Fig. 10.89 Fracture of a carburized gear in AISI 8620 steel. The fracture happened in the radial plane. To the right, fracture initiation at the root of one of the gear teeth (some secondary initiation also toward the gear hub). The fracture aspect changes highlight the carburized region More

Fig. 8.12 Grain growth in a plain carbon 1018 steel versus a triple-alloyed 8620 steel at 1010 °C (1850 °F). The alloying elements cause a grain-boundary drag effect and inhibit grain growth. Source: Ref 8.7 More

Fig. 40 Bending fatigue fractures in several teeth of a grade 8620 steel spur gear, carburized and hardened to 60 HRC in the case. It can be seen that tooth A fractured first, for it has the largest fatigue area, originating in the fillet on the arrow side of the tooth. Gear teeth More

Fig. 23 Comparison of Jominy hardenability curves for 8620H and 8620 steels. Chemistry at maximum and minimum of the chemistry range. Source: Ref 11 More

Fig. 1 Chart for plotting 8620 steel test pin variation by characteristic. (a) Effective case depth characteristic. (b) Surface hardness characteristic. (c) Center core hardness characteristic. (d) Chart to plot data from (a), (b), and (c) by cycle and furnace. Source: Ref 1 More

Fig. 9 Fatigue striations in low-carbon alloy steel (8620). This scanning electron microscope fractograph shows the roughly horizontal ridges, which are the advance of the crack front with each load application. The crack progresses in the direction of the arrow. Original magnification at 2000× More

Fig. 8 Carbon gradients for gas-carburized 1020 and 8620 steels. The 1020 steel was carburized in a batch furnace, and the 8620 was carburized in a pit furnace. More

Fig. 35 Microcracks in the martensitic case of a coarse-grained SAE 8620 steel More

Fig. 38 The case and core microstructure of carburized SAE 8620 test specimens (0.95% C potential); carburized at 955 °C (1750 °F), quenched into a 50:50 mixture of sodium nitrate and potassium nitrate at 250 °C (480 °F), held 120 min, then air cooled and tempered at 250 °C (480 °F) for 240 More

Fig. 46 Microstructure of SAE 8620 case of a mold taken just below the surface. Etchant: alkaline sodium picrate boiling (60 s), area just below the surface. Original magnification: 500×. Courtesy of G. Vander Voort, Buehler Ltd., Lake Bluff, IL More

Fig. 49 Micrograph of poorly carburized SAE 8620 mold showing decarburization at the surface (note patches of ferrite and pearlite). Below this zone is where the grain-boundary carbides are seen. Original magnification: 500×. Courtesy of G. Vander Voort, Buehler Ltd., Lake Bluff, IL More

Fig. 3 Lath (low-carbon) martensite in SAE 8620 alloy steel (Fe, 0.2% C, 0.8% Mn, 0.55% Ni, 0.5% Cr, 0.2% Mo) after heat treatment (954 °C, or 1750 °F, for 1 h, water quench) More

Fig. 16.28 Hardenability of an 8620 type steel, as measured by ideal diameter and multiplying factor, as a function of effective boron content. Source: Ref 16.38 More

Fig. 21.14 Microstructure adjacent to surface of 8620 steel carburized at 1050 °C (1920 °F), oil quenched from 845 °C (1550 °F), and reheated to 845 °C (1550 °F) and quenched. Original magnification at 1000×. Source: Ref 21.28 More

Fig. 21.15 High austenite (white phase) content in corner of an 8620 steel sample carburized and diffused at 1050 °C (1920 °F) and cooled to 845 °C (1550 °F) before oil quenching. Source: Ref 21.29 More

Fig. 21.17 Microcracks in the martensite of a carburized coarse-grained 8620 steel. Source: Ref 21.31 More

Fig. 21.19 Fatigue crack initiation in carburized coarse-grained 8620 steel (a) quenched directly from carburizing at 927 °C (1700 °F) and (b) reheated after carburizing to 788 °C (1450 °F). Both specimens tempered at 145 °C (300 °F). Scanning electron micrographs. Source: Ref 21.31 More

Fig. 21.20 Overload case fracture surfaces in carburized 8620 steel (a) quenched directly after carburizing at 927 °C (1700 °F) and (b) reheated to 788 °C (1450 °F). Both specimens tempered at 145 °C (300 °F). Scanning electron micrographs. Source: Ref 21.37 More

Fig. 21.28 Stress versus cycles to failure for gas-carburized 8620 and 4615 steels. Source: Ref 21.52 More

Fig. 21.29 Residual stress profiles for gas-carburized 8620 and 4615 steels. Source: Ref 21.52 More