Fully Austenitic Structure 304L

[Eburonia]

Hello

I wonder if the austenitic structure of a 304L material says something about the corrosion resistance.
For example in a document I have there is stated that the 304L may have a maximum ferrite content of 2%.
If this will be more than 2% it will automatically decreases the austenite level I guess.

thanks in advance

 

Ferrite can appear at very low fractions in the form of isolated stringers. It is sensitive to composition within the allowable Cr and Ni ranges (remember steelmakers are not overly generous with those). It is normally not detrimental, but it can degrade toughness at very low temperatures and corrosion resistance in some environments. Magnetic permeability is also affected, since the ferrite phase is ferromagnetic. A ferrite scope (I recommend Fischer) is the quick and dirty way to detect ferrite phase if you have concerns.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

Residual delta ferrite in austenitic stainless will lower corrosion resistance in low pH (acidic) environments.
In some applications it also poses issues with galvanic corrosion leading to pitting.
In general you only see these when the actual ferrite content is >5%.

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P.E. Metallurgy, Plymouth Tube

 

[Dhurjati Sen]

Dear Eburonia,

Ferrite is a real bother in austenitic SS welding. So ferrite content of the welds are measured and electrodes and wires with specified ferrite numbers are used.

Regards.

DHURJATI SEN

 

[EdStainless]

You need some delta ferrite to form when welding.
It helps with resisting hot cracking of the welds.
This is why weld filler often have a higher calculated FN than the base metal.

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

The effects of residual ferrite is pretty controversial. It may be necessary to prevent corner cracking in continuously cast austenitic SS and hot cracking of austenitic welds, it may also increase SCC resistance, any residual ferrite in finished product is generally considered detrimental in austenitic SS. biggest issues are, 1. reduce hot workability, 2. undesirable magnetics, 3. degrade pitting performance.

Good thing is it can be minimized/eliminated by, sufficient soak time before hot roll; or solution anneal.