50Mn ,strength, elasticity and hardness were higher, welding performance Used as a stress parts. High wear-resistant parts, high stress parts, such as diameter less than 80 mm spindle. High frequency quenching after to still can make fire axle, worm, connecting rod and automobile crankshaft, such as gear. Gear shaft. Friction disc. Spindle. Flat spring, etc. C :0.48~0.56 Si :0.17~0.37 Mn :0.70~1. ...