On dislocation hardening in a new manufacturing route of fer-ritic ODS Fe-14Cr cladding tube

International audienceThe microstructure evolution associated to the manufacturing of a Fe-14Cr-1W-0.3Ti-0.3Y$_2$O$_3$ grade ferritic stainless steel strengthened by dispersion of nano oxides (ODS) was investigated. The material was initially hot extruded, then shaped into cladding tube geometry via cold pil-gering and stress release heat treatments. Each step of the process was analyzed to better under-stand the high microstructure stability of the material. Slight grain refinement and alpha fiber texture reinforcement was obtained after cold pilgering. Despite high levels of stored en-ergy the following heat treatment did not recrystallize the material. Only the Vickers hardness showed significant variations in the manufacturing steps, which was attributed to the recovery of statistically stored dislocations (SSD), as concluded from a combination of EBSD and X-ray diffraction measurements

Dislocation Hardening in a New Manufacturing Route of Ferritic Oxide Dispersion-Strengthened Fe-14Cr Cladding Tube

The microstructure evolution associated with the cold forming sequence of an Fe-14Cr-1W-0.3Ti-0.3Y2O3 grade ferritic stainless steel strengthened by dispersion of nano oxides (ODS) was investigated. The material, initially hot extruded at 1100 °C and then shaped into cladding tube geometry via HPTR cold pilgering, shows a high microstructure stability that affects stress release heat treatment efficiency. Each step of the process was analyzed to better understand the microstructure stability of the material. Despite high levels of stored energy, heat treatments, up to 1350 °C, do not allow for recrystallization of the material. The Vickers hardness shows significant variations along the manufacturing steps. Thanks to a combination of EBSD and X-ray diffraction measurements, this study gives a new insight into the contribution of statistically stored dislocation (SSD) recovery on the hardness evolution during an ODS steel cold forming sequence. SSD density, close to 4.1015 m−2 after cold rolling, drops by only an order of magnitude during heat treatment, while geometrically necessary dislocation (GND) density, close to 1.1015 m−2, remains stable. Hardness decrease during heat treatments appears to be controlled only by the evolution of SSD