Thanks, I was a bit confused by the different allotropes. Interesting that the martensite transform naturally only happens on the surface (which as you say is a

Thanks, I was a bit confused by the different allotropes. Interesting that the martensite transform naturally only happens on the surface (which as you say is actually desirable) due to the rapid cooling it requires, I didn't know that. But of course it makes sense that quenching doesn't instantly cool the bulk of the workpiece.