Advanced Heat Treatment Technologies For Bearing Manufacturing | Shangdong Yueheng

Heat treatment governs bearing performance metrics including contact fatigue life (L10 rating), wear resistance, and dimensional stability. Modern production requires ±3°C temperature control and process capability CPK≥1.33. Core sequence: Spheroidizing Annealing → Quenching → Low-Temperature Tempering → Stabilization.

1.Spheroidizing Annealing

Objective: Eliminate forging carbide networks (≤Grade 2), form homogeneous spheroidized pearlite (carbide spheroidization ≥90%, diameter 0.2-0.6μm), hardness 179-207 HB. Two-stage protocol:

• Stage 1: 790±10°C × 2-4h austenitization (partial carbide dissolution)
• Stage 2: 710±10°C × 4-6h slow cooling (≤20°C/h) to 650°C, controlled cooling curveprevents coarse carbide precipitation

Critical parameter: Grain size 7-8 (ASTM E112)

2.Quenching Process

Salt bath (BaCl₂:KCl=3:1) or protective atmosphere (N₂-CH₃OH, oxygen probe ≤0.5%):

• GCr15 steel: 845±5°C × time factor (wall thickness × 0.8-1.2 min/mm)
• Cooling kinetics: 800→500°C cooling rate ≥45°C/s (avoid ferrite formation), slow cooling below 300°C
• Target: Cryptocrystalline martensite (>95%, needle length ≤0.02mm) + retained austenite (<5%)

3.Low-Temperature Tempering

150-180°C × 2-4h (±3°C) in forced convection air furnace:

• ε-Fe₂.₄C precipitation in martensite, hardness 61-65 HRC
• Austenite decomposition: >80% (XRD verified)
• Stress relief model: σ_residual=σ_initial×e^(-0.02t) (t in hours)

4.Special Processes & Innovations

• Austempering: 230±10°C salt bath × 2h → lower bainite (58-62 HRC, KCV≥50J/cm²)
• Deep Cryo: -70°C × 4h (liquid nitrogen spray), austenite→martensite transformation >95%
• Laser Hardening: 1064nm wavelength creates 0.3mm case depth, ↑40% contact fatigue life

Quality Assurance Framework: