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A Complete Guide to 20CrMnTi Low-Carbon Alloy Carburizing Steel Abstract
20CrMnTi is a widely used medium-hardenability low-carbon alloy carburizing steel specified under GB/T 3077, dominating the manufacturing of automotive and construction machinery transmission components. After carburizing, quenching and low-temperature tempering, it achieves a hard wear-resistant surface and tough ductile core (case hardening characteristic), balancing abrasion resistance, contact fatigue strength and impact toughness. This paper systematically covers its grade definition, chemical composition, mechanical properties, full heat treatment workflow, metallographic structure, typical applications, comparison with quenched & tempered steels (40Cr, 42CrMo), and key manufacturing design notes for industry engineers and production technicians.
1. Grade Definition & Chemical Composition
1.1 Meaning of Grade Marking
- 20: Average carbon mass fraction ~0.20% (low-carbon matrix to retain core toughness)
- Cr, Mn, Ti: Alloying elements chromium, manganese and titanium added for hardenability, wear resistance and grain refinement
It is equivalent to SAE 5120 (US), SMnC420H (JIS) and 1.7147 (EU) international steel grades.
1.2 Standard Chemical Composition (Mass Fraction, %)
| Element | Content Range | Core Function |
|---|---|---|
| C | 0.17–0.23 | Low carbon ensures core ductility after quenching; provides carbon source for carburized case |
| Si | 0.17–0.37 | Deoxidation + mild solid-solution strengthening |
| Mn | 0.80–1.10 | Improve steel hardenability and overall tensile strength |
| Cr | 1.00–1.30 | Boost hardenability and surface wear resistance; not corrosion-resistant stainless steel |
| Ti | 0.04–0.10 | Inhibit austenite grain coarsening under high carburizing temperature; reduce heat treatment distortion |
| P / S | ≤0.035 each | Strict impurity control to avoid brittleness and fatigue defects |
2. Standard Mechanical Properties
All data apply to standard test specimens after specified heat treatment per GB/T 3077:
| Mechanical Index | Minimum Standard Value |
|---|---|
| Tensile Strength (Rm) | ≥1080 MPa |
| Lower Yield Strength (ReL) | ≥850 MPa |
| Elongation (A) | ≥10% |
| Reduction of Area (Z) | ≥45% |
| Charpy Impact Energy (KU₂) | ≥55 J |
Delivery State Hardness
Annealed / high-temperature tempered raw material: ≤217 HBW, good machinability for blank cutting and gear rough machining.
Post-Carburizing Finished Part Hardness
- Surface carburized layer: 58–62 HRC (high hardness, anti-wear, anti-contact fatigue)
- Part core: 30–45 HRC (strong and tough to resist impact load and tooth breakage)
Core hardness varies with part cross-section, quenching cooling rate and steel hardenability.
3. Complete Heat Treatment Process Route
Standard production workflow:
Forging blank → Normalizing / Isothermal Normalizing → Precision Machining → Local Anti-Carburizing Treatment (if required) → Carburizing → Quenching → Low-Temperature Tempering → Descaling → Finish Grinding (Gear Grinding / Cylindrical Grinding)
3.1 Normalizing / Isothermal Normalizing
- Heating temperature: 880–950°C
- Purposes: Refine uneven forged microstructure, optimize cutting performance, reduce post-heat-treatment distortion, lay uniform metallographic foundation for subsequent carburizing.
3.2 Carburizing
- Standard temperature range: 900–950°C
- Pub Time : 2026-07-23 09:21:18 >> News list
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