Investigation of the Peritectic Phase Transition in a Commercial Peritectic Steel Under Different Cooling Rates Using In
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UNWEI HUANG, JIE YANG, HUAMEI DUAN, LINTAO GUI, and PEI XU are with the Chongqing Key Laboratory of Vanadium-Titanium Metallurgy and New Materials, College of Materials Science and Engineering, Chongqing University, Chongqing 400044, P.R. China. MUJUN LONG and DENGFU CHEN are with the Chongqing Key Laboratory of Vanadium-Titanium Metallurgy and New Materials, College of Materials Science and Engineering, Chongqing University and also with the Room 522, Chongqing 400030, P.R. China. Contact e-mails: [email protected], [email protected] Manuscript submitted 30 May, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
INTRODUCTION
HIGH-STRENGTH low-alloy (HSLA) and advanced high-strength (AHS) steel products, designed with a close to peritectic carbon content and with an addition of microalloying elements, have been widely applied in the automotive, oil transportation, and marine industries in recent years.[1–3] The excellent combination in mechanical properties and the tremendous customer demand are prompting steelmakers to produce these steel grades in high volumes.[2] Nevertheless, steel products with an equivalent carbon content between 0.09 and 0.17 wt pct will inevitably undergo a peritectic phase transition in the copper mold. The shrinkage volume of the emerging austenite (c) phase is larger than that of primary d-ferrite (d) phase during the peritectic reaction, due to the tighter
atomic packing of the c phase (FCC structure) compared to the d phase (BCC structure).[4] The peritectic reaction usually leads to a significant volume shrinkage, leading to the formation of a large air gap between the steel shell and the copper mold.[1] The locally detached areas in the mold generally result in a lower heat transfer and a reduced heat extraction from the molten metal, delaying the shell growth.[5] Consequently, these series of interlocking events lead to form a thin and uneven solidified shell, which may result in cracking when the shell is unable to withstand the ferrostatic pressure.[6] Further imposition of external and internal stresses applied on this uneven shell may increase the crack size, induce hot tears and surface cracks, and, in the worst cases, may induce the accidental breakouts.[7,8] A mass of obvious cracks on the shell surface require off-line conditioning because these cracks are still retained in the edge of slabs even after hot-rolling.[9,10] Casting slabs with obvious surface defects will deteriorate the quality of final steel products and limit the productivity.[11] It is widely accepted that the source of surface defects is generally linked to the volume shrinkage and stress accumulation appearing in the early stage of solidification.[12] With steelmakers’ continuous efforts, some effective measures were developed to prevent the formation of surface crack defects in the as-cast products. The relevant improvement methods include chemistry modifications, casting at lower speeds, the application of mold powder with a moderate heat transfer rate, maintaining a moderate superheat level, ensuring an op
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