Tempering Hardness and Red-hardness of Strengthen-layer after Plasma W-Mo-Y Surface Alloying Process

A uniform dense alloying-diffusion-layer on the surface of Q235 steel was formed by the double glow plasma W-Mo-Y surface alloying process and W-Mo surface alloying process respectively in order to form.Then they were conducted low temperature tempering process at 200 ℃ for 1 h after carburizing and quenching process at 960 ℃,980 ℃ and 1 020 ℃ for 8 h respectively.Afterwards two surface alloys were carburized and quenched at 1 020 ℃,and then tempered at 200~700 ℃ respectively.The micro-hardness and its distribution,microstructure and content distribution of alloying layer were analyzed respectively by microhardness tester,metalloscope,SEM and EDS.The results is showed as follows: the tempering behavior of the layers is the same as that of the metallurgy high speed steel.The secondary hardening occures at 500 ℃,when the tempering hardness reaches the maximum,higher than that of W-Mo surface alloy.When two surface alloys that are conducted by carburizing and quenching process at 1 020 ℃ are air cooled after thermal insulating at 600℃ for 1 h,their maximum hardness values become 750 HV0.05 and 650 HV0.05 respectively after being repeated for 4 times.