The Effect of Sintering Process on the Microstructure and Mechanical Properties of Hot Isostatically Pressed 25Cr Low-Nitrogen Duplex Stainless Steel

This study investigates the effects of hot isostatic pressing (HIP) temperature and pressure on the microstructure and mechanical properties of 25Cr low-nitrogen duplex stainless steel. Room-temperature tensile testing, microstructural characterization, and X-ray diffraction were performed on the as-sintered and solution-treated samples. The initial ferritic powders, after HIP sintering, exhibited precipitation of the detrimental σ phase during slow furnace cooling, which enhanced strength but severely degraded ductility, yielding 559–605?MPa and 2.5–10.5% elongation. After solution treatment at 1050?°C for 30?min followed by water quenching, the σ phase was completely dissolved, producing a ferrite–austenite dual-phase microstructure and improving elongation to 28–34%. For samples sintered at 1150?°C, increasing pressure caused little variation in yield and tensile strengths, while elongation first increased and then decreased. At 130?MPa, raising the sintering temperature led to a gradual decrease in strength with elongation also showing a rise-then-fall trend. Microstructural analysis revealed that higher sintering temperatures promoted densification but induced grain coarsening, reducing strength, whereas higher pressures suppressed grain growth but excessive pressure limited ductility. Optimal combined properties were obtained when the average ferrite grain size was below 10?μm, with a yield strength of 547–548?MPa and elongation of 33–34%.