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SAE 4320H high-strength gears steel
SAE 4320H is a high-performance carburizing steel specifically designed for the manufacture of gears and shafts that must withstand heavy impact loads while possessing high surface wear resistance. The "H" suffix in its designation ensures that its hardenability falls within a controlled range, thereby providing a stable and consistent heat treatment response for critical components. The nominal chemical composition of this steel grade includes 1.65–2.00% nickel, 0.40–0.60% chromium, and 0.20–0.30% molybdenum—with its higher nickel content serving as the key distinguishing feature that sets it apart from low-alloy steel grades such as 8620H.
The high nickel level delivers exceptional core toughness and impact resistance, even at case hardness levels of 58–62 HRC after carburizing. Typical heat treatment involves carburizing at 925°C, followed by oil quenching and tempering at 150–200°C. This produces a effective case depth of 1.0–1.5 mm while maintaining a ductile core with Charpy V-notch impact values exceeding 60 J at room temperature.
Application Case – Mining Dump Truck Final Drive Gears:
A leading off-highway vehicle manufacturer experienced premature tooth breakage in final drive gears made from SAE 8620H, operating in abrasive underground mining conditions. The failure mode was impact fatigue from sudden load spikes when hauling 40-ton loads over uneven terrain. Switching to SAE 4320H increased core impact strength by 65% while maintaining identical case hardness. After 5,000 field hours, the 4320H gears showed no tooth fracture, extending service intervals from 12 to 24 months.
In summary, SAE 4320H is the preferred choice for heavy-duty drivetrain components where high core toughness must accompany wear-resistant surfaces. Applications include off-highway truck gears, construction equipment final drives, and helicopter transmission components.
The high nickel level delivers exceptional core toughness and impact resistance, even at case hardness levels of 58–62 HRC after carburizing. Typical heat treatment involves carburizing at 925°C, followed by oil quenching and tempering at 150–200°C. This produces a effective case depth of 1.0–1.5 mm while maintaining a ductile core with Charpy V-notch impact values exceeding 60 J at room temperature.
Application Case – Mining Dump Truck Final Drive Gears:
A leading off-highway vehicle manufacturer experienced premature tooth breakage in final drive gears made from SAE 8620H, operating in abrasive underground mining conditions. The failure mode was impact fatigue from sudden load spikes when hauling 40-ton loads over uneven terrain. Switching to SAE 4320H increased core impact strength by 65% while maintaining identical case hardness. After 5,000 field hours, the 4320H gears showed no tooth fracture, extending service intervals from 12 to 24 months.
In summary, SAE 4320H is the preferred choice for heavy-duty drivetrain components where high core toughness must accompany wear-resistant surfaces. Applications include off-highway truck gears, construction equipment final drives, and helicopter transmission components.
