JP3520818B2 - H-shaped steel for high-strength support with excellent strain-age aging embrittlement resistance - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an H-section steel for steel arch support used as a strength member for supporting an excavated section such as a tunnel or a tunnel. More specifically, it can be manufactured at low cost and has good strain aging resistance. Brittleness, yield strength 440
The present invention relates to a high-strength H-section steel for supporting and supporting, which has a tensile strength of 590 MPa or more at MPa or more.

[0002]

2. Description of the Related Art As a strength member for supporting an excavated cross section such as a tunnel or a tunnel, a steel arch support structure formed by processing a shaped steel into an arch shape is widely used. Steel H-shaped steel for arch support is mainly required to have good ductility, good cold workability, and good weldability. Conventionally, steel materials equivalent to SS400 specified in JISG3101 have been used. ing. However, with the recent increase in the size of excavating equipment and the expansion of the tunnel width, the excavated cross section tends to be enlarged and flattened, and the steel arch support is also required to have high strength.
Also, if the cross-sectional area of the structural steel for supporting work can be reduced by increasing the strength, it is possible to reduce the amount of steel used and the transportation cost, and contribute to the reduction of the construction cost of excavated structures such as tunnels and tunnels. .

In response to such demands, a technique relating to a high-strength H-shaped steel for supporting and supporting having a tensile strength of 590 MPa or more is disclosed in JP-A-10-152751 and JP-A-10-1.
No. 76240 and Japanese Patent Laid-Open No. 10-195603.

By the way, the steel arch support is manufactured by forming H-section steel into an arch shape by cold working. Therefore, in addition to the basic mechanical properties of the base metal, the mechanical properties after cold working become important. In particular, attention should be paid to the change with time of mechanical properties after cold working. The temporal change in ductility and toughness after cold working is caused by strain aging. Strain aging is due to the formation of a so-called "atmosphere" where N atoms mainly in solid solution in the steel diffuse and gather around the dislocations introduced into the steel material by cold working and diffuse over time. Dislocations become difficult to move and are triggered. Therefore, in the conventional H-section steel for high-strength support, consideration has been given to the N content in the steel.

For example, in Japanese Unexamined Patent Publication No. 10-195603, the N content is specified to be 0.0050% by weight (hereinafter simply referred to as "%") or less, and in Japanese Unexamined Patent Publication No. 10-1.
In Japanese Patent No. 52751, the N content is 0.0150% or less, and the value of Ns defined by the following formula (3) is 0.
It is specified to be 0030% or less. Here, the Ns value defined by the equation (3) is presumed to be an index representing the amount of N dissolved in steel. This is because N reacts with Ti, V, and Nb to form a compound with them, and the amount of solute N in steel decreases. In the formula (3),% N,% Ti,%
V and% Nb represent the content of each element in steel. Ns = [% N]-(10 × [% Ti] / 48 + 4 × [% V] / 51 + 3 × [% Nb] / 93 …… (3)

On the other hand, according to the experience of the present inventors, for example, 0.
Considering a V-added steel containing 0150% N, it is necessary to sufficiently reduce the amount of solute N while securing sufficient strength by precipitation of nitride even if the V content is 0.09%. It has been confirmed that it is possible to secure sufficient elongation even after strain aging. However, the steel of this component system does not satisfy the above formula (3). This is because the amount of solid solution N in steel has not been sufficiently grasped in the past, so the N content is excessively regulated, or V is excessive in order to fix N with nitride or the like. Therefore, it cannot be said that the strengthening mechanism itself of the steel due to the precipitation of VN was excessively regulated.

When it is difficult to obtain a strengthening mechanism by combining a sufficient reduction in an unrecrystallized region and the addition of a microalloy such as Nb in a sufficiently stable manner, as in the case of shaped steel rolling, strengthening by vanadium nitride (VN) Is a suitable strengthening method for obtaining stable strength as rolled. However, because of the excessive regulation of N content in steel,
This strengthening method has not been fully utilized for H-section steel for supporting work.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to control excessively N which has been conventionally regarded as a cause of causing strain aging.
By positively utilizing as a cheap strengthening element, its manufacturing cost is low and excellent in strain aging embrittlement resistance,
Yield strength of 440 MPa or more and tensile strength of 590 MPa
It is an object of the present invention to provide the above H-shaped steel for high strength support.

[0009]

In order to solve the above-mentioned problems, the present inventors have collected the solubility of VN in austenite and the N analysis data of electrolytic extraction residue to determine the amount of solid solution N in steel. More accurately grasped, and at the same time, systematically studied the relationship between the amount of solute N and the decrease in elongation of steel after strain aging, and as a result, the composition range of N and V that has sufficient elongation even after strain aging. Found out that there is. That is, even if N, which has been conventionally restricted excessively as a cause of causing strain aging, is positively added as an inexpensive strengthening element, it is possible to suppress a decrease in ductility due to strain aging by adding an appropriate amount of V. I got the knowledge of.

The present invention has been made based on the above findings. The first invention is C: 0.10 to 0.20 in mass%.
%, Si: 0.05 to 0.65%, Mn: 0.9 to 1.
8%, N: 0.0109 to 0.018% , Al: 0.0
5% or less, P: 0.035% or less, S: 0.020% or less, H: 0.0004% or less, and further satisfy the range of the following formula (1) according to the N content. V, with the balance consisting essentially of Fe and unavoidable impurities,
The carbon equivalent (Ceq) defined by the following formula (2) is 0.4.
A high-strength H-section steel for high-strength supporting work, which has a yield strength of 440 MPa or more and a tensile strength of 590 MPa or more and is excellent in strain aging embrittlement resistance, which is 7 or less and a flange thickness of 8 mm to 14 mm. is there. 0.014 + 3.6 * [% N] ≦ [% V] ≦ 0.044
+3.6 * [% N] ... (1) Ceq = [% C] + [% Mn] / 6 + [% Si] / 24 + [%
Cr] / 5 + [% Mo] / 4 + [% Ni] / 40 + [%
V] / 14 ... (2)

The second aspect of the present invention is, in mass%, C: 0.10 to 0.10.
0.20%, Si: 0.05 to 0.65%, Mn: 0.
9-1.8%, N: 0.0108-0.018%, A
1: 0.05% or less, P: 0.035% or less, S: 0.
020% or less, H: 0.0004% or less, and further Cu:
0.6% or less, Ni: 0.6% or less, Cr: 0.6% or less, Mo: 0.3% or less, Co: 0.6% or less, W:
0.6% or less, Nb: 0.1% or less, Ti: 0.03%
Below, B: 0.0050% or less, Ca: 0.0050%
Hereinafter, V containing one or more selected from the group of Mg: 0.01% or less and REM: 0.01% or less and satisfying the range of the following formula (1) according to the N content. And the balance substantially consists of Fe and unavoidable impurities, the carbon equivalent (Ceq) defined by the following formula (2) is 0.47 or less, and the flange thickness is 8 mm to 14 mm.
mm, the yield strength is 440 MPa.
As described above, the H-section steel for high-strength supporting work having a tensile strength of 590 MPa or more and excellent in strain aging embrittlement resistance. 0.014 + 3.6 * [% N] ≦ [% V] ≦ 0.044
+3.6 * [% N] ... (1) Ceq = [% C] + [% Mn] / 6 + [% Si] / 24 + [%
Cr] / 5 + [% Mo] / 4 + [% Ni] / 40 + [%
V] / 14 ... (2)

Below, in the present invention, the yield strength is 44.
A steel arch support having a high strength of 0 MPa or more and a tensile strength of 590 MPa or more, and excellent cold workability, ductility, and weldability for processing into an arch shape, and excellent strain aging embrittlement resistance. The reasons for limiting the chemical composition of the H-section steel for industrial use as described above will be explained together with their respective actions.

C: C is an essential element for strengthening steel. However, if the C content is less than 0.10%, sufficient strength cannot be obtained by leaving it to cool after rolling. On the other hand, if it exceeds 0.20%, the ductility and weldability deteriorate. Therefore, the C content must be limited to the range of 0.10 to 0.20%.

Si: Si is an element not only effective as a deoxidizing agent, but also an important element as a strengthening element for obtaining a high tensile strength of 590 MPa or more. However, if the content is less than 0.05%, the effect is not sufficient,
On the other hand, if it exceeds 0.65%, ductility and weldability are impaired.
Therefore, the Si content should be limited to the range of 0.05 to 0.65%.

Mn: Mn is an important element as a strengthening element for obtaining a high tensile strength of 590 MPa or more. However, if the content is less than 0.9%, the desired strength cannot be obtained, while if it exceeds 1.8%, the weldability is deteriorated. Therefore, the Mn content should be limited to the range of 0.9 to 1.8%.

N: In the present invention, N is an essential element for precipitating V to strengthen the steel material. If the amount of solute N in the steel is too large, strain aging embrittlement will occur, but if it is appropriate, it acts effectively to secure a yield shelf in a tensile test and obtain a yield strength of 440 MPa or more. Further, it reacts with V to form a precipitate in the form of VN, and contributes greatly to the strengthening of the steel material by the precipitation strengthening and the transformation structure refinement strengthening. N content is 0.
Less than 0108% (0.01% if no selective element is contained)
(Less than 09%) , sufficient reinforcement cannot be obtained. On the other hand, if the content exceeds 0.018%, not only is it difficult in steelmaking operation, but also the ductility is greatly reduced. Therefore, the N content is 0.0108% (does not contain selective elements).
In the case of 0.0109%) to 0.018%.

V: V is for obtaining a high tensile strength of 590 MPa or more by solid solution strengthening by solid solution in steel and precipitation strengthening and transformation structure refinement strengthening by forming VN. It is essential as a strengthening element. Further, since N is consumed by the formation of VN, solid solution N in steel
And has an effect of improving strain aging embrittlement resistance.
As in the present invention, N is 0.0108 (does not contain selective elements).
In the case of steel containing 0.018% to 0.018%, if the steel material is strengthened by VN and the solid solution N is reduced, the V content is 0.014+.
When it is less than 3.6 * [% N], the strain aging embrittlement becomes large, and the room temperature elongation value after aging treatment at 250 ° C for 1 hour after prestraining 3.5% is made 17% or more. I can't. Further, since V is relatively expensive as an additional alloying element, 0.04 + 3.V, which is determined considering the component neutrality in the steelmaking operation, with 0.014 + 3.6 * [% N] as the lower limit value.
Including more than 6 * [% N] is not economically disadvantageous, but also leads to deterioration of ductility and weldability. Therefore, the V content must be limited to the range of the above formula (1).

The method of limiting the V content according to the N content will be described in detail below. The amount of VN that dissolves in austenite during hot working is known as the solubility product. The solubility product is log ₁₀ [% V] [% N} = ab / T
It is given in the form of (a, b: constant, T: temperature). The present inventors proceeded with the investigation on the solubility product of VN, and clarified the amount of solute N in the as-rolled steel material by experiments and analysis centering on electrolytic extraction residue analysis. As a result, the amount of solid solution N in the as-rolled steel material of the H-section steel for steel arch support having a flange thickness of 8 mm to 14 mm containing V and N is determined by the following (4) from the V content and the N content. It turned out that it was arranged by the formula. However, in the equation (4), Nso is the amount of solid solution N. Nso = [% N]-{([% V] + 3.64 × [% N])-[([% V] + 3.64 × [% N]) ² -14.6 × ([% V] [% N]- 1.32 × 10 ^-4 )] ^1/2 } /7.29 …… (4)

This equation (4) was obtained from the result of arranging the N analysis value in the electrolytic extraction residue in the form of a solution of a quadratic equation derived from the solubility product and the V content and N content in steel. It is a thing. When the flange thickness is out of the range of 8 mm to 14 mm, the cooling rate at the time of air cooling after rolling is different, and therefore the above formula (4) may not be applicable. However, as H-shaped steel for supporting work, the flange thickness is 14m.
The adoption of shaped steel exceeding m is due to the strengthening of S
It is not possible to obtain the merit of reducing the weight of members with respect to S400. Therefore, in the present invention, the flange thickness of the H-section steel is 8 m.
It was limited to m to 14 mm.

On the other hand, extensive experiments and analyzes were carried out on the elongation value after strain aging. As a result, it was found that there is a clear correlation between the difference (ΔEl) between the elongation value of the as-rolled steel material and the elongation value after strain aging and the amount of dissolved N (Nso).
That is, when the N content is in the range of 0.002 to 0.018%, the relationship between the difference (ΔEl) between the elongation value of the as-rolled steel and the elongation value after strain aging and the amount of solid solution N (Nso) is It was confirmed that the equation (5) below was used. As the strain aging condition, prestrain was 3.5% and aging treatment at 250 ° C. for 1 hour was adopted. The value of this pre-strain is such that the web height (H) is 1
It is a strain amount corresponding to a bending radius of 2.2 m, which is a standard of the minimum bending radius in cold working of a steel arch support work having a 50 mm flange width (B) of 150 mm. The tensile properties of H-section steel with a flange thickness of 8 mm to 14 mm are J
Normally JIS1 as recommended by ISZ2201
In order to evaluate the No. A test piece, a tensile test was performed using this test piece. ΔEl = 26 + 8.5 × log ₁₀ Nso …… (5)

Therefore, with respect to the elongation value after strain aging, JISG310 for the steel material thickness (8 to 14 mm) of SS400 steel material conventionally used for steel arch support work.
In order to guarantee the same elongation as the elongation value (17%) specified in 1, the elongation after strain aging, which is the value obtained by subtracting ΔEl determined by the above equation (5) from the elongation value (El) of the as-rolled steel material Value (El _SA ) Value must be above 17%. That is, the following expression (6) must be satisfied. El _SA = El-(26 + 8.5 × log ₁₀ Nso) ≧ 17 …… (6)

The elongation value (El) of the as-rolled steel material varies depending on the alloy composition, but the yield strength is 440 to 540 MPa,
The elongation of the steel material having a plate thickness of 8 mm to 14 mm satisfying the tensile strength of 590 to 670 MPa was distributed at a value of 22% or more.
Therefore, the elongation value (El) of the as-rolled steel is set to 22%, and by considering the above equations (4) and (6), the minimum required V for obtaining the elongation value after strain aging of 17% is obtained. The content is required. Specifically, if the elongation value (El) of the as-rolled steel is set to 22%, it is substituted into the equation (6), and the obtained solid solution N amount (Nso) is substituted into (4) to analyze it. The relationship with the V content can be defined as the following equation (7), that is, the inequality on the left side of the equation (1). 0.014 + 3.6 × [% N] ≦ [% V] …… (7)

The V content determined by the equation (7) is the minimum necessary amount, and is ± 0.0 in consideration of the component ratio in the steelmaking operation.
If the component range width is 15%, the upper limit is the inequality on the right side of Expression (1). As described above, the addition of more V is disadvantageous both economically and in terms of material. FIG. 1 shows the component ranges of N content and V content in the present invention.

Al: Al is an important element as a deoxidizing agent, but if its content exceeds 0.05%, a large amount of AlN is formed and the strengthening ability due to the precipitation of VN is reduced. Therefore, the Al content must be limited to 0.05% or less.

P: P is contained as an impurity, and if its content exceeds 0.035%, the toughness is significantly impaired. Therefore, the P content must be limited to 0.035% or less.

S: S is contained as an impurity, and if its content exceeds 0.020%, ductility and toughness are significantly impaired. Therefore, the S content must be limited to 0.020% or less.

H: H is an element that causes delayed fracture, and is an element that should be strictly controlled and regulated particularly in high strength steel. Therefore, from the viewpoint of suppressing delayed fracture, the H content must be limited to 0.0004% or less.

Carbon equivalent (Ceq): When the carbon equivalent (Ceq) defined by the above formula (2) exceeds 0.47, weld cracking occurs and it is not suitable as an H-section steel for supporting work. Therefore, the carbon equivalent (Ceq) must be limited to 0.47 or less.

In the present invention, in addition to the above alloying elements, Cu, Ni, Cr, Mo, Co,
One or more selected from the group consisting of W, Nb, Ti, B, Ca, Mg and REM can be contained. The reasons for limiting the components will be described below.

Cu: Cu is not only an important element as a strengthening element for obtaining a high tensile strength of 590 MPa or more, but also has an effect of improving weather resistance. However,
If the content exceeds 0.6%, the occurrence of surface flaws during rolling becomes remarkable, which impairs productivity such as rolling and finishing. Therefore, the Cu content must be limited to 0.6% or less.

Ni: Ni exists mainly as a solid solution in steel,
It contributes to the strengthening of steel by improving hardenability together with solid solution strengthening. Further, it has an effect of suppressing the generation of surface defects caused by the addition of Cu, and when Cu is added, the content of Cu is 1/2
It is preferable to contain the above. On the other hand, it is expensive as an additive element, and addition of more than necessary is not economically preferable and also causes deterioration of weldability. Therefore, the Ni content must be limited to 0.6% or less.

Cr: Cr is also present mainly as a solid solution in steel,
It contributes to the strengthening of steel by improving hardenability together with solid solution strengthening. Further, it has an effect of improving weather resistance together with Cu. However, it is expensive as an additional element, and addition of more than necessary is not economically preferable, and also causes deterioration of weldability.
Therefore, the Cr content must be limited to 0.6% or less.

Mo: Mo contributes to solid solution strengthening and strength increase due to improvement of hardenability. Further, since it has the effect of increasing the strength at high temperatures, it is an effective element when fire resistance performance (high temperature strength) is required. However, if the content exceeds 0.3%, not only the weldability is impaired, but also the bainite structure fraction is significantly increased, and the yield shelf is eliminated in the tensile test, resulting in a decrease in yield strength. . Therefore, the Mo content must be limited to 0.3% or less.

Co: Co is also mainly present as a solid solution in steel,
It contributes to the strengthening of steel by improving hardenability together with solid solution strengthening. However, it is expensive as an additional element, and addition of more than necessary is not economically preferable, and also causes deterioration of weldability. Therefore, the Co content must be limited to 0.6% or less.

W: W is an element that improves the strength of steel. However, it is expensive as an additional element, and addition of more than necessary is not economically preferable, and also causes deterioration of weldability. Therefore, the W content must be limited to 0.6% or less.

Nb: an element effective as a strengthening element for steel. However, if the Nb content exceeds 0.1%, the ductility is markedly reduced, so the Nb content must be limited to 0.1% or less.

Ti: An element that acts as a strengthening element for steel. However, if the Ti content exceeds 0.03%, Ti
As a result of consuming a large amount of N and consuming N, not only the strengthening ability due to the precipitation of VN is significantly reduced, but also the bainite structure fraction is increased and the yield shelf disappears in the tensile test, resulting in a yield strength of 440 MPa or more. You won't get it.
Therefore, the Ti content must be limited to 0.03% or less.

B: B tends to segregate and exist in the austenite grain boundaries during hot rolling, which improves hardenability and contributes to strengthening of steel. However, its content is 0.0050%
If it exceeds the range, the weldability is significantly deteriorated. Therefore, the B content must be limited to 0.0050% or less.

Ca: Ca reacts with S to form a compound, which fixes S existing in the steel as an impurity and reduces the adverse effect of S on mechanical properties. However,
If its content exceeds 0.0050%, a coarse compound is formed and ductility and toughness are deteriorated. Therefore, the Ca content must be limited to 0.0050% or less.

Mg, REM: Mg and REM combine with O and S to form a compound and improve ductility. However, if its content exceeds 0.01%, a coarse compound is formed,
Reduces ductility and toughness. Therefore, the Mg content and R
The EM content should be limited to 0.01% or less.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION A converter, an electric furnace, or a combination of these refining furnaces and a secondary refining furnace such as an RH vacuum degassing apparatus is used for ordinary ingot casting or continuous casting of molten steel melted to the above chemical composition. Solidification is performed by a casting method to obtain a steel piece or a cast piece having a predetermined shape. After that, H-shaped steel is processed by hot rolling.

In the hot rolling, the heating temperature of the steel slab or the cast slab may be a high temperature at which sufficient dimensional accuracy can be obtained by shaping by rolling, for example, 1150 which is usually performed.
It may be set at ℃ or higher. Then, the H-shaped steel having a flange thickness of 8 mm to 14 mm is rolled by hot rolling. No particular consideration is required for the rolling end temperature, and the rolling may be completed at a temperature of about 800 ° C. which is usually performed. Even after the rolling is finished, there is no need for special accelerated cooling, and the desired characteristics can be obtained by cooling.

By manufacturing the H-section steel for supporting work by controlling the carbon equivalent (Ceq) while adding an appropriate alloying element as described above, N has been excessively controlled as a source of the conventional strain aging embrittlement. While being positively added as a strengthening element, it is possible to reduce the amount of solute N at the same time sufficiently. As-rolled, the yield strength is 440 MPa or more and the tensile strength is 590M.
It becomes possible to inexpensively and stably manufacture an H-section steel for steel arch support having high strength of Pa or more and good weldability, and having excellent strain aging embrittlement resistance.

[0044]

[Example] [Example 1] Steel of 21 kinds of chemical composition was melted by a combination of a converter and an RH vacuum degassing device, and then a continuous caster was used to form a bloom slab, which was then cast. The piece was heated to 1250 ° C. and hot rolled into an H-section steel. The hot rolling was completed at about 850 to 900 ° C., and after the rolling was air cooled. 21 types in Table 1 (Steel No. A1 to A21)
The chemical composition and carbon equivalent (Ceq) of each of the sample steels are shown. The underlined values in Table 1 indicate that the values are outside the range of the steel of the present invention.

[0045]

[Table 1]

JIS Z2201 is rolled along the longitudinal direction from the position 1/4 in the flange width direction of the H-section steel obtained by rolling.
The JIS No. 1A test piece specified in No. 1 was sampled and subjected to a tensile test as a steel material as it was rolled, subjected to 3.5% bending and then subjected to an aging treatment at 250 ° C. for 1 hour, and then subjected to a tensile test. The tensile properties after strain aging were evaluated. The pass / fail judgment criteria were that the yield strength was 440 MPa or more, the tensile strength was 590 MPa or more, and the elongation was 17% or more.
Further, the H-shaped steel end portion and the tie plate were joined by T-joint welding, and the presence or absence of weld cracks was examined. The results of the evaluation test are shown in Table 2. In Table 2, the dimensions of the H-section steel are web height (H), flange width (B),
The web thickness (t1) and the flange thickness (t2) are also shown. The underlined values in Table 2 indicate failure.

[0047]

[Table 2]

As is clear from Table 2, the steel Nos. A1 to A5 and A14 to A21, which are the steels of the present invention, have a yield strength, a tensile strength and an elongation which are the tensile properties of the as-rolled steel and the tensile properties after strain aging. All passed, and welding cracks did not occur. On the other hand, comparative steels No. A6 to A1
In No. 3, any of the above characteristics was not satisfied.

That is, in steel Nos. A6 to A8 in which the relationship between the N content and the V content did not satisfy the present invention, the elongation after strain aging did not reach 17%. Further, in steel Nos. A9 to A12 in which the C content or the Mn content did not satisfy the present invention, the as-rolled characteristics did not satisfy the acceptable range, or the carbon equivalent exceeded 0.47 and weld cracking occurred. Steel No. A13 having a lower N content than the present invention lacked in tensile strength.

[Example 2] Steels of five kinds of chemical composition were melted by a combination of a converter and an RH vacuum degassing device, and then made into bloom cast pieces by a continuous casting machine. Was heated to 1250 ° C. and hot rolled into H-section steel. The dimensions of the rolled H-section steel are web height (H) x flange width (B) x web thickness (t1) x flange thickness (t
In the order of 2), 154 mm x 151 mm x 8 mm x 12 m
m and 150 mm × 150 mm × 7 mm × 10 mm 2
It is a kind. The hot rolling was completed at about 850 to 900 ° C., and after the rolling was air cooled. Table 3 shows 5 types (steel No. B1 to B
The chemical composition and carbon equivalent (Ceq) of each sample steel of 5) are shown. The underlined values in Table 3 indicate that the value is outside the range of the steel of the present invention.

[0051]

[Table 3]

JIS Z2201 is rolled along the longitudinal direction from the position 1/4 in the flange width direction of the H-section steel obtained by rolling.
The JIS No. 1A test piece specified in 1. was sampled and subjected to a tensile test as a rolled steel material. Also, the bending radius is 2.
A steel arch supporting work was performed by bending for 2 m, and a test piece was sampled from a part of the steel arch support and subjected to an aging treatment at 250 ° C. for 1 hour, and then a tensile property investigation was performed using JIS No. 1A test piece. The pass / fail judgment criteria were that the yield strength was 440 MPa or more, the tensile strength was 590 MPa or more, and the elongation was 17% or more. Table 4 shows the results of the evaluation test. In Table 4, the web height (H), the flange width (B), the web thickness (t1), and the flange thickness (t2) of the H-section steel are also shown. The underlined values in Table 4 indicate that the test was rejected.

[0053]

[Table 4]

As is clear from Table 4, the steels No. B1 to B3, which are the steels of the present invention, have a yield strength, a tensile strength and an elongation which are the same as the tensile properties of the as-rolled steel and the tensile properties after strain aging at any size. All passed. On the other hand, steel No. B whose relationship between the N content and the V content does not satisfy the present invention.
In Nos. 4 and B5, the as-rolled steel material exceeded the acceptance criteria, but the elongation after bending-aging was large, and the elongation after strain aging was less than 17%.

[0055]

EFFECTS OF THE INVENTION According to the present invention, the amount of solute N in steel is sufficiently reduced, while N, which has been conventionally regulated excessively as a source of strain aging embrittlement, is positively added as an inexpensive strengthening element. Therefore, the H-shaped steel for steel arch support, which has a high yield strength of 440 MPa or more and a tensile strength of 590 MPa or more and good weldability and has excellent strain aging embrittlement resistance in an as-rolled state, is inexpensive. It can be manufactured in a stable manner, and has an industrially beneficial effect.

[Brief description of drawings]

FIG. 1 is a diagram showing component ranges of N content and V content in the present invention.

Continuation of the front page (56) References JP-A-11-131188 (JP, A) JP-A-10-152751 (JP, A) JP-A-10-195603 (JP, A) JP-A-10-176240 (JP , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00

Claims (2)

(57) [Claims] 1. In mass% , C: 0.10 to 0.20%,
Si: 0.05 to 0.65%, Mn: 0.9 to 1.8
%, N: 0.0109 to 0.018% , Al: 0.05
% Or less, P: 0.035% or less, S: 0.020% or less, H: 0.0004% or less, and V satisfying the range of the following formula (1) according to the N content. And the balance consists essentially of Fe and unavoidable impurities,
The carbon equivalent (Ceq) defined by the following formula (2) is 0.4.
A high-strength H-section steel for supporting work, which has a yield strength of 440 MPa or more and a tensile strength of 590 MPa or more and is excellent in strain aging embrittlement resistance, which is 7 or less and a flange thickness of 8 mm to 14 mm. 0.014 + 3.6 * [% N] ≦ [% V] ≦ 0.044
+3.6 * [% N] ... (1) Ceq = [% C] + [% Mn] / 6 + [% Si] / 24 + [%
Cr] / 5 + [% Mo] / 4 + [% Ni] / 40 + [%
V] / 14 ... (2) 2. C: 0.10 to 0.20% by mass% and S
i: 0.05 to 0.65%, Mn: 0.9 to 1.8%,
N: 0.0108 to 0.018%, Al: 0.05% or less
Below, P: 0.035% or less, S: 0.020% or less,
H: 0.0004% or less, further Cu: 0.6% or less,
Ni: 0.6% or less, Cr: 0.6% or less, Mo: 0.
3% or less, Co: 0.6% or less, W: 0.6% or less, N
b: 0.1% or less, Ti: 0.03% or less, B: 0.0
050% or less, Ca: 0.0050% or less, Mg: 0.
01% or less, REM: 0.01% or less, one or more kinds selected from the group are contained, V containing the range of the following formula (1) is contained according to the N content, and the balance is Substantially Fe and unavoidable impurities, the carbon equivalent (Ceq) defined by the following formula (2) is 0.47 or less,
Further, the flange thickness is 8 mm to 14 mm, the yield strength is 440 MPa or more and the tensile strength is 59.
H-shaped steel for high-strength support with excellent strain aging embrittlement resistance of 0 MPa or more. 0.014 + 3.6 * [% N] ≦ [% V] ≦ 0.044
+3.6 * [% N] ... (1) Ceq = [% C] + [% Mn] / 6 + [% Si] / 24 + [%
Cr] / 5 + [% Mo] / 4 + [% Ni] / 40 + [%
V] / 14 ... (2)