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Bob, Tom, William and anyone else interested,
The 41xx series is known as chromium-molybdenum steel, has a very high tinsile & yield stringth and is generally used in shafting applications and high strength bolts. 4142 in particular has .4-.45 carbon, .75-1.0 manganese, .8-1.1 chromium and .15-.25 molybdenum. The shock resisting tool steels are S1, S2, S5, and S7. S7 is an air hardening tool steel but the rest are not. S7 can also be oil hardened but suffers a stability loss if hardened this way. It is known for high stability if air hardened, poor wear resistance and good toughness (obviously if it is shock resistant). The mix for S7 is .5 carbon 1.4 molybdenum and 3.25 chromium. The hardining temperature is higher than most other tool steels (1700-1750) and the tempering range is 400-1150. The hardness will fall between Rockwell 45-57 on the C scale.