KR20010057596A - a method for welding a duplex stainless steel - Google Patents

Abstract

PURPOSE: A method for welding a duplex stainless steel having an excellent welding performance is provided to improve the property of metals to weld without using any additional welding materials and carrying out any heat treatment after the welding. CONSTITUTION: In a method for welding a duplex stainless steel consisting of main components of Cr 20-30%, Ni 4-10%, Mo 1.5-5.0%, N 0.1-0.5%, and C 0.01-0.05%, and the rest of Fe and inevitable impurities, and having an excellent welding performance, a mixture gas of Ar or He gas as an inert gas and nitrogen gas 10-20% for increasing an austenite phase ratio is supplied for preventing oxidization of the surface and improving the welding performance of the stainless steel.

Description

Welding method of two-phase stainless steel with excellent weldability {a method for welding a duplex stainless steel}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding method of two-phase stainless steel, and more particularly to a welding method of two-phase stainless steel excellent in corrosion resistance used in chemical plant materials, line pipes, oil well tubes, and the like.

In general, two-phase stainless steel is a steel having a complex structure in which the ferrite phase and the austenite phase have a ratio of approximately 50:50, and are controlled in the chlorine ion environment and the carbon dioxide gas environment by controlling the amount of Cr, NI, Mo, and N. It shows excellent corrosion resistance and is known to be high strength compared to austenitic and ferritic stainless steels. When the two-phase stainless steel excellent in corrosion resistance and high strength properties is melt-welded, solidification is terminated in the delta ferrite single phase, and austenite phase of Wudmantaten structure is precipitated from grain boundaries and in the mouth during the subsequent cooling process. Since the welding heat cycle is rapidly heated and cooled, the austenite phase precipitation from the ferrite phase does not reach an equilibrium state, so that the ratio of the ferrite phase is higher than that of the base material. For this reason, there exists a problem which causes deterioration of mechanical property and corrosion resistance.

Due to these problems, in general, when a high Ni content welding material is supplied or a welding material is not used, the properties of the weld metal are improved by controlling the phase ratio of the ferrite phase and the austenite phase of the weld metal through heat treatment after welding. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object thereof is to improve the properties of a weld metal without using a welding material during welding of two-phase stainless steel and without performing heat treatment after welding.

In order to achieve the above object, the present invention includes Cr: 20 to 30%, Ni: 4 to 10%, Mo: 1.5 to 5.0%, N: 0.1 to 0.5%, and C: 0.01 to 0.05%, and the balance is In the welding method of two-phase stainless steel containing Fe and unavoidable impurities, two-phase excellent in anti-oxidation and weldability of the surface supplying a mixed gas containing 10-20% of nitrogen gas to Ar or He gas, which is an inert gas, as a protective gas. Provides welding method of stainless steel.

Hereinafter, the present invention will be described.

The present invention contains Cr: 20-30%, Ni: 4-10%, Mo: 1.5-5.0%, N: 0.1-0.5%, C: 0.01-0.05%, and the balance includes Fe and unavoidable impurities. When welding two-phase stainless steel containing, it is used as a protective gas supplied for the purpose of preventing oxidation of the surface and improving weldability, using a mixed gas containing 10-20% of nitrogen gas in Ar or He gas, which is an inert gas. It relates to a welding method of two-phase stainless steel.

The reason for supplying nitrogen gas as a protective gas during welding of two-phase stainless steel is that the nitrogen molecules in the protective gas are decomposed into nitrogen atoms and diffused into the molten metal by welding heat to increase the nitrogen concentration of the weld metal to increase the austenite phase ratio. Because it raises. This is because nitrogen is a strong austenite forming element. However, if more than 20% of nitrogen gas is supplied, there is a concern that porosity occurs in the weld metal to cultivate weld defects. On the contrary, if the amount of nitrogen gas is less than 10%, it does not contribute significantly to the improvement of the properties of the weld metal.

Hereinafter, embodiments of the present invention will be described.

(Example)

Plasma arc welding was performed on a two-phase stainless steel sheet having a thickness of 3 mm having a chemical component shown in Table 1 while supplying a mixed gas of argon gas and nitrogen gas as a protective gas. At this time, the nitrogen gas content was changed to 0-25%.

Table 2 shows the ferrite content and 180 degree bending test results of weld metal according to welding conditions and nitrogen gas content. When the nitrogen content was 0% and 5%, the ferrite content of the weld metal was 64% and 61%, respectively, which was significantly higher than that of the base metal, which was 53% of the base metal. Thus, cracking occurred in the bending test. However, when the nitrogen content was 10%, the ferrite content was 54%, which was almost the same as that of the base material, and the bending test showed good results. On the other hand, the ferrite content in the case of nitrogen content of 25% was almost the same as the base material, but the bending characteristics were poor because a large amount of pores in the weld metal.

C Si Mn Cr Mo Ni N 0.02 0.52 1.12 22.5 3.24 5.65 0.165

No Ar +% N2 ferrite(%) Bend Remarks One 0 64 Bad -Plasma arc welding welding current: 180A Connection degree: 0.9m / min 2 5 61 Bad 3 10 54 Great 4 25 50 Bad Base material 53

As described above, the present invention provides a welding method of two-phase stainless steel having excellent surface oxidation prevention and weldability improvement.

Claims (1)

2-phase stainless steel containing Cr: 20-30%, Ni: 4-10%, Mo: 1.5-5.0%, N: 0.1-0.5%, C: 0.01-0.05%, the balance being Fe and unavoidable impurities A welding method for steel, wherein the mixed gas containing 10 to 20% of nitrogen gas to Ar or He gas, which is an inert gas, is supplied as a protective gas.