JP2733866B2 - Gas shielded arc welding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for welding steel plates used in construction, civil engineering, marine structures, shipbuilding, and the like, and more specifically, a method for reducing the amount of deformation generated during welding work. The present invention relates to a gas shielded arc welding method capable of reducing or omitting a strain removing operation.

(Prior Art) In various steel structures, when welding steel, solidification shrinkage of molten metal and subsequent shrinkage / expansion due to cooling and phase transformation cause, for example, in the case of a joint shape of fillet welding, a surface called angular deformation. Outer 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 production and impairs the aesthetic appearance. So, for example, the Journal of the Japan Welding Society, 1983
As can be seen in "Occurrence and Prevention of Welding Deformation" serialized in Vol. 52, Nos. 4 to 9, many techniques have been empirically proposed to correct residual deformation generated during welding by local heating. I have. However, in addition to the inevitable deterioration of the material due to the reheating of the welded portion, the time and cost required for the straightening work are a serious obstacle in practical use, and a welding method that can reduce or omit this. The development of was desired.

Regarding the mechanism of the occurrence of residual stress and deformation in welds, see Sato's Handbook of Welding Structures 1988 (Kuroki Publishing),
`` Analysis of Welded Structures '' by K. Masubuchi 198
Learn more about 0, PERGAMON PRESS. However, it does not focus on the detailed properties of the welding material used, as the welding deformation is mainly determined by the geometry of the component to the heat input during welding. Although the above-mentioned book clearly states that the phase transformation temperature of the welded portion of steel structures is a factor that affects the residual stress and deformation, the specific degree of effect of welding materials for steel structures is No quantification of the substance and no studies on its components have been made. In addition, there is a report on the study of relaxation and deformation reduction of residual stress, focusing on the superplastic phenomenon of phase transformation (Summary of the National Meeting of JWS, pp.314-315, p.7, p.7
8-79, Vol. 39, p. 338-339, p340-341). All of them focus on the martensitic transformation temperature of low alloy steels and stainless steels, and are not findings that can be directly applied to the composition and structure of ordinary steel materials. Further, when such a high value of Ni is contained, the cost of the welding material increases, and even if the strain removing operation can be omitted, it is not practical from an economic viewpoint. Furthermore, when this is applied to ordinary steel and low-alloy steel for shipbuilding and offshore structures, the weld metal becomes excessively noble, causing selective corrosion in the heat affected zone. Inconvenience occurs.

The greatest influencing factor on the welding deformation is the welding heat input to the steel sheet thickness, followed by the phase transformation temperature of the weld metal. In addition to these, the strength of the material that resists the deformation at the temperature at which the deformation occurs can be mentioned. The phase transformation temperature is approximately in the range of 400 to 700 ° C., and it is possible to reduce the amount of deformation by increasing the strength in this temperature range by adding elements such as Cr, Mo, V, and Nb.
It can be inferred from knowledge of the high-temperature strength of steel. However, studies have not been made to ensure high-temperature strength at the transformation point temperature of the weld metal part, and these additional elements tend to increase the transformation point temperature described above and increase welding deformation. However, the appropriate addition amount could not be easily determined.

(Problems to be Solved by the Invention) As described above, assuming that the welding member / shape and the heat input are given, the influence of the phase transformation point temperature of the welding material on the deformation generated during welding is quantified, It is considered effective to provide guidelines for setting welding material components. The present invention provides a welding method that reduces the amount of deformation of ordinary steel materials most commonly used for steel structures.

(Means for Solving the Problems) The gas shielded arc welding method of the present invention includes the following:
It is as follows.

% By weight, C: 0.2% or less, Si: 0.35% or less, Mn: 0.60 to 1.20%, the balance being Fe and unavoidable impurities. 0.05-9.0%, Mn; 0.4-2.5%, Cu; 0.1-1.5%, C; 0.01-0.15%, and Mo; 0.2-2.0%, V; 0.1-0.5% And the balance of Fe and unavoidable impurities, and the parameter T determined by the following formula based on the weight% of each element in the wire is less than 650, and the welding heat input should be 10 kJ / cm or less. A gas shielded arc welding method characterized by a small welding deformation.

T = 630.0-476.5C + 56.0Si-19.7Mn-16.3Cu-26.6Ni-4.9Cr + 38.1Mo + 124.8V + 136.3Ti-19.1Nb + 198.4Al + 3315.0B ... (1) When the wire is weight%, Cr; The above-described gas shielded arc welding method with little welding deformation, further comprising one or two types of 3.0%, Nb; 0.01 to 0.05%.

(Operation) Within the range of the cooling rate of the normal arc welding method, Ar ₃
The transformation point temperature T can be roughly predicted by equation (1).
As is clear from equation (1), Ni, Mn, C
It is possible to reduce the Ar ₃ transformation point by adding a predetermined amount of u, Nb, C. In general, the lower the transformation point temperature, the greater the transformation expansion, which reduces the residual welding deformation caused by shrinkage during cooling.Thus, it is thought that an increase in the transformation expansion contributes to a reduction in welding deformation. Can be However, the transformation of supercooled austenite does not exhibit a simple transformation expansion amount and clear response from the emergence of bainite structure, hence are focused on Ar ₃ transformation point temperature.

On the other hand, the amount of angular deformation occurring in the T-shaped fillet weld joint is the first.
As shown in the figure, it was found that there was a clear correlation with the Ar ₃ transformation point temperature of the welding material, and that the lower the transformation point temperature, the smaller the amount of generated angular deformation. This is thought to be because the transformation temperature increases as the transformation point temperature decreases, and the shrinkage accompanying solidification is eliminated to some extent. In addition to the component systems of Ni, Mn, Cu and C
When the element of Cr, Mo, Nb, or V is contained, even if the value of the phase transformation temperature T given by the equation (1) is slightly higher than the case where the latter is not included, the angle generated We found that the amount of deformation was small. This fact is considered to be due to the fact that the elements Cr, Mo, Nb, and V all increase the mechanical strength at the temperature at which the transformation occurs, thereby restraining the deformation. For example, from the consideration of the reduction in buckling strength against compressive load due to welding deformation and the dimensional accuracy in the production of joints, the transformation point temperature that gives the limit value of the amount of angular deformation that does not require the above-mentioned deformation correction work, Cr , Mo, Nb, and V are represented by T <650.

Hereinafter, the specification of the component elements of the welding wire and the addition amount thereof in the present invention will be described (the value of the element addition amount is the weight% in the welding wire).

Ni is a typical γ-former and has a great effect of lowering the transformation point. At least 0.05%, preferably 3.0% or more is added. If the addition amount is too large, in addition to the increase in cost, for example, in a marine steel structure, the weld metal portion becomes too noble electrically, forming a local battery and selectively affecting the weld heat affected zone. Will be done. Therefore, the upper limit of the amount of Ni needs to be 9%.

Mn has a large effect of lowering the transformation point, and is added at least 0.4% or more, preferably 0.8% or more as an aid of Ni. Excessive addition leads to an increase in hot cracking susceptibility of the weld metal and a decrease in toughness, so it is necessary to set the upper limit to 2.5%.

Since Cu also has the effect of lowering the transformation point, it must be contained at 0.1% or more. Excessive addition leads to a decrease in toughness of the weld metal, so the upper limit is made 1.5%.

C also has the effect of lowering the transformation point, and 0.01% in terms of strength.
, Preferably 0.05% or more. Excessive addition leads to an increase in hot cracking susceptibility of the weld metal and a deterioration in toughness, so the upper limit is made 0.15%.

The above elements are elements that are effective in lowering the transformation point. In addition, the following elements are included as elements that increase the strength in a temperature range in which transformation occurs. In order to ensure high-temperature strength, either Mo or V is essential.

In order to obtain the effect of increasing the strength due to Cr, it is necessary to add 0.5% or more. If the addition amount is too large, the room temperature strength and hardness increase, the toughness deteriorates, and the weldability also decreases. Therefore, the upper limit is set to 3%.

Mo must be added in an amount of 0.2% or more from the viewpoint of strength. Because the effect of raising the transformation temperature is great, the upper limit is 2%
And

V also has the effect of increasing the strength when added at 0.1% or more. Since the addition of a pedestal deteriorates the toughness due to the increase in strength and hardness at room temperature and increases the transformation temperature, the upper limit is 0.5
%.

Nb also has the effect of increasing the strength when added at 0.01% or more. Excessive addition increases the room temperature strength and hardness and deteriorates toughness, so the upper limit is made 0.05%.

The components of the welding material used in the present invention are as described above, and the balance consists of Fe and unavoidable impurities.

Hereinafter, the specification of the component elements of the steel sheet in the present invention will be described.

As for C, an excessive addition leads to an increase in hot cracking susceptibility of the weld metal part and a deterioration in toughness, so the upper limit is made 0.2%.

 Si needs to be 0.35% or less due to the toughness of the steel sheet.

Mn also needs to be 0.60 to 1.20% for toughness at the same time.

The balance must be iron and unavoidable impurities. Further, if the welding heat input is excessive, the deformation increases, and the effect of controlling the transformation point of the welding wire cannot be sufficiently exerted. Therefore, the welding heat input needs to be 10 KJ / cm or less.

(Examples) Ten kinds of wires shown in Table 1 were prototyped. The wire diameter is 1.2mm. Table 1 also shows the Ar ₃ points (T) calculated by equation (1). As the steel sheet, a commercially available SM41B material shown in Table 2 was used. This steel sheet is
In order to produce a T-shaped fillet welded joint test specimen shown in the figure, welding was performed on both sides one pass at a time under the welding conditions shown in Table 3. Two types of welding conditions having different heat inputs were examined. After the welding was completed, the amount of angular deformation δ was measured, and then the longitudinal section of the weld metal was observed to determine the presence or absence of cracks in the weld metal. As a comprehensive evaluation, the value of the angular deformation δ calculated by the formula δ = 0.5 sin ⁻¹ (2d / w) using the values of w and d shown in FIG. 3 is less than 1.2 × 10 ⁻² radian and the crack Was passed when no occurrence was observed, and rejected otherwise. Table 4 shows the symbols, welding conditions and test results of the wires used. The wire symbols WS1 to WS5 are within the proper component range, and WD1 to WD2 and WS6 to WS8 are illustrated for comparison and are outside the proper component range. Test Nos. 1 to 5 have proper welding heat input, and Test No. 6 has excessive welding heat input.

Test numbers 1 and 2 are for Cr and Mo amounts, and 3 and 4 are for V and
The appropriate amount of Nb was examined and all passed. 5 has a relatively high value of T but less than 650, which is a pass. Even if the wire is in the proper component range, welding heat input 6 is excessive and the amount of angular deformation is large. When no element group for increasing the high-temperature strength is added, as shown in FIG.
Is 572, the amount of angular deformation is large, and cracks occur when Ni is excessively added as shown in FIG. Likewise
Cr in excess of 9, V and Nb in excess of 10 will cause cracking due to excessive hardening. Further, when the value of T exceeds 650 even if each component value is within the appropriate range, the deformation amount becomes large and the sample is rejected.

In this experiment, although the SM41B material was used, the effect of reducing the amount of angular deformation by the method of the present invention is not lost even if the type of the steel plate is changed because the base material dilution is small.

(Effect of the Invention) The present invention is a welding method in which welding deformation is small in automatic and semi-automatic welding processes without impairing various characteristics of a joint portion, and a work for correcting deformation can be omitted within an economically acceptable range. Becomes

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the transformation point temperature and the amount of angular deformation, FIG. 2 is a diagram schematically showing a T-shaped fillet welded joint, and FIG. 3 is a diagram for explaining the definition of the amount of angular deformation δ.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-158955 (JP, A) JP-A-61-71185 (JP, A) JP-A-4-22596 (JP, A) JP-B-45 27450 (JP, B1) JP-B 63-32558 (JP, B2)

Claims (2)

(57) [Claims] 1. A gas shielded arc welding of a steel sheet containing 0.2% or less of C; 0.35% or less of Si and 0.60 to 1.20% of Mn, with the balance being Fe and unavoidable impurities. %; Ni; 0.05-9.0%, Mn; 0.4-2.5%, Cu; 0.1-1.5%, C; 0.01-0.15%, and Mo; 0.2-2.0%, V; 0.1-0.5% Using a wire containing one or two kinds, the balance being Fe and unavoidable impurities, and a parameter T determined by the following formula based on the weight% of each element in the wire being less than 650, the welding heat input is 10 KJ / A gas-shielded arc welding method with less welding deformation characterized by being at most cm. T = 630.0-476.5C + 56.0Si-19.7Mn -16.3Cu-26.6Ni-4.9Cr + 38.1Mo + 124.8V + 136.3Ti-19.1Nb + 198.4Al + 3315.0B 2. The gas according to claim 1, wherein the wire further contains one or two types of Cr: 0.5 to 3.0% and Nb; 0.01 to 0.05% by weight. Shield arc welding method.