JP2653616B2 - Manufacturing method of high strength steel for large heat input welding with excellent low temperature toughness - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high-strength steel for large heat input welding having excellent low-temperature toughness as a steel material used for shipbuilding, pressure vessels, tanks, bridges, buildings, marine structures and the like. .

[0002]

2. Description of the Related Art In recent years, there has been a demand for an increase in welding efficiency along with an increase in the size of a structure, and the application of large heat input welding to the joining of steel structures has become common. The steel for large heat input welding has been put into practical use, and is disclosed in JP-A-61-270354 and 62-5651.
No. 8, JP-A-02-250917, and JP-B-51-44 developed basically by the present inventors.
Each of the improvements described below has been added based on TiN, which is the technical concept of Japanese Patent No. 088, but all have had problems in their stability and overall quality characteristics in consideration of other steel material characteristics.

That is, Japanese Patent Application Laid-Open No. 61-270354 discloses that C: 0.03 to 0.20% and Si: 0.01 to 0.
50%, Mn: 0.30 to 2.0%, P: 0.02% or less, S: 0.015% or less, B: 0.0003 to 0.0
030%, N: 0.0080% or less as a basic component, and if necessary, one or more of Ni, Cu, Cr, Mo, Nb, V, and 0.03% or less of Ti ,
One or two or more of REM and Ca in total 0.003 to
High toughness welding steel containing 0.03% and not more than 0.003% of total Al. Further, Japanese Patent Application Laid-Open No. Sho 62-56518
Publication No. C: 0.03-0.12%, Si: 0.05-
0.40%, Mn: 0.7 to 1.6%, P: 0.015
%, S: 0.010% or less, Sol. Al: 0.0
01-0.010%, Ti: 0.005-0.020
%, B: 0.0003 to 0.0020%, N: 0.00
It contains one or more of Cu, Ni, V, and Ca as necessary, with 40 to 0.0060% as a basic component.
A steel having an i / N of 1.5 to 3.4 and a Ceq of 0.34% or less is subjected to a predetermined hot rolling, and immediately quenched to room temperature.
A method for producing high-strength steel for large heat input welding of 50 kg steel, characterized by performing low-temperature tempering at 00 to 450 ° C.

On the other hand, Japanese Patent Application Laid-Open No. H02-250917 aims to improve large heat input characteristics only by TiN + MnS without adding B, C: 0.02-0.3%, Si: 0.3.
% Or less, Mn: 0.50 to 2.50%, Ni: 0.2 to
4.5%, Nb: 0.003 to 0.015%, Cu:
0.2-2.0%, N: 0.01% or less, Ti / N:
2.0-4.0, Al: 0.005-0.1%, S:
Low temperature characterized by heating steel containing one or more of Cr, V, and Mo as required, with a basic component of 0.003 to 0.008%, to a predetermined cooling rate and 1150 ° C or higher. This is a method for producing high-strength steel for large heat input welding with excellent toughness.

[0005]

Japanese Unexamined Patent Publication (Kokai) No. 61-270354, which aims to improve large heat input characteristics, discloses that Al is contained in an amount of 0.0.
Since the content is set to not more than 03%, deoxidation becomes unstable, and the yield of Ti, REM, and Ca, which have a strong affinity for oxygen, is poor and the added amount varies, resulting in unstable large heat input characteristics. Was. The heat affected zone (HA) during large heat input welding
Z, Ti, REM, C
Since acids and sulfides having different properties a are used, the instability of large heat input characteristics is increased, and B is also actively used. Further, JP-A-62-56518 discloses Sol. Al is 0.010% or less, N is 0.004%
The purpose is to stabilize the precipitation of TiN in molten steel at 0 to 0.0060% and also to precipitate BN in the HAZ to improve the large heat input characteristics. It has the disadvantage that TiN and high N cannot be obtained, but also has the problem of actively adding B.

[0006] On the other hand, Japanese Patent Application Laid-Open No. H02-250917 discloses a stable TiN
+ MnS is difficult to form a composite precipitate and
Of 0.003 to 0.008%, the lamellar tear resistance was degraded, and the large heat input characteristic was unstable. The present invention eliminates the instability of large heat input characteristics, improves lamellar tear resistance,
An object of the present invention is to provide a method for producing a high-strength steel for large heat input welding, which is excellent in low-temperature toughness and eliminates quality problems associated with the addition of B.

[0007]

The inventor of the present invention has examined the problems of the prior art described above in detail, and found that B and M
It has been found that elimination of sulfide-forming elements other than n and clarification of the deoxidation method are effective for improving the stability of large heat input characteristics. JP-A-61-270354 and 62-565
In order to solve the problem of containing B and the problem of instability of the large heat input characteristic in JP-A No. 18, no B was added, and the use of sulfide-forming elements other than Mn was eliminated, and deoxidation was stabilized. Al was regulated to 0.010% to 0.10% in order to convert the Al.

On the other hand, for the deterioration of the lamellar tearing resistance disclosed in Japanese Patent Application Laid-Open No.
The regulation was improved to 0.0044%. Furthermore, TiN + M
For the unstable precipitation of the nS complex precipitate, the deoxidation at the time of tapping is weakly deoxidized by Si + Mn to form a Mn-Si complex oxide (Mn-Silicate) -based primary deoxidation product. In the subsequent secondary refining (vacuum degassing or ladle refining, etc.), the addition of Ti before the complete deoxidation with Al can result in intragranular ferrite (IGF) in the HAZ.
When forming a composite precipitate of TiON (Oxy-Nitride) or TiN and MnS, which is a generation nucleus, it is extremely effective in miniaturizing and increasing the number of the precipitates.
Even under a low S of 4% or less, stable formation of the composite precipitate was made possible for the first time.

That is, the gist of the present invention is as follows. (1) C: 0.05 to 0.18% by weight, Si: 0.
10 to 0.50%, Mn: 0.80 to 1.80%, P:
0.015% or less, S: 0.0008 to 0.0044
%, Al: 0.010 to 0.10%, Nb: 0.005
０．０0.024%, Ti: 0.005 to 0.018%,
N: In steel containing 0.0020 to 0.0060% and comprising balance iron and unavoidable impurities, Mn as an impurity
When S forms a composite precipitate with TiON or TiN,
In the secondary refining following weak deoxidation by Si and Mn at the time of tapping, Ti addition was performed before complete deoxidation by Al.
A method for producing a high-strength steel for large heat input welding having excellent low-temperature toughness, comprising forming a composite precipitate with MnS having iON or TiN as a nucleus.

(2) Cu: 0.05 to 0.80 by weight%
%, Ni: 0.05-1.50%, Cr: 0.05-
0.80%, Mo: 0.05 to 0.50%, V: 0.0
The method for producing high-strength steel for large heat input welding excellent in low-temperature toughness according to the above (1), wherein one or two or more kinds of 1 to 0.09% are contained in the steel.

[0011]

The present invention will be described below in detail. C is 0.05% as the cheapest and effective element to increase the strength
If it is added in excess of 0.18%, the weldability and joint toughness deteriorate, so the content is limited to 0.05 to 0.18%. Si
Is added together with Mn to form Mn-Silicate at the time of tapping to form stable precipitation nuclei of MnS after solidification, and if it exceeds 0.50%, it impairs weldability and joint toughness. , 0.10 to 0.50%. Mn was added at 0.80% or more as a useful element for increasing the strength inexpensively next to C. Mn was limited to 0.80 to 1.80% if it exceeds 1.80% because the weldability deteriorates. Incidentally, the addition in this range is sufficient for Mn-Silicate during tapping and MnS formation after solidification,
Sulfide-forming elements such as Ca, REM, and Zr must not be added.

P is limited to 0.015% or less from the viewpoint of weldability and low-temperature toughness. S is 0.0008% or more for the formation of MnS which forms a composite precipitate with TiON or TiN which is an IGF generation nucleus from the viewpoint of improving the joint toughness, and 0.004% or more.
If it exceeds 4%, the resistance to lamellar tearing is impaired.
Although it is limited to 0008 to 0.0044%, when severe lamellar tear resistance is required, it is 0.0008 to 0.0044%.
Preferably, it is limited to 003%.

Al is the most important element in deoxidation, and is added in an amount of 0.010% or more to reduce nonmetallic inclusions.
% Exceeds 0.010% because of impairing weldability and low-temperature toughness.
０．１0.10%. Further, the addition of Al is performed after the end of the addition of Ti at the time of ladle refining or vacuum degassing, so that Mn-Silicate is generated during tapping and Ti in a weakly deoxidized state.
Stable precipitation of TiON or TiN by addition. N
b is added in an amount of 0.005% or more for controlling the crystal grain during hot rolling and preventing HAZ softening, and an addition of more than 0.024% impairs the joint toughness, so is limited to 0.0005 to 0.024%. did.

Ti is used in the HAZ during high heat input welding.
0.018% or more is added to suppress the growth of austenite (γ) grains by ON or TiN and to form a composite precipitate of TiON or TiN and MnS which becomes ferrite (α) transformation nuclei in γ grains, Excessive addition of more than 0.005% may impair weldability and joint toughness.
It was limited to 0.018%. Incidentally, the addition of Ti is stable T
In order to form a composite precipitate of iON or TiN and MnS, it is limited to performing Ti addition before complete deoxidation with Al in secondary refining such as vacuum degassing followed by weak deoxidation with Si + Mn at the time of tapping at the time of tapping. . Also, even if Ti is in this range, its addition is equivalent to N (N × 3.
4) is preferable. N is set to 0.0020% or more for TiON or TiN formation. If it exceeds 0.0060%, the slab flaw is deteriorated and the joint toughness is deteriorated.
It was limited to 0.0020 to 0.0060%.

Elements other than the above basic components (Cu, N
The effect of the present invention is not impaired even if one or more of i, Cr, Mo, V) are added for improving the strength and toughness, but other elements (Ca, REM, Zr, B, etc.) Must not be added in order to avoid the inhibition of MnS formation and the property deterioration accompanying the addition of B, which are important technical ideas of the present invention. C
u is replaced by C, Si, and Mn for the purpose of reducing Ceq in order to improve weldability and low-temperature toughness, and is added at 0.05% or more. Since at least half of Ni addition is required, which is not preferable from the viewpoint of cost, the content is limited to 0.05 to 0.80%.

Ni is Ceq for improving weldability and low-temperature toughness.
0.05% by substituting with C, Si, Mn for reduction
The above addition is not preferred from the viewpoint of cost, and the addition of more than 1.50% is limited to 0.05 to 1.50%.

Cr is added in an amount of 0.05% or more to improve hardenability and secure strength. However, excessive addition of more than 0.80% impairs weldability and low-temperature toughness.
It was limited to 05-0.80%. Mo is added in an amount of 0.05% or more to improve hardenability and secure strength.
Addition of more than 0.50% is not preferable from the viewpoint of weldability and cost, and is limited to 0.05 to 0.50%.

[0018]

EXAMPLES Examples of the present invention are shown in Tables 1 and 2 together with Comparative Examples. Table 1 shows the chemical components of the present invention examples (steel A to steel G) and comparative examples (steel H, steel I). In steel H, S is higher than the range of the present invention, and in steel I, Ca, which is a sulfide forming element that should not be added in the present invention, is added. In the steel making results, in the present invention, complete deoxidation by Al after addition of Ti was performed in vacuum degassing after weak deoxidation by Si + Mn at the time of tapping. On the other hand, in the comparative example, the addition of Ti and the addition of Ca were performed after complete deoxidation by Al + Si at the time of tapping.
Casting was performed by ordinary continuous casting. Table 2 shows the production results of the inventive examples and the comparative examples together with the rolling results.

[0019]

[Table 1]

[0020]

[Table 2]

Steel A is a normal controlled rolling (CR), steels B, C and H are recently developed thermomechanical treatments (TMCP), and steels D to F are direct quenching (DQ) and low temperature tempering (TMQ). T), steel G was manufactured by normal quenching and tempering (QT). The steels A to C and H are HT490 steels, and the steels D to G and I are HT580 steels, each of which satisfies the corresponding strength level. On the other hand, as for the low temperature toughness of the base material, all steels stably satisfy the required values of the applicable standards.

The draw value (RAz) and the HAZ toughness in the Z-direction tensile test are all high in the examples of the present invention. TiN
Steel H of the comparative example, which aimed at improving the joint toughness by increasing the amount of + MnS, had the highest HAZ toughness, but had the lowest RAz and did not satisfy the lamellar tear resistance standard. In addition, the steel I of the comparative example to which Ca for improving the lamellar tear resistance is added does not form a composite precipitate of TiN and MnS which is an α transformation nucleus in the coarsened γ grains in the joint HAZ portion.
AZ toughness is extremely poor.

On the other hand, according to the present invention, a stable composite precipitate of TiON or TiN and MnS is formed by specifying a deoxidation method without repeating, and a large heat input characteristic in a low S region is used by using an expensive REM or the like. The properties of the steel material (lamin resistance and hardness increase due to the addition of B) were also significantly improved without significant improvement.

[0024]

According to the steel of the present invention, by specifying the component system and the deoxidizing method, the lame resistance as well as the large heat input characteristics can be improved, and the quality problem (the problem due to an increase in hardness) associated with the addition of B can be avoided. I made it. As a result, large heat input characteristics can be stabilized without using expensive elements, and steel with excellent overall steel material properties can be provided, enabling the construction period of large structures to be shortened by large heat input welding. It is a thing. Accordingly, there are significant economic benefits to industry as well as those skilled in the art with the present invention.

Claims (2)

(57) [Claims] C: 0.05 to 0.18%, Si: 0.10 to 0.50%, Mn: 0.80 to 1.80%, P: 0.015% or less by weight%, S : 0.0008 to 0.0044%, Al: 0.010 to 0.10%, Nb: 0.005 to 0.024%, Ti: 0.005 to 0.018%, N: 0.0020 to 0 .0060% In a steel consisting of iron and unavoidable impurities, MnS as an impurity forms a complex precipitate with TiON or TiN. In the secondary refining following weak deoxidation by Si and Mn at the time of tapping, Before complete deoxidation
A method for producing a high-strength steel for large heat input welding excellent in low-temperature toughness, characterized by forming a composite precipitate with MnS having TiON or TiN as a nucleus by addition. 2. Cu: 0.05 to 0.80%, Ni: 0.05 to 1.50%, Cr: 0.05 to 0.80%, Mo: 0.05 to 0.50% by weight. %, V: 0.01 to 0.09% of the steel according to claim 1, characterized in that the steel contains one or more of the following: .