Page 166 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Section 5.7 Tool and Die Steels |45

resistance and ductility, and they have high strength at elevated temperatures.
Their main application is in aircraft and aerospace structural components.

Duplex Structure. These steels have a mixture of austenite and ferrite. They have
good strength and have higher resistance to both corrosion (in most environments)
and stress-corrosion cracking than do the 300 series of austenitic steels. Typical
applications are in Water-treatment plants and in heat-exchanger components.

EXAMPLE 5.2 Stainless Steels in Automobiles

The types of stainless steel usually selected by materi~ exhaust manifolds (replacing cast-iron manifolds to
als engineers for use in automobile parts are 301, 409, reduce weight, increase durability, provide higher
430, and 434. Because of its good corrosion resistance thermal conductivity, and reduce emissions), mufflers
and mechanical properties, type 301 is used for wheel and tailpipes (to offer better corrosion protection in
covers. Cold working during the forming process in- harsh environments), and brake tubing.
creases its yield strength (by means of strain harden- Another example of the use of stainless steel in
ing) and gives the wheel cover a springlike action. automobiles is the DeLaurean sports car, manu-
Type 409 is used extensively for catalytic factured during 1981-1982 in Northern Ireland by
converters. Type 430 had been used for automotive the DeLautean Motor Company. The DMC-12 model
trim, but it is not as resistant as type 434 is to the of this car (at an original price of $12,000) had a body
deicing salts used in colder climates in winter. As a made of buffed 304 stainless~steel panels attached to a
result, its use is now limited. In addition to being more fiberglass underbody; the cars were sold unpainted.
corrosion resistant, type 434 closely resembles the For a variety of reasons, however; the car was not
color of chromium plating, so it has become an commercially successful in spite of its innovative
attractive alternative to 430. Stainless steels also are features. It is estimated that about 6,500 are still in
well suited for use in other automobile components: existence.

5.7 Tool and Die Steels

Tool and die steels are specially alloyed steels (Tables 5.6 and 5.7) designed for high
strength, impact toughness, and Wear resistance at room and elevated temperatures.
They commonly are used in the forming and machining of metals (Parts III and IV).

TABLE 5.6
Basic Types ofTool and Die Steels
Type AISI
High speed M (molybdenum base)
T (tungsten base)
Hot work H1 to H19 (chromium base)
H20 to H39 (tungsten base)
H40 to H59 (molybdenum base)
Cold Work D (high carbon, high chromium)
A (medium alloy, air hardening)
O (oil hardening)
Shock resisting S
Mold steels P1 to P19 (low carbon)
P20 to P39 (others)
Special purpose L (low alloy)
F (carbon-tungsten)
Water hardening W