316L Stainless-Steel Carburizing Close to Eutectic Transformation Using the Spark Plasma Sintering Process

Abstract

This work focuses on the 316L austenitic stainless-steel case-hardening microstructure, after the SPS process near the solid/liquid state transition temperature. This process, faster than conventional carburizing techniques, is equivalent to weld cladding, allowing the achievement of high surface carbon contents with large-size carbide grains in the case of partial melting. Three distinct zones were formed: internal carburizing, carburizing with melting, and carburizing with melting and chromium depletion; all three composed of mixed carbides (Cr0.4Fe0.6)7C3 distributed in an austenitic matrix. The internal carburizing layer growths following a parabolic kinetic law with kp 1027 cm2/s, while the advancement of the melting front is very fast and follows a linear law with kl = 1.0 3 1024 cm2/s at 1100 °C. The Cr-depleted fusion zone microstructure is similar to a composite material with a metallic matrix, which includes graphite particles, Mo-rich intermetallic phases, and core-shell eutectic carbides. The partial melting zone without Cr depletion shows the formation of a dense carbide layer with diameters exceeding 10 µm, constituting 60% of the volume, and achieving a hardness of 850 HV5. Its wear rate is about 100 times lower than the 316L steel, indicating a significant improvement in the alloy's wear behavior.

This work focuses on the 316L austenitic stainless-steel case-hardening microstructure, after the SPS process near the solid/liquid state transition temperature. This process, faster than conventional carburizing techniques, is equivalent to weld cladding, allowing the achievement of high surface carbon contents with large-size carbide grains in the case of partial melting. Three distinct zones were formed: internal carburizing, carburizing with melting, and carburizing with melting and chromium depletion; all three composed of mixed carbides (Cr0.4Fe0.6)7C3 distributed in an austenitic matrix. The internal carburizing layer growths following a parabolic kinetic law with kp 1027 cm2/s, while the advancement of the melting front is very fast and follows a linear law with kl = 1.0 3 1024 cm2/s at 1100 °C. The Cr-depleted fusion zone microstructure is similar to a composite material with a metallic matrix, which includes graphite particles, Mo-rich intermetallic phases, and core-shell eutectic carbides. The partial melting zone without Cr depletion shows the formation of a dense carbide layer with diameters exceeding 10 µm, constituting 60% of the volume, and achieving a hardness of 850 HV5. Its wear rate is about 100 times lower than the 316L steel, indicating a significant improvement in the alloy's wear behavior.

This work focuses on the 316L austenitic stainless-steel case-hardening microstructure, after the SPS process near the solid/liquid state transition temperature. This process, faster than conventional carburizing techniques, is equivalent to weld cladding, allowing the achievement of high surface carbon contents with large-size carbide grains in the case of partial melting. Three distinct zones were formed: internal carburizing, carburizing with melting, and carburizing with melting and chromium depletion; all three composed of mixed carbides (Cr0.4Fe0.6)7C3 distributed in an austenitic matrix. The internal carburizing layer growths following a parabolic kinetic law with kp 1027 cm2/s, while the advancement of the melting front is very fast and follows a linear law with kl = 1.0 3 1024 cm2/s at 1100 °C. The Cr-depleted fusion zone microstructure is similar to a composite material with a metallic matrix, which includes graphite particles, Mo-rich intermetallic phases, and core-shell eutectic carbides. The partial melting zone without Cr depletion shows the formation of a dense carbide layer with diameters exceeding 10 µm, constituting 60% of the volume, and achieving a hardness of 850 HV5. Its wear rate is about 100 times lower than the 316L steel, indicating a significant improvement in the alloy's wear behavior.