"1" Medium carbon Steel: The Representative Steel has 30, 35, 40, 45, also has ML30, ML35, ML40, ML45, has a more stable room temperature performance, for medium and small structural parts, fasteners, transmission shafts, gears and so on. "2" manganese Steel: stands for 40Mn2, 50Mn2. There is overheating sensitivity, high temperature temper brittleness, water quenching easily cracking, hardenability is higher than carbon steel. "3" Silicon manganese Steel: representing the grades 35SiMn, 42SiMn. High fatigue strength, decarburization and overheat sensitivity and temper brittleness. For the manufacture of medium-speed, high load but small impact of gears, shafts, hinges, connecting rods, worm, etc., can also be manufactured 400 ℃ following fasteners. "4" boron steel: On behalf of grades 40B, 45B, 50BA, ML35B. High hardenability, comprehensive mechanical properties than carbon steel, and 40Cr is quite used in the manufacture of parts of small size, fasteners and so on. "5" Manganese boron steel: representing the grade 40MnB. Hardenability slightly higher than 40Cr, high strength, toughness and low temperature impact toughness, temper brittleness. 40MnB used to replace 40Cr manufacturing large cross-section parts, instead of 40CrNi manufacturing small pieces; 45MnB replaces 40Cr and 45Cr;45Mn2B instead of 45Cr and partial substitution of 40CrNi and 45CrNi as important axes, and also ML35 MnB for fastener production.