Machinery's Handbook, 31st Edition
Heat Treatment of Steel 487 before hardening. A wide latitude in choice of built-up webs and easily machined hubs is afforded because the hardness of neither web nor hub is affected by the induction-harden- ing operation although slight dimensional changes may occur in certain designs. Regular carbon steels can be used in place of alloy steels for a wide variety of gears, and steel with a higher carbon content can frequently be substituted for a carburizing steel so that the carburizing operation can be eliminated. Another time-saving benefit is elimination of cleaning after hardening. In heating spur gear teeth by induction, the gear is usually placed inside a circular unit that combines the applicator coil and quenching ring. An automatic timing device controls both the heating and quenching cycles. During the heating cycle, the gear is rotated at 25 to 35 rpm to ensure uniform heating. In hardening bevel gears, the applicator coil is wound to conform to the face angle of the gear. In some spiral-bevel gears, there is a tendency to obtain more heat on one side of the tooth than on the other. In some sizes of spiral-bevel gears, this tendency can be overcome by applying slightly more heat to ensure hardening of the concave side. In some forms of spiral-bevel gears, it has been the practice to carburize that part of the gear surface which is to be hardened after the teeth have been rough-cut. Carburizing is followed by the finish-cutting operation, after which the teeth can be induction heated, using a long enough period to heat the entire tooth. When the gear is quenched, only the carburized surface will become hardened. Table 4a. Typical Heat Treatments for SAE Carbon Steels (Carburizing Grades) SAE No. Normalize, Deg. F Carburize Reheat 2nd Reheat, Deg. F Temper, b Deg. F Deg. C Deg. F Deg. C Deg. F Deg. C
… 1650–1700 899–927 A … … … … … 250–400 121– 204 … 1650–1700 899–927 B 1400–1450 760–788 A … … 250–400 121– 204 … 1650–1700 899–927 C 1400–1450 760–788 A … … 250–400 121– 204 … 1650–1700 899–927 C 1650–1700 899–927 B 1400–1450 A 250–400 121– 204 … 1500–1650 c, d 816–899 c,d B … … … … … Optional Optional … 1350–1575 e, d 732–857 e,d D … … … … … Optional Optional 1650–1750 f 1650–1700 899–927 E …… …… … … … 250–400 121– 204 … 1350–1575 e, d 732–857 e,d D … … … … … Optional Optional … 1650–1700 899–927 A … … … … … 250–400 121– 204 … 1500–1650 c, d 816–899 c,d B … … … … … Optional Optional … 1350–1575 e, d 732–857 e,d D … … … … … Optional Optional … 1500–1650 c , d 816–899 c,d B … … … … … Optional Optional … 1350–1575 e, d 732–857 e,d D … … … … … Optional Optional
1010 to 1022
1024 1025 1026 1027 1030 1111 1112 1113
1500–1650 c, d 1350–1575 e, d
816–899 c, d 732–857 e, d
… …
B D
… …
… …
… …
… …
… …
Optional Optional
Optional Optional
… 1650–1700 899–927 A … … … … … 250–400 121– 204 … 1650–1700 899–927 B 1400–1450 760–788 A … … 250–400 121– 204 … 1650–1700 899–927 C 1400–1450 760–788 A … … 250–400 121– 204 … 1650–1700 899–927 C 1650–1700 899–927 B 1400–1450 A 250–400 121– 204 … 1500–1650 c, d 816–899 c,d B … … … … … Optional Optional … 1350–1575 e, d 732–857 e,d D … … … … … Optional Optional
1109 to 1120
1126 … 1500–1650 c, d 816–899 c,d B … … … … … Optional Optional … 1350–1575 e, d 732–857 e,d D … … … … … Optional Optional a Symbols: A = water or brine; B = water or oil; C = cool slowly; D = air or oil; E = oil; F = water, brine, or oil. b Even where tempering temperatures are shown, tempering is not mandatory in many applications. Tempering is usually employed for partial stress relief and improved resistance to grinding cracks. c Activated or cyanide baths. d May be given refining heat as in other processes. e Carbonitriding atmospheres. f Normalizing temperatures at least 50°F (28°C) above the carburizing temperature are sometimes recommended where minimum heat-treatment distortion is of vital importance.
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