Study of the Heat Transfer Behavior and Naturally Deposited Films in Strip Casting by Using Droplet Solidification Techn
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rip casting process produces thin strips directly from the liquid metal and shows a great potential for the reduction of operating and investment costs by eliminating several rolling steps.[1] The interfacial heat transfer through the melt–mold interface is extremely important for controlling the solidification of molten materials and solidification structure in these processes,[2,3] as the heat flux approaches 5 to 6 MW/m2 or even higher, which is far higher than that in traditional continuous casting (1 to 2 MW/m2).[2–4] In addition, during the process of strip casting, there are naturally deposited films occurring on the surface of the mold leading to variations in the interface thermal resistance between the mold and the cast strip, which subsequently affect the heat transfer during casting.
WANLIN WANG, CHENYANG ZHU, CHENG LU, JIE YU, and LEJUN ZHOU are with the School of Metallurgy and Environment, Central South University, Changsha 410083, China and also with the National Center for International Research of Clean Metallurgy, Central South University, Changsha 410083, China. Contact e-mail: [email protected] Manuscript submitted November 25, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Intensive research regarding the heat transfer phenomenon in strip casting has been conducted,[1,3–13] and studies on the character of the deposited films are also available in the literature.[4,6,8,9,11–14] In previous studies, two kinds of experimental apparatus were used to simulate the process of strip casting, i.e., immersion-type experiment and droplet solidification technique. Strezov et al.[6,8] designed an immersion-type experimental apparatus to simulate the initial contact between molten steel and mold in a twin-roll caster, and they have reported that after immersion of a substrate into a stainless steel melt, the substrate surface was coated with a thin layer of gray colored powder that was mainly composed of low melting point manganese- and silicon-based oxides, and the maximum heat flux jumped suddenly after several immersions. Todoroki et al.[7,9,10] developed a droplet solidification technique to simulate the heat transfer phenomena in strip casting process of 304 stainless steel, and the heat flux was reduced due to the formation of Mn-O-S-based deposited film on the mold surface. Ha et al.[11] also obtained a black oxide layer deposited on the roll surface during the casting of an AISI 304 stainless steel in a pilot twin-roll strip caster, mainly composed of manganese, chromium, iron, silicon, and oxygen. Their results suggested the film acted as a
thermal barrier between the rolls and melt, leading to an increase of air gap and inconsistent solidification. Evans and Strezov[12] also used an immersion-type experimental apparatus to simulate the process of strip casting, and their results suggested that the oxide and sulfide particles were deposited on the substrate surface, leading to a reduction in interfacial thermal resistance and an increase of the corresponding heat flux. Phinichka[13] conducted the droplet
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