Optimization of Aging Cycle of Stainless Maraging Steel using Dilatometric and Differential Scanning Calorimetric Analysis to improve its Strength

摘要

04X13H5M5 is a stainless maraging steel with high strength and excellent toughness. This alloy has been selected for making Impeller casting which is subjected to localized stresses reaching as high as 700 MPa at the tip of its vanes. The impeller rotates at 19000 RPM for 253 seconds.This alloy comprises of austenitic - martensitic dual phase at room temperature, in which martensite exhibits Body Centered Cubic (BCC) structure with moderate hardness (HRC 30) and high toughness. The required strength is achieved by precipitation of second phase particles in soft martensite matrix at suitable aging temperature. There is always a chance of reversion of martensite to austenite on heating either for extended period or at higher temperature. Thus optimization of aging temperature and time becomes highly critical keeping in mind the functional stress requirements of the component. The optimization has been done using Differential Scanning Calorimetric (DSC) analysis, dilatometric studies and experimental iterations of heat treatment temperatures and aging time.Different combination of strength and ductility could be achieved by varying heat treatment parameters. Martensite start and finish temperatures and austenitic reversion temperatures were established through DSC and dilatometric studies. Effect of subzero temperature on properties and microstructure of this steel is also presented here. Scanning Electron Microscopy and Energy Dispersive Spectroscopy were also carried out to analyze phases in different heat treatment conditions.