What is 42CrMo (AISI 4140 Alloy Steel)?
AISI 4140 Alloy Steel is a high-performance alloy steel designed for demanding applications requiring high strength, wear resistance, and good hardenability. This comprehensive guide covers chemical composition, mechanical properties, heat treatment, and machining characteristics per ASTM/GB standards.
Chemical Composition (ASTM A29/GB/T 3077)
| Element | Content (%) | Specification |
|---|---|---|
| Carbon (C) | 0.38-0.45% | GB/T 3077 |
| Chromium (Cr) | 1.35-1.65% | GB/T 3077 |
| Molybdenum (Mo) | 0.15-0.25% | GB/T 3077 |
| Aluminum (Al) | 0.70-1.10% | GB/T 3077 |
| Manganese (Mn) | 0.45-0.70% | GB/T 3077 |
| Silicon (Si) | 0.20-0.45% | GB/T 3077 |
Mechanical Properties (Quenched & Tempered)
| Property | Value | Standard |
|---|---|---|
| Tensile Strength | ≥980 MPa | GB/T 3077 |
| Yield Strength | ≥835 MPa | GB/T 3077 |
| Elongation | ≥14% | GB/T 3077 |
| Impact Strength (KV) | ≥63 J | GB/T 229 |
| Hardness | 28-34 HRC | ASTM E18 |
Key Features
- Excellent nitriding properties: Forms hard nitride layer for superior surface hardness
- High strength: Excellent tensile and yield strength after heat treatment
- Good toughness: Balanced mechanical properties for demanding applications
- Wear resistant: Superior wear resistance after nitriding treatment
- Good hardenability: Uniform hardness throughout cross-section
- Fatigue resistant: Excellent fatigue strength for cyclic loading applications
Common Applications
- Injection molding: Mold cores, cavities, inserts for high-volume production
- Extrusion: Extrusion screws, barrels, dies for plastic processing
- Automotive: Crankshafts, camshafts, gears, cylinder liners
- Machinery: High-strength bolts, studs, shafts, spindles
- Power generation: Turbine blades, valve components, boiler parts
- Petrochemical: Reactor components, heat exchanger parts, valve bodies
Heat Treatment
Quenching & Tempering
- Austenitizing: 930-950°C, oil quench
- Tempering: 580-620°C for desired hardness
- Hardness after Q&T: 28-34 HRC
Nitriding Treatment
- Gas nitriding: 500-530°C, 20-50 hours
- Plasma nitriding: 480-520°C, 10-30 hours
- Surface hardness: 900-1200 HV (65-70 HRC equivalent)
- Case depth: 0.3-0.6mm typical
CNC Machining Guidelines
Tool Selection
- Tool material: Carbide (YG/YW class) or coated carbide
- Tool geometry: Positive rake angle (5-10°), relief angle (8-12°)
- Nose radius: 0.4-0.8mm for finishing, 0.8-1.2mm for roughing
- Coating: TiAlN or AlTiN for improved tool life
Recommended Cutting Parameters (Annealed Condition)
| Operation | Cutting Speed (m/min) | Feed Rate (mm/rev) | Depth of Cut (mm) |
|---|---|---|---|
| Rough Turning | 80-120 | 0.2-0.4 | 2-5 |
| Finish Turning | 120-180 | 0.05-0.15 | 0.2-0.5 |
| Milling | 100-150 | 0.1-0.3 | 1-4 |
| Drilling | 50-80 | 0.1-0.2 | N/A |
Coolant & Lubrication
- Coolant type: Emulsion or semi-synthetic coolant with EP additives
- Coolant pressure: ≥5 MPa, directed at cutting zone
- Through-tool coolant: Recommended for deep hole drilling
Surface Finish Options
- As-machined: Ra 1.6-3.2 μm
- Fine turning: Ra 0.8-1.6 μm
- Grinding: Ra 0.4-0.8 μm
- Polishing: Ra 0.2-0.4 μm
- Nitriding: Surface hardening for wear resistance
- Chrome plating: Decorative and corrosion resistant
- Nickel plating: Corrosion resistant coating