THE RELATIONSHIP BETWEEN WORK HARDENING AND THE NATURE OF SERRATIONS OBSERVED IN A 15Cr-15Ni-2.3Mo-Ti MODIFIED AUSTENITIC STAINLESS STEEL DURING TENSILE TESTING

The variation of work hardening rate (WHR) on the serrations has been analysed with respect to the type of serrations for a 15Cr-15Ni-2.3Mo-titanium modified austenitic stainless steel in the temperature range 300 to 1023 K. The results showed that the WHR, its rate sensitivity and the nature of serrations are strongly related. A clearly periodic locking type serrations occurred under conditions where the material in general exhibited high WHRs and when the WHR has a small positive rate sensitivity, as at low temperatures and at high strain rates. The serrations changed over to partial or fully unlocking serrations under conditions when WHRs would be lowered due to strain induced or thermally assisted recovery processes, and the rate sensitivity of the WHR becomes very large, as seen at high temperatures, large strains and low strain rates. At still higher temperatures, the serrated flow ceases when the WHR becomes negligible. It is concluded that under conditions of high WHR and low rate sensitivity of WHR periodic locking type serrations occur and under conditions of low WHR and high rate sensitivity of WHR unlocking type serrations occur.