Study on the Effect of Rare Earth Compound Additives in Near Net Forming Hot Forging Die Steel

The application object is hot fogring dies, the effect of RE compound additive on the microstructure, mechanical and thermal fatigue properties of the casting hot forging die steel were investigated by OM, SEM, electron-tensile tester, impact testing machine and hardness tester etc. On that basis, a hot forging die camshaft was manufactured by vacuum full-mold casting (V-EPC) near net forming technique. The results showed that the matrix microstructure was more uniform, grain was refined obviously, mechanical properties were improved significantly, and the initiation and growth of thermal fatigue crack were effectively inhibited for the hot working die steel by RE compound additive modifying. Compared with the casting hot forging die steel without adding RE compound additive, the impact toughness was increased by 1.15 times and reached 67.9 J/cm², the ultimate tensile strength (UTS) were respectively increased by more than 200 MPa at both room and high temperature (600 ℃) and reached 1457 MPa and 1108 MPa, thermal fatigue property was obviously improved, and with same hardness for the hot forging die steel adding RE compound additive. The camshaft die made from the hot forging die steel forged the engine camshafts up to 15648 pieces at 2500 tons crank press. Compared with 5CrNiMo hot forging die under the same forging conditions, the service life of the test die was increased by more than 2 times, and the processing cost could be reduced by about 25%.