JP3007247B2 - Method for producing TS590N / mm2 class high strength steel with excellent weldability and yield ratio of 80% or less - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention weldability excellent yield ratio 8
TS of 0% or less (tensile strength) 590N / mm This is related to the method of manufacturing high-grade steel of class ^{2 and} is most preferably applied to thick plate mills in the steel industry, but also applicable to hot coils and section steels. it can.

[0002]

^2. Description of the Related Art Conventionally, TS590N / mm2 high-strength steel (hereinafter referred to as HT60) is manufactured by quenching and tempering a hardenable steel by adding B or adding a large amount of various alloys. I was However, the addition of B or the addition of a large amount of the alloy significantly deteriorates the weldability, and requires preheating of 100 ° C. or more from the viewpoint of preventing welding cracks at the time of on-site welding, resulting in a significant decrease in construction efficiency and work environment. Had worsened. On the other hand, a steel utilizing the precipitation hardening of Cu represented by ASTM A710 steel is known as HT60 having good weldability. However, high-rise building steel requires a low yield ratio (YR) steel (YR ≦ 80%) in order to absorb the energy during an earthquake and prevent the collapse of the building. High and poor earthquake resistance.

[0003]

SUMMARY OF THE INVENTION The present invention relates to an HT6 for architectural use.
0 inexpensive manufacturing technology. HT60 manufactured based on the method of the present invention is less likely to cause welding cracks even in small heat input welding and restraint welding, and can reduce or omit preheating in welding work.
A building using the HT60 has features such as absorbing earthquake energy and having excellent earthquake resistance.

[0004]

Means for Solving the Problems Specific means of the present invention are shown in the following (1) and (2). (1) C: 0.04 to 0.11%, Si: 0.5% or less, Mn: 0.6 to 1.6%, P: 0.03% or less, S: 0.01% by weight ratio Hereinafter, Cu: 0.7 to 1.2%, Ni: 0.30 to 1.00%, Cr: 0.05 to 0.50%, Mo: 0.05 % or more and less than 0.20% , Ti: 0.005 to 0.025%, Al: 0.06% or less, N: 0.006% or less, and the balance satisfies the following formula 1 without substantially containing B consisting of iron and unavoidable impurities. Hot rolling the steel to be
Excellent weldability with a thickness of 20 mm or more and 75 mm or less, characterized by being reheated to a temperature range of 750 to 870 ° C., quenched, and subsequently tempered in a temperature range of Ac ₁ transformation point or less.
A method for producing TS590N / mm2 class ² high strength steel with a yield ratio of 80% or less .

[0005]

(Equation 2)

(2) Nb: 0.01 to 0.03%, V: 0.01 to 0.05%, Ca: 0.001 to 0.006 by weight ratio to the component (1). % Of one or more of the above
(1) preparation of TS590N / mm ² class high strength steel of 20mm thick or more 75mm less weldability good yield ratio below 80%, wherein.

[0007]

The present invention will be described below. According to the study of the inventors, in order to simultaneously realize the excellent weldability and low yield ratio of HT60, the addition of B, the precipitation hardening of Cu by quenching and tempering, and the further hardening of the steel components to appropriate hardenability. I found it necessary to adjust. Further, in steel in which crystal grains are refined by adding a small amount of Ti and optimizing heat treatment conditions, Cu
It was found that even when precipitation hardening was performed, excellent low-temperature toughness was exhibited.

[0008] The minimum amount of Cu required for obtaining the characteristics as HT60 is 0.7%. However, since addition of Cu exceeding 1.2% makes it difficult to sufficiently lower YR, the upper limit is set to 1.2%. In addition, the YR
In order to reduce the hardness to 80% or less , it is necessary to adjust the hardenability of the steel to an appropriate range.
It is necessary to adjust to a range of 5 to 2.5.

[0009]

(Equation 3) The reason is that if it is less than 1.5, the YR does not decrease to 80% or less by the two-phase structure heat treatment described below,
This is because the strength is over 60.

Next, in order to sufficiently exert the effect of Cu as described above and sufficiently reduce YR, a manufacturing method must be appropriate. Therefore, it is necessary to limit the heat treatment conditions after hot rolling. 750-870 ° C after hot rolling
After the reheating, the steel is quenched, and reheated to a temperature of Ac ₁ or less to perform a tempering treatment. The reason for reheating and quenching to 750 to 870 ° C. is to reduce the yield ratio. Generally, steel precipitation-hardened with Cu has a remarkably high YR. Therefore, reheating and quenching are performed in the (γ + α) two-phase region at 750 to 870 ° C. The untransformed region is softened by partial γ transformation, and the γ transformation region is hardened to form a two-phase microstructure (a soft phase and a hard phase).
Thus, the yield ratio can be reduced. Reheating temperature is 750 ℃
In the following, the above-mentioned effects cannot be obtained because the region transformed into γ is small. However, when the temperature exceeds 870 ° C., most of them undergo γ transformation, and the desired two-phase structure cannot be obtained, so that low YR cannot be achieved.

The tempering treatment is indispensable for exhibiting the effect of depositing Cu. However, if the temperature exceeds the Ac ₁ point, the strength is remarkably reduced. Therefore, the temperature must be lower than the Ac ₁ point (a desirable tempering temperature is 450 to 650 ° C.). However, even if the addition amount of Cu and the production method are appropriate, excellent characteristics as HT60 cannot be obtained unless the basic components are appropriate. Hereinafter, this point will be described.

The lower limit of 0.04% of C is a minimum amount for ensuring the strength of the base material and the welded portion and for exerting these effects when Nb, V and the like are added. However, if the amount of C is too large, the weldability is remarkably deteriorated.
1%. Since the addition of a large amount of Si deteriorates the weldability and the HAZ toughness, the upper limit is set to 0.5%. Al and Ti alone are sufficient for deoxidizing steel, and Si need not always be added. Mn is an element indispensable for securing strength and toughness, and its lower limit is 0.6%. But Mn
If the amount is too large, the hardenability increases and not only deteriorates the weldability and the HAZ toughness, but also promotes the center segregation of the continuously cast slab, so the upper limit was made 1.6%.

The reason why the impurities P and S in the steel of the present invention are set to 0.03% and 0.01% respectively is to further improve the low-temperature toughness of the base material and the welded portion. The reduction of P prevents grain boundary destruction, and the reduction of S content is MnS
To prevent toughness degradation. Preferred P and S contents are 0.01% and 0.005% respectively. Ni is 0.
When it is 30% or more, it has the effect of improving the strength and toughness of the base material without adversely affecting the weldability and the HAZ toughness, and is also effective in preventing Cu-cracks. However, if it is 1.0% or more, it becomes extremely expensive and loses economy, so the upper limit is 1.0%.
%. Cr is an element that increases the strength of the base material and the welded portion, and requires at least 0.05% or more. However, if the content is too large, the weldability and the HAZ toughness are significantly deteriorated, so the upper limit is set to 0.50%.

Mo is an element that improves both strength and toughness, and HT60 must have 0.05% or more. However, if it is too large, it is not preferable in terms of weldability and HAZ toughness, and the upper limit is less than 0.20% . Ti forms a carbonitride to improve HAZ toughness. When the amount of Al is small, an oxide of Ti is formed to improve the HAZ toughness.
If it is less than 0.025%, there is no effect.
Limited to 25%. Al is generally an element contained in the deoxidized upper steel, but the lower limit is not limited for the steel of the present invention because deoxidation is also performed by Si and Ti. But Al
If the amount increases, the cleanliness of the steel deteriorates, and the toughness of the welded portion deteriorates. Therefore, the upper limit was made 0.06%.

N is generally contained in steel as an unavoidable impurity. However, N is combined with Nb and V to form carbonitride to increase the strength, and to form TiN to form N as described above. To enhance the properties of HT60. For this reason, at least 0.001% is required as the N amount. However, an increase in the amount of N promotes deterioration of HAZ toughness and generation of surface flaws in the continuously cast slab, so the upper limit is made 0.006%.

The basic components of the steel of the present invention are as described above, and the purpose can be sufficiently achieved. However, in order to further enhance the properties for the purpose, the elements described below, namely, Nb, V, and Ca are selectively added to increase the strength. As for the improvement in toughness, more preferable results are obtained. Next, the additional elements and the amounts of the elements will be described. Nb forms fine carbonitrides, increases strength, and improves HAZ toughness. However, if the content is less than 0.01%, the effect is small, and if it exceeds 0.03%, it becomes difficult to sufficiently lower the YR.

V is an element having almost the same effect as Nb, but has a slightly lower precipitation hardening ability than Nb. 0.01%
Below, the effect is small, and if it exceeds 0.05%, it becomes difficult to sufficiently reduce YR. Ca is a sulfide (Mn
It has the effect of controlling the form of S), increasing the Charpy absorbed energy and improving the low-temperature toughness. However, if the Ca content is less than 0.001%, there is no practical effect, and 0.006%
If Ca is exceeded, CaO and CaS are generated in large amounts to form large inclusions, which impair not only the toughness of the steel but also the cleanliness and adversely affect the weldability and the lamella tear resistance. 0.006%.

[0018]

EXAMPLE A steel plate was manufactured by a well-known converter, continuous casting, and thick plate process, and its strength, toughness, weldability (y-slit cracking property) and the like were examined. Tables 1 to 7 show the steels of the present invention, 8 to 1
6 shows the chemical composition of the comparative steel. Table 2 shows the steel sheet production conditions of the steel of the present invention and the comparative steel, and their mechanical properties and weldability.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

The steels 1 to 7 of the present invention in Table 2 show the strength of the base material, Y
R, toughness and weldability can be achieved in a well-balanced manner. On the other hand, the comparative steel 8 has a low Di value, and thus has a high YR. Comparative steel 9 has a high C content and a very high y-slit crack stop temperature. In comparative steel 10, B
Is added, the y-slit crack stop temperature is extremely high. In Comparative Steel 11, the Cu content was low and the strength was insufficient. In Comparative Steel 12, the Cu content was high,
YR is high. In Comparative Steel 13, since the Di value was too high, the strength was extremely high and exceeded the standard strength of HT60. In Comparative Steel 14, the reheating temperature during the two-phase quenching was as low as 720 ° C., and γ was insufficient and YR was high. In Comparative Steel 15, since the reheating temperature at the time of quenching in the two-phase region was as high as 880 ° C., almost all of the steel was gamma-converted, so that YR
Is high.

[0023]

The steel materials such as thick steel plate, section steel, hot coil and the like manufactured by the chemical composition and manufacturing method of the present invention have a low yield ratio HT60 excellent in weldability. As a result, the efficiency and safety of welding work at the site are significantly improved, and the safety of buildings and the like can be greatly increased.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-179343 (JP, A) JP-A-62-142723 (JP, A) JP-A-2-205626 (JP, A) JP-A 7-142 90365 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C21D 8/00-8/02

Claims (2)

(57) [Claims] 1. C: 0.04 to 0.11%, Si: 0.5% or less, Mn: 0.6 to 1.6%, P: 0.03% or less, S: 0. 01% or less, Cu: 0.7 to 1.2%, Ni: 0.30 to 1.00%, Cr: 0.05 to 0.50%, Mo: 0.05 % to less than 0.20% , Ti: 0.005 to 0.025%, Al: 0.06% or less, N: 0.006% or less, the balance substantially does not contain B consisting of iron and unavoidable impurities and satisfies the following formula 1. 750-8 after hot rolling steel
Reheating to a temperature range of 70 ° C. and quenching, followed by Ac ₁
Preparation of weldability excellent yield ratio of 80% or less TS590N / mm ² class high strength steel, which comprises tempering at a temperature range of the transformation point. (Equation 1) The components of the claim 1, further a weight ratio, Nb: 0.01~0.03%, V: 0.01~0.05%, Ca: of from 0.001 to 0.006% The TS59 having excellent yieldability and a yield ratio of 80% or less according to claim 1, characterized in that it contains one or more kinds.
0N / mm A method for producing Class ² high-strength steel.