Enhancement of properties of SS 410 track forging by suitable heat treatment

ASTM - 479A SS Type 410 forgings are used in Reactivity Mechanism Carriage Track as a guide path for the movement of the control rod assemblies in 235 MWe PHWR. Recently few samples of this material showed lower impact properties as evaluated by U-notch testing. The metallurgical investigation was undertaken to ascertain reasons behind the lower impact properties and to evaluate the feasibility of the salvage heat-treatments for the improvement in the same. Samples from the same lot and from the virgin material (not-hardened, not-tempered, in solution-annealed condition) were given different combination of hardening and tempering treatment in the range of 950 to 1100 °C. The microstructural examination was carried out after each heat-treatment and mechanical and impact properties were further evaluated depending upon the microstructural details. A suitable combination of the heat-treatment that gives higher impact properties was chosen and it was applied on the actual component. The details of the metallurgical investigation are described in this paper