It might be 52100,but it might not be.Thats the bad part of working with unknown steels.Bring it up to critical and quench in a thin oil.If you dont have real heat treating oils then a veggy will work.Pre-heat the oil to around 100 F .Temper in your oven at 375f to 400f for an hour.Let it cool and check the edge for brittleness.If its chippy ,put it back in for another hour at 400f.Continue this untill you get what you want for an edge.