Surface microstructure of 316L austenitic stainless steel by the salt bath nitrocarburizing and post-oxidation process known as QPQ

✍ Scribed by Gui-jiang Li; Qian Peng; Jun Wang; Cong Li; Ying Wang; Jian Gao; Shu-yuan Chen; Bao-luo Shen

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 869 KB
• Volume: 202
• Category: Article
• ISSN: 0257-8972
• DOI: 10.1016/j.surfcoat.2007.10.032

✦ Synopsis

Systematic materials characterization of the Quench-Polish-Quench complex salt bath heat-treatment process (QPQ) surface modified 316L steel was investigated. The results reveal that the nitro-carburized sample surfaces consist of Cr 2 N/γ´-Fe 4 N and CrN/γ-Fe, while the post-oxidized sample surfaces are comprised of CrO 3 , (Fe 3 O 4 )/ε-Fe 2 (N,C), γ′-Fe 4 N and S(γ N )/CrN/α-Fe. Nuclei ε-Fe 2 N 1 -x accumulates at the interface between oxide layer and nitride compound layer by the help of post-oxidation. The diffraction peak lines of S-phase (γ N ) move gradually towards higher diffraction angles as increasing depth of 15 μm to 35 μm. An increased content of oxygen is recorded in the post-oxidized surface layer down to the depth of approximately 15 μm, a small peak concentration of carbon occurs at the front of the nitrided layer. Micro-hardness of the post-oxidized samples reaches about 1300 HV 0.1 near the surface region and then reduces sharply across the case/substrate interface.