JP3298678B2 - Steel plate with low welding distortion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for removing a strain or preventing the occurrence of a strain, since a small amount of deformation occurs when welding a steel plate used in shipbuilding, marine structures, buildings, bridges, civil engineering and the like. The present invention relates to a high-yield-point type high-strength steel for a welded structure capable of reducing or omitting the above operation.

[0002]

2. Description of the Related Art Conventionally, during welding of steel materials in various steel structures, solidification shrinkage of a weld metal and subsequent shrinkage and expansion due to cooling and phase transformation cause, for example, in the case of a joint shape of fillet welding, angular deformation. A so-called out-of-plane deformation occurs.
Such residual deformation causes a decrease in structural strength such as a decrease in buckling strength when a compressive load is applied. In addition, if this deformation is forcibly prevented by a restraining jig, an excessive residual stress will be generated. Further, the dimensional accuracy is insufficient, which causes inconvenience in manufacturing the steel structure and impairs the appearance.
Therefore, for example, the Journal of the Japan Welding Society, vol.
As shown in “Generation of welding deformation and its prevention” in No. 9, a number of techniques for correcting residual stress generated during welding by local heating have been empirically proposed and implemented. However, the reheating of the welds causes deterioration of the steel material, and the time and cost required for straightening work are serious obstacles in practical use. Was desired.

[0003] Regarding the mechanism of generation of residual stress and deformation in a welded part, Sato's “Handbook of Welding Structures” 1988 (Kuroki Publishing), Masabuchi “Analys
isof Welded Structures "19
80, Learn more about PERGAMONPRESS. But,
Welding deformation does not focus on the detailed properties of the steel material used, as it is mainly determined by the geometry of the component to the heat input during welding. In addition, as can be seen in "Influence of welding conditions on welding residual stress and welding deformation of structural materials" in Sato et al. It is mentioned that yield stress is considered rather than transformation expansion as a factor of welding deformation.
Welding deformation of 0% and 9% Ni steel is 9% N with small yield stress.
It is shown that welding deformation is larger in steel i.

[0004] However, this is not a knowledge that can be directly applied to the composition and structure and yield strength of ordinary steel materials used for ordinary steel structures, and further, the strength of the material against deformation is determined by the alloy such as Cr, Mo, V, and Nb. What is presumed by adding an element is not actually confirmed, although it is described in “Gas shielded arc welding method” by Nishino et al. In JP-A-4-22597. Therefore, it does not pay attention to the relationship between the composition and the structure of the steel material.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a steel material having a small welding distortion, which reduces welding deformation in welding of a steel structure and enables a large amount of labor and cost reduction such as deformation prevention work and shape correction work. Is provided.

[0006]

The present invention provides (1) C: 0.
05 to 0.20%, Si: 0.05 to 0.50%, M
n: 0.6 to 1.60%, P: 0.025%, S: ≤
0.010%, Al: 0.010 to 0.050%, N:
The microstructure of the steel sheet containing 0.0020 to 0.0050%, the balance being iron and unavoidable impurity elements is composed of bainite having an area ratio of 30% or more and having carbide dispersed therein, and yielding. The strength is more than 36kg.
It is a steel plate with little weld distortion. (2) above
In addition to steel components, V: ≤ 0.050%, Nb: 0.003
0.035%, Cu: 0.50%, Mo: 0.05
０．２0.25%, Ni: ≦ 0.50%, Cr: ≦ 0.50
%, Ti: 0.005 to 0.020%, B: ≦ 0.00
20%, Ca: ≦ 0.0050%, REM: ≦ 0.00
It is characterized by containing 60% of one or more kinds
This is a steel plate with less welding distortion.

In the present invention, the microstructure of the steel sheet is bainite having an area ratio of 30% or more, and has a yield strength of 3%.
The reasons for adding the chemical composition to obtain a steel material of 6 kg or more and the reasons for limiting the amount of addition are as follows. C is added for the purpose of forming bainite structure and securing the strength, and the lower limit is set to 0.05% from the limit of its effect. Also, C is adversely affected by base material toughness, weldability is deteriorated, and high carbon island martensite is formed. The upper limit is 0.20% in order to prevent the deterioration of the weld joint toughness.

Since Si is an element necessary for deoxidation and is an element effective for further increasing the strength, the lower limit is set to 0.05%, and in order to prevent deterioration in weldability and weld joint toughness, 0% is added. The upper limit is .50%. Since Mn is effective for ensuring bainite structure and ensuring strength and toughness, Mn is set to 0.1%.
The lower limit is 6%, and a large amount increases the hardenability to form a hardened structure and deteriorates the weldability, so 1.60%
Is the upper limit.

P and S, which are impurity components, are set to P ≦ 0.025% and S ≦ 0.010% in order to maintain the base metal and the weld joint toughness at required levels, respectively, and Al is necessary for deoxidation. Since it is an element, the lower limit is 0.010%,
A large amount impairs the cleanliness of the steel, so the upper limit is 0.050%. N combines with Al, refines the crystal grains of the steel material, and sets the lower limit to 0.0020%, which is effective for increasing the toughness. If contained in a large amount, the toughness of the steel material is impaired.
The upper limit is 50%.

Further, in addition to the above elements, one of the following elements
The reason and amount of the chemical composition for obtaining a steel material having a microstructure of 30% or more in area ratio of bainite and a yield strength of 36 kg or more when the microstructure of the steel sheet according to the present invention described above contains two or more species. Are as follows. V is an element effective for enhancing the bainite structure and the yield strength. However, if the V content is large, the toughness is impaired, so the upper limit is 0.05%. Nb is an element effective for refining the structure together with the formation of bainite and increasing the yield strength. Therefore, the lower limit is 0.003%, and a large amount of Nb forms a structure harmful to toughness.
Is the upper limit.

Both Cu and Ni are effective elements for increasing the strength at the same time as forming the bainite structure without impairing the toughness. However, since they are expensive elements, the upper limit is 0.5% from the viewpoint of economy. . Mo is an element effective for increasing the strength together with the bainite structure, so the lower limit is 0.05% at which the effect of increasing the strength occurs, and the upper limit is 0.25% because a large amount of Mo impairs the weldability. Cr is an element effective for increasing the strength together with the bainite structure, but the upper limit is 0.5% because a large amount impairs the toughness.

[0012] Since Ti is an element effective in ensuring the toughness of the weld heat affected zone, the lower limit is 0.005%, and 0.020% in order to prevent deterioration of toughness due to excessive addition.
Is the upper limit. B is an element effective not only for increasing the strength of the steel material together with the bainite structure but also for refining the crystal grains of the weld heat affected zone. Therefore, the upper limit is 0.0020%, which does not cause toughness deterioration due to excessive inclusion. And

[0013] Ca is an effective element for controlling the morphology of sulfides, but a large amount of Ca impairs the cleanliness of steel.
The upper limit is 0%.

REM refines the structure of the weld heat affected zone,
Although it is an element effective for increasing toughness, the upper limit is 0.0060% because a large amount of addition impairs the cleanliness of steel. Further, it goes without saying that N is effective not only for steel material itself but also for bonding with Ti, preventing crystal grains in the heat affected zone from becoming coarse and increasing toughness. In the present invention, these elements can be selectively used in the same amount range based on the same reason without interfering with the operation and effect of the present invention. include.

[0015]

In order to overcome the above-mentioned problems, the present inventors
Through repeated experiments and studies, the inventors have found a steel sheet that does not contain a large amount of special elements and has little welding deformation. Hereinafter, the operation and effect of the present invention will be described. The present invention is based on a new method which is completely different from the method of the conventional welding material in order to realize the reduction of the welding deformation of the steel structure.

That is, according to the present invention, as a means for reducing welding deformation, deformation occurs due to stress acting on the steel material due to contraction in the cooling process of the weld metal and expansion due to phase transformation. It is intended to prevent deformation of the steel sheet by increasing the yield strength. That is, various measures for increasing the yield strength of a steel sheet affected by welding heat were studied, and the microstructure of the steel material was set to at least 30% or more of a bainite structure in which fine carbides were dispersed.
By setting the yield strength to 36 kgf / mm ² or more, it is possible to increase the yield strength in the middle temperature range of 400 ° C. or more where welding deformation occurs, and as a result, welding at the time of fillet welding usually performed on steel structures It has been found that the deformation amount is reduced to １ ／ or less. The yield strength in the medium temperature range where welding deformation occurs is Solut
N where e drag likeeffect can be expected
It was also confirmed that the addition of an element having a strong affinity for C, such as b, Mo, Ti, Cr, and V, could further increase the content.

[0017]

EXAMPLES Steels 1 to 32 shown in Tables 1 and 2 are steel materials satisfying the component range of the present invention. In each of the steel materials, the microstructure of the steel material was made into two types: a steel sheet having a bainite area ratio of 30% or more and a steel sheet having a bainite area ratio of less than 30% by controlling the control cooling conditions in the manufacturing process following the hot rolling. Further, in the production process of these steel materials, by controlling the control rolling of hot rolling,
If the bainite area ratio is 30% or more, the yield strength is 36kg
Two types, a steel sheet of f / mm ² or more and a steel sheet of less than 36 kgf / mm ² were used. The yield strength of steel sheets having a bainite area ratio of less than 30% is at various levels by the same means.

In each of these steels having the same chemical composition, 1) the yield strength is 36 kgf / at a bainite area ratio of 30% or more.
mm ² or more 2) Yield strength of 36 kgf / with bainite area ratio of 30% or more
Less than mm ² 3) Three types of steel sheets with bainite area ratio of less than 30% and yield strength of various levels were prepared, and fillet welding was performed by the construction method shown in FIG.

The welding deformation was investigated in accordance with the method of calculating the amount of angular deformation shown in FIG. 1. As a result, in all the steel materials, only when the bainite area ratio was 30% or more and the yield strength was 36 kgf / mm ² or more, the angular deformation was The amount is 0.7 × 10 ^-2 radians or less, whereas the amount of welding deformation is extremely small,
Other bainite area ratio is 30% or more and yield strength is 3
Those with less than 6 kgf / mm ² and those with bainite area ratio of less than 30% and various levels of yield strength have an angular deformation of 1.
5 × 10 ^-2 radians and the amount of angular deformation remain at a normal level. From this example, the effectiveness of the present invention is clear.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

[0024]

[Table 5]

[0025]

[Table 6]

[0026]

[Table 7]

[0027]

[Table 8]

[0028]

[Table 9]

[0029]

According to the present invention, in welding performed on steel structures such as shipbuilding, marine structures, buildings, bridges, civil engineering, etc., the amount of welding deformation generated at the time of welding can be reduced. It is possible to reduce or omit the operation for preventing occurrence, and it is possible to save a great deal of labor and cost.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a method for calculating an amount of angular deformation.

FIG. 2 is an explanatory view of a method of constructing a fillet weld joint.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-130319 (JP, A) JP-A-51-20718 (JP, A) JP-A-64-34598 (JP, A) 21180 (JP, B1) JP 47-15580 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00 301 C22C 38/06

Claims (2)

(57) [Claims] 1. A weight ratio of C: 0.05 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.6 to 1.60%, P: ≦ 0.025%, S: ≦ 0.010%, Al: 0.010 to 0.050%, N: 0.0020 to 0.0050%, and the microstructure of the steel sheet composed of the balance iron and unavoidable impurity elements is the area ratio. in 30% or more, and Kaaba
It consists dispersed bainite id-less steel plate welding distortion yield strength and having a least 36 kilometers. 2. The steel composition further comprises : V: ≦ 0.05%, Nb: 0.003-0.035%, Cu: ≦ 0.50%, Mo: 0.05-0.25 by weight ratio. %, Ni: ≦ 0.50%, Cr: ≦ 0.50%, Ti: 0.005 to 0.020%, B: ≦ 0.0020%, Ca: ≦ 0.0050%, REM: ≦ 0. The steel sheet according to claim 1, wherein the steel sheet contains one or more of 0060%.