Tool steel

The alloy carbide phases which precipitate and give rise to secondary hardening are listed in Table 3.1-76. 

The basic properties of tool steels that determine their performance in service are hardness, wear 

1 Type of carbide 1 Prototype II Lattice type II Occurrence, composilion  

M23C6 Cr23C6 Face-centered cubic In high-Cr steels M = Cr, Fe, W, Mo 

Air-hardening, medium-alloy, cold-worked steels 

Type of carbide II Prototype Lattice type Occurrence, composition  

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Vanadium is used in producing rust resistant and high speed tools steels. It is an important carbide stabilizer in making steels. 

Tools, cutting Tools, power Tool steels... 

By the 1950s P/M parts were used in postage meters and home appHances. In the 1970s P/M superaHoys for aerospace appHcations were used, followed by steel P/M forgings. The 1980s opened the way for rapid soHdification processing, P/M tool steels, and metal injection molded parts. 

Metal injection mol ding (MIM) holds great promise for producing complex shapes in large quantities. Spray forming, a single-step gas atomization and deposition process, produces near-net shape products. In this process droplets of molten metal are coUected and soHdifted onto a substrate. Potential appHcations include tool steel end mills, superalloy tubes, and aerospace turbine disks (6,7). 

P/M Tool Steels. In conventionally produced high alloy tool steels (slowly cooled cast ingots), carbide tends to segregate (48). Segregated clusters of carbide persist even after hot working, and cause undesirable effects on tool fabrication and tool performance. P/M tool steels, on the other hand, provide very fine and uniform carbides in the compact, the final bar stock, and the tools. Several tool steel suppHers consoHdate gas-atomized tool steel powder by HIP to intermediate shapes, which are then hot-worked to final mill shapes. Water-atomized tool steel powder is also available (see also T OOL materials). ... 

Small complex tool steel parts are being made by conventional compaction and sintering in vacuum to near theoretical density. AppHcations include spade drills, knife blades, slotting cutters, insert blades for gear cutters, reamer blades, and cutting tool inserts. 

EAE-based plants were once used primarily to produce highly specialized grades of steel, such as stainless and tool steels. The EAE-based minimill... 

About 800 million metric tons of raw steel is produced annually throughout the world. Its usehilness is enhanced by the fact that it is inexpensive. The price as of the mid-1990s ranged from ca 440/kg for the common grades to several dollars per kg for special steels such as certain tool steels. Prices have remained relatively constant since the early 1980s. 

Induction Furnace. The high frequency coreless induction furnace is used in the production of complex, high quaUty alloys such as tool steels. It is used also for remelting scrap from fine steels produced in arc furnaces, for melting chrome—nickel alloys and high manganese scrap, and more recentiy for vacuum steelmaking processes. 

High Speed Steels. Toward the latter part of the nineteenth century, a new he at-treatment technique for tool steels was developed in the United States (3,17) that enabled increased metal removal rates and cutting speeds. This material was termed high speed steel (HSS) because it nearly doubled the then maximum cutting speeds of carbon—low alloy steels. Cemented carbides and ceramics have since surpassed the cutting speed capabiUties of HSS by 5—15 times. 

AISI tool steel type Chemical composition, nominal % ... 

Fig. 4. Microstructure of AISI T15 tool steel (quenched and tempered) produced (a) from particles and (b) by the conventional technique (picral etch). In (a), the median and maximum carbide sizes are 1.3 and 3.5 mm, respectively in (b), 6.2 and 34 mm, respectively.

Fig. 5. Micrographs of the microstructure of fully hardened and tempered tool steels produced by the powder metallurgy technique, showing uniform distribution and fine carbide particles in the matrix, (a) M-42 (see Table 6) and (b) cobalt-free AlSl T-15 having a higher concentration of fine carbide...

Threshold limit values for the components of cemented carbides and tool steels are given in Table 14 (176). There is generally no fire or explosion hazard involved with tool steels, cemented carbides, or other tool materials. Fires can be handled as metal fires, eg, with Type D fire extinguishers. Most constituents of tool materials do not polymerize. 

G. A. Roberts,. C. Hamaker, and A. R. Johnson, Tool Steels, American Society for Metals, Metals Park, Ohio, 1962. 

R. Wilson, Metallurgy and Heat Treatment of Tool Steels, McGraw-HiU Book Co., Inc., New York, 1975. 

The injection mold need not be made of noncatalytic metals any high grade tool steel may be used because the plastic cools in the mold and undergoes Httle decomposition. However, the mold requires good venting to allow the passage of small amounts of acid gas as well as air. Vents tend to become clogged by corrosion and must be cleaned periodically. 

A hard, mst-resistant shaft of at least 0.25 micrometer finish is usually required. Common shaft surfaces are hardened tool steel, chrome plate, high strength bronze, and carbide and ceramic overlays. Test results over a broad speed range from 0.05 to 47 m/s (10 to 9200 fpm) iadicate that a coefficient of friction of 0.16—0.20 and a wear factor of 14 X 10 m /N(70x 10 ° in. min/ft-lb-h) are typical for dry operation of weU appHed grades of carbon—graphite (29). 

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