Submicron Microstructure and Mechanical Properties Achieved in a Short Annealing of Cold-Rolled Austenitic Stainless Steels

摘要

The effects of chemical composition and cold rolling reduction on the reversion kinetics and the formation of ultra-fine grained austenite due to a short (0.1-100 s) annealing treatment has been investigated in two commercial Cr-Ni austenitic stainless steels (Types 301LN and 301). Microstructural characterization was done by optical, scanning and transmission electron microscopes and the phase fractions were analyzed with X-ray diffraction and magnetic methods. It was observed that in Type 301LN stainless steel a cold rolling reduction as low as 45% was high enough to result in the formation of a submicron-scale austenite grains in a subsequent reversion annealing at 700-800℃, the average grain size being about 0.6 μm at 800℃. After a partial reversion, a phase mixture of retained austenite, tempered martensite and reversed austenite was formed, leading to an excellent combination of yield strength and elongation with enhanced strain hardening rate. The reversion mechanism was found to be diffusion controlled in Type 301LN and shear reversion in Type 301 steel, affecting the formation of ultra-fine grains.