Research On Deformation Properties And Dislocation Dynamic Model For 42CrMo Steel

As a common engineering medium carbon alloy steel,42CrMo was widelyused in shaft,gear parts,etc．,the mechanical properties was cOmprehensiVelyexcellent after quenching and tempering,but it would be changed at differenttemperatures．In this paper,the mechanical properties at the temperatures ranging from一150~C to 700~C of quenched and tempered 42CrMo steel was studied underquasi-static load and different strain rates．The results show that a decrease oftemperature or an increase of strain rate reduces the plasticity but increases thestrength,and there is a"stress plateau''found in a certain temperature range onthe stress—temperature curve．By using scanning electron microscopy and optical microscopy,thefracture morphology and microstructure of specimens were observed aftermechanical tests．The results show that there were a small amount of tiny andshallower dimples at一150~C．Increased,larger and deeper dimples,as well asgradually reducing quasi—cleavage facets were observed with a risen oftemperature．Dense dimples but not obvious quasi—cleavage facets werefound at 700~C．Tempered sorbite was obtained after quenching and tempering,large deformation was observed on axial direction,and grains were smaller withan increase of temperature．Based on the dislocation dynamic theory,a constitutive model wasestablished．Flow stress was expressed as a sum of non—thermal stress,thermally-activated stress and viscous drag．Simulation results show that themodel fitted well with the experimental data and could reflect the trend ofplastic deformation,flow st ress was mainly controlled by rlogl—the rmalcomponents and the rmall,v—activated st ress．the effect of viscous d rag was very small．Comparing with the calculated results of J—C model,this constitutivemodel could reflect the plastic deformation characteristics better under lowstrain rate and at different temperatures．Based on dislocation motion,plastic deformation behavior of metals wasstudied．The"stress plateau"in the experiment need to meet the conditions ofcertain temperatures and strain rates,this phenomenon was mainly due to thepinning effect of solute atoms in the course of dislocation motion．...