DYNAMIC RECRYSTALLIZATION UNDER WARM DEFORMATION OF A 304-TYPE AUSTENITIC STAINLESS-STEEL

Warm land hot) deformation of a 304 type austenitic stainless steel wa s studied in connection with microstructural developments in compressi on at temperatures of 873-1223 K (0.5-0.7 T-m) under strain rates of 1 0(-4)-10(-1) s(-1). The two deformation domains can be categorized due to their different mechanical and microstructural behaviors. In the r egion of how stresses lower than around 400 MPa, the deformation behav iors are typical for hot working accompanied with dynamic recrystalliz ation (DRX). New grains are evolved mainly by dynamic bulging mechanis m, which can be accelerated by the development of serrated grain bound aries and strain induced dislocation subboundaries. The relationship b etween dynamic grain sizes ranged from 2 to 7 mu m and peak flow stres s can be expressed by a power law function with a grain size exponent of - 0.72. In contrast, in the region of flow stresses higher than 400 MPa, the deformation behaviors hardly depend on strain rate and tempe rature and so can be in the region of athermal deformation. The stress -strain curves under such warm deformation are similar to those affect ed only by dynamic recovery. The microstructures evolved at high strai ns are mainly characterized by the dense dislocation walls evolved in pancaked original grains, while grain boundary serration also takes pl ace even at such warm deformation. Mechanisms of this microstructural evolution are discussed in combination with analysis of deformation me chanisms operating under warm deformation. (C) 1997 Elsevier Science S .A. All rights reserved.