JPS5841678A - Gas shielded arc welding method for dead soft steel - Google Patents

Abstract

PURPOSE:To prevent the generation of high temp. cracking in the state of gas shielded arc welding of dead soft steel by using a composite wire contg. a specific content of C. CONSTITUTION:In the case of subjecting steel contg. 0.005-0.06wt% C to gas shielded arc welding, at least the 1st layer thereof is welded by using a composite wire contg. 0.1-0.34wt% C. The content of C in the composite wire is determined by the iron powder, disoxidizing agent, alloying materials, graphite, carbonate, etc. of the sheath material and packed flux of the wire. Good results are obtained if the content of C in the wire is controlled beforehand according to specifications.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas-shielded arc welding method for ultra-low carbon steel.

In recent years, steel materials, including line pipe materials, have been developed with low C to improve weldability or reduce costs as well as advances in controlled rolling.
There is a trend toward It has been generally thought that the hot cracking susceptibility of these low C steel weld metals is low.

However, according to the studies of the present inventors, in the welding of steel, it has generally been considered desirable to reduce the carbon content of the weld metal in order to prevent hot cracking of the weld metal that occurs during welding. When ultra-low carbon steel, such as one with a carbon content of 0.06% or less, is gas-shielded arc welded using existing welding materials, even if the carbon content of the weld metal is sufficiently low, It was found that hot cracking is likely to occur regardless of the situation.

That is, the present invention can prevent hot cracking of weld metal of ultra-low carbon steel.
He has discovered that there is an appropriate weld metal carbon content and provides a gas-shielded arc welding method for ultra-low carbon steel to obtain this appropriate range.

Therefore, the gist of the present invention is CO,005-0,'06% by weight
When gas-shielded arc welding steel containing 0
．． A composite wire having a C content of 1-0.34% by weight is used to weld the first layer of the composite wire.

Fukaiji Temple will be explained in detail below.

In order to improve the hot cracking and cold cracking susceptibility and toughness of the weld metal, it is conventional wisdom that the C content of the weld metal should be set to a value similar to or lower than that of the base metal.
It was believed that hot cracking would not occur if the amount of C was less than 1%, and it was believed that this idea would hold true even if the amount of C was less than 1%.

However, according to the studies conducted by the present inventors, it was found that the hot cracking susceptibility of the weld metal obtained by gas-shielded arc welding of ultra-low C steel using a conventionally commonly used composite wire was rather increased, and Figure 1 was obtained. .

In other words, Figure 1 shows the amount of C in the weld metal ((6) and the X-ray cracking rate @)
Although hot cracking in the area AK where C is over 0.15% has been experienced in the past, it has become clear that hot cracking has occurred in area B where C is less than 0.07%, confirming the stable cracking area Z. . That is, it has become clear that the high-temperature cracking susceptibility of weld metal is different from the conventional wisdom, and that below the limit C, the susceptibility to cracking increases on the contrary. The reason for this is thought to be that in the low C region, the dendrite abutting portion undergoes δ solidification, and in order to reduce cracking, it is necessary to increase the amount of C, which is a γ stabilizing element.

Therefore, the target steel of the present invention is ultra-low carbon steel, such as general structural steel and low-alloy steel for low temperature use, which contains C0.06% by weight or less, and contains C0.005% or more, which is considered to have the strength of steel. For example, stainless steel and the like containing gamma former elements such as , Ni, etc. are excluded.

Although the dilution rate of the welding base metal changes depending on the welding conditions, it has been confirmed that it is in the range of 20-45% in the gas shielded arc welding method. We learned that the quantity is given by the following formula.

0.07 (CWM-βCp+(1-β)αcw<
0.15-=-(]) CwM: Weld metal C amount CP: @ Material C amount Cw: Wire C amount β: Steel dilution rate α: C yield rate The inventors conducted research based on the above knowledge. As a result, when gas-shielded arc welding is performed using a composite wire with a C content adjusted to 0.1-0.3'4% by weight according to a conventional method, a weld metal that satisfies the above formula (1) is used. The scales were established.

The amount of C in the composite wire is determined by the wire sheathing material, iron powder in the filling flux, deoxidizing agent, alloying agent, graphite, carbonate, etc., but it is preferable to adjust the amount of C in the wire according to predetermined specifications. The welding conditions of the method of the present invention are not particularly limited, but in multi-layer welding, it is preferable to perform the first layer in particular by the method of the present invention.

Example Three types of steel plates shown in Table 1 were used.

Welding conditions Groove shape: See Figure 2 θ; 60°l l; 300m
m.

jl: 15mm+ j2: 20mm wire diameter
= 1,6 to φ Current: 450A Voltage: 33V Speed: 45 crrL/min Gas: CO□ 251/min 5- After welding, the presence or absence of cracks was confirmed by an X-ray transmission test.

Table 2 shows 0.06% C steel, Table 3 shows 0.03% C steel, and Table 4 shows 0.005% C steel.

6- No X-ray cracking rate was observed in any of the samples within the scope of the present invention.

[Brief explanation of drawings]

FIG. 1 is a graph of the C content (%) in the weld metal and the X-ray cracking rate (%), and FIG. 2 is an explanatory diagram of the groove shape.

Claims (1)

[Claims] When gas-shielded arc welding steel containing 0.005-0.06% by weight of C, at least the first layer thereof is welded using a composite wire containing 0.1-0.34% by weight of C. A gas-shielded arc welding method for ultra-low carbon steel.