Section 13. qxd

CUTTING-TOOL MATERIALS
A wide variety of 
cutting-tool materials
are available. The selection of a
proper material depends on such factors as the cutting operation
involved, the machine to be used, the workpiece material, production
requirements, cost, and surface finish and accuracy desired. The major
qualities required in a cutting tool are (1) hot hardness, (2) resistance
to mechanical impact and thermal shock, (3) wear resistance, and 
(4) chemical stability and inertness to the workpiece material being
machined. (See Table 13.4.1 and Figs. 13.4.6 and 13.4.7.)
Materials for cutting tools include high-speed steels, cast alloys,
carbides, ceramics or oxides, cubic boron nitride, and diamond.
Understanding the different types of 
tool steels
(see Sec. 6.2) requires
knowledge of the role of different alloying elements. These elements
are added to (1) obtain greater hardness and wear resistance, (2) obtain
greater impact toughness, (3) impart hot hardness to the steel such that
its hardness is maintained at high cutting temperatures, and (4) decrease
distortion and warpage during heat treating.
Table 13.4.1
Characteristics of Cutting-Tool Materials
High-
Cast
Polycrystalline
speed
cobalt
Coated
cubic boron
steels
alloys
Carbides
carbides
Ceramics
nitride
Diamond
Hot hardness
increasing
Toughness
increasing
Impact strength
increasing
Wear resistance
increasing
Chipping resistance
increasing
Cutting speed
increasing
Thermal shock
resistance
increasing
Tool material cost
increasing
N
OTE
: These tool materials have a wide range of compositions and properties; thus overlapping characteristics exist in many categories of tool materials.
S
OURCE
: After R Komanduri.
Section_13.qxd 10/05/06 10:32 Page 13-52

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Carbon
forms a carbide with iron, making it respond to hardening and
thus increasing the hardness, strength, and wear resistance. The carbon
content of tool steels ranges from 0.6 to 1.4 percent.