The microstructure evolution

and mechanical properties of new-type slot edge steel 30MnSiCrMo quenched at 900-920 ℃ for 30 min and tempered at 350-550 ℃ for2 h are studied by using optical microscope

scanning electron micro- scope

tensile

impact and Brinell hardness tester. The results show that martensite decomposition

transformation-aggregation-growth of carbide

and recovery-recrystallization of α phase happen during 350-550 ℃ different tempering process

the room temperature microstructure transits from tempered martensite to tempered troostite and tempered sorbite. With the in- crease of tempering temperature

the solid solution strengthening and carbide precipitation strengthening gradually weaken

the strength and hardness of testing steel continuously decrease

while the plasticity and toughness gradually increase. The excellent strengthen and toughen matching of the testing steel is obtained i.e. with austenitizing at 900 and 920 ℃ for 30 min

water quenching and tempering at 450-520 ℃ for 2h

the tensile strength of steel is 1159- 1008 MPa

the yield strength is 1107-944 MPa

the elongation after fracture is 11.8%- 15.0%

the room temperature hardness is 336- 293HBW

and the V-shaped impact absorption energy is 45.5-67.5 J

which could meet the requirements of strength and toughness of the central trough ledge.