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SAE 8620H(S) Gear Steel
SAE 8620H is a representative grade of nickel-chromium-molybdenum carburizing gear steel (containing 0.18–0.23% C, 0.40–0.70% Cr, 0.40–0.70% Ni, and 0.15–0.25% Mo). The "H" suffix indicates that the steel is supplied according to the hardenability bands defined in SAE J1268, while the "(S)" designation denotes a "narrow-band" version—a tighter specification that further restricts the hardenability range, resulting in less variation in end-quench (Jominy) curves and superior consistency during heat treatment.
Its unique advantage lies in its nickel content. While nickel does not significantly increase hardness, it substantially improves core toughness and reduces notch sensitivity—critical factors for gears subjected to high impact loads. Compared to plain chromium steels (such as 20Cr or 5120), 8620H offers superior core toughness after carburizing and quenching, provides a longer bending fatigue life at the gear root, and lowers the risk of tooth fracture in heavy-duty applications.
The era of new energy vehicles (NEVs) has provided a new arena for this alloy. Although gears in electric vehicle reducers are spared the shocks associated with a clutch, they must contend with high instantaneous torque. Furthermore, the push for lightweight design often leads to smaller gear modules, which concentrates stress at the gear root. When combined with the stringent gear-grinding precision required for NVH (noise, vibration, and harshness) performance, the batch-to-batch consistency of the narrow-band 8620H(S) becomes a significant asset; it ensures minimal variation in the depth of the carburized (hardened) layer across a single heat, allowing for more precise design of grinding allowances.
Typical applications include heavy-duty transmission gears, differential bevel gears, commercial vehicle drivetrain components, and safety-critical parts where gear-tooth fracture is absolutely unacceptable. When procuring this material, it is essential to specify whether the standard "H" band or the "S" narrow-band version is required, and to define the necessary carburized case depth, grain size, and banding limits; additionally, one should request the actual measured end-quench (Jominy) curves. Given the high volatility of nickel prices, the cost of 8620H(S) is significantly influenced by the market price of nickel, making long-term supply agreements with locked-in pricing a key strategy for cost control.
Its unique advantage lies in its nickel content. While nickel does not significantly increase hardness, it substantially improves core toughness and reduces notch sensitivity—critical factors for gears subjected to high impact loads. Compared to plain chromium steels (such as 20Cr or 5120), 8620H offers superior core toughness after carburizing and quenching, provides a longer bending fatigue life at the gear root, and lowers the risk of tooth fracture in heavy-duty applications.
The era of new energy vehicles (NEVs) has provided a new arena for this alloy. Although gears in electric vehicle reducers are spared the shocks associated with a clutch, they must contend with high instantaneous torque. Furthermore, the push for lightweight design often leads to smaller gear modules, which concentrates stress at the gear root. When combined with the stringent gear-grinding precision required for NVH (noise, vibration, and harshness) performance, the batch-to-batch consistency of the narrow-band 8620H(S) becomes a significant asset; it ensures minimal variation in the depth of the carburized (hardened) layer across a single heat, allowing for more precise design of grinding allowances.
Typical applications include heavy-duty transmission gears, differential bevel gears, commercial vehicle drivetrain components, and safety-critical parts where gear-tooth fracture is absolutely unacceptable. When procuring this material, it is essential to specify whether the standard "H" band or the "S" narrow-band version is required, and to define the necessary carburized case depth, grain size, and banding limits; additionally, one should request the actual measured end-quench (Jominy) curves. Given the high volatility of nickel prices, the cost of 8620H(S) is significantly influenced by the market price of nickel, making long-term supply agreements with locked-in pricing a key strategy for cost control.
