JPH0565593A - High tensile strength steel for welded structure excellent in galvanizing cracking resistance in heat affected zone - Google Patents

Abstract

PURPOSE:To improve the tensile strength and plating cracking resistance of a steel by specifying C, Si, Mn, Zr, Al, B, Nb and V, and satisfying a prescribed componental relational inequality. CONSTITUTION:This high tensile strength steel is formed of a compsn. constituted of, by weight, 0.06 to 0.15% C, 0.1 to 0.5% Si, 0.8 to 2% Mn, 0.012 to 0.04% Zr, 0.005 to 0.1% SolAl, <=0.0O015% B, 0.01 to 0.1% Nb, 0.001 to 0.1% V and the balance Fe. Then, the componental content is limited so that the componental relational inequalities of 244-265C-120Si,-82Mn+415Zr=49Al-145Nb and 329V >=40 are satisfied. This high tensile strength steel has >=580MPa tensile strength and excellent in galvanizing cracking resistance in the weld heat affected zone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention aims to improve plating cracks that are likely to occur in a weld heat affected zone (abbreviated as HAZ) in a steel material which is processed and assembled as a welded structure and then plated in a molten zinc bath. High strength steel.

[0002]

2. Description of the Related Art Hot-dip galvanizing is useful and has been widely used in the past, from the viewpoint of rust prevention of steel structures or, more particularly, aesthetics, especially paintability. Recently, under the strong demand of increasing the size or weight of steel structures, there is a growing tendency to increase the strength of the steel materials for welded structures to be subjected to the plating treatment. That is especially 580MPa
Steel materials with a level of over 100% are not welded to the H, when they are subjected to galvanizing treatment by immersion in a molten zinc bath after welding and assembly.
So-called plating cracks in AZ or intergranular cracks called liquid metal embrittlement tend to occur frequently. This is because the residual stress due to welding work becomes larger as the welded structure becomes larger and more complicated, and the higher the tensile strength of the material, the more significant it becomes. is there. To reduce hot dip galvanizing cracks (hereinafter abbreviated as "plating cracks"), we will reduce the residual stress during welding and the thermal stress during dipping in the hot dip galvanizing bath. Although consideration is added and stress-relief refining treatment is also performed, it is not a fundamental solution such as impairing economic efficiency or base material properties, and improvement of steel itself is needed.

Several proposals have hitherto been made on steel materials with reduced plating cracks. For example, JP-A-58-84959, JP-A-59-126754, JP-A-62-50448 and JP-A-59.
In Japanese Laid-Open Patent Publication No. 113131/1993, the countermeasure is taken by satisfying a specific quantitative relationship in the amount of additive alloy elements in the steel material. However, these measures are not always sufficient to completely avoid HAZ plating cracks, and further improvement is desired. The inventors of the present invention have previously disclosed Japanese Patent Publication No.
In the publication, a technique has been proposed in which the plating crack resistance is remarkably improved by adding Zr while maintaining a constant relationship between the amounts of alloying elements. However, due to the larger size and complexity of the welded structure, the residual stress during welding becomes larger, the thermal stress generated during immersion in the galvanizing bath also becomes larger, and the heat input during welding also increases. It was found that the HAZ has a wide range from a small heat input to a large heat input, and that the HAZ does not always have sufficient resistance to plating cracks during small heat input welding.

[0004]

In view of the above situation, the present invention has a base material having a tensile strength of 580 MPa or more and a HAZ having excellent plating crack resistance, welding of a wide range of heat input, The purpose of the present invention is to provide a steel material having improved resistance to plating cracking at the portion to which small heat input welding is performed.

[0005]

[Means for Solving the Problems] Various experiments were conducted for the purpose of improving the resistance to plating cracks of the small heat input welded HAZ.
As a result of diligent examination of the effect of the composition of components on the plating crack resistance, it was found that Zr-added composition steel in which the amount of alloying elements was kept in a specific relationship was limited to the B content, and the B content was also limited to Ti +. It has been found that the combined addition of Zr significantly improves the plating crack resistance of the small heat input HAZ, and the present invention has been completed based on the findings. That is, the present invention is
C: 0.06-0.15wt%, Si: 0.10-0.50wt%, Mn: 0.80-2.
00wt%, Zr: 0.012-0.040wt%, Al: 0.005-0.100wt%,
B: 0.00015wt% or less, Nb: 0.010-0.100wt% and V: 0.010
Content of 0.100 wt% and satisfy the following formula (1), 244-265C-120Si-82Mn + 415Zr-49Al-145Nb-329V ≧ 40 ・ ・
・ (1), The balance is substantially Fe and inevitable impurities, and the tensile strength is 580MPa or more. And C: 0.06 ~ 0.15wt%, Si: 0.10 ~ 0.50wt%
, Mn: 0.80 to 2.00 wt%, Zr: 0.012 to 0.040 wt%, solAl:
0.005-0.100wt%, B: 0.00015wt% or less, Nb: 0.010-0.10.
0wt%, V: 0.010 to 0.100wt%, and Ti: 0.005 to 0.030w
24% or more and 0.05 to 1.00% by weight of Ni, Cu, Cr, or Mo, which satisfy at least the following formula (2), 244-265C-120Si-82Mn + 415Zr-49Al -145Nb-329V + 167Ti-17
Ni-85Cu-81Cr-73Mo ≧ 40 ・ ・ ・ (2), The balance is substantially Fe and inevitable impurities, and the tensile strength is 580MPa or more. A high-strength steel for welded structures with excellent plating cracking resistance.

[0006]

In the present invention, the reason for limiting the component composition is as follows.
It is as follows. C: 0.06 to 0.15 wt% (hereinafter abbreviated as%) C
Is a component that helps increase the strength of steel in the simplest way, and if it is less than 0.06%, its effect is not expected, while 0.15%
If it exceeds the range, the weldability will decrease and it will not be suitable for the purpose.
The range is 0.06 to 0.15%. Si: 0.10 to 0.50% Si is 0.10 for the purpose of utilizing deoxidizing action and contributing to strength.
% Is required, but if it exceeds 0.5%, the plating crack resistance is adversely affected and the low temperature toughness is deteriorated, so the content is made 0.10 to 0.50%. Mn: 0.80 ~ 2.00% Mn also needs a minimum of 0.80% to secure strength, while 2.
If it exceeds 00%, the plating crack resistance is adversely affected and
0.80 to 2.00% because it impairs basic performance such as weldability and workability
To the range of. Zr: 0.012 to 0.040% Zr is an important component which, according to the present invention, serves to ensure plating crack resistance under tensile strength of 580 MPa or more without the disadvantages mentioned in the description of the prior art. And 0.012%
When the content is above, under the refinement of the HAZ structure, it is remarkably effective in improving the plating crack resistance. However, the range is limited to 0.012 to 0.040%.

Sol Al: 0.005 to 0.100% Al requires 0.005% or more for deoxidizing action and improvement of hardenability, but if it exceeds 0.100%, plating crack resistance and weldability deteriorate, so 0.005%. ~ 0.100% Nb and V: 0.01 to 0.10% Strengthening with Nb and V requires 0.01% or more, while if it exceeds 0.10%, plating crack resistance and weldability decrease, so 0.01 to 0.10% respectively. %. B: 0.00015% or less B has the effect of increasing the strength by adding a small amount, but reduces the plating crack resistance of HAZ for small heat input welding by adding a small amount. In particular, if the content exceeds 0.00015%, the plating crack resistance is significantly reduced, so the upper limit is made 0.00015%. Ti: 0.005-0.030% Ti is generally added for the purpose of improving the toughness of steel materials, but is an element that impairs plating crack resistance. However, B is reduced and the plating crack resistance is improved only when Zr + Ti composite is added. However, if it is less than 0.005%, there is no effect, and if it exceeds 0.030%, the combined effect with Zr disappears and the plating crack resistance decreases, so the content is made 0.005 to 0.030%.

Further, Ni, Cu, Cr and Mo are useful as toughening components for steel materials, and at least one of them is 0.05.
% Or more is required, but if it exceeds 1.00%, weldability, hot workability, economic efficiency and plating crack resistance will deteriorate.
Each is 0.05 to 1.00%. Next, as impurities in steel
For S and P, 0.020% and 0.030% or less are acceptable, respectively, but especially when N exceeds 0.012%, the toughness is significantly deteriorated, so 0.012% or less is desirable. In the above composition range, (1) or (2) the molten steel subjected to the component adjustment according to the formula, after obtaining by ordinary steel making means, for the slab, bloom or billet by the ingot making method or continuous casting method,
The high-strength steel of the present invention can be manufactured by subjecting the necessary rolling process to a conventional method.

Evaluation of plating crack resistance of the welded structural steel according to the present invention will be described based on experimental results. The test pieces were obtained by cutting round bars of 10 mmφ from steel plates of various chemical compositions shown in Table 1, applying a heat cycle equivalent to a welding heat input of 6 KJ / cm by high frequency heating, and then applying circumferential notch processing. is there. Galvanization was applied only to the notch of each test piece, various static load stresses were applied at 470 ° C. where the zinc was in a molten state, and the time at which the stress fractured was measured.
Load stress at this time and 470 ° C of the test piece without plating
The relationship between the ratio of tensile strength (in%) Rσ and the breaking time at that time is shown in FIG. Here, Rσ is a parameter that indicates the percentage of stress to the tensile strength of the unplated test piece at 470 ° C that led to fracture.
The higher Rσ is at least 40%, the more difficult it is to crack even when the residual stress or thermal stress is large. Considering the plating bath immersion time in actual operation, the value of Rσ at 400 seconds was calculated and multiple regression was performed with the chemical components to obtain the coefficients of each term on the left side of Eqs. (1) and (2). As can be seen in Fig. 1, B is 0.0002.
In steel materials containing more than%, the value of Rσ decreases significantly, so that multiple regression of chemical composition is B ≦ 0.00015% of the range of the present invention.
The composition steel was used as a target.

On the other hand, in order to cope with the cracking condition in the plating process after the actual welding, the restraint joint shown in FIG. 2 was manufactured, immersed in a hot dip galvanizing bath, and the cracking in HAZ was examined. In the figure, 1a and 1b are test beads, 2a and 2b are restraining beads, and 3 is a test plate. The test plate 3 was assembled in such a manner that plates whose one side was ground were assembled in a cross shape, and the fillet bead 1a between the grinding surfaces and the fillet bead 1b between the black skins were formed. The test plate has a thickness of 15 mm and a test bead length L.
＝ 50mm, and each overhang length of the cross l ₁ = l ₂ = l ₃ = l ₄ = 50mm,
And the total length W of the test plate 3 is 150 mm. Restrained bead 2
The number of beads in each of a and 2b is 20. This restraint joint was immersed in a hot dip galvanizing bath to test beads 1a, 1
The presence or absence of cracks in b was confirmed, and the results are shown in Table 1. From this, it is understood that cracks do not occur in the restraint joint if the composition is within the scope of the claims and the calculated value Rσ on the left side of the equations (1) and (2) satisfies Rσ ≧ 40.

[0011]

EXAMPLES The present invention will be described below based on examples. Each of the materials whose chemical composition is shown in Table 2 was 10 by vacuum melting method.
It was melted in a 0 kgf steel ingot, and allowed to cool after rolling or accelerated cooling after rolling to obtain a test steel. For each steel material, the tensile strength by a round bar tensile piece was obtained, and the crack investigation in the above-mentioned restraint joint test was conducted. For the crack investigation of the restraint joint test piece, after degreasing, pickling and fluxing the test body shown in FIG. 2,
After removing the plating obtained by immersing in molten zinc at 455 ° C. for 6 minutes, the HAZ was inspected. Further, Table 2 also shows the value of Rσ calculated by the regression equation according to the present invention.

As is clear from Table 2, all of the examples of the composition of the present invention in which the Rσ value according to the regression equation exceeds 40 have a tensile strength of 580 MPa or more, and the H of the restraint joint is high.
No cracks are found in AZ. On the other hand, in the comparative examples in which the components underlined in Table 2 and the calculated Rσ values deviate from the requirements of the present invention, there are differences in the degree of cracking, but H
Occurrence of AZ cracking was recognized. Especially steel No. 1, 7 and 11
In the comparative example, the calculated Rσ value is 40 or more, but since a small amount of B is contained, HAZ cracking occurs, and it can be seen that B significantly impairs the plating cracking resistance of HAZ for small heat input welding.

[0013]

EFFECTS OF THE INVENTION According to the present invention, it is possible to manufacture a steel material in which the plating crack resistance of the small heat input welding HAZ is remarkably improved.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between an Rσ value and a breaking time.

FIG. 2 is a front view (a) and a side view (b) of a test body for a restrained joint test.

[Explanation of symbols]

 1a Test bead (fillet bead) 1b Test bead (fillet bead) 2a Restraint bead 2b Restraint bead 3 Test plate

[Table 1]

[Table 2]

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] September 24, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Detailed explanation of the invention

[Correction method] Change

[Correction content]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention aims to improve plating cracks that are likely to occur in a weld heat affected zone (abbreviated as HAZ) in a steel material which is processed and assembled as a welded structure and then plated in a molten zinc bath. High strength steel.

[0002]

2. Description of the Related Art Hot-dip galvanizing is useful and has been widely used in the past, from the viewpoint of rust prevention of steel structures or, more particularly, aesthetics, especially paintability. Recently, under the strong demand of increasing the size or weight of steel structures, there is a growing tendency to increase the strength of the steel materials for welded structures to be subjected to the plating treatment. That is especially 580
A steel material having a level of more than MPa undergoes welding and assembly, and is subjected to a galvanizing treatment by immersion in a molten zinc bath, so-called plating cracking in HAZ, or intergranular cracking called liquid metal embrittlement. Tend to occur frequently. This is because the residual stress due to welding work becomes larger as the welded structure becomes larger and more complicated, and the higher the tensile strength of the material, the more significant it becomes. is there. Hot dip galvanizing crack (hereinafter abbreviated as "plating crack")
In order to reduce the residual stress during welding and the thermal stress during dipping in the hot dip galvanizing bath, consideration is given to welding work conditions and dipping conditions. However, it cannot be said to be a fundamental solution such as impairing the economical efficiency or the characteristics of the base material, and the improvement of the steel material itself is required.

Several proposals have hitherto been made on steel materials with reduced plating cracks. For example, JP-A-58-84959, JP-A-59-126754, JP-A-62-50448 and JP-A-59.
In Japanese Laid-Open Patent Publication No. 113131/1993, the countermeasure is taken by satisfying a specific quantitative relationship in the amount of additive alloy elements in the steel material. However, these measures are not always sufficient to completely avoid HAZ plating cracks, and further improvement is desired. The inventors of the present invention have previously disclosed Japanese Patent Publication No.
In the publication, a technique has been proposed in which the plating crack resistance is remarkably improved by the addition of Zr while maintaining a constant relationship between the amounts of alloying elements. However, due to the larger size and complexity of the welded structure, the residual stress during welding becomes larger, the thermal stress generated during immersion in the galvanizing bath also becomes larger, and the heat input during welding also increases. It was found that the HAZ has a wide range from a small heat input to a large heat input, and that the HAZ does not always have sufficient resistance to plating cracks during small heat input welding.

[0004]

SUMMARY OF THE INVENTION In view of the above situation, the present invention has a base material having a tensile strength of 580 MPa or more, and H
The purpose of the present invention is to provide a steel material having excellent resistance to AZ plating cracking, and a steel material having improved resistance to plating cracking in a region where welding with a wide range of heat input, particularly small heat input welding is performed.

[0005]

[Means for Solving the Problems] Various experiments were conducted for the purpose of improving the resistance to plating cracks of the small heat input welded HAZ.
As a result of diligent examination of the effect of the composition of components on the plating crack resistance, in the Zr-added composition steel in which the amount of alloying elements was kept in a specific relationship, the B content was limited, and the B amount was further limited, and then Ti + Zr It has been found that the combined addition significantly improves the plating crack resistance of the small heat input HAZ, and the present invention has been completed based on the findings. That is, the present invention is
C: 0. O6 to 0.15 wt%, Si: 0.10
0.50 wt%, Mn: 0.80 to 2.00 wt%, Z
r: 0.012 to 0.040 wt%, Al: 0.005
~ 0.100 wt%, B: 0.00015 wt% or less,
Nb: 0.010 to 0.100 wt% and V: 0.0
10-0.100 wt%, and satisfies the following formula (1): 244-265C-120Si-82Mn + 415Zr
-49Al-145Nb-329V ≧ 40 ...
(1) The balance is substantially Fe and unavoidable impurities, and the tensile strength is 580 MPa or more. Yes, C: 0.06-0.15 wt
%, Si: 0.10 to 0.50 wt%, Mn: 0.80
~ 2.00 wt%, Zr: 0.012-0.040 wt
%, SolAl: 0.005 to 0.100 wt%, B:
0.00015 wt% or less, Nb: 0.010 to 0.1
00 wt%, V: 0.010 to 0.100 Wt%, and further Ti: 0.005 to 0.030 wt% and / or 0.05 to 1.00 wt% Ni, Cu, Cr, M.
containing one or more of o and satisfying the following formula (2): 244-265C-12oSi-82Mn + 415Zr
-49Al-145Nb-329V + 167Ti-17
Ni-85Cu-81Cr-73Mo ≧ 40 ...
(2) The balance is substantially Fe and unavoidable impurities, and the tensile strength is 580 MPa or more. is there.

[0006]

In the present invention, the reason for limiting the component composition is as follows.
It is as follows. C: 0.06 to 0.15 wt% (hereinafter abbreviated as%) C is a component that helps increase the strength of steel in the most simple manner, and if it is less than 0.06%, its effect is not expected. If it exceeds 15%, the weldability deteriorates and it is not suitable for the purpose, so the content is made 0.06 to 0.15%. Si: 0.10 to 0.50% Si requires 0.10% or more in order to utilize the deoxidizing action and contribute to strength, but if it exceeds 0.5%,
The plating crack resistance is adversely affected and the low temperature toughness is deteriorated, so the content is made 0.10 to 0.50%. Mn: 0.80 to 2.00% Mn also needs a minimum of 0.80% to secure strength,
On the other hand, if it exceeds 2.00%, the plating crack resistance is adversely affected and the basic performance such as weldability and workability is impaired, so the content is limited to the range of 0.80 to 2.00%. Zr: 0.012 to 0.040% According to the present invention, Zr ensures plating crack resistance under a tensile strength of 580 MPa or more without the disadvantages mentioned in the description of the prior art. It is an important component that helps to improve the plating crack resistance under the refinement of the HAZ structure when the content is 0.012% or more. However, if it exceeds 0.040%, the cleanliness of steel is improved. As it causes obstacles and deteriorates mechanical properties, especially toughness,
It is limited to the range of 0.012 to 0.040%.

SolAl: 0.005 to 0.100% Al is 0.005% in order to improve deoxidizing action and hardenability.
The above is required, but if it exceeds 0.100%, the plating crack resistance and weldability deteriorate, so 0.005-0.100.
%. Nb and V: 0.01 to 0.10% Strengthening with Nb and V requires 0.01% or more, while when it exceeds 0.10%, plating crack resistance and weldability deteriorate. Therefore, 0.01 to 0.
10%. B: 0.00015% or less B has the effect of increasing the strength by adding a trace amount, but reduces the plating crack resistance of HAZ for small heat input welding by adding a trace amount. In particular, if the content exceeds 0.00015%, the plating crack resistance is significantly reduced, so the upper limit is set to 0.00015.
%. Ti: 0.005 to 0.030% Ti is generally added for the purpose of improving the toughness of steel materials, but is an element that impairs plating crack resistance. However, B is reduced and the plating crack resistance is improved only when Zr + Ti composite is added. However, if it is less than 0.005%, there is no effect, and if it exceeds 0.030%, the combined effect with Zr disappears and the plating crack resistance decreases, so 0.005% to 0.005%.
It is set to 0.030%.

Further, Ni, Cu, Cr and Mo are useful as toughening components for steel materials, and at least one of them requires 0.05% or more, but if 1.00% is exceeded, welding is performed. Property, hot workability, economic efficiency and plating crack resistance are deteriorated, so the content is made 0.05 to 100%.
Next, regarding S and P as impurities in the steel, respectively.
020% and 0.030% are acceptable, but especially N
Is more than 0.012%, the toughness is significantly deteriorated.
0.012% or less is desirable as it is low. After obtaining molten steel in which the components are adjusted according to the formula (1) or (2) in the above-mentioned compositional range, by a usual steelmaking means, a slab, bloom or billet produced by the ingot making method or the continuous casting method,
The high-strength steel of the present invention can be manufactured by subjecting the necessary rolling process to a conventional method.

Evaluation of plating crack resistance of the welded structural steel according to the present invention will be described based on experimental results. The test pieces are 10 mm from steel plates with various chemical components shown in Table 1.
A φ round bar was cut out, subjected to a high frequency heating to provide a heat cycle equivalent to a welding heat input of 6 KJ / cm, and then subjected to circumferential notch processing.

[ 0010 ]

[ Table 1 ]

[0011] subjected to notch only galvanized of each specimen, subjected to various static load stress at 470 ° C. of the zinc is melted, the time was measured to break at the stress. Load stress at this time and 470 ° C of the test piece without plating
The relationship between the ratio of tensile strength (expressed in%) Rσ and the breaking time at that time is shown in FIG. Here, R σ is a parameter indicating how much stress with respect to the tensile strength of the unplated test piece at 470 ° C. is reached, and fracture occurs. The higher R σ is at least 40%, the higher It indicates that cracking is difficult even when residual stress or thermal stress is large. In consideration of the immersion time in the plating bath in actual operation, the value of Rσ at 400 seconds was obtained and multiple regression was performed with the chemical components to obtain the coefficient of each term on the left side of the equations (1) and (2). As you can see in Figure 1,
In the steel containing B in an amount of 0.0002% or more, the value of Rσ was remarkably decreased. Therefore, the multiple regression of the chemical composition was performed for the composition steel having B ≦ 0.00015% of the range of the present invention.

Meanwhile, for taking a correspondence between cracking conditions in the plating process after the actual welding, to prepare a restraint joint shown in FIG. 2, after dipping in molten zinc plating bath to examine the plating cracks in HAZ. In the figure, 1a and 1b are test beads, 2a and 2b are restraining beads, and 3 is a test plate. The test plate 3 was assembled in such a manner that plates whose one side was ground were assembled in a cross shape, and the fillet bead 1a between the grinding surfaces and the fillet bead 1b between the black skins were formed. The size of the test plate is such that the plate thickness is 15 mm, the length L of the test bead is L = 50 mm, and the overhang length of each cross is l ₁ = l ₂ =
l ₃ = l ₄ = 50 mm, and the total length of the test plate 3 W = 15
It is 0 mm. The number of beads of each of the restraining beads 2a and 2b is 20. This restraint joint was dipped in a hot dip galvanizing bath to check the presence or absence of cracks in the test beads 1a and 1b. The results are shown in Table 1. The constituent organization within the scope of the claims, and (1),
For the calculated value Rσ on the left side of the equation (2), it can be seen that if Rσ ≧ 40 is satisfied, the restraint joint is not cracked.

[ 0013 ]

EXAMPLES The present invention will be described below based on examples. Each of the feed materials whose chemical composition is shown in Table 2 was 1 by vacuum melting method.
It was melted in a 00 kgf steel ingot, and allowed to cool after rolling or accelerated cooling after rolling to obtain a test steel. For each steel material, the tensile strength by a round bar tensile piece was obtained, and the crack investigation in the above-mentioned restraint joint test was conducted. The cracking of the restraint joint test piece was carried out by degreasing, pickling and fluxing the test piece shown in FIG. 2 and immersing it in molten zinc at 455 ° C. for 6 minutes to remove the obtained plating. The HAZ was inspected. Further, in Table 2, the value of Rσ calculated by the regression equation according to the present invention is also shown.

[ 0014 ]

[ Table 2 ]

As it is apparent from Table 2, a component of the present invention, examples of Rσ value by regression equation exceeds 40 all tensile strength is at least 580 MPa, yet cracking HAZ constraining joint is not observed .. On the other hand, in the comparative examples in which the components underlined in Table 2 and the calculated Rσ values deviate from the requirements of the present invention, the occurrence of HAZ cracking was recognized, although there was a difference in the degree of cracking. In particular, steel N01,
In the comparative examples of 7 and 11, the calculated Rσ value is 40 or more, but HAZ cracking occurs because a small amount of B is contained, and B significantly impairs the plating cracking resistance of HAZ for small heat input welding. I understand.

[ 0016 ]

EFFECTS OF THE INVENTION According to the present invention, it is possible to manufacture a steel material in which the plating crack resistance of the small heat input welding HAZ is remarkably improved.

Claims (2)

[Claims] 1. C: 0.06-0.15 wt%, Si: 0.10-0.50 wt%
, Mn: 0.80 to 2.00 wt%, Zr: 0.012 to 0.040 wt%, solAl:
0.005-0.100wt%, B: 0.00015wt% or less, Nb: 0.010-0.10.
0 wt% and V: 0.010 to 0.100 wt%, and
Satisfying the formula (1), 244-265C-120Si-82Mn + 415Zr-49Al-145
Nb-329V ≧ 40 ・ ・ ・ (1). The balance is substantially Fe and unavoidable impurities, and the tensile strength is 580 MPa or more, which is a high-strength steel for welded structure excellent in hot-dip galvanizing crack resistance of the heat-affected zone of welding. 2. C: 0.06-0.15 wt%, Si: 0.10-0.50 wt%
, Mn: 0.80 to 2.00 wt%, Zr: 0.012 to 0.040 wt%, solAl:
0.005-0.100wt%, B: 0.00015wt% or less, Nb: 0.010-0.10.
0wt%, V: 0.010-0.100wt%, and further Ti: 0.005-0.030w
It contains t% and / or 0.05 to 1.00 wt% of Ni, Cu, Cr, Mo, or two or more, and satisfies the following formula (2):
-265C-120Si-82Mn + 415Zr-49Al-145Nb-329V + 167Ti-17Ni-
85Cu-81Cr-73Mo ≧ 40 ・ ・ ・ (2). The balance is substantially Fe and unavoidable impurities, and the tensile strength is 580 MPa or more, which is a high-strength steel for welded structure with excellent hot dip galvanizing crack resistance in the heat-affected zone of the weld.