability, tensile strength, yield strength, and impact absorption energy does not satisfy the required characteristics.

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TABLE 2

Finishing temperature of finish rolling

The average cooling rate of the target product 2 from the cooling start temperature (finish rolling end temperature) to 500 ℃ is underlined and falls outside the scope of the present invention.

Symbol description

1: h-shaped steel

2: flange

3: web plate

4: flange 1/6B part (test piece cutting position)

Claims

1. An H-section steel having a steel structure containing C:0.05 to 0.20 mass% of Si:0.05 to 1.00 mass percent of Mn:0.50 to 2.00 mass percent, P:0.003 to 0.035 mass%, S:0.035 mass% or less, cu:0.01 to 0.50 mass% and Ni:0.01 to 0.50 mass% and further comprises W:0.005 to 0.30 mass% of Mo:0.005 to 0.50 mass% and contains Cu, P, W and Mo in a range satisfying the following formula (1), the balance being Fe and unavoidable impurities,

the H-shaped steel has a tensile strength of 400MPa or more, a yield strength of 235MPa or more, and an impact absorption energy at 0 ℃ of 27J or more,

0.25≤2.6×[％Cu]+0.8×[％P]+4.2×[％W]+1.1×[％Mo]≤1.30…(1)

here, in the formula (1) [%cu ], [%p ], [%w ], and [%mo ] are the mass% contents of Cu, P, W, and Mo in the steel, respectively, and are not contained, and are set to 0.

2. The H-section steel according to claim 1, wherein the steel composition further contains a composition selected from the group consisting of Cr:1.00 mass% or less, sn:0.200 mass% or less, sb:0.200 mass% or less, al:0.100 mass% or less, nb:0.50 mass% or less, V:0.50 mass% or less, ti:0.50 mass% or less, B:0.0100 mass% or less, zr:0.100 mass% or less, ca:0.100 mass% or less, mg:0.100 mass% or less and REM:0.100 mass% or less of one or two or more kinds.

3. The H-shaped steel according to claim 1 or 2, which has a coating film on a surface.

4. The H-shaped steel according to claim 3, wherein the coating film has an anticorrosive base layer made of an inorganic zinc-rich paint, an undercoat layer made of an epoxy resin paint, an intermediate coating layer made of an intermediate coating material for a fluororesin top coating, and a top coating layer made of a fluororesin top coating.