Microstructure of Plasma Nitrided AISI420 Martensitic Stainless Steel at 673 K

• Published in: Crystals (Basel) Vol. 9; no. 2; p. 60
• Main Authors: Aizawa, Tatsuhiko, Yoshino, Tomoaki, Morikawa, Kazuo, Yoshihara, Sho-Ichiro
• Format: Journal Article
• Language: English
• Published: MDPI AG 01.02.2019
• Subjects: fine two-phase structuring; low temperature plasma nitriding; martensitic stainless steels; nanolamination in α’-grains; nitrogen supersaturation
• ISSN: 2073-4352; 2073-4352
• DOI: 10.3390/cryst9020060

Martensitic stainless steel type AISI420 was plasma nitrided at 673 K for 3.6 ks to investigate the initial stage of the nitrogen supersaturation process without the formation of iron and chromium nitrides. SEM-EDX, electron back-scattering diffraction (EBSD), and TEM analyses were utilized to characterize the microstructure of the nitrided layer across the nitriding front end. The original coarse-grained, fully martensitic microstructure turned to be α’- γ two phase and fine-grained by high nitrogen concentration. Below this homogeneously nitrided layer, α’-grains were modified in geometry to be aligned along the plastic slip lines together with the α’ to γ-phase transformation at these highly strained zones. Most of these α’-grains in the two-phase microstructure had a nano-laminated structure with the width of 50 nm.