‘Back‐annealing’ of cold rolled steels through recovery and/or partial recrystallisation

Abstract

An evaluation of the ‘back‐annealing’ approach for the production of high strength steel sheet is presented. This approach is different from those used in conventional current practice, e.g. for rephosphorised, microalloyed, dual phase, multiphase and transformation induced plasticity steels. The principle is to retain as much as possible of the hardening due to cold rolling while gaining ductility by controlled low temperature heat treatment (back‐annealing) through recovery and/or partial recrystallisation. Unlike other processes to achieve high strength, this approach offers the possibility of cost effective high speed production in continuous annealing lines. The important role of ‘back‐annealing’ or recovery annealing in the production of ultrafine grains in steels and in the development of higher strength ultra‐thin strip cast products has also been widely recognised. In the present review, the fundamentals of the back‐annealing process are discussed in terms of the constituent phenomena of recovery and recrystallisation and their kinetics. The challenges of back‐annealing in steels, in terms of the production of sheets of thin gauges, are identified and possible methods to overcome these are suggested. Theoretically model approaches to the back‐annealing process are also discussed.