Grain growth in Nickel Alloys 2

[tensilecvn]

Hi All
Can someone please offer some advice on the above. I am encountering issues with grain size after forging and heat treatment of nickel alloys, predominantly Alloy 925 and Alloy 718. I am achieving the required grain size at all locations apart from centre (flat bar and round), where I am obtaining bi modal grain sizes of 1 to 6 (opposed to a uniform 5/6 in other locations). I have considered the effect of forging, and possible tool wear, and am now wondering if re-heats between forging cycles may be having a detrimental effect, or indeed the initial pre-soak.

Can you please advise at which temepratures grian growth may occur in nickel alloys so I can maybe amend our forging procures to suit

Thanks in advance for you valuable assistance

 

[EdStainless]

Have you looked at samples from the billets prior to forge?
My hunch is that they are very coarse, and that you are putting very little work into the center.
These alloys should be well pinned against grain growth, that is why they work at high temps.
Perhaps you are too hot for too long at some point in the process.
There are lots of technical papers on 718 and grain size.

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P.E. Metallurgy, Plymouth Tube

 

[tensilecvn]

Thanks for your reply ED
I think the problem may come from the fact that all the forging was not carried out in one series of operations, and the material was allowed to cool completley before being re-started/heated hence the information on grain growth vs temp/time that I am looking for. The reduction ratio was well above 5:1 carried out from ingot to bar. Can you point me in the direction of these papers - I tried goolge scholar but was not successful

Thanks for your time

 

[metengr]

http://web.ornl.gov/info/reports/1958/3445603611955.pdf

 

[tensilecvn]

Thanks for the link metengr