It  is  available  to  fine  grain  size  of case-hardened  steel  for  gear

increase  cutting  properties  and  fatigue property  of steel  by  adding  microalloying  elements  such  as  Al

Nb

Ti

N  and  B

while  to  shorten  carburizing  time

simplify  procedures  and  decrease  production  cost  by  adding  Nb

Ti  etc.elements.The  grade

chemical  compositions

production process characteristics and research progress of microalloying cold forging steels for gear

case-hardening steels for gear carburizing at high temperature and high strength-toughness steels for gear are presented in this article.