Metallurgical Analysis & Alloy Selection (20CrMnTi vs 8620H) for Tractor Differential Gears

Material Selection Criteria for Differential Gearing

Planetary pinions and side gears within a tractor differential operate under extreme sliding contact friction, severe shock loads during differential lock engagements, and intense Hertzian contact pressures on gear flank profiles.

Chemical & Mechanical Comparison: 20CrMnTi vs. AISI 8620H

Two primary case-hardening steel grades dominate modern heavy agricultural gear production:

1. 20CrMnTi Alloy (GB/T 3077 / DIN 1.7147 equivalent): Enriched with Chromium, Manganese, and Titanium. Titanium micro-alloying acts as an effective grain refiner, stabilizing austenitic grain size during high-temperature carburizing cycles.
2. AISI 8620H Alloy (ASTM A304): Formulated with Nickel, Chromium, and Molybdenum. Nickel presence substantially bolsters fracture toughness (K1c) under sudden shock impacts.

Closed-Die Forging & Grain Flow Optimization

At PSNT, pre-machining billets undergo closed-die hot forging. This creates uninterrupted grain flow lines conforming to tooth geometry, augmenting tooth root bending strength by over 25% compared to bar-stock machining.