Optimization of Hot Rolling and Annealing Process of Low Ni Stainless Steel Using Simulation Studies

Abstract

Processing of low Ni Stainless Steel poses a serious problem during rolling both in roughing and finishing stands owing to high load. This is primarily attributed to high work hardening rate due to low Ni and high Mn in such steels. An increase in temperature to bring down the rolling load deteriorates the surface quality. In addition to this, high hardness in the cold rolled and annealed product posses problem during further forming operation. To overcome these problems, simulation studies were carried out using Gleeble Thermo-mechanical Simulator (i) to determine flow stress under different hot rolling conditions and (ii) to simulate continuous strip annealing process to optimize annealing parameters to bring down the hardness. It was observed that the flow stress increases gradually with a decrease in temperature till 1050C and thereafter, at a significantly high rate. It was further observed that continuous dynamic recovery occurred at 1050 – 1150C which gradually diminished and resulted in work hardening at lower temperatures. In view of this, rolling schedule was modified which led to smooth rolling without any over-load problem. It was also found based on simulation studies that the hardness was minimum in the temperature range of 950-975 C, however, no/ little recrystallisation occurred at these temperatures. A fully recrystallised grain with significant drop in hardness was observed at 1050C. Annealing cycle was accordingly modified for regular commercial production which has given good result.