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Korean Journal of Metals and Materials > Volume 55(12); 2017 > Article
Korean Journal of Metals and Materials 2017;55(12): 880-887. doi: https://doi.org/10.3365/KJMM.2017.55.12.880
쾌삭 303계 스테인레스강의 열간성형성에 미치는 균질화처리, Mn/S 비 및 델타-페라이트의 영향
정재영
경북대학교 자동차부품소재연구소
Effects of Homogenization Treatment, Mn/S ratio and δ -ferrite on the Hot Workability of Free-Machining 303-series Austenitic Stainless Steels
Jae-Young Jung
Automobile Parts & Materials Research Center, Kyungpook National University, Daegu 41566, Republic of Korea
Correspondence  Jae-Young Jung ,Tel: +82-53-950-7504, Email: jaeyjung7@knu.ac.kr, jaeyjung7@gmail.com
Received: 4 August 2017;  Accepted: 30 August 2017.  Published online: 4 December 2017.
ABSTRACT
To improve the hot-workability of free-machining austenitic stainless steel, we studied the effects of homogenization treatment, Mn/S ratio and the retained δ-ferrite on the hot-workability of 303 austenitic stainless steels. The reduction of area was measured as a function of homogenization temperature in the range of 1160-1250 ℃ and 1-50 s−1 using a Gleeble 3800. The hot-workability of the 303-series austenitic stainless steels reached a maximum value at a homogenization temperature of ~1240 ℃. The high temperature (e.g. ~1250 ℃) hot-workability increased with the Mn/S ratio and reached a constant value above ~7.0. At the same time, medium temperature (e.g. ~900 ℃) hot-workability increased linearly with the Mn/S ratio. The fraction of δ-ferrite decreased with increasing Mn/S ratio in STS 303-series VIM ingots. The retained δ-ferrite was found to seriously deteriorate hot-workability at above a critical volume fraction. The critical value was determined to be ~0.06. The Cr content in the (Mn, Cr) S compounds decreased with increasing Mn/S ratio. The hardness of (Mn, Cr) S increased with increasing Cr content. The hot ductility deteriorated with increasing Cr content within MnS. The evaluation of the harmful effects of Pbeq. on the hot workability of a STS 303 series billet was ineffective.
Keywords: hot workability, STS303, austenitic stainless steel, free-machining stainless steel, Mn/S ratio, delta-ferrite
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