Hadfield's manganese steel (prison bars application)

12-13% Mn steel that work-hardens during machining, making it nearly impossible to saw or file. Used historically for prison bars. Distinct alloy class from the 200-series stainless steels Tom is discussing. ## Figures and recurring statistics

201 and 202 add manganese and nitrogen, and lower the nickel, to get higher strength — 80 to 100 KSI, and it's cheaper. Manganese instead of chrome. Manganese is a lot cheaper than chrome. I don't actually see these that often. If you go really high manganese — like 12 to 13% — you get what they call Hadfield's manganese steel, which is not officially a stainless steel, but it's an alloy that work-hardens so rapidly that you literally cannot cut it with a saw. It's easily formable in its annealed condition, but you go to saw it and as you're cutting, those chips harden — about triples its strength — and it will dull saw blades. One of the uses of Hadfield's manganese steel was prison bars. You got a file? Yeah, you want to dull your file. Try to file through Hadfield's manganese steel, because it transforms as you're work-hardening it to this hard martensitic steel.

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