Experimental Study On Multi - Pass Hot Press Forming Of 42CrMo Steel Based On Compound Casting Of Ring Parts

Cast-rolling compound forming short-flow process is a kind of new technology to manufacture ring components from cast billets directly, which have characteristics of high efficiency, energy saving, materials saving and other advantages. Rolling forming is the most important step in the production of ring components, in which the microstructure changes constantly. Therefore,one of the key factors during rolling expand forming is the transforming of the cast microstructure to the forging microstructure of ring components. Because rolling expand forming is a multiple deformation process with multi discontinuous deformations, the study of multi-pass thermal compression deformation behavior and microstructure evolution is of great importance.Gleeble-3500 thermal simulation machine was used to carry out the thermal compression simulation experiments about cast 42 CrMo steel,and the flow stress of cast 42 CrMo steel were studied under different multi-pass thermal compression deformation parameters. With the stress- strain curve obtained experimentally,softening law of the material was analyzed.The microstructure of multi-pass thermal compression specimens were observed using optical microscopy. The results show that:(1) With the increasing of multi-pass deformation temperature, the flow stress in the same passes decreases, the softening rate increases between different passes, and the microstructure of recrystallization occurs more fully.(2) With the increasing of thermal compression deformation strain rate, the peak flow stress gradually increases at the same passes, recrystallization is more difficult, and the material contains a lot of microstructure has not recrystallized. The micro-hardness of the specimens will increase with the increasing of multi-pass thermal compressed strain rate.(3) The peak flow stress is not influenced significantly by the extension of the intervals, thermal compression deformation results to work hardening of the material and dynamic softening is a balancing process.(4) The influences of different thermal compression times to peak flow stress is not obvious. With the increasing of the number of thermal compression, each compression deformation decreases, the grain size was uniform and equiaxed,which is beneficial to the refinement of the microstructure. And which eventually leads to a micro-hardness increasing of the thermal compressed specimens.(5) With the rising of the multi-pass thermal compression final temperatur,every pass flow stress peak value decreases, the softening phenomenon occurred obvious in the material, then a corresponding reduction occurred in the crystal structure, with results to the reduction of the sample micro-hardness.The above study provides certain theoretical basis for the research of ring microstructure evolution of ring components during short flow cast rolling compound forming process, and is of great importance for the actual production.