Most likely a 300 or 400 series steel and not hardenable. I will tell you from personal experience forging any stainless is a bit tougher than forging carbon steel. I've never forged stainless knife steels, but I have forged low carbon stainless and it's a bear to forge and you have a smaller forging window. Get some 1084, or 5160, or even car springs and with a little work and a half way decent heat treat will make a decent knife. There is no point to forging stainless steel. I remember reading where David Boye was forging 440C to shape in the 60's or 70's as there was no flat stock available at the time. He sent some off for micrographs and discovered there was no grain refinement from forging so just started turning round stock into flat stock. That was a long time ago, you want a stainless knife, the easiest way is to grind it out of flat stock.
