True, inthe case of a pure Fe-C system. Quenching some low-alloy content stainless steels fast enough (granted, not possible with large billets) should keep the microstructure intact, but it will put the FCC austenite into a "metastable" situation, but transitions of less then
50% to martensite over long periods of time are typical. As you mention below, in high-Ni or certain Ni-Cr ratios, austenite is stable to room temperature, demonstrating the effect of austenite stabilization.You are quite right, I tied my thoughts up in a knot here and called them non-related when they were. Alloying and impurity control are critical to most material systems. Materials and thermo 201 there...don't know what happened in the gray matter.
I'm not sure this disagrees with my above paragraph, as martensite is not truly aviodable in a pure Fe-C system, but in Fe-Ni-Cr-C systems it is. But I think we say that depending on the alloying, and cooling rate, we can get either martensite or austenite. Some restrictions may apply. :-)
This one still has me thinking...can all austenitic stainless steels even be hardened by heat treatment? If the microstructure can not be changed appreciably, and we can not achieve grain refinement, what will the hardening mechanism be?
I believe I straightened myself out, now.