Machinery's Handbook, 31st Edition
456 Special Tool Steels tools, reamers, hand taps, and threading dies, wood augers; die parts, drawing and heading dies, shear knives, cutting and forming dies; and fixture elements, drill bushings, lathe centers, collets, and fixed gages. Group III (C 1.05 to 1.20%): The higher carbon content of this group increases the depth of hardness penetrations, yet reduces toughness, thus the resistance to shock loads. Preferred for applications where wear resistance and cutting ability are the prime considerations. Used for such applications as hand tools, woodworking chisels, paper knives, cutting tools (for low-speed applications), milling cutters, reamers, planer tools, thread chasers, center drills, die parts, cold blanking, coining, bending dies. Group IV (C 1.20 to 1.30%): The high carbon content of this group produces a hard case of considerable depth with improved wear resistance yet sensitivity to shock and concentrated stresses. Selected for applications where the capacity to withstand abrasive wear is needed and where the retention of a keen edge or the original shape of the tool is important. Used for such applications as cutting tools for finishing work, like cutters and reamers, and for cutting chilled cast iron and forming tools, for ferrous and nonferrous metals, and burnishing tools. By adding small amounts of alloying elements to W-steel types 2 and 5, certain charac teristics that are desirable for specific applications are improved. The vanadium in type 2 contributes to retaining a greater degree of fine-grain structure after heat treating. Chromium in type 5 improves the deep-hardening characteristics of the steel, a property needed for large sections, and assists in maintaining the keen cutting edge that is desirable in cutting tools like broaches, reamers, threading taps, and dies. Mill Production Forms of Tool Steels Tool steels are produced in many different forms, but not all those listed in the following are always readily available; certain forms and shapes are made for special orders only. Hot-Finished Bars and Cold-Finished Bars: These bars are the most commonly pro duced forms of tool steels. Bars can be furnished in many different cross sections, the round shape being the most common. Sizes can vary over a wide range, with a more limited number of standard stock sizes. Various conditions may also be available; however, tech nological limitations prevent all conditions applying to every size, shape, or type of steel. Tool steel bars may be supplied in one of the following conditions and surface finishes: Conditions: Hot-rolled or forged (natural); hot-rolled or forged and annealed; hot-rolled or forged and heat treated; cold- or hot-drawn (as drawn); and cold- or hot-drawn and annealed. Finishes: Hot-rolled finish (scale not removed); pickled or blast-cleaned; cold-drawn; turned or machined; rough ground; centerless ground or precision flat ground; and pol ished (rounds only). Other forms in which tool steels are supplied are the following: Rolled or Forged Special Shapes: These shapes are usually produced on special orders only, for the purpose of reducing material loss and machining time in the large-volume manufacture of certain frequently used types of tools. Forgings: All types of tool steels may be supplied in the form of forgings that are usually specified for special shapes and for dimensions that are beyond the range covered by bars. Wires: Tool steel wires are produced either by hot or cold drawing and are specified when special shapes, controlled dimensional accuracy, improved surface finish, or special mechanical properties are required. Round wire is commonly produced within an approximate size range of 0.015 to 0.500 inch (0.38 to 12.7 mm), and these dimensions also indicate the limits within which other shapes of tool steel wires, like oval, square, or rectangular, may be produced. Drill Rods: Rods are produced in round, rectangular, square, hexagonal, and octagonal shapes, usually with tight dimensional tolerances to eliminate subsequent machining, thereby offering manufacturing economies for the users.
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