Steel hot-work tool

Group H covers hot work tool steels, which retain strength, toughness and resistance to softening at elevated temperatures. Group H steels are very strong and have important structural applications, such as rolls and fasteners (e.g., HI 1 and HI3). 

Hot work tool steels are used in most shearing applications that take place at hot rolling temperatures (1600-2000°F for steel). Good knife cooling practices are important to minimize heat checking and assure proper knife performance. 

Superalloys are much more costly than tool steels, but these grades are applicable when a significantly longer knife life is desired. These high-performance alloys are not as susceptible to thermal cracking and maintain their strength at elevated temperatures, therefore knife cooling is not as critical compared to hot work tool steels. 

Hot-work tool steel DIN 1.2343 steel (hardness approximately 44 on the Rockwell C Hardness Scale (HRC), thermal conductivity around 25 W/mK) for nozzle casings and bodies ... 

P/M Tool Steels. In conventionally produced high alloy tool steels (slowly cooled cast ingots), carbide tends to segregate (48). Segregated clusters of carbide persist even after hot working, and cause undesirable effects on tool fabrication and tool performance. P/M tool steels, on the other hand, provide very fine and uniform carbides in the compact, the final bar stock, and the tools. Several tool steel suppHers consoHdate gas-atomized tool steel powder by HIP to intermediate shapes, which are then hot-worked to final mill shapes. Water-atomized tool steel powder is also available (see also T OOL materials). ... 

Hot working causes plastic deformation to occur at a temperature high enough to prevent the material from becoming strain hardened. Instead, it spontaneously recovers plastic deformation. Hot-worked materials therefore do not have the internal energy characteristic of cold-worked materials. In practice, hot-work threshold temperatures are dictated by factors such as tool life. These temperatures range from as low as 350°F (175°C) for aluminum alloys to as high as 23(X)°F (1260°C) for steels and nickel alloys. 

Special alloy tool steel forgings with the necessary properties of red hardness, shock resistance, and abrasion resistance are used in the manufacture of shear knives for hot work. The knives are frequently used in shears where water is employed as a coolant. Applications include hot strip mill crop shears, flying shears in strip, billet, and bar mills, as well as cobble and dividing shears. 

Hot workability of ledebuiitic tool steels is important economic factor. This means that for each tool steel individuallysafe range of hot working parameters should be revealed. Publications in the literature with regard to the hot workability of tool steels are rare and therefore more information from this research area is desired.The relatively low hot workability of ledeburitic tool steels, i.e. steels in whieh the solidifieation is completed by a eutectic transformation of the residual interdendritic liquid to austenite and various alloy carbides (ledeburitic carbides), is usually characterized by the produetion of surface and internal cracks during the hot deformation. 

R. Thome and W. Dahl, On the crack susceptibility of high alloyed tool steels during continuous casting and in the temperature region of hot working, Steel research, 66 (1995), 63-71. 

---