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 for the movement of the control rod assemblies in pressurized heavy water reactors (PHWRs). This material has been selected primarily for the strength and hardness; however, the material is also expected to have adequate impact energy. During the fabrication of the carriage track, samples removed from the same after final heat treatment showed lower impact energy. Metallurgical investigation was undertaken to ascertain reasons behind 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 (solution-annealed, not hardened, not tempered) were given different combinations of hardening and tempering treatment in the range of 950-1100 deg 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 selected and followed on the actual component. The details of the metallurgical investigation are described in this chapter. (author)