The continuous heat treatment of tool steel is applied to low- or medium-alloyed carbon steel strips as well as martensitic stainless steels. The described lines produce high-quality strip with respect to uniform structure, flatness, and bright surface finish. Steel grades with 0.4 to 1.2% C, low and high alloyed, can be processed. Strip dimensions range between 10 to 750 mm (0.4 to 29.5 in.) wide and 0.05 to 4 mm (0.002 to 0.16 in.) thick. High quenching rates are necessary, especially for plain carbon steels. Cooling gradients of up to 600 K/s are possible in a molten lead-bismuth quench. Because two-stage quenching technology provides considerable advantages over quenching in oil, this method has been adopted worldwide. It is also possible to achieve isothermal transformation to bainite and pearlite using a molten metal quench, so this type of hardening and tempering line is extremely versatile.
The configuration of a high-performance line involves an entry and exit section of the strip handling equipment (Fig. 10). The hardening section consists of the austenitizing furnace, the molten metal quench or hydrogen quench, and a martensite cooler. Beyond the martensite cooler the strip is martensitic and fully hardened, and then it passes through the tempering section—consisting of a leveling furnace, tempering furnace equipped with an atmosphere recirculation system, and an atmosphere jet cooler—to finally leave the facility, completely flat, with a bright surface finish and tempered to very uniform tensile strength.
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R Schneider ; R. Mesquita ; H. Altena ; T. Müller ; P. Seemann,Processes and Furnace Equipment for Heat Treating of Tool Steels, ASM International, 2014, https://doi.org/10.31399/asm.hb.v04d.a0005958
