Fatigue Properties of Solution-Treated Type 304 Stainless Steel after Nitriding

Abstract:

The solution treatment after nitriding (STAN) was performed to stabilize the γ- phase in a metastable austenitic stainless steel, type 304, and to improve the strength of type 304 by the solid solution of nitrogen. Plasma nitriding was conducted at 500°C for 8.5h, and then solution treatment was performed at 1200°C for 1h. As a result, the static strength and the hardness were improved by the STAN. Rotary bending fatigue tests were performed on the specimens with STAN (solid solution strengthened) together with the untreated and the nitrided ones in laboratory air and in 3%NaCl solution. In laboratory air, the fatigue strength of the solid solution strengthened specimen increased compared to that of the untreated specimens, where fatigue limits were 340MPa and 290MPa for the solid solution strengthened and the untreated, respectively. However, the fatigue limit of the solid solution strengthened specimen was lower than that of the nitrided specimen, that is, 380MPa. On the other hand, in 3%NaCl solution, the fatigue strengths of the nitrided specimens and the solid solution strengthened specimens decreased significantly compared to those in laboratory air. After the fatigue tests at the stress level of fatigue limit in laboratory air, the strain-induced martensitic transformation was examined by XRD. In the solid solution strengthened specimens, the strain-induced martensitic transformation was not detected during fatigue tests until 3x10⁷ cycles, indicating that the γ- phase was stabilized by the solid solution of nitrogen.

• Periodical: Key Engineering Materials (Volumes 525-526)
• Pages: 217-220
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.525-526.217
• Online since: November 2012
• Authors: Yuki Nakamura, Masaki Nakajima, Toshihiro Shimizu, Kentaro Suzuki, Yu Bai, Yoshihiko Uematsu
• Keywords: Austenitic Stainless Steel, Fatigue, Nitriding, Solution Treatment, Strain-Induced Martensitic Transformation

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