Macroscopic Distribution of Residual Elements As, S, and P in Steel Strips Produced by Compact Strip Production (CSP) Pr
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INTRODUCTION
RESIDUAL elements such as arsenic, sulfur, and phosphorous have great effects on the mechanical properties of steels. For example, arsenic and sulfur can lead to embrittlement of the steel at high temperatures, whereas phosphorous might cause embrittlement at room temperature.[1–3] Substantial efforts have been made to eliminate these elements.[4,5] However, arsenic is difficult to remove completely in economically sound steelmaking processes; hence, it tends to remain in final steel products.[6,7] Therefore, it is important to determine the elements distribution in the final products. For the microscopic distribution of these elements, namely, the distribution within a scale of the grain size, strong effects of this type distribution were found on the mechanical properties of steels. If the elements are distributed on austenite grain boundaries, then intergranular fracture can result.[8–11] Otherwise, when these elements are not distributed at the grain boundaries, the mechanical properties will be improved greatly. The effects of residual elements on mechanical properties were found to depend largely on the amount of these elements at the grain boundaries. Many investigations have been carried out on this subject.[12,13] However, the effects of the macroscopic segregation (distribution in a scale larger than the grain size) of these YUANZHI ZHU, Professor, is with the Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science & Technology, Wuhan 430081, P.R. China and is also with the School of Materials and Metallurgy, Wuhan University of Science & Technology. Contact e-mail: [email protected] JUNCHAO LI, Graduate Student, is with the School of Materials and Metallurgy, Wuhan University of Science & Technology. JIANPING XU, Professor, is with the Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science & Technology. Manuscript submitted February 11, 2011. Article published online February 25, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
residual elements on the mechanical properties were not studied equally. Optical microscopy is used typically to investigate the macroscopic segregation of elements.[14] However, no detailed information of the segregation of the elements can be obtained because of the small concentration of these elements, for instance, the minor residual elements of arsenic, sulfur, and phosphorous. Moreover, macroscopic segregation could be much smaller in a cast thin slab by a compact strip production (CSP) process than that in a traditional continuous cast billet. In CSP, the continuous casting process is followed directly by the hotrolling process after only a simple homogenization treatment. In a traditional continuous casting plus hot rolling process, the continuous cast billet is cooled to room temperature and then the cooled billet is reheated to a temperature (~1373 K [~1100 C]) above the austenization temperature (~1073 K [~800 C]). The reheated billet is defo
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