Effect of Spheroidizing Annealing on Hardness of GDL-4 Tool Steel

The effects of spheroidizing annealing on microstructure and hardness of GDL-4 new new type tool steel were studied.The phase transition point and annealing temperature of the steel was determined using DIL 402C dynamic and static expansion instrument and software determination.The results show that the best process is 910 ℃ keeping 90 min and 810 ℃ keeping 8 h respectively for 30 ℃/h of cool rate to 600 ℃ and then air cooling.