Speaker
Description
Stress relaxation cracking (SRC) in austenitic stainless steels is an intergranular fracture resulting from relaxation of residual stresses introduced by welding due to further temperature exposure. This phenomenon has been associated to a residual stress threshold, the material pre-strain and grain boundary carbides. While the material damage has been observed on a macro and micro scale, little information is available regarding the early stages of the cracking mechanism at a lower scale for 316L(N) steels.
The aim of this work is to get insight into SRC in the 316L(N) steel through the analysis of cavity nucleation, the intergranular phases precipitation and their respective effect on damage. First, CT-like samples were pre-strained at 20% to be further compressed at room temperature to induce residual stresses. After compression, these samples were aged at temperatures between 500 and 600 °C for holding times of 580 and 1470 h, allowing stress relaxation. Cavities and precipitates were characterized by SEM-EDS observations.
For shorter ageing duration at 575 °C, very little damage was observed, nucleated by the decohesion of intergranular chromium carbides from the matrix. For longer ageing time and higher temperature, numerous creep-type cavities were observed in the regions presenting the highest residual stresses, exclusively formed on large chromium carbides. These were accompanied by small Mo-rich intermetallics (chi or R phase), though they do not seem to play any role in cavity nucleation. Some of the largest cavities contained small chromium carbides, precipitated after cavities growth. SEM-EDS cartographies carried out nearby these cavities show the presence of a Mo, Mn and Cr rich precipitates in direct contact with large chromium carbides at the bottom of some of the smaller cavities. These precipitates are only observed in cavities, which seems to be the source of damage development.
| Speaker Country | France |
|---|