Can a Stainless wire(er309L) be used to weld mild steel plates?

Yes, it is possible to use a Stainless steel wire (ER309L) to weld mild steel plates as ER309L or E309L is having good weldability with mild steel, carbon steel and low alloy steel. However, it is important to note that ER309L is a type of stainless steel filler wire that is mainly used for welding dissimilar metals or for welding austenitic steels to mild steels.

It is not the best choice for welding mild steel plates only because:

High cost of ER309L compared to carbon steel rods (E.g., E7018, E6013).

Discoloration of welds.
High hardness and strength of weld compared to mild steel.
Difference in thermal coefficient of weld and mild steel materials.

Different thermal expansion between weld and base metal.

Best welding rod for Mild Steel Welding

The best welding rod for welding mild steel are:

E6010

E6013
E7015
E7016

E8018
ER70S-2
ER70S-6

E71T1C

The above welding electrodes and wires provided matching properties for mild steel in terms of strength, color match, chemical compositions and physical properties.

Welding Dissimilar Metals: ER309L as a Filler Metal

ER309L is a stainless steel welding wire commonly used for joining stainless steel to carbon steel or low alloy steel. It is an austenitic stainless steel filler metal with a nominal composition of 24% chromium and 13% nickel. The high alloy content of ER309L provides enhanced resistance to corrosion and oxidation, making it suitable for many applications.

Using ER309L as a filler metal for welding mild steel plates has some advantages:

Improved corrosion resistance: The higher chromium and nickel content in ER309L filler metal offers better corrosion resistance than a standard carbon steel filler metal.
Reduced susceptibility to weld cracking: The ER309L wire reduces the chances of solidification cracking and hydrogen-induced cracking due to its relatively low carbon content and austenitic structure.

Factors to Consider When Welding with ER309L

While ER309L has some advantages, there are also factors to consider when using this filler metal to weld mild steel plates:

Dilution: The mixing of base metals with the filler metal during welding can affect the final weld metal composition, potentially reducing its corrosion resistance and mechanical properties. To minimize dilution, use proper welding techniques and parameters.
Galvanic corrosion: When two dissimilar metals are joined, the less noble metal (in this case, mild steel) can corrode preferentially in the presence of an electrolyte, causing galvanic corrosion. To mitigate this risk, apply protective coatings or isolate the dissimilar metals from the electrolyte.

Cost: ER309L stainless steel wire is generally more expensive than mild steel filler metals. Consider the cost implications when deciding whether to use ER309L for your mild steel welding project.

Precautions and Best Practices

To achieve successful welds with ER309L stainless wire on mild steel plates, consider the following precautions and best practices:

Joint design: Ensure proper joint preparation and fit-up to minimize the risk of weld defects and ensure adequate penetration.

Preheat and interpass temperature: Control preheat and interpass temperatures to reduce the risk of hydrogen-induced cracking and other weld defects.
Welding technique: Use appropriate welding techniques and parameters, such as the correct welding current, voltage, and travel speed, to minimize dilution and ensure a sound weld.
Post-weld heat treatment: In some cases, post-weld heat treatment may be necessary to relieve residual stresses and improve the mechanical properties of the weld joint.