strengthening austenitic stainless steel

[gieter]

We have made some castings in CF-8A. The tensile tests failed. Instead of a Rm of min. 530MPa we have typically 470MPa. Yield strength is typically 225MPa for 240MPA required. Elongation is 50% for 35% required. Typical analysis: C=0.026%, Mn=1.23%, Si=0.74%, P=0.02%, S=0.005%, Cr=18.4%, Ni=9.4%, Mo=0.41%, N=0.04%.

I know there is no phase transition at normal heat treatment temperatures for austenitic stainless steel so strengthening in the sense of low-alloyed steels is not possible. Is there any other way to achieve higher strength without seriously compromising corrosion resistance (especially inter granular corrosion)?

Thanks for any help,

Mik

 

[arunmrao]

Geiter,I am surprised that with such a good chemistry the test bar has failed. I still suspect the test bar if it contaned some porosity or machining marks.

Can you cold work the test bar once and then test. TS will improve. What kind of castings are these? If it is not a pressure part you may seek a concession from the buyer for this variance.

Pl keep us informed the progress.

GoodLuck!!

 

[EdStainless]

Agreed, the chemistry looks nice. With the high elongation I doubt that there were any problems with the test bar.
Have these been annealed?
What is the residual ferrite content?
So the mechanical properties for the cast grades are not the same as for the wrought grades? Which spec are these beeing made to?

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[gieter]

Calculated ferrite number according to Shoefer is between 5.4 and 8.7, which is quite low. If it was between 10 and 15 we probably wouldn't have had the problems. The real ferrite content wasn't measured as of yet.

The spec is ASME II, SA 351 CF8A. The castings are flange bodies for flow meters and range from 3 to 15 kg.

The castings have had a solution treatment at 1080°C followed by a water quench.

We have thought about cold working, but we see it as sheating.

What about aging?