A comparison of the dynamic shear properties and fracture behaviour of continuous and pulsed current plasma arc weldments of 304L stainless steel

Abstract
The dynamic shear behaviour and fracture characteristics of continuous current (CC) and pulsed current (PC) plasma arc weldments of 304L stainless steel are studied and compared by means of torsional split-Hopkinson bar and SEM metallographic techniques under strain rates ranging from  s ^-1 to  s ^-1 at room temperature (25 °C). Results show increasing strain rates increase flow stress, fracture strain and work hardening rate of 304L weldments. For all tested strain rates, strain rate sensitivity increases as work hardening stress increases, but activation volume decreases. Shear stress and strain rate sensitivity of PC weldments are all higher than CC weldments at the same strain rate, but activation volume is lower. SEM fracture surfaces are found to contain fusion zone dimples, heat affected zone dimples and smooth shallow dimples. With increasing strain rate, FZ and HAZ dimple density and depth increase while smooth shallow dimples decrease, in all cases more significantly in PC weldments than in CC weldments. Constitutive equations for both weldments are proposed and successfully describe the dependence of dynamic shear properties on applied strain rate. The significantly superior performance of the PC weldments under high strain rate conditions should be taken into consideration when designing structural elements containing 304L SS.