Influence of material flow constraints during cold forming on the deformation and densification behaviour of hypoeutectoid P/M steel ring preforms

The deformation and densification behaviour of sintered hypo-eutectoid steel ring preforms with carbon contents of 0.35% and 0.65%, under cold axial deformations, have been studied in order to understand the influence of various forming parameters such as flow stress and percentage axial height reduction on the densification process. Four different conditions of material deformations, namely, pure upsetting, deformation constrained along radial inward direction, deformation constrained along radially outward direction and, finally, deformation of material and pores constrained along both inward and outward radial directions have been applied during the axial cold forming tests. Results of the investigations have established that highest densification rate is achieved in rings subjected to the most severe flow constraint of fully restrained radial flow, at comparatively lower levels of axial deformations. Both carbon content and initial sintered ring geometry are also found to influence the deformation as well as densification rates during the cold forming process. Ring preforms of lower initial geometry, namely, 6:3:2 exhibit better densification rates irrespective of the mode of flow, but require lesser flow stress values, compared to those of initial geometry of 6:3:4. The densification process is observed to follow an almost linear trend in the case of fully constrained axial deformation, whereas, under less severe flow constraints, the same is observed to follow second or third order polynomials.