Effect of ferrite ratio on mechanical properties in austenitic steels 1

[stanislasdz]

Hi everybody

I would like to know what is the effect of the ferite ratio on the mechanical properties in an austenitic stainless steel

Ex:

What is the difference on the mechanical properties between 2 austenitic stainless steels (304L) with :

1 % of ferrite et 5 % of ferrite

Thanks

 

[metengr]

Stan;
I personally have not seen specific data presented where ferrite content (volume fraction) is plotted to show the effects on mechanical properties at ambient service temperature. Intuitively, an increase in volume fraction of ferrite would increase the ultimate tensile and yield strength of an austenitic weld deposit.

Most are concerned with delta ferrite content during exposure to either elevated temperature service (where sigma can be formed) or during low temperature service where delta ferrite content becomes critical because of the reduction in notch toughness for the austenitic weld deposit.

As you know, a balance needs to be struck where one needs the presence of delta ferrite during solidification to avoid hot cracking, yet not have too much delta ferrite present because of corrosion concerns (lower corrosion resistance) and notch toughness (as I explained above).

 

[stanislasdz]

Thanks metenger

You are always SO HELPFUL !

 

[stanislasdz]

I am looking for the hadrness of the

ferrite & the austenite

Any values ?

 

[abassett]

Reduction or elimination of ferrite makes it easier to roll 304L into sheet, bar, etc. If you are making CF3 castings, you don’t have this restriction so you adjust your Ni / Cr ratio for a little ferrite for all the reasons mentioned above.

For reference, yield strength of CF8M is normally 35,000 to 45,000 psi. If the composition were adjusted to eliminate the ferrite, you get yield strengths as low as 20,000 psi. No data for 304L hardness, but you could collect it easily enough with a ferritescope and hardness tester.

 

[EdStainless]

SS mills usually aim for FN of 6-10, for better castabilty and hot rolling.
We autogenously weld 300 series grades and have to anneal the heck out of them to get rid of residual delta ferrite.

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