Machinery's Handbook, 31st Edition
High-Speed Tool Steels 445 AISI M42: In applications where high hardness both at regular and at elevated tempera tures is needed, this type of high-speed steel with high cobalt content can provide excellent service. Typical applications are tool bits, form tools, shaving tools, fly cutters, roll turning tools, and thread rolling dies. Important uses are found for M42, and for other types of the “M40” group, in the working of “difficult-to-machine” alloys. Tungsten-Type High-Speed Tool Steels.— For several decades following their intro duction, the tungsten-base high-speed steels were the only types available for cutting oper ations involving the generation of substantial heat and are still preferred by users who do not have the kind of advanced heat-treating equipment that efficient hardening of the molybdenum-type high-speed tool steels requires. Most tungsten high-speed steels dis play excellent resistance to decarburization and can be brought to good hardness by simple heat treatment. However, even with tungsten-type high-speed steels, heat treatment using modern methods and furnaces can appreciably improve the metallurgical qualities of the hardened material and the performance of the cutting tools made from these steels. Table 7. Tungsten High-Speed Tool Steels—Identifying Chemical Composition and Typical Heat-Treatment Data AISI Type T1 T2 T4 T5 T6 T8 T15 Identifying Chemical Elements in Percent C 0.75 0.80 0.75 0.80 0.80 0.75 1.50 W 18.00 18.00 18.00 18.00 20.00 14.00 12.00 Cr 4.00 4.00 4.00 4.00 4.50 4.00 4.00 V 1.00 2.00 1.00 2.00 1.50 2.00 5.00 Co … … 5.00 … … 5.00 5.00 Heat-Treatment Data Hardening Temperature Range ° F 2300– 2375 2300– 2375 2300– 2375 2325– 2375 2325– 2375 2300– 2375 2200– 2300 ° C 1260– 1302 1260– 1302 1260– 1302 1274– 1302 1274– 1302 1260– 1302 1204– 1260 Tempering Temperature Range ° F 1000– 1100 1000– 1100 1000– 1100 1000– 1100 1000– 1100 1000– 1100 1000– 1200 ° C 538– 593 538– 593 538– 593 538–593 538–593 538–593 538–649 Approx. Tempered Hardness, RC (Rockwell C scale) 65–60 66–61 66–62 65–60 65–60 65–60 68–63 Characteristics in Heat Treatment a Safety in Hardening C C D D D D D Depth of Hardening A A A A A A A Resistance to Decarburization A A B C C B B
Air or Salt
C D D B B E
C D D B B E
C D D A B E
C D
C D
C D
C D
Stability of Shape in Heat Treatment
Quenching Medium
Oil
Service Properties
Machinability Hot Hardness Wear Resistance Toughness
D D/E
D D/E
A B E
A B E
A B E
A A E
a Relative Ratings of Properties (A = greatest to E = least) Frequently Used Tungsten Types: AISI T1: Also mentioned as the 18-4-1 type with ref erence to the nominal percentage of its principal alloying elements (W-Cr-V), it is consid ered to be the classical type of high-speed tool steel. The chemical composition of T1 was developed in the early 1900s, and has changed very little since. T1 is still considered to be perhaps the best general-purpose high-speed tool steel because of the comparative ease of its machining and heat treatment. It combines a high degree of cutting ability with relative toughness. T1 steel is used for all types of multiple-edge cutting tools like drills, reamers, milling cutters, threading taps and dies, light- and medium-duty lathe tools, and is also used for punches, dies, and machine knives, as well as for structural parts that are subjected to elevated temperatures, like lathe centers and certain types of antifriction bearings. AISI T2: Similar to T1 except for somewhat higher carbon content and twice the vana dium contained in the former grade. Its handling ease, both in machining and heat treating, is comparable to that of T1, although it should be held at the quenching temperature slightly
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