Machinery's Handbook, 31st Edition
GEAR MATERIALS
2321
Table 2. Compositions of Forged and Rolled Alloy Steels for Gears Steel Specification Chemical Composition a C Mn Si Ni Cr Mo AISI 4130 0.28–0.30 0.40–0.60 0.20–0.35 … 0.80–1.1 0.15–0.25 AISI 4140 0.38–0.43 0.75–1.0 0.20–0.35 … 0.80–1.1 0.15–0.25 AISI 4340 0.38–0.43 0.60–0.80 0.20–0.35 1.65–2.0 0.70–90 0.20–0.30 AISI 4615 0.13–0.18 0.45–0.65 0.20–0.35 1.65–2.0 … 0.20–0.30 AISI 4620 0.17–0.22 0.45–0.65 0.20–0.35 1.65–2.0 … 0.20–0.30 AISI 8615 0.13–0.18 0.70–0.90 0.20–0.35 0.40–0.70 0.40–0.60 0.15–0.25 AISI 8620 0.18–0.23 0.70–0.90 0.20–0.35 0.40–0.70 0.40–0.60 0.15–0.25 AISI 9310 0.08–0.13 0.45–0.65 0.20–0.35 3.0–3.5 1.0–1.4 0.08–0.15 Nitralloy Type N b 0.20–0.27 0.40–0.70 0.20–0.40 3.2–3.8 1.0–1.3 0.20–0.30 135 Mod. b 0.38–0.45 0.40–0.70 0.20–0.40 … 1.4–1.8 0.30–0.45 a C = carbon; Mn = manganese; Si = silicon; Ni = nickel; Cr = chromium, and Mo = molybdenum. b Both Nitralloy alloys contain aluminum 0.85–1.2% Steel Castings for Gears.— It is recommended that steel castings for cut gears be purchased on the basis of chemical analysis and that only two types of analysis be used, one for case- hardened gears and the other for both untreated gears and those which are to be hardened and tempered. The steel is to be made by the open hearth, crucible, or electric furnace processes. The converter process is not recognized. Sufficient risers must be provided to secure soundness and freedom from undue segregation. Risers should not be broken off the unannealed castings by force. Where risers are cut off with a torch, the cut should be at least one-half inch above the surface of the castings, and the remaining metal removed by chipping, grinding, or other noninjurious method. Steel for use in gears should conform to the requirements for chemical composition indi cated in Table 3. All steel castings for gears must be thoroughly normalized or annealed, using such temperature and time as will entirely eliminate the characteristic structure of unannealed castings. Table 3. Compositions of Cast Steels for Gears Steel Specification Chemical Composition a C Mn Si SAE-0022 0.12–0.22 0.50–0.90 0.60 Max. May be carburized SAE-0050 0.40–0.50 0.50–0.90 0.80 Max. Hardenable 210–250 a C = carbon; Mn = manganese; Si = silicon. Effect of Alloying Metals on Gear Steels.— The effect of the various alloying elements on steel are here summarized to assist in deciding on the particular kind of alloy steel to use for specific purposes. The characteristics outlined apply only to heat-treated steels. When the effect of the addition of an alloying element is stated, it is understood that reference is made to alloy steels of a given carbon content, compared with a plain carbon steel of the same carbon content. Nickel: The addition of nickel tends to increase the hardness and strength, with but little sacrifice of ductility. The hardness penetration is somewhat greater than that of plain carbon steels. Use of nickel as an alloying element lowers the critical points and produces less distortion, due to the lower quenching temperature. The nickel steels of the case- hardening group carburize more slowly, but the grain growth is less. Chromium: Chromium increases the hardness and strength over that obtained by the use of nickel, though the loss of ductility is greater. Chromium refines the grain and imparts a
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