Review of Peritectic Solidification Mechanisms and Effects in Steel Casting
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Review of Peritectic Solidification Mechanisms and Effects in Steel Casting GHAVAM AZIZI, BRIAN G. THOMAS, and MOHSEN ASLE ZAEEM Surface quality and castability of steels are controlled greatly by initial solidification. Peritectic steels suffer more from surface quality problems, including deep oscillation marks and depressions, crack formation, and breakouts than other steels. This paper reviews current understanding of the fundamental mechanisms of initial solidification of peritectic steels that lead to these problems. First, different empirical relations to identify peritectic steel grades from their alloy compositions are summarized. Peritectic steels have equivalent carbon content that takes their solidification and cooling path between the point of maximum solubility in d-ferrite and the triple point at the peritectic temperature. Surface defects are related more to the solid-state peritectic transformation (d-ferrite fi c-austenite) which occurs after the peritectic reaction (L + d fi c) during initial solidification. Some researchers believe that the peritectic reaction is controlled by diffusion of solute atoms from c phase, through the liquid, to the d phase while others believe that c growth along the L/d interface involves microscale heat transfer and solute mixing due to local re-melting of d-ferrite. There is also disagreement regarding the peritectic transformation. Some believe that peritectic transformation is diffusion controlled while others believe that massive transformation is responsible for this phenomenon. Alloying elements and cooling rate greatly affect these mechanisms. https://doi.org/10.1007/s11663-020-01942-5 The Minerals, Metals & Materials Society and ASM International 2020
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INTRODUCTION
THE castability of high-quality steel depends on avoiding breakouts, cracks, and surface quality problems. The surface quality of steel products is mainly determined by the early stages of solidification in the meniscus region of the mold.[1–8] Steels which undergo the peritectic transition are the most difficult to cast.[2,9–14] This is attributed to the volume contraction (shrinkage) associated with the peritectic phase transformation.[15–17] This shrinkage leads to the formation of an air gap between the steel shell and the mold during the CC process and decreases the heat flux. This leads to locally thinner and hotter regions of the solidified shell,
GHAVAM AZIZI, BRIAN G. THOMAS, and MOHSEN ASLE ZAEEM are with the Department of Mechanical Engineering, Colorado School of Mines, 1610 Illinois Street, Golden, CO, 80401. Contact e-mail: [email protected] Manuscript submitted April 14, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
which causes uneven shell growth that leads to surface depressions, deep oscillation marks, cracks, and breakouts.[18–24] Steels within the peritectic composition range include high-strength low-alloy (HSLA) Steels, and recently advanced high-strength steels (AHSS), which are all used extensively in different products due to their excellent mechanical properties, which incl
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