Analysis of residual strain and stress states due to heat treatment and thermal processing

Abstract

This paper dwells on the nature of the highly non-linear interactions occurring during heat treatments with the aim of developing an improved understanding of the process and of the residual strains and stresses formed in heat-treated components during processing. As an example, two industrial quench processes are analysed. A general analytical strategy is presented to study not only these processes, but is formulated in such a way that it may also be extended to other thermomechanical processes. This strategy may therefore serve as a roadmap for industrial designers to analyse thermomechanical processes for optimization. Results in the broad framework of thermomechanical processing indicate that careful characterization and correct representation of the heat transfer conditions leads to significant improvements in accuracy over the current quench modelling techniques. In addition to this, the nature of the thermomechanics involved in spray and bath quench processes is analysed. Neutron diffraction experiments and finite element analyses indicate that the use of water sprays reduces the depth of permanent deformation in quenched components compared to those treated in a water bath. It is shown that this is a direct consequence of the rewetting condition. Understanding the processes involved enables the processing engineer to perform optimization studies of the thermomechanical process, before processing. This ultimately allows production of engineering components with superior mechanical properties, reduced distortion and well-controlled beneficial residual stress states.