Welding Stainless Steel to Non-Stainless Metals: Flux Core MIG Wire Options and Considerations

When welding stainless steel to non-stainless metals, the choice of welding process and wire type is crucial. This article explores the feasibility of using flux core MIG wires for this purpose and provides guidance on best practices and considerations.

Types of Welding Processes and Recommended Filler Metals

A MIG or GMAW (Gas Metal Arc Welding) process typically utilizes a solid wire by default, making flux core MIG wires less common. However, there are specific situations where flux core MIG wires might be used, especially when dealing with high-cost materials and specific alloy combinations. For welding stainless steel to non-stainless metals, solid wire is generally recommended. Here are some specific recommendations:

Welding Stainless Steel to Carbon Steel

To weld stainless steel to carbon steel, the AWS ER309L or ER309L-Si filler metal is recommended with a GMAW process. These alloys provide a solid weld with minimal dilution issues. In certain cases, when welding stainless steel to nickel alloys, a complementary nickel alloy (e.g., Inconel W) should also be evaluated and tested for performance. This step is vital to avoid undesirable precipitates due to alloy dilution.

Welding Stainless Steel to Ferritic Alloys

For joining 400 series ferritic stainless steels to more common 300 series austenitic stainless steels, ER309L is again an excellent choice. This filler metal is versatile and suitable for various applications in stainless steel welding.

Welding Copper Alloys to Stainless Steel

When welding copper alloys like bronze to stainless steel, the preferred method is Silver brazing. This process ensures a strong, reliable bond without the potential issues associated with fusion welding processes.

Low-Cost Alternatives: Flux Core MIG Wires

While flux core MIG wires are more expensive per pound, flux core stainless steel wires can be used for welding stainless steel to non-stainless metals. However, the choice of flux core MIG wire should be made with caution. High-quality flux core wires designed specifically for stainless steel welding are available, though they come at a higher cost.

Project Example

A personal project involved welding stainless steel pieces together to create a trailer bed, then attaching the bed to a carbon steel trailer frame. The project used stainless steel electrodes and an old AC arc welder, resulting in a successful outcome. This example demonstrates the viability of using stainless steel filler metals in a practical application.

Code Compliance and Documentation Requirements

When welding stainless steel to non-stainless metals, especially in structural or pressure equipment applications, adherence to relevant codes and standards is essential. These codes include:

AWS D1.1 for fusion welding processes ASME VIII for pressure vessel applications AS1554 Part 6 for structural steel welding AS3992.2017 for pressure equipment

For these applications, a documented weld procedure must be tested and approved in accordance with the appropriate code. The specific alloys and grades of stainless steel and ferritic material to be welded must be clearly specified.

General Guidelines

Without specific information about the stainless steel and ferritic material grades, a general recommendation would be to use ER309L filler metal, which is a versatile alloy suitable for a wide range of applications in stainless steel welding. Major manufacturers of welding consumables often provide detailed charts and guidelines for specific weld transition requirements.

Conclusion

The choice of welding process and filler metal is critical when welding stainless steel to non-stainless metals. Solid wire welding with recognized filler metals like ER309L is the recommended approach for most applications. Flux core MIG wires are available but come at a higher cost. Regardless of the method chosen, adherence to relevant codes and standards is essential for safe and reliable welds.