Improvement in Mechanical Properties of Austenitic-Martensitic Stainless Steel for Investment Castings

Investment castings are part of turbo-pumps of rocket engines. Most of the castings belong to austenitic-martensitic (AM class) stainless steels due to the advantage of high strength, good impact strength, and corrosion resistance. Many a time lower 77 K properties are observed. Different approaches have been taken to improve the 77 K properties of the alloy castings. Mainly three areas were identified and monitored, which are chemistry (nickel content), hot isostatic pressing and tempering cycle. It is observed that nickel on the higher side improves the 77 K impact strength. Hot isostatic pressing helps to close the solidification-generated shrinkage and internal defects, which is found to reduce the scatter in mechanical properties. Tempering at 600 °C improves the 77 K impact strength with a marginal reduction in tensile strength. A large number of melts were analyzed and the effect of suggested parameters on improvement in mechanical properties has been observed. © 2023, The Institution of Engineers (India).