Kinetics of peritectic reaction and transformation in Fe-C alloys
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I. INTRODUCTION
THE peritectic reaction, L(liquid) 1 d(ferrite) → g(austenite), occurring during solidification of carbon steels containing 0.10 to 0.51 mass pct carbon was investigated extensively for its particular segregation characteristics.[1] When g is formed between L and d by the peritectic reaction, a partition of solutes into L changes due to the difference in the solubility of the solutes between d and g. Also, the solutes in g show less uniform redistribution than those in d as their diffusion in g is slower. Recently, the peritectic reaction for carbon steels containing 0.09 to 0.18 mass pct has attracted renewed attention as it causes surface cracks[2] in strands that are continuously cast at relatively high speeds of approximately 2 m/min or more in conventional slab casting or approximately 4 m/ min and above in thin-slab casting. This has been attributed to uneven shell growth[3] caused by the large volume contraction of the d → g transformation that makes the solidified shell detach locally from the mold wall.[4,5] Recalescence occurs at this detached area, which causes a decrease of strength and delayed shell growth. When stress is applied to the shell, this thin and weak area tears and cracks. In reality, the peritectic reaction forms intervening g that separates L and d. The peritectic reaction is followed by the growth of the intervening g as a consequence of the transformations of d to g and L to g. Although the growth H. SHIBATA, Research Associate, is with the Institute for Advanced Materials Processing, Tohoku University, Sendai 980-8577, Japan. Y. ARAI, formerly Graduate Student, Graduate School of Engineering, Tohoku University, is Research Engineer, Materials Research Department, Corporate R & D Laboratories, Sumitomo Metal Industries, Ltd., Amagasaki 6600891, Japan. M. SUZUKI, formerly Associate Professor, Institute for Advanced Materials Processing, Tohoku University, is Chief Research Engineer, Steelmaking Research Department, Materials and Processing Research Center, NKK Corporation, Fukuyama 721-8510, Japan. T. EMI, formerly Professor, Institute for Advanced Materials Processing, Tohoku University, is Jernkontoret Professor, Royal Institute of Technology, SE-10044, Stockholm, Sweden. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS. METALLURGICAL AND MATERIALS TRANSACTIONS B
of g is not due to the peritectic reaction, it has been named by Kerr et al.[6] and followed by Fredriksson[7] as the peritectic transformation. A modelistic mechanism of the peritectic reaction, L 1 a → b, to acount for the shape of the advancing three-phase point, L/b/a, along the phase boundary L/a has been given by Hillert.[8] The shape was later confirmed by St. John[9] in quenched specimens of Cu-70 mass pct Sn alloy. Fredriksson and Nylen[10] considered that the diffusion of solute in front of the advancing b crystal is driven by the concentration difference caused by supercoo
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