Research On Hot Work Die Steel Used For Extrusion Wheel

The composition of extrusion wheel experimental steels were designed by usingJMatPro software analysis of the effects of Cr, V, Mo and N content on the phasecomposition, type and proportion of the precipitation phase of the steels. The bestcomposition of experimental steels was optimized by microstructure, mechanicalproperties and thermal fatigue tests, and then heat treatment processes of the bestcomposition steel were optimized. Finally influencing thermal fatigue mechanism wasstudied.The designed compositions of Cr, Mo, V and N of the extrusion wheel steelrange from3to4wt%,1.1to1.4wt%,1.0to1.5wt%,0.008to0.02wt%,respectively. The best compositions of V, Cr, N, Mo optimized by microstructure,mechanical properties and thermal fatigue tests are1.0wt％,3.75wt％,0.01wt％and1.39wt％, respectively. The optimized heat treatment process for the bestcomposition steel is that spheroidizing annealing880℃×1h+720℃×1h, quenching at1080℃, first tempering550℃×2h and second tempering530℃×2h.TEM and EDS analysis showed that in5wt%Cr-steel there are face-centeredM₂3C₆type alloy carbide participates which contain a large proportion of Cr and arenot stable and easy to coarsen, these participates will reduce the softening resistancein tempering and are deleterious to thermal fatigue property; however in steelcontaining Cr≤3.9wt%there are face-centered M₄C₃, MC type alloy carbides richin V and orthorhombic M3C cementite particles without M₂3C₆type alloy carbides.M4C3and MC type alloy carbides can improve the thermal fatigue performance,whereas M₃C type cementite particles will be deleterious to thermal fatigueperformance. The main effect of Mo element in experimental steels is solid solutionstrengthening and N element can play a role of stabilizing carbides and promote theprecipitation of vanadium carbonitrides and improve the thermal fatigue properties.