Page 160 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Section 5.5 Carbon and Alloy Steels

TABLE 5.2

Typical Mechanical Properties of Selected Carbon and Alloy Steels
Ultimate Yield Elongation Reduction
tensile strength strength in 50 mm of area Hardness
AISI Condition (MPa) (MPa) (%) (%) (HB)
1020 As-rolled 448 346 36 59 143
Normalized 441 330 35 67 131
Annealed 393 294 36 66 111
1080 As-rolled 1010 586 12 17 293
Normalized 965 524 11 20 293
Annealed 615 375 24 45 174
3140 Normalized 891 599 262
Annealed 689 422 197
4340 Normalized 1279 861 363
Annealed 744 472 217
8620 Normalized 632 385 183
Annealed 536 357 149

Table 5.2. The machinability, formability, and Weldability of such steels are described
in various chapters throughout this text.

° Low-carbon steel, also called mild steel, has less than 0.30% C. It often is used
for common industrial products (such as bolts, nuts, sheets, plates, and tubes)
and for machine components that do not require high strength.
° Medium-carbon steel has 0.30 to 0.60% C. It generally is used in applications re-
quiring higher strength than is available in lovv-carbon steels, such as in machin-
ery, automotive and agricultural equipment parts (gears, axles, connecting rods,
and crankshafts), railroad equipment, and parts for metalworking machinery.
° High-carbon steel has more than 0.60% C. Generally, high-carbon steel is used
for applications requiring strength, hardness, and Wear resistance, such as cut-
ting tools, cable, music vvire, springs, and cutlery. After being manufactured into
shapes, the parts usually are heat treated and tempered. The higher the carbon
content of the steel, the higher is its hardness, strength, and wear resistance after
heat treatment.
' Carbon steels containing sulfur and phosphorus are known as resulfurized car-
bon steels (11xx series) and rephosphorized and resulfurized carbon steels (12xx
series). For example, 1112 steel is a resulfurized steel with a carbon content of
0.12%. These steels have improved machinability, as described in Section 21.7.
5.5.5 Alloy Steels

Steels containing significant amounts of alloying elements are called alloy steels;
they usually are made with more care than are carbon steels. Structural-grade alloy
steels are used mainly in the construction and transportation industries because of
their high strength. Other alloy steels are used in applications Where strength, hard-
ness, creep and fatigue resistance, and toughness are required. These steels can be
heat treated to obtain the desired properties.

5.5.6 High-strength Low-alloy Steels
In order to improve the strength-to-weight ratio of steels, a number of high-strength,
low-alloy steels (I-ISLA) have been developed. First developed in the 1930s, HSLA