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Metal Casting Technologies : September 2006
WHO'S WHO OF METALS -- ANNUAL 2006/7 43 Test drive your designs Optimization -- Integration -- Casting Property Prediction Committed to Casting Excellence MAGMA Engineering Asia-Pacific Pte Ltd. · 25 International Business Park · #03-76/79 German Centre 609916 Singapore · Phone +65 65643435 · Fax +65 65640665 · email@example.com · www.magmasoft.com.sg MAGMA GmbH, Phone +49 241 889010, firstname.lastname@example.org, www.magmasoft.com called martensite (2). Tempering of the martensite is needed to relieve internal stress and to improve toughness without reducing strength and hardness by too much. During tempering Carbon atoms come out of supersaturated solution to combine with carbide forming elements to produce a fine dispersion of very small tempered carbides in a ferrite matrix (3). Hence the main alloying elements in hot work die steels are Chromium, Molybdenum, Tungsten and Vanadium. These elements increase hardenability and all produce hard stable alloy carbides. Mo, W and V also increase softening resistance during tempering and in later service. The main types of tool steels and some typical compositions are given in Tables 1 and 2. The classification given is according to the American Iron & Steel Institute (AISI) which is the most widely used system. This is based on quenching method, application, special characteristics and composition (5, 6). The Hot Work Die Steels are given the prefix letter H and are divided into three groups: Cr base H1-H19, W base H20- H-39 and Mo base H40-H49. The Hot Work (H grade) steels have lower Carbon contents (normally between 0.3 and 0.45 wt.%) than most other tool steels in order to obtain sufficient thermal shock resistance. Tool steels with C contents above 0.5 wt.% have greater hardness and wear resistance but are more prone to cracking on cycling between lower and higher temperatures. Grade H42, listed in Table 2 for comparison purposes with Series Type of Steel A AIR-HARDENING, MEDIUM ALLOY COLD WORKING D HIGH CARBON, HIGH CHROMIUM COLD WORKING H HOT WORKING L LOW ALLOY SPECIAL PURPOSE M MOLYBDENUM HIGH SPEED O OIL-HARDENING COLD WORKING P LOW CARBON MOULD S SHOCK RESISTING T TUNGSTEN HIGH SPEED W WATER-HARDENING Table 1. Main Series of Tool Steels AISI Designation.