Flow and fracture of a multiphase alloy MP35N for study of workability

The flow and fracture of MP35N (35 Co, 35 Ni, 20 Cr, 10 Mo) has been studied by uniaxial com-pression and plane strain bending in the temperature range 1000 to 1200 °C and strain rate range 0.01 to 10 s^•1. This covers the normal bar rolling production conditions (∼1100 °C and 1 to 5 s“^•1). The strain to fracture in plane strain bending was found to increase with increasing strain rate, roughly coinciding with the increase of the strain to the peak stress in the flow curves. Within most of the temperature and strain rate ranges investigated and under plane strain bending deformation conditions, microvoid nucleation was found to be concurrent with or greatly enhanced by the onset of dynamic recrystallization. Under these deformation conditions, flow concentration or localization along the soft layers of newly recrystallized grains oriented along the maximum shear stress directions near the surface generated microvoid nucleation and damage, in effect overriding the stress relieving and crack isolation effects normally associated with the occurrence of dynamic recrystallization. As the tem-perature was decreased toward 1000 °C and the strain rate was increased toward 10 s^•1, an apparent transition to a microvoid nucleation mode by wedge cracking was observed, even at the maximum rate of 10 s^•1. A further decrease in deformation temperature to 900 °C at a strain rate of 10 s^•1, however, removed all evidence of microvoid nucleation (of the wedge type or otherwise) as well as any trace of dynamic recrystallization within the maximum strain imposed in the plane strain bending tests.