FEATURE ADVANCED MATERIALS & PROCESSES | MAY/JUJNE 2024 46 T here are many industrial processes that require intimate contact between an alloy and a corrosive gaseous environment at high temperatures. The alloys used under these conditions are designed to form an external protective oxide scale, typically Al2O3, Cr2O3, or SiO2-based scales that protect the underlying alloy at high temperatures and preserve structural soundness for extended periods of service time. However, if these components are subject to temperature cycles and/or subjected to sufficiently high temperatures in the presence of air mixed with aggressive species such as water vapor, carbon, or sulfur, the oxide scales can spall and/or volatilize, resulting in degradation of the environmental protection. When exposed to temperature cycles that can result in the spallation or degradation of the protective nature of the oxide scale, the oxide scale must form again rapidly from elements present in the underlying alloy for continued protection of the substrate alloy from the high temperature corrosive environment. This repeated loss and formation of the fresh oxide scale from the protective oxide-forming elements contained within the alloy (e.g. Al, Cr, Si) results in near-surface depletion of these elements eventually leading to the loss of ability to form new, protective oxide. The loss of protective scale leads to loss of substrate integrity and ultimate failure of the component[1]. FURNACE ROLLS IN STEEL MANUFACTURE The steel industry in the United States is one of the largest consumers of energy and any improvements in the processing of steel would have a significant beneficial CAST ALUMINA-FORMING AUSTENITIC STAINLESS STEELS FOR HIGH TEMPERATURE HEAT TREATMENT FURNACE ROLLS Research on using a novel cast alumina-forming austenitic stainless steel won the prestigious Engineering Materials Achievement Award at IMAT 2023 in Detroit. G. Muralidharan, FASM,* Y. Yamamoto,* M.P. Brady, FASM,* D.N. Leonard, Roger Miller, and Sujit Das Oak Ridge National Laboratory Stanley Fauske and Tanya Ros-Yanez Cleveland-Cliffs Daniel Limpert, Roman Pankiw, and Ryan Richter Duraloy Technologies Jim Myers* MetalTek International impact on energy usage, emissions, and costs. Many of the steel plates typically undergo an austenitizing heat treatment during which the steel is heat treated to a temperature of about 900°C. Plates are transported through a large austenitizing heat treatment furnace using furnace rolls, which are exposed to high temperatures for long periods of time. The transfer roll alloy in widespread use today is an H-series, cast austenitic stainless steel (typically HP-type-25Cr-35Ni-0.45C) which provides reasonably good oxidation resistance through the formation of a chromia scale and provides limited high-temperature strength and creep resistance. While chromia-scales are effective in protecting the substrate at temperatures of up to about 750° to 800°C, spallation and volatilization of these scales above this temperature reduces their protective ability. In addition, several problems are commonly observed with the use of furnace rolls manu- factured from H-series austenitic stainless steels[2]. The first one is that the rolls tend to sag during operation due to lack of high-temperature creep and fatigue strength and become eccentric in their rotation. The second common problem is the formation of large, randomly localized bulges on the surface of the rolls. The third issue is that the rolls pick up scale from steel plates which adheres to the roll surface to form surface blisters or nodules. These, in turn cause surface imperfections in the heat-treated plates. The presence of surface imperfections in the final product results in the downgrading of the product and hence affects the ability to produce steels that can meet critical surface finish requirements. To avoid these problems, current furnace operating practice 9 *Member of ASM International
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