What do you see happening in additive manufacturing of metallic components, and what impact do you think that will have on traditional heat treating in the next five years?
I'd like to just follow up on this with some supporting evidence. Again, specifically for 17-4, some literature [1-2] has speculated that the extremely fine grain sizes produced in an AM process like laser powder bed fusion alter the kinetics of austenite-to-martensite phase transition during the quenching stage of the solutionizing process for this alloy. I've seen Takaki et al. referenced to explain this . It's certainly true that lots of authors (pick a paper w/ phase analysis of LPBF 17-4) have observed more retained austenite than expected in LPBF processed 17-4, even after a standard solutionizing and aging heat treatment.
My colleague, Ben Sutton gave a webinar for ASM last week on the application of CALPHAD based simulation tools to stainless steels and Ben included an example related to Additive Manufacturing of 17-4 PH Stainless Steel. The focus was more on the nitrogen effects of 17-4, but included a property model graph that showed predicted lath Ms temp as a heat map with grain size on y-axis and nitrogen concentration on x-axis (attached).
He said, in his judgement the problem is 3 fold.
1) residual segregation after the solution treatment can suppress Ms;
2) small prior austenite grains can suppress Ms;
3) elevated nitrogen concentrations (from N2 atomization or uptake from processing gas) can drastically reduce Ms
It doesn't look like ASM have the on-demand recording of the webinar available yet but I believe it will be accessible from here:
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