The influence of quenchant agitation on the heat transfer coefficient and residual stress development in the quenching of steels

This paper is concerned with the effect of variation in part orientation and quenchant circulation and agitation on the heat transfer coefficient during the quenching of steel parts, and subsequently on the development of residual stresses in the quenched part. Residual stresses arise from complex coupled interactions between phase transformation, thermal and stress effects during the rapid thermal transient of quenching. The nature of these interactions is described briefly, and their incorporation into an analytical programme using finite element analysis is outlined. In an experimental programme the effect of quenchant flow velocity was investigated for flow parallel and perpendicular to the axis of cylindrical bar specimens. Heat transfer coefficients were obtained from thermocouples embedded in the specimens, using the inverse method to process the results. Results are presented for varying positions on the bars, as well as for variation in orientation and flow velocity. Axial residual stresses are presented for two flow conditions at each orientation and are compared with experimental measurements made using the X-ray diffraction technique.