Abstract
The persistence of the effects of prior cold work through subsequent annealing treatment has been investigated by examining the changes in 0·2%yield strength and the microstructural evolution in phosphorus free and phosphorus containing type 316Ti stainless steels with various amounts of mechanical pretreatment. The results showed no specific influence of phosphorus on changes to a cold worked structure during short term treatment carried out in the range 800–1200°C where no second phase precipitation was observed. However, when second phase precipitation did occur the behaviour of the alloys examined was found to be slightly different. For long term annealing in the 600–800°C temperature range an abundant nucleation of fine carbides particles, particularly in the phosphorus containing steel, considerably improved the stability of the cold worked structure by decorating grain boundaries and by pinning the dislocations and, consequently, impeding their climb. This study has highlighted clearly the existence of an optimum annealing temperature for a given level of cold work and that there is an optimum amount of initial deformation for a given annealing temperature. The addition of phosphorus has been shown to result in an increase of strength in type 316Ti with perhaps an insignificant drop in ductility, although a full explanation of how the presence of phosphorus affects the recrystallisation process in a prestrained 316Ti type steel remains to be ascertained.
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