Please do not google your welding questions, Aabco Welding Services have a free advice hotline! Email or call us and we will help you free of charge.

Often as in this case you will get wrong or misleading information that could cost your business thousands. 

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google search result can i mig weld stainless steel

So, lets answer this question and explain why google is wrong in this instance.

"Can I weld stainless steel with a mig welder?"

Yes you can use MIG, the key is to use a low hydrogen process, thus you could also use;

 TIG, MMA and SAW.

More information would be required to advise which of the above is the best for a particular application; material thickness, joint type, weld acceptance standard, one-off or large batch are a few of the variables to be considered to select the right weld process for a given application.

Ensure that the flux/flux coated consumables you use are stored and dried according to the manufacturer's instructions to maintain the low hydrogen content.

Let's expand on the welding of stainless steels.

The welding of stainless steel is relatively simple, though there are common weld defects specific to the type of stainless steel to be welded of which all are avoidable. Using the Fe-cr equilibrium and Schaeffler/DeLong diagrams we can predict the likely outcome phase structures, allowing us to take preventative action to avoid defects and obtain the desired mechanical properties.

To be classed as stainless steel it must have above 10% chromium, there are 4 main types of stainless steels;

  • Austenitic
  • Ferritic
  • Martensitic
  • Duplex

 

Austenitic:

Weldability issues: Solidification cracking, distortion

Preventative measure: use a filler wire with more ferrite than the parent metal, use the Schaeffler diagram to select the correct filler wire composition. Example, weld type 304 parent material with type 308 filler wire.

Ferrite reduces the risk of solidification cracking by dissolving impurities in the weld. These impurities if left to exist in the weld can lead to crack propagation upon cooling, resulting in solidification cracking.

Low thermal conductivity and high thermal expansion properties of this material create a recipe for high distortion, distortion control techniques should be considered such as; weld sequencing, heat sinks and use of a welding fixture.

Ferritic:

Weldability issues: Poor HAZ toughness due to large grain growth in the HAZ, may lead to cracking in the HAZ on thicker material (no grain refinement with this material so the grains will only grow and grow).

Preventative measure: firstly use a low heat input welding technique to reduce the heat input, in turn reducing the width of the HAZ. An austenitic filler wire will help to provide a tough weld metal even with a low heat input weld.

Reduce the HAZ cooling rate, pre-heat (50-250 depending on the material composition)

Reduce residual stress, main the weld above the ductile to brittle transition temperature. Reduce joint restraint when welding.

Martensitic:

Weldability issues: cracking in the HAZ, caused by High HAZ hardness and hydrogen absorption. The greater the carbon content the greater the risk of hydrogen cracking.

Preventative measure: use a very low hydrogen process such as MIG or TIG.

If the material is above 3mm thickness, utilise pre-heat, inter-pass temperature and post weld heat treat to diffuse the hydrogen. Temperatures depend on the material thickness and carbon content.

Duplex:

Weldability issues: Loss of toughness and corrosion resistance in the weld and HAZ, caused by imbalance of austenite and ferrite.

Preventative actions: careful control of and adherence to heat input and inter-pass temperatures. Too little heat input and there will be excess ferrite, too much heat input and there will be excess austenite. Both can cause loss of toughness and corrosion resistance.

Use a filler wire with a high nickel content to promote formation of austenite, avoiding excess ferrite formation.

 

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