Challenges in Pressureless Sintering of Interstitially Alloyed TRIP Steel and Resulting Mechanical Properties

The focus of the current study is to investigate the challenges encountered in processing an interstitially alloyed stainless steel powder by means of an extrusion process derived from the manufacture of ceramics with subsequent pressureless sintering. Previous investigations reveal a distinct loss of nitrogen during conventional sintering in pure argon atmospheres due to the temperature/time regimes applied and the absence of a suitable partial pressure of nitrogen. Consequently, different flushing gases (consisting of argon and nitrogen) are used to keep the nitrogen content in the pre-alloyed steel powder constant during consolidation. The resulting chemical compositions of the manufactured compacts are determined, as are the microstructures and the mechanical properties, which are recorded under quasi-static compressive loading. A detailed analysis is conducted to determine the reasons for the loss of interstitial elements in the materials studied, a phenomenon caused by oxidation and reduction reactions throughout the processing chain. In addition, the differences between the materials in their work-hardening behavior and in the kinetics of the TRansformation Induced Plasticity (TRIP) effect are discussed as a function of the amount of interstitial elements remaining in the sintered materials.