| 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.
(Received August 4, 2017; Accepted August 30, 2017) |
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| Key Words |
| hot workability, STS303, austenitic stainless steel, free-machining stainless steel, Mn/S ratio, delta-ferrite |
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