| Distinct yield drops and serrations were observed on the stress-strain curves of a 304 type stainless steel when tested at high temperatures (850--1200°C). A proposed explanation for the behavior is static strain aging (SSA) and dynamic strain aging (DSA), respectively, caused by the presence of substitutional elements.; Much of the previous work on this topic has been focused on the effects of interstitials, namely carbon and nitrogen, at lower temperatures (100--300°C, depending on the strain rate). However, for substitutional elements to have the same effect, the temperature range must be significantly higher. To further investigate the likelihood that SSA and DSA are caused by substitutional elements, the domain (i.e. temperature and strain rate range) within which yield drops and serrated yielding are observed was studied.; The results of this investigation showed that the appearance of SSA is dependent upon the pass strain, interpass time and strain rate, whereas the presence of DSA serrations was strongly dependent upon strain rate. The disappearance of yield drops involves interpass times in excess of one second. This is hypothesized to result from the disappearance of the deformation vacancies and of the associated non-equilibrium segregation. The impurity element phosphorus was isolated as the most probable cause of the observed phenomenon. This is a result of its high diffusivity, combined with its high binding energy. |
