Tool steel for punches

I have slowly started experimenting with punches for matrices and with hardening tool steel; this is in addition to regularly using tool steel with my milling machine. I have come across a very machinable tool steel called O6 (trade name Graph-Mo). O6 is not common and much more expensive than O1, why use the stuff? Its machinability is about 125% compared to other high carbon tool steels. When I attempt a punch, it is noticeably easier to use than O1. Here are the main alloys:

C=1.45    Mn=1.0     Si=0.90   Mo=0.25

Of course, it is the carbon content that stands out; it is a tool steel that has excess carbon in the grain boundaries. This makes it exceptionally machinable and for hardening, the original supplier Latrobe Steel states “Graph-Mo tool steel can be hardened to over Rockwell 60 C from a relatively low hardening temperature, which minimizes size change and distortion during heat treatment”. It is worth trying out.


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