Machinery's Handbook, 31st Edition
448 Hot-Work Tool Steels AISI H12: The properties of this type of steel are comparable to those of H11, with increased abrasion resistance and hot hardness resulting from the addition of tungsten, yet in an amount that does not affect the good toughness of this steel type. The applications based on these properties are hot-work tools that often have to withstand severe impact, such as various punches, bolt header dies, trimmer dies, and hot shear blades. H12 is also used to make aluminum extrusion dies and die-casting dies. AISI H13: This type of tool steel differs from the preceding ones particularly in proper ties related to the addition of about 1 percent vanadium, which contributes to increased hot hardness, abrasion resistance, and reduced sensitivity to heat checking. Such properties are needed in die casting, particularly of aluminum, where the tools are subjected to drastic heating and cooling at high operating temperatures. Besides die-casting dies, H13 is also widely used for extrusion dies, trimmer dies, hot gripper and header dies, and hot shear blades. AISI H19: This high-alloyed hot-work tool steel containing chromium, tungsten, cobalt, and vanadium has excellent resistance to abrasion and shocks at elevated temperatures. It is particularly well adapted to severe hot-work uses where the tool, to retain its size and shape, must withstand wear and the washing-out effect of molten work material. Typical applications include brass extrusion dies and dummy blocks, inserts for forging and valve extrusion dies, press forging dies, and hot punches. Hot-Work Tool Steels, Tungsten Types.— A substantial amount of tungsten and very low-carbon content characterize the hot-work tool steels of this group. These tool steels have been developed for applications where the tool is in contact with the hot-work mate rial over extended periods of time; therefore, the resistance of the steel to the softening effect of elevated temperatures is of prime importance, even to the extent of accepting a lower degree of toughness. Frequently Used Tungsten Types: AISI H21: This medium-tungsten alloyed hot-work tool steel has substantially increased abrasion resistance over the chromium-alloyed types yet possesses a degree of toughness that represents a transition between the chro- mium and the higher-alloyed tungsten-steel types. The principal applications are for tools subjected to continued abrasion yet to only a limited amount of shock loads, like tools for the extrusion of brass, both dies and dummy blocks, pierces for forging machines, inserts for forging tools, and hot nut tools. Another typical application is dies for the hot extrusion of automobile valves. AISI H24: The comparatively high tungsten content (about 14 percent) of this steel results in good hardness, great compression strength, and excellent abrasion resistance, but makes it sensitive to shock loads. By taking these properties into account, the principal applications include extrusion dies for brass in long-run operations, hot-forming and grip per dies with shallow impressions, punches that are subjected to great wear yet only to moderate shocks, and hot shear blades. AISI H20: The composition of this high-alloyed tungsten-type hot-work steel resembles the tungsten-type high-speed steel AISI T1, except for the somewhat lower carbon content for improved toughness. The high amount of tungsten provides the maximum resistance to the softening effect of elevated temperature and assures excellent wear-resistant properties, including withstanding the washing-out effect of certain processes. However, this steel is less resistant to thermal shocks than the chromium hot-work steels. Typical applications comprise extrusion dies for long production runs, extrusion mandrels operated without cooling, hot piercing punches, hot forging dies and inserts. It is also used as special structural steel for springs operating at elevated temperatures. Hot-Work Tool Steels, Molybdenum Types.— These steels are closely related to certain types of molybdenum high-speed steels and possess excellent resistance to the softening effect of elevated temperature, but their ductility is rather low. These steel types are gener ally available on special orders only.
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online