Material Machining
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What is the difference between machining different alloy steels (40Cr, 42CrMo, 20CrMnTi, 38CrMoAl)?
Differences when machining different alloy steels and tool selection: Alloy steels add alloying elements (chromium, molybdenum, nickel, titanium, aluminum) to carbon steel for higher strength, hardness, toughness and wear resistance. 1) 40Cr - the most common alloy structural steel: chromium steel, good all-round performance; stronger and tougher than 45 steel, better after quenching/tempering. Machinability: good, slightly harder than 45 - a bit more force and wear. Use cobalt HSS + TiAlN, 500-1000rpm, feed 0.06-0.12mm/rev, generous cooling. 2) 42CrMo - chromium-molybdenum steel: high strength, toughness and hardenability; large critical parts (crankshafts, gears, rods); very strong after Q/T. Machinability: medium, harder than 40Cr - high force, fast wear. Use cobalt HSS + AlCrN or carbide, 400-800rpm, feed 0.05-0.1mm/rev, generous cooling, sharp tools. 3) 20CrMnTi - carburizing steel: low-carbon alloy structural steel; hard surface (HRC58-62) with tough core after carburizing/hardening; gears and shafts. Machinability: good annealed (low carbon - soft, tacky); very hard after carburizing. Annealed: cobalt HSS + TiAlN, 600-1200rpm, feed 0.08-0.15mm/rev, anti-welding; carburized surface: carbide or CBN, low speed, small feed. 4) 38CrMoAl - nitriding steel: chromium-molybdenum-aluminum; extremely hard surface after nitriding (HV1000+), excellent wear resistance; precision parts (boring bars, spindles, valves). Machinability: medium annealed; very hard after nitriding. Annealed: cobalt HSS + TiAlN, 400-800rpm, feed 0.05-0.1mm/rev; nitrided surface: CBN or diamond, low speed, very small feed. 5) Other common alloy steels - 20Cr (carburizing), 40MnB (boron), 35CrMo (Cr-Mo), 60Si2Mn (spring), GCr15 (bearing) - machinability depends on composition and heat treatment. Summary: alloy steels are harder to machine than carbon steel - higher strength, more force, faster wear; the more alloying, the harder. Use cobalt HSS + AlCrN or TiAlN, reduce speed 20%-30% vs carbon steel, smaller feed, generous cooling. Q/T or hardened alloy steels need carbide or CBN. Our cobalt HSS countersinks suit most alloy steels - ask us.
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