TITLE:
The Phenomenon of High Hardness Values on the S-Phase Layer of Austenitic Stainless Steel via Screen Plasma Nitriding Process
AUTHORS:
Sang-Gweon Kim, Kook-Hyun Yeo, Yong-Ki Cho, Jae-Hoon Lee, Masahiro Okumiya
KEYWORDS:
Double-Folded Electrode, Austenitic Stainless Steel (ASS), Screen Plasma Nitriding (SPN) Process, S-Phase, Corrosion Resistance, High Hardness
JOURNAL NAME:
Advances in Materials Physics and Chemistry,
Vol.8 No.6,
June
29,
2018
ABSTRACT: The purpose of this study is to improve the surface properties of
austenitic stainless steel using the double-folded electrode screen plasma
nitriding (SPN) process. In general, the S-phase is well-known for its
excellent properties such as improved hardness and wear resistance along with
sustained corrosion resistance. The concentrated nitrogen via SPN process was
injected to form S-phase with time at 713 K. This
study was carried out under the conditions of 44 at% of
nitrogen injection, which was higher than 25 at%
known as the condition of no precipitation of S-phase formed by the SPN
process, and 20 K higher than the maximum temperature
without precipitation phase. The hardness analysis of stainless steel sample
treated by the SPN process at 713 K showed a much higher value than the typical
nitriding hardness at a depth of lower nitrogen than the maximum nitrogen
concentration. The SPN 20 hr treated specimen showed the average value of 2339 HV while 40 hr showed the average value of 2215 HV. The result is attributed to the concentrated
nitrogen formed in the SPN process reacting with the alloying elements
contained in the base material to form fine precipitates, thus producing a synergy effect of the extreme
hardening effect; that is, the movement of precipitates and
dislocations due to the GP-zone (Guinier-Preston zone).