Structure and sulfide comparative analysis of sulfur, tellurium and lead free-cutting steels
CAO Chen-wei1, ZHANG Pan-pan1, HU Shao-hui1, ZHOU Lei2, FU Jian-xun*1
1. Center for Advanced Solidification Technology (CAST), School of Materials Science and Engineering, State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai 200444,China; 2. Nanjing Iron and Steel Co., Ltd., Nanjing 210035, China
Abstract：The inclusion and structure in free-cutting steel are two important factors influencing the machinability. In order to develop environmental friendly lead-free free-cutting steels, and to explore the difference of structure and sulfide compared to the lead-bearing free-cutting steels, the matrix structure and sulfide inclusions in 1215MS (sulfur), 1215Te (tellurium) and 12L14 (lead) free-cutting steels were observed and statistically analyzed by optical microscope and electron microscope. The influence of Pb and Te on the inclusion morphology in steel was analyzed by non-aqueous solution electrolysis method. The results showed that the structures of three kinds of free-cutting steels were all composed of ferrite and pearlite. Tellurium could reduce the length-width ratio of MnS inclusions, and the proportion with length-width ratio in range of 1-3 was 57%, which was higher than the 40% of 1215MS and the 33% of 12L14 steel. Tellurium could form MnTe in free-cutting steel, and the morphology of MnS trended to spherical, ellipsoid and spindles after rolling, which had remarkable effect of modification. Lead existed as Pb simple substance in free-cutting steel, which had limited effect on the modification of sulfide.
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