Low temperature deformation behaviour of ASTM A-203D nuclear structural steel

The steel A-203D in martensitic tempered martensitic and ferritic - pearlitic microstructural conditions, was deformed in tension at temperatures between 77 to 300 K and at a strain rate of 6.67 x 10 super(-5) sec super(-1). The thermal component of the flow stress and the activation parameters were measured as a function of temperature. It was observed that the microstructure did not affect either the thermal part of the flow stress ( sigma *) or the activation parameters (V* and Delta H) and that its effect was felt only on the athermal component ( sigma sub( mu )) of the flow stress. Further the relations of the activation parameters with stress, strain and temperature were found to be consistent with Dorn-Rajnak theory of Peierls mechanism of plastic deformation. In addition measurements of slow blend and impact transition were also carried out for ferritic-pearlitic structure. Based on these observations, it is shown that the impact transition temperature of this structure can be empirically correlated with the thermal activation parameters.