Study of medium-carbon steels structure after electromechanical processing

Abstract

The results of the microstructure and microhardness of the surface layer of medium-carbon 40Cr, 38CrNi3MoA steels after electromechanical processing are presented. The results of tests on the heat stability of samples made of 38CrNi3MoA steel when they are consistently heated from 150 to 550 °C, in the temperature range of 50 °C are presented. The samples are heated in muffle furnaces with exposure at each temperature of 10 min and cooled in air. The heat stability of the surface layer after electromechanical processing is controlled by changes in microhardness. The results of the microstructure indicate the formation of fine martensite and retained austenite in the upper layers of the quenching zones. High speed heating of local volume of the surface with parallel thermoplastic shaping by work-hardening tool and following high-intensity cooling through heat rejection in deep into work material take place in the time of electromechanical processing. The structure of sorbite is form in the overlap zone of electro-mechanical hardening and in the transition near original structure section. The average surface microhardness of the 40Cr steel samples before hardening is HV = 2000...2400 MPa, after electromechanical hardening — HV = 6640 MPa, and the 38CrNi3MoA steel samples before hardening is HV = 2000...2200 MPa, after electromechanical hardening — HV = 7060 MPa. The graded layer has hardening depth to 0.8 mm with stepwise degradation of hardness is detected. The research results show that using electromechanical processing in the manufacture of wide range of parts in order to increase the wear resistance of the surface layer.