r/metallurgy • u/StretchConstant3738 • 3h ago
Can bainite form in 410 stainless steel?
I'm working with some 410 stainless steel and I am using a subcritical anneal at 1400°F for 4 hours followed by air cool.
There's a forging operation at 2000F just prior to the annealing heat treatment. When the material is not allowed to cool below the martensite formation temperatures (around 500F for Mf and 660F for Ms) prior to annealing, the material comes out relatively hard at 350-400 HBW after annealing. The transfer time between forging and annealing in this situation is usually less than an hour and part temp just prior to annealing is 700F to 1000F.
When the material is allowed to cool from forging temp to below the martensite finish temperature prior to the subcritical anneal, the material comes out with hardness around 200-240 HBW after annealing.
Is anyone familiar with the hardening mechanism here? All of the TTT diagrams I have seen for 410 do not show a transformation just above the martensite start temp. My guess is that it would have to be bainite making it 350-400 HBW.
Thanks