Welding technology operations of copper and stainless steel
I. Overview
Welding of copper and stainless steel is often encountered, and the welding is difficult. The main manifestations are: they are very sensitive to penetration cracks of copper during welding. In order to prevent penetration cracks from occurring, we must first choose a reasonable process and choose a small welding line energy. ; The second step is to select appropriate filling materials, control elements that are prone to produce low-melting eutectics, such as: S, P, O, etc., and add elements such as Al, Si, Mn, V, Mo, Ni, etc. to the weld.
2. Welding method
1. Manual arc welding
When manual arc welding of copper and stainless steel, be aware that if you choose austenitic stainless steel welding rods, it will easily cause thermal cracks; it is best to choose nickel-copper welding rods (70% nickel + 30% copper), or nickel-based alloy welding rods, and copper welding rods ( T237); When welding, use a small diameter, low current, fast welding without swing welding process, and make the arc deflect to the copper side to avoid penetration cracks.
2. Submerged arc welding
The main problems when using submerged arc welding between copper and stainless steel are cracks and pores; before welding, the surface of the weldment and the welding wire must be strictly cleaned. Weldments with a thickness of 8 to 10 mm generally have a 70° V-shaped groove, and the pure copper side has a 70° V-shaped groove. The breaking angle is 40°, the groove angle on the stainless steel (1Cr18Ni9Ti) side is 30°, the flux is HJ431 or HJ430 (baked at 200°C for 2 hours), the welding wire is generally copper wire, and 1 to 3 nickel wires or wires are placed in the groove. Nickel-copper alloy wire; select a larger welding line energy, and use a cooling water-type copper pad. The welding wire points to the copper side and is 5 to 6 mm away from the center of the groove.
3. Tungsten arc welding (TIG)
When copper and its alloys are welded with stainless steel using tungsten arc welding, good welding joints can be obtained, but proper techniques must be mastered to obtain satisfactory results; the basic forms of welding joints include butt joints and corner joints. There is no bevel on the copper side, and it is best to have a half V bevel on the stainless steel side. Before welding, clean the surface of the weldment, apply flux (70% H3BO3, 21% Na2B4O2, 9% CaF2) on the front and back, dry it and then weld. Try to use Monel alloy (70% Ni, 30% Cu) as the welding wire, or Copper alloy welding wire containing silicon and aluminum, such as: HS221, QAl9-2, QAl9-4, QSi3-1, QSn4-3, etc.; during TIG welding, the tungsten arc is biased toward the copper side, and the distance from the center of the groove is about 5 to 8 mm. Control the melting amount of stainless steel; most of the welding materials are copper welding wire or copper-nickel welding wire, or bronze welding wire containing aluminum. This is to improve the mechanical properties of the weld metal and prevent copper penetration cracks; usually fast welding is used without Swinging technique; when using the argon arc welding-brazing process, try to reduce the amount of melting on the stainless steel side, which is equivalent to a brazing connection for the stainless steel, and a fusion welding connection for the copper side.
4. Gas welding
When copper and stainless steel are welded by gas, since the gas welding flame temperature is not as high as the arc temperature, the base metals on both sides may melt unevenly due to different melting points, the heat-affected zone may become wider, deformation may increase, or even fusion may not occur; during welding, When pure copper and 18-8 stainless steel are used, HSCuZn-2, HSCuZn3, HSCuZnNi and other welding wires are usually used, and 301 welding powder (copper powder) or borax is used for welding with a neutral flame; if the weld is long, the stainless steel can be welded before welding A layer of brass is surfacing on one side of the groove surface and then welded.
5. Brazing
When brazing copper and stainless steel, the solder used is mainly silver-based solder, such as HL302, HL309, HL312, etc. The process method is similar to that of general brazing. It should be noted that the temperature on the stainless steel side should not be too high, and the heat source during heating Toward the copper side.
