Effect of Spark Plasma Sintering (SPS) at Temperatures of 900 and 950oc for 5 Minutes on Microstructural Formation of Fe-25Ni-17Cr Austenitic Stainless Steel

Abstract

Purpose: This research is related to fabricate Fe-25Ni-17Cr austenitic stainless steel. Methodology: Fe-25Ni-17Cr austenitic stainless steel were made by spark plasma sintering at 900 and 950oC for 5 minutes. Results: The microstructure of both the steels sintered at 900 and 950°C consists of particles with high Cr content, a'-Cr and austenite matrix containing of fine grains of g-FeNi. Sintering at high temperatures causes the fine grains to be seen more clearly. The fine grains of g-FeNi are twin grains that contain defects such as dislocations, stacking faults and trapped air bubbles. The defects are formed during the mixing process through milling and compacting under a 30 MPa load during the sintering process. The density of the first two defects decreased with increasing the sintering temperature. By contrast, more trapped air bubbles were noticed as increasing the sintering temperature and the distribution of fine a’-Fe particles higher. Since beside of higher the density of steel sintered at the high temperature, smaller grain size of austenite matrix and higher distribution of fine a’-Fe in the austenite matrix, the hardness of this steel is greater than the steel sintered at temperature of 900oC. Applications/Originality/Value: This study fabricated austenitic stainless steel made from powders of 58% Fe, 25% Ni and 17% Cr. The manufacturing process is carried out through a sintering by spark plasma at temperatures of 900 and 950°C for 5 minutes. The microstructure of austenitic stainless steel that formed very well at 950°C consisted of very fine grains of austenite g-FeNi and a'-Fe particles were distributed throughout the g-FeNi grains, resulting in a high hardness of 399.3 HV0.2.