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Learn how to weld copper and stainless steel

1. Overview

Welding copper and stainless steel is a common process, but it can also present some challenges. One of the main difficulties in welding these two materials is the sensitivity to copper penetration cracks.

Welding copper and stainless steel

To avoid penetration cracks, two measures must be taken:

  • Choose an appropriate welding process and use a low level of welding energy.
  • Select suitable filler materials, control elements that tend to cause low melting point eutectics such as S, P and O, and add elements such as Al, Si, Mn, V, Mo, Ni and others to the weld.

By following these steps, the risk of penetration cracks can be minimized during the copper and stainless steel welding process.

2. Welding method

Manual arc welding

When using manual arc welding for copper and stainless steel, it is important to keep in mind that selecting an austenitic stainless steel electrode may increase the likelihood of thermal cracking.

For this reason, it is advisable to choose a nickel-copper electrode (70% nickel and 30% copper) or a nickel-based alloy electrode. An alternative is to use a copper welding rod (T237).

Related Reading: How to Choose the Right Welding Rod?

During the welding process, it is recommended to adopt a fast welding technique, with a small diameter and low current, without arc oscillation. The arc should also be angled towards the copper side to reduce the risk of penetration cracks.

Submerged Arc Welding

When using submerged arc welding for copper and stainless steel, the main concerns are cracking and porosity.

To minimize these problems, it is important to thoroughly clean the surfaces of welds and welding wires before welding.

For welds with a thickness of 8 to 10 mm, a 70° V-shaped groove is typically used. The groove angle on the copper side is 40° and the angle on the stainless steel side (1Cr18Ni9Ti) is 30°.

A flux of HJ431 or HJ430 (which is baked at 200°C for 2 hours) together with a copper solder wire is recommended. One to three nickel wires or nickel-copper alloy wires should be placed in the slot.

Additionally, higher levels of welding energy must be used and a cooling water-type copper pad must be employed. The welding wire should point toward the copper side and be 5 to 6 mm away from the center of the groove.

Process parameters of submerged arc welding of pure copper and stainless steel

Welding Joint form Thickness mm Welding wire diameter mm Welding current A Welding voltage
V 		welding speed mm/s Wire feed speed cm/min
T2+1Cr18Ni9 Butt V 10-10 4 600-650 36-38 6.4 232
12-12 4 650-680 38-42 6.0 227
14-14 4 680-720 40-42 5.6 223
16-16 4 720-780 42-44 5.0 217
18-18 5 780-820 44-45 4.5 213
20-20 5 820~850 45-46 4.3 210

Argon tungsten arc welding (TIG)

Good welding joints can be obtained when TIG welding is used on copper, its alloys and stainless steel. However, satisfactory results can only be obtained by mastering the appropriate processes. The joints produced are mainly butt and corner joints in a groove. There is no groove on the copper side, and it is better to open a half V-groove on the stainless steel side.

Before welding, the welding surface must be cleaned and flux (70% H 3 BO 3 21% Na 2 B 4 Ó 2 9% CaF 2 ) must be applied to the front and back. Then carry out welding after drying.

Try to use Monel alloy (70% Ni, 30% Cu) or copper alloy welding wire containing silicon and aluminum, such as HS221, QAI9-2, QAI9-4, QSi3-1, QSn4-3, etc. the tungsten arc should be tilted towards the copper side and kept at a distance of 5 to 8 mm from the center of the groove to control the amount of stainless steel that melts.

Most welding materials are copper welding wire, copper-nickel welding wire or aluminum-containing bronze welding wire, which improves the mechanical properties of the welding metal and prevents copper penetration cracks. Fast welding without oscillation is generally adopted. When the argon arc welding brazing process is used, the amount of fusion on the stainless steel side should be reduced as much as possible, making it equivalent to a brazing connection for stainless steel and a fusion welding connection for the copper side.

The process parameters for TIG welding between brass and stainless steel are shown in the attached figure.

TIG welding of H62Sn-1 brass and 1Cr18Ni9Ti stainless steel

Welding thickness mm Tungsten electrode diameter mm Tungsten Electrode Extension Length Nozzle diameter mm Welding current Argon flow L/min
3+3 3 5-6 12 100~120 10
3+6 3 5-6 12 140-180 10
3+18 3 5-6 12 150-200 1０

Gas welding

When gas welding is used for copper and stainless steel, the temperature of the gas welding flame is not as high as that of the arc. This can result in uneven melting of the base metals on both sides due to their different melting points, causing a wider heat-affected zone, increased deformation, and even non-melting.

For welding pure copper and 18-8 stainless steel, welding wires such as HSCuZn-2, HSCuZn3 and HSCuZnNi are typically selected. Neutral flame welding uses 301 welding powder (brazing powder) or borax.

If the weld is long, a layer of brass can be deposited on the groove surface on one side of the stainless steel before welding.

Brazing

When brazing copper and stainless steel, the main type of solder used is silver-based solder, such as HL302, HL309, HL312, etc.

It is important to note that the temperature on one side of the stainless steel should not be too high and the heat source should be directed to the copper side when heating.

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