To go back to structure and how it relates to impurities:
A.) Microstructure ideally is driven thermodynamically, but in practice mostly a kinetic problem (since this is mostly a diffusion and transport problem), which obviously will change microstructure even if composition is the same. Obviously, for this the entire tempering history from the melt on is important.
B.) I was not necessarily thinking of *identical* composition, but about steels that look similar on paper but were small additions or lack there of, including impurites, have a large effect on the microstructure. Nitrogen has been notorious in that regard, it is apparently very difficult to keep the Nitrogen in the steel matrix.
C.) Obviously, a PM steel will have a different microstructure than an ingot steel, even if the composition is identical.
A.) Microstructure ideally is driven thermodynamically, but in practice mostly a kinetic problem (since this is mostly a diffusion and transport problem), which obviously will change microstructure even if composition is the same. Obviously, for this the entire tempering history from the melt on is important.
B.) I was not necessarily thinking of *identical* composition, but about steels that look similar on paper but were small additions or lack there of, including impurites, have a large effect on the microstructure. Nitrogen has been notorious in that regard, it is apparently very difficult to keep the Nitrogen in the steel matrix.
C.) Obviously, a PM steel will have a different microstructure than an ingot steel, even if the composition is identical.