Development of thermo-mechanical processing to form high density of uniformly distributed nanosized carbides in austenitic stainless steels

Model alloys and thermomechanical processing (TMP) were developed to form a high density of uniformly distributed nanosized (<10 nm) carbides in an austenitic stainless steel matrix. The composition of the model alloys was determined to control the formation of precipitates during the TMP. The TMP consisted of homogenization at 1200 degrees C for 1 h, multiple hot-rolling passes above and below the non-recrystallization temperature (TNR), and precipitation heat treatment at 800 degrees C for 2 h. By proper division of the rolling passes above and below T-NR, a microstructure with a homogeneous grain size and a well-developed dislocation structure was obtained. Then, subsequent precipitation heat treatment produced a microstructure containing a high density (similar to 1.1 x 10(22)/m(3)) of uniformly distributed and coherent NbC precipitates in the austenitic matrix. The evolution of the nanosized NbC during the precipitation heat treatment was coupled with the dislocation characteristics, such as the density and distribution, which were controlled by the hot-rolling conditions.