JPH0249832B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to AC MIG welding, and particularly to a high-efficiency welding method in which a weld metal with excellent low-temperature toughness can be obtained by adjusting the combination of shielding gas composition and welding material composition. Recently, multi-electrode submerged arc welding and DC high-current MIG welding have come into widespread use as high-efficiency welding methods for steel materials. However, with these conventional high-efficiency welding methods, it is difficult to obtain a microstructure because the cooling time of the weld metal increases with the increase in welding heat input, and it is difficult to ensure low-temperature toughness because the oxidation of the weld metal increases. It was impossible. As is well known, in ordinary Si-Mn weld metals, as the oxygen level decreases, the toughness improves up to 250 ppm, but when the oxygen level decreases even further, the structure deteriorates due to the lack of oxides that form the nucleus of the γ→α transformation. becomes coarse and has low toughness. On the other hand, Ti-containing weld metal has the possibility of maintaining its ability to generate acicular ferrite nucleation even in low-oxygen regions;
Even higher toughness can be expected in the low oxygen range of ~250ppm. However, in submerged welding, low-oxygen fluxes capable of high-efficiency welding have not generally been put to practical use to date. In addition, in DC high current MIG welding, a considerable amount of oxidizing gas (e.g.
10-30% _CO2 in Ar gas) was essential. Therefore, when using multi-electrode submerged arc welding or DC high-current MIG welding as a high-efficiency welding method, the oxygen content of the weld metal should be set to 50 to 250 ppm.
It was not possible to carry out actual welding. In order to solve the above-mentioned problem, the present inventors have developed a direct current
AC MIG with different arc characteristics from MIG welding
We focused on welding. In other words, when AC MIG welding is used as a high-efficiency welding method, it is possible to reduce the amount of oxidizing gas in the shielding gas without causing fusion defects, and by adjusting the shielding gas composition, the amount of oxygen in the weld metal can be reduced. We confirmed that it is possible to control the target value to any desired value within the range of approximately 50 to 250 ppm. As a result of various studies on the toughness of low-oxygen weld metal produced by AC MIG welding, we found that weld metal with significantly superior low-temperature toughness can be obtained by a welding method that limits the quantitative relationship between the shielding gas composition and the welding material components. This is what I discovered. That is, the gist of the present invention is that in a shielding gas atmosphere consisting mainly of inert gas and mixed with 0.5 to 20% carbon dioxide gas and/or 0.1 to 5% oxygen, the component parameter P shown in the following formula is but
0.7 to 1.9, and the deoxidizing agent is added to 1 part of the flux weight.
~50%, Fe-Ti and Fe-B alloying agents up to 50% of the flux weight, metal oxides for slag adjustment up to 90% of the flux weight, and at least Ti0.005 in terms of metal elements. ~0.15%, B0.0005~0.015
%, C0.01~0.3%, Si0.6% or less, Mn2.5% or less, welding current
High-toughness AC MIG characterized by welding at AC150-1500A and obtaining weld metal with vTrs −60℃ or less
Welding method. Here, P=log Ti%/4√%×10 ³ However, G% is the inert shielding gas (Ar, He
etc.) depending on the volume percentage of CO ₂ and/or O ₂ , where G% = (√ ₂ % + √4 ₂ %) ² ,
Ti (%) is the weight percentage of Ti in the welding wire. Next, the welding method of the present invention will be explained. The most distinctive feature of the present invention is to find a parameter that regulates the relationship between the oxidizing gas content in the shielding gas and the Ti content in the wire, and adjust the shielding gas so that the parameter is between 0.7 and 1.9. The purpose is to perform AC MIG welding by controlling the wire components. That is, in order to quantitatively understand the effects of the shielding gas composition and the amount of Ti in the wire on the low-temperature toughness of AC MIG weld metal, the inventors conducted an experimental study using the welding test strips shown in Table 1. The experimental results shown in Figure 2 were obtained.

[Table] Figure 1 shows the relationship between the amount of oxygen in the weld metal (ppm) and the amount of Ti in the wire (%), which is suitable for the toughness of the weld metal. ₂ or O ₂ content (%) and weld metal oxygen amount (ppm). From Figure 1, the region where the low-temperature toughness of the weld metal is particularly excellent (vTrs is -60°C or less) is expressed by the following equation (1). Diagram display marks and vTrs of weld metal
is as shown in the following table.

[Table] log7.5×10 ^-4 √0log Ti%log 9.5×10 ^-3
√0……(1) Relationship between 0ppm and CO ₂ % and 0ppm and O ₂ in Figure 2
From the relationship of %, 0ppm=55√ ₂ %...(2) 0ppm=110√ ₂ %...(3) Therefore, in the case of shielding gas where CO ₂ and O ₂ coexist, 0ppm=55√ ₂ %+110√ ₂ %...(4) Further transforming equation (4), 0ppm=55( _√2 %+ _√42 %)...(5) Here, "depending on the volume percentage of CO ₂ and/or O ₂ " G% in equation (6) is defined to uniformly express the amount of G% = (√ ₂ % + √4 ₂ %) ² ...(6) By the way, from equation (6), when the oxidizing gas in the shielding gas is only CO ₂ , G% = CO ₂ %, only O ₂ In this case, G%= _4O2 , and it can be interpreted that _O2 in the shielding gas in AC MIG welding of the present invention has an oxygen potential four times that of _CO2 . From equations (5) and (6), 0ppm=55√% ...(7) Next, from the relationship between equations (1) and (7), By transforming equation (8), the following equation (9) is obtained. 0.74log Ti%/4√%×10 ³ 1.85 …(9) Furthermore, rounding up the definition of equation (9), 0.7log Ti%/4√%×10 ³ 1.9 …(10) However, G%=√ ₂ % + √4 ₂ %) ² Therefore, if the variable log Ti%/4√%×10 ³ in equation (10) is P, then the shield mainly consists of an inert gas mixed with CO ₂ and/or O ₂ gas. The inventors have newly discovered a high toughness AC by using gas and Ti-containing wire and controlling the parameter P between 0.7 and 1.9.
There are characteristics of MIG welding method. In the present invention, we define high-toughness AC MIG welding as the case where vTrs of JIS No. 4 (2 mm V notch) shear peace test shows a toughness of -60°C or less, and based on the above-mentioned experimental results, The parameter P was limited to 0.7 to 1.9 based on the quantitative relationship between the amount of Ti in the welding material and the amount of oxygen in the weld metal. Also, from Figure 1, the amount of oxygen is less than 40 ppm and
If it exceeds 250ppm, vTrs will exceed -59℃ and high toughness cannot be obtained.
_CO2 % in shielding gas to 250ppm
was limited to 0.5% to 20%, and _O2 % was limited to 0.1% to 5%. Similarly, from Figure 1, the amount of oxygen that can obtain high toughness is 40
From the upper and lower limits of Ti amount corresponding to ~250ppm,
Ti was limited to 0.005-0.15%. Regarding B, when it coexists with Ti in the weld metal,
It is well known that B0 has the effect of improving toughness, and in the present invention, the effect of increasing toughness was observed in the range of B0.0005 to 0.015%, so these were set as the upper and lower limits, and B0. It was limited to 0.0005% to 0.015%. Furthermore, Ti and B in the welding material used in the present invention
Other chemical compositions will be explained. The reason why C is set at 0.01 to 0.3% is that if C exceeds 0.03%, even in extremely low C steel, the hardness of the weld metal will increase and the toughness will decrease. The lower limit was set at 0.01% because this is the practical limit when melting the wire material. Si is necessary as a deoxidizer for weld metal, but
If it exceeds 0.6%, the low temperature toughness decreases, so Si0.6%
Limited to the following. For the same reason as Si, Mn
Limited to 2.5% or less. Other alloying elements that are effective in further improving toughness when one or both are added to the wire components of the present invention include Mo at 0.6% or less and Ni at 5% or less. The reason why these substances are limited as described above is that adding them in excess causes an increase in strength and a decrease in toughness. In addition, the welding current in the present invention is AC 150A ~
Limited to 1500A. The reason is less than 150A and
This is because it is difficult to maintain a stable AC MIG arc at over 1500A. The present invention uses a flux-cored wire, which preferably has a cross-sectional area of 0.6 to 33 ^mm2 . If it is a round wire, the wire shape should be 0.9 to 6.4 mmφ. The cross-sectional shape of the wire may also be square, triangular, or oval. The reason why the wire cross-sectional area is set as above is that if the wire cross-sectional area is outside this range, the AC MIG arc will be unstable unless special measures are taken to the wire feed mechanism of the welding machine. In the case of flux-cored wire, alloying elements such as Ti can be added either from the outer steel plate (hoop material) or from the filling flux, and the above-mentioned composition is basically determined by the total content of the hoop material and the filling flux relative to the wire weight. Treated as amount (%). However, when the flux contains oxides such as TiO ₂ and B ₂ O ₃ , very small amounts of Ti and B are reduced and added to the weld metal, so this amount is used as the effective amount of Ti and B. It is added as in the embodiment described later. The filling flux is usually put in the form of powder, and its composition accounts for about 1 to 50% of the total weight of the wire, and its composition is such that deoxidizing agents such as Fe-Si and Fe-Mn account for the weight of the flux. Approximately 1 to 50%, and Fe-Ti, Fe-B, Ni, Fe-Mo, etc. as alloying agents are less than 50% of the flux weight, for slag adjustment.
Metal oxides such as CaO, CaF ₂ , SiO ₂ , Al ₂ O ₃ , TiO ₂ , MnO, etc. are added to approximately 90% or less of the flux weight, and for the purpose of arc stabilization, approximately 5% of the flux weight is added.
% or less, such as Na ₂ CO ₃ and K ₂ CO ₃ , and one or more of them can be appropriately combined to constitute a filling flux. In addition, for the purpose of adjusting the ingredients, iron powder is often mixed in at about 90% or less. The layered welding method of the present invention is not limited. Single-layer or multi-layer welding using a single electrode and multi-electrode welding using two or more electrodes are possible. Next, we will discuss the welding power source. As the AC MIG welding power source of the present invention, currently used AC power sources for submerged arc welding or manual welding can be used. When using flux-cored wire, there is no problem in welding with the pulse generator connected, but if a small amount of a compound of easily ionized elements such as sodium or potassium is added to the flux,
Does not require a pulse generator for restriking. Examples Table 2 shows welding conditions and results for inventive examples Nos. 1 to 3, and Table 3 shows welding conditions and results for conventional examples Nos. 4 to 6 for comparison. As is clear from Table 3, when low-temperature steels were welded by the conventional method, there was a drawback that the toughness of the weld metal decreased. However, in the example of the present invention, excellent results were obtained, unlike the conventional example. Methods 1, 2, and 3 of the present invention are conventional example 4,
Compared to No. 5 and No. 6, both the soundness of the weld and the toughness of the weld metal are good.

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[Front] Board

Claims (1)

[Claims] 1 In a shielding gas atmosphere consisting mainly of inert gas and mixed with 0.5 to 20% carbon dioxide gas and/or 0.1 to 5% oxygen, the component parameter P shown in the following formula is 0.7 to 0.7. 1.9, containing 1 to 50% of the weight of the flux as a deoxidizing agent, less than 50% of the weight of the flux as alloying agents of Fe-Ti and Fe-B, and less than 90% of the weight of the flux as a metal oxide for slag adjustment. and at least 0.005 to 0.15% Ti in terms of metallic elements,
B0.0005~0.015%, C0.01~0.3%, Si0.6% or less,
Using flux-cored steel wire containing Mn 2.5% or less, welding is performed with a welding current of AC150 to 1500A,
A high-toughness AC MIG welding method characterized by obtaining weld metal with vTrs −60℃ or less. Here, P=log Ti%/4√%×10 ³ However, G% is the inert shielding gas (Ar, He
etc.) depending on the volume percentage of CO ₂ and/or O ₂ , where G% = (√ ₂ % + √4 ₂ %) ² ,
Ti (%) is the weight percentage of Ti in the welding wire.