Design of dynamic recrystallisation controlled rolling schedules for seamless tube rolling

Abstract

A model developed by Sellars and Dutta, for strain induced carbonitride precipitation under isothermal conditions, is extended to precipitation under continuous cooling conditions. It is applied here to laboratory simulations of the stretch reducing stage of a seamless tube mill. The model predictions are compared with experimental observations of the contrasting rolling behaviours of Ti–V and Nb–V steels and excellent agreement is obtained. It is shown that in order to design dynamic recrystallisation controlled rolling (DRCR) stretch reducing mill schedules, the critical strain for dynamic recrystallisation must be achieved well before the onset of strain induced precipitation. If, however, precipitation begins before the critical strain is reached, then ‘pancaking’ occurs. Thus, Ti–V steels are more suitable for DRCR processing, because strain induced precipitation takes place only at very low temperatures in these materials. As a result, rolling can be carried out at relatively low temperatures, which results in very fine dynamically recrystallised austenite (and therefore ferrite) grain sizes.

MST/1443