Optimization design of cold rolling and annealing processes for 690 alloy tubes based on microstructure uniformity

Single and double-pass cold rolling and annealing tests were carried out aiming at the poor control of grain size uniformity for 690 alloy tubes in China.A heterogeneous factor Z was introduced to evaluate the uniformity of microstructures.The results show that the grain size is most homogeneous in 690 alloy pierced billets by single-pass cold rolling with a deformation of 50% and annealing at 1 100℃ for a holding time of 5 min.The best uniform grain size distribution can be obtained by the first pass cold rolling with a deformation of 50%,the second pass cold rolling with a deformation of 70%,and annealing at 1 100℃ for a holding time of 5 min between the two cold rolled processes,followed by solution heat treatment at 1 060℃ for 5 min or 1 100℃ for 3 min.