Machinery's Handbook, 31st Edition
Alloy Steels 411 carburizing steels discussed earlier. In general, these steels can be used for average-size case-hardened automotive parts, such as gears, pinions, piston pins, ball studs, universal joint crosses, crankshafts, etc. Satisfactory case hardness is usually produced by oil quenching. Core Properties: The core properties of case-hardened steels depend on both carbon and alloy content of the steel. Each of the general types of alloy case-hardening steel is usually made with two or more carbon contents to permit different hardenability in the core. The most desirable hardness for the core depends on the design and functioning of the individual part. In general, where high compressive loads are encountered, relatively high core hardness is beneficial in supporting the case. Low core hardnesses may be desirable where great toughness is essential. The case-hardening steels may be divided into three general classes, depending on hard enability of the core. a) Low-Hardenability Core: SAE 4017, 4023, 4024, 4027 * , 4028 * , 4608, 4615, 4617 * , 8615 * , 8617 * b) Medium-Hardenability Core: SAE 1320, 2317, 2512, 2515 * , 3115, 3120, 4032, 4119, 4317, 4620, 4621, 4812, 4815 * , 5115, 5120, 8620, 8622, 8720, 9420 c) High-Hardenability Core: SAE 2517, 3310, 3316, 4320, 4817, 4820, 9310, 9315, 9317 Heat Treatments: In general, all the alloy carburizing steels are made with fine grain and most are suitable for direct quenching from the carburizing temperature. Several other types of heat treatment involving single and double quenching are also used for most of these steels. See Table 4a on page 487 and Table 4b on page 488. Directly Hardenable Grades of Alloy Steels.— These steels may be considered in five groups on the basis of approximate mean carbon content of the SAE specification. In gen eral, the last two figures of the specification agree with the mean carbon content. Conse quently the heading 0.30–0.37 Mean Carbon Content of SAE Specification includes steels such as SAE 1330, 3135, and 4137. It is necessary to deviate from the above plan in the classification of the carbon molybde num steels. Because of the low alloy content of carbon molybdenum steels, it is customary to specify a higher carbon content for any given application than would be specified for other alloy steels. For example, SAE 4063 is used for the same applications as SAE 4140, 4145, and 5150. Consequently, in the following discussion, the carbon molybdenum steels have been shown in the groups where they belong on the basis of applications rather than carbon content.
Mean Carbon Content of SAE Specification (a) 0.30–0.37 percent (b) 0.40–0.42 percent (c) 0.45–0.50 percent (d) 0.50–0.62 percent (e) 1.02 percent
Common Applications
Heat-treated parts requiring moderate strength and great toughness. Heat-treated parts requiring higher strength and good toughness. Heat-treated parts requiring fairly high hardness and strength with moderate toughness.
Springs and hand tools.
Ball and roller bearings. For the present discussion, steels of each carbon content are divided into two or three groups on the basis of hardenability. Transformation ranges and consequently heat- treating practices vary somewhat with different alloying elements even though the hardenability is not changed. 0.30–0.37 Mean Carbon Content of SAE Specification: These steels are frequently used for water-quenched parts of moderate section size and for oil-quenched parts of small section size. Typical applications of these steels are connecting rods, steering arms and steering knuckles, axle shafts, bolts, studs, screws, and other parts requiring strength * Borderline classifications might be considered in the next higher hardenability group.
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