High strength carbon steel, treated with a high surface hardness and strength, but ductility, toughness is poor, moderate machinability, weldability, hardenability poor water quenching has a tendency to crack formation. After normalizing or quenching general use, used as a higher strength and wear resistance or flexibility, dynamic load and impact load small parts, such as gears, rims, flat springs, crankshafts, etc., but also for casting.