Chromium Hot-Work Steels

The chromium hot-work tool steels are the most widely used for forging and die-casting applications. Originally developed for die casting of aluminum alloys, the alloy design objectives for the steels included air-hardening capability from relatively low austenitizing temperatures, little movement during hardening, minimum scaling tendency during air cooling, resistance to erosion by aluminum, resistance to thermal fatigue or heat checking, and reasonable alloy content and cost . The outstanding characteristics of H11 and other chromium hot-work steels are their high toughness and shock resistance. Although their hot hardness is lower than that of the other types of hot-work steels, the high shock resistance of the chromium H-type steels makes them preferable for most hot-work operations, especially when dies must be cooled with water or other flushing media. Typical applications include die-casting dies for aluminum, zinc, and magnesium castings, forging dies and inserts, punches, piercers and mandrels for hot work, hot-extrusion tooling, shear blades for hot work, and all types of dies for hot work. Some of the chromium H-type steels have been used for structural parts that require ultrahigh strength.

Tungsten Hot-Work Steels

The compositions of the tungsten hot-work tool steels, also designated as group H steels in the AISI classification system, are listed in Table 13-1, and processing and performance ratings are given in Table 13-2. Tungsten H-type steels were historically the first high-alloy steels used for hot-work tooling. They contain from 9 to 19% W, low carbon, and moderate amounts of chromium and vanadium. The tungsten hot-work steels have greater hot hardness than any class of hot-work steels and therefore have excellent resistance to softening and washing of dies during hot-work operations. However, the same high-carbide-containing microstructures that provide hot hardness also cause the tungsten steels to have lower toughness and higher susceptibility to brittle fracture. In order to offset this low fracture resistance, tungsten hot-work tool steel alloy design incorporates low carbon content. Despite this low content, tungsten H-type steels have lower resistance to thermal shock than do the chromium hot-work steels and cannot be rapidly cooled with water during operation without danger of breakage. Tungsten die steels are used where maximum hot strength and resistance to softening at elevated temperatures are the principal requirements, and resistance to shock, while important, is a secondary consideration. Within this general characterization, the various types of tungsten hot-work steels offer various combinations of elevated-temperature wear or erosion resistance and toughness, depending on carbon and alloy content and heat treatment as described below. Typical applications for the tungsten H-type steels include extrusion dies for brass, bronze, and steel, hot-press dies, dummy blocks, hot-swaging and drawing dies, shear blades for hot work, and hot punches.

Molybdenum Hot-Work Steel

the single molybdenum hot-work tool steel still widely used. As a result of wartime shortages of tungsten, a number of molybdenum hot-work steels were developed, but gradually the use of these steels has declined. The properties of these steels for hot-work applications were intermediate to the chromium and tungsten hot-work tool steels discussed earlier, and the availability of H42 offers a roughly comparable alternative to the tungsten steels when cost is considered. H42 steel contains nominally 5% Mo, 6% W, 2% V, and 4% Cr and is available in several carbon ranges. The high content of carbide-forming elements controls hardening and makes possible high hardness as a result of secondary hardening during tempering. Preheating at 760 to 815 °C (1400 to 1500 °F) prior to heating to forging temperatures is recommended, and because of the high hardenability and air-hardening capability of H42 steel, forgings should be slow cooled and should not be normalized. Molybdenum hot-work steels are highly susceptible to decarburization and must be protected during annealing and hardening heat treatments.

Hardening of hot work steels is one of the most complicated heat treatment processes due to its high austenitic temperature (usually between 1000 and 1100 degrees Celsius) .

this company with Using the technical knowledge of its engineers and suitable equipment such as electric electrode furnace and other available furnaces , has provided the field for the complete cycle of heat treatment of these steels.

Hot work steels are mainly used in aluminum extrusion industries such as; Mold parts and other extrusion press components such as ram, liner, blaster, ring, etc. are used. Among other applications of these steels are steel and brass forging industries, aluminum diecast and zamak, steel rolling industry, etc. The most used steels of this group are 1.2344, 1.2714, 1.2365, 1.2367 and 1.2581.