Metallurgical and Ballistic Investigation of a 3 1/2% Nickel Modified Hadfield Manganese Steel Proposed for Use in the M1 Helmet.
WATERTOWN ARSENAL LABS MA
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Helmets fabricated from an experimental heat of a 312 nickel manganese steel are ballistically comparable to regular production helmets. In the annealed flat sheet form, the nickel modified steel is approximately 8 inferior to normal manganese steel in ballistic properties when tested with caliber .45 ball ammunition. Hardness surveys show that nickel manganese steel helmets are from 3-6 points Rockwell C softer than managanese steel helmets in indentical areas, and consequently have lower residual stresses. Bend tests performed on sections cut from the visors of helmets demonstrate the superior ductility of nickel manganese steel over manganese steel in an equally cold-worked condition. High magnetic properties of some nickel manganese steel discs were traced to a harmless oxide layer containing either a magnetic oxide or other phase of iron. The bend test remains the best criterion of quality helmet steel. Nickel, as an austenite stabilizers, is apparently capable of preventing or reducing the amount of transformation to martensite which occurs when Hadfield steel is cold worked.
- Metallurgy and Metallography