C95800 - elongation

[bruv]

We have a couple of heats of ASTM B148 C95800 with poor elongation (12-13% against a 15% minimum). Both have been heat treated at 675C and air cooled.

Chemistries are:

Heat 1) 1.3% Mn, 4.9% Ni, 4.35% Fe, 9.4% Al.
Heat 2) 1.15% Mn, 4.9% Ni, 4.1% Fe, 9.1% Al.

Residuals (Si, Cr etc) are all <0.01%. The tensile strengths are nicely above minimum spec.

Does anybody know of a heat treatment that we can use to improve the elongation?

Thanks

 

[metengr]

bruv:
What size are the castings? It may be that the first anneal treatment was inadequate, especially when you report that the UTS values are "nicely above" the minimum if 85 Ksi. Also, check the tensile report for any errors, I have seen this before.

Per ASM Handbook, Volume 2 (on-line), the typical annealing temperature range for C95800 is 650 to 705 deg C. I would attempt a second anneal and see if this drops the UTS and increases your elongation.

 

[bruv]

Thickest section on any of the castings is 4".

I have re-checked the HT traces - times and temperatures were fine. We HT at 675C for 6hrs.

Yields were in the region of 310MPa (45ksi) and UTS for both was around 680MPa (98ksi). I have looked back in our records and these are fairly typical values.

I have already tried the re-anneal for the same time/temp combination, and then pulled the test bar myself. There was no difference in the before and after results.

 

[metengr]

bruv;
Last item, did you verify chemical composition of the castings with your own analysis? If not, I would verify.

 

[EdStainless]

The only other thing that comes to mind is to look at the grain size of the test bars. Is it very large?
Aren't your typical elongations about 20%?
Are you sure that the bars are machined properly, not too rough?

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Plymouth Tube

 

[bruv]

That's our own analysis - matches that supplied by the ingot manufacturer.

Test bars were machined as smooth as we could get them. We haven't looked at grain size. Typically, elongations are around 20%.

We don't think we've done anything different this time, which is why the lack of elongation is puzzling us.