If you’re designing parts that need a tough coreet a hard, surface résistante à l'usure, comme les engrenages automobiles, puits industriels, or aerospace fasteners—you need a material that balances ductility and surface strength.AISI 8620 acier allié is the perfect solution: comme nickel-chrome-molybdène à faible teneur en carbone (Ni-Cr-Mo) alliage, c'est idéal pour la carburation (un traitement thermique qui ne durcit que la surface), delivering a hard outer layer (jusqu'à 60 CRH) and a tough inner core. Ce guide détaille ses propriétés, applications du monde réel, processus de fabrication, and material comparisons to help you solve “tough core + hard surface” design challenges.
1. Material Properties of AISI 8620 Acier allié
AISI 8620’s performance comes from its low-carbon (0.18–0.23%) and Ni-Cr-Mo composition: low carbon keeps the core ductile, nickel boostsdureté, chromium enhances surface hardenability, and molybdenum improveslimite de fatigue. Let’s explore its key properties in detail.
1.1 Chemical Composition
AISI 8620 adheres to ASTM A29/A29M standards, with elements optimized for carburizing. Below is its typical composition:
| Element | Symbol | Content Range (%) | Key Role |
|---|---|---|---|
| Carbon (C) | C | 0.18 – 0.23 | Low enough to keep the core ductile; reacts with carbon during carburizing to harden the surface |
| Nickel (Dans) | Dans | 0.40 – 0.70 | Core toughness booster; maintainsimpact toughness at low temperatures (-30 °C) |
| Chromium (Cr) | Cr | 0.40 – 0.60 | Enhances surface hardenability; améliorerésistance à la corrosion of the carburized layer |
| Molybdène (Mo) | Mo | 0.15 – 0.25 | Raiseslimite de fatigue; prevents brittleness in the carburized surface |
| Manganese (Mn) | Mn | 0.70 – 0.90 | Refines grain structure; boosterésistance à la traction without reducing ductility |
| Silicium (Et) | Et | 0.15 – 0.35 | Aids deoxidation; supports stability during carburizing |
| Phosphorus (P.) | P. | ≤ 0.035 | Minimized to avoid brittle fracture in the carburized layer |
| Sulfur (S) | S | ≤ 0.040 | Controlled to balanceusinabilité et qualité de surface (lower S = smoother carburized surfaces) |
| Vanadium (V) | V | ≤ 0.03 | Trace element; refines grains for uniform surface hardening |
| Cuivre (Cu) | Cu | ≤ 0.30 | Trace element; adds mild atmospheric corrosion resistance for outdoor parts |
1.2 Physical Properties
These traits make AISI 8620 ideal for carburized parts across industries:
- Densité: 7.85 g/cm³ (same as standard steels)—simplifies weight calculations for gears, arbres, or fasteners
- Point de fusion: 1,420 – 1,450 °C (2,588 – 2,642 °F)—compatible with carburizing and forging processes
- Conductivité thermique: 42.0 W/(m·K) à 20 °C; 38.0 W/(m·K) à 300 °C—ensures even carbon diffusion during carburizing (no uneven surface hardness)
- Coefficient de dilatation thermique: 11.5 × 10⁻⁶/°C (20 – 100 °C)—minimizes distortion during carburizing and quenching
- Magnetic Properties: Ferromagnetic—enables non-destructive testing (CND) like magnetic particle inspection to check surface cracks after carburizing.
1.3 Propriétés mécaniques
AISI 8620’s mechanical performance depends on carburizing: the surface is hard, while the core remains tough. Below are typical values for carburized and non-carburized conditions:
| Propriété | Measurement Method | Non-Carburized (Annealed) | Carburized (0.8–1.0% Surface C) |
|---|---|---|---|
| Surface Hardness | CRH | 18 – 22 CRH | 58 – 60 CRH |
| Core Hardness | CRH | 18 – 22 CRH | 30 – 35 CRH |
| Résistance à la traction | MPa (ksi) | 600 MPa (87 ksi) | 1,100 MPa (159 ksi) |
| Yield Strength | MPa (ksi) | 350 MPa (51 ksi) | 800 MPa (116 ksi) |
| Élongation | % (dans 50 mm) | 28 – 32% | 12 – 15% |
| Impact Toughness | J (à -30 °C) | ≥ 90 J | ≥ 45 J (core toughness) |
| Fatigue Limit | MPa (rotating beam) | 300 MPa | 650 MPa |
1.4 Other Properties
AISI 8620’s traits solve “tough core + hard surface” challenges:
- Weldability: Excellent—low carbon allows welding without preheating (for non-carburized parts); carburized parts need grinding to remove surface carbon before welding.
- Formabilité: Great—soft in the annealed condition (18–22 HRC), so it can be bent, forged, or stamped into complex shapes (par ex., ébauches d'engrenages) before carburizing.
- Usinabilité: Excellent—annealed AISI 8620 cuts easily with HSS or carbide tools; carburized parts require grinding for final shaping.
- Résistance à la corrosion: Moderate—chromium in the carburized layer resists mild rust; pour environnements difficiles, add zinc plating or epoxy coating.
- Surface Wear Resistance: Outstanding—carburized surface (58–60 HRC) resists metal-to-metal wear, extending part life by 3–4x vs. non-carburized steels.
2. Applications of AISI 8620 Acier allié
AISI 8620’s carburizing advantage makes it ideal for parts that need to resist wear while absorbing impact. Here are its key uses:
- Engrenages: Engrenages de transmission automobile, industrial gearbox gears, and helicopter rotor gears—hard surface resists tooth wear; tough core absorbs shock from gear meshing.
- Arbres: Drive shafts, arbres à cames, and axle shafts—hard surface resists abrasion; tough core handles torque and bending.
- Roulements: Bearing races and bushings—smooth, hard surface minimizes friction; tough core prevents cracking from heavy loads.
- Pièces automobiles: Pinions, sprockets, and clutch hubs—withstand engine heat and repeated contact; carburized surface resists wear from daily use.
- Machines industrielles: Chain links, rouleaux de convoyeur, and fasteners—hard surface resists dirt/abrasion; tough core handles impact from material handling.
- Composants aérospatiaux: Landing gear pins, engine accessory gears, and fasteners—carburized surface resists wear; tough core tolerates takeoff/landing stress.
3. Manufacturing Techniques for AISI 8620 Acier allié
Producing AISI 8620 focuses on carburizing to create a “hard surface + tough core” structure. Here’s the step-by-step process:
- Steelmaking:
- AISI 8620 is made using an Electric Arc Furnace (EAF) (recycles scrap steel) ou Basic Oxygen Furnace (BOF). Nickel (0.40–0.70%), chrome (0.40–0.60%), and molybdenum (0.15–0.25%) are added during melting to ensure uniform alloy distribution.
- Roulement & Forgeage:
- The steel is Hot Rolled (1,100 – 1,200 °C) into bars, assiettes, or tubes—hot rolling makes it easy to form. Pour pièces complexes (par ex., ébauches d'engrenages), c'est Hot Forged to shape, then annealed to soften (18–22 HRC) pour usinage.
- Usinage:
- Annealed AISI 8620 is machined into near-final shapes (par ex., gear teeth blanks) using turning, fraisage, ou perçage. HSS tools work well for most cuts; carbide tools are used for tight tolerances.
- Cémentation (Critical Step):
- Gas Carburizing: Parts are heated to 880–920 °C in a carbon-rich gas (par ex., methane) for 4–12 hours (longer = thicker hard layer). Carbon diffuses into the surface (0.8–1.0% C), while the core remains low-carbon (0.18–0.23% C).
- Trempe: After carburizing, parts are cooled to 830–850 °C, held briefly, then quenched in oil. This hardens the surface to 58–60 HRC and the core to 30–35 HRC.
- Tempering: Parts are reheated to 180–220 °C for 1–2 hours, then air-cooled. This reduces surface brittleness without lowering hardness.
- Traitement de surface:
- Affûtage: Carburized parts are ground to smooth the surface (removes oxidation) and achieve final tolerances (par ex., gear tooth precision).
- Placage: Zinc plating (résistance à la rouille) pour les parties extérieures; chromage (extra wear resistance) for high-friction parts.
- Grenaillage: Optional—blasts the surface with small metal balls to reduce residual stress and boost limite de fatigue.
- Contrôle de qualité:
- Chemical Analysis: Spectrometry verifies nickel, chrome, and molybdenum levels (per ASTM A29/A29M).
- Hardness Testing: Rockwell testing checks surface (58–60 HRC) and core (30–35 HRC) dureté.
- Microstructural Analysis: Optical microscopy confirms a uniform carburized layer (no gaps or uneven carbon distribution).
- CND: Ultrasonic testing checks for internal defects; magnetic particle inspection finds surface cracks from carburizing.
4. Études de cas: AISI 8620 in Action
Real projects show how AISI 8620 solves “wear + impact” challenges.
Étude de cas 1: Automotive Transmission Gears (Germany)
A car manufacturer needed transmission gears that could resist tooth wear and absorb shift shock. They switched from AISI 1045 carbon steel to carburized AISI 8620 engrenages. The AISI 8620 gears lasted 200,000 km—double the lifespan of 1045 gears—because the carburized surface (59 CRH) prevented tooth pitting, and the tough core (32 CRH) absorbed shift impact. This reduced warranty claims by 40%.
Étude de cas 2: Industrial Conveyor Shafts (NOUS.)
A warehouse had to replace conveyor shafts every 2 years due to surface wear and bending cracks. They used AISI 8620 arbres, carburized to 58 HRC and shot-peened. Les nouveaux arbres ont duré 5 years—no wear or cracks—because the hard surface resisted abrasion from dirt, and the tough core handled conveyor loads. This saved the warehouse $35,000 in replacement costs.
5. AISI 8620 contre. Other Materials
How does AISI 8620 compare to other carburizable and wear-resistant steels?
| Matériel | Similarities to AISI 8620 | Différences clés | Idéal pour |
|---|---|---|---|
| AISI 4140 | Cr-Mo alloy steel | Higher carbon (0.38–0.43%); not ideal for carburizing (core too hard); 15% moins cher | Non-carburized, medium-wear parts |
| AISI 8630 | Ni-Cr-Mo alloy steel | Higher carbon (0.28–0.33%); harder core after carburizing; 10% pricier | Heavy-load carburized parts (par ex., truck gears) |
| AISI 1018 | Acier à faible teneur en carbone | No alloying; poor carburized surface strength; 30% moins cher | Low-wear, low-load carburized parts |
| 52100 Acier à roulement | High-carbon steel | Better wear resistance; no nickel (poor toughness); 20% pricier | Precision bearings (no impact) |
| Acier inoxydable 410 | Résistant à la corrosion | Carburizable; better rust resistance; 3× pricier | Wet-environment carburized parts |
Yigu Technology’s Perspective on AISI 8620 Acier allié
Chez Yigu Technologie, AISI 8620 is our top pick for carburized “tough core + hard surface” parts. Its low-carbon Ni-Cr-Mo composition solves the biggest pain point for clients: getting wear resistance without sacrificing impact toughness—critical for gears, arbres, et attaches. We supply AISI 8620 in bars, forged blanks, or machined components, with custom carburizing (0.5–1.2 mm layer thickness) et grenaillage. For clients moving from plain carbon steel, AISI 8620 delivers 3–4x longer part life at a small cost premium—saving money on maintenance and downtime.
FAQ About AISI 8620 Acier allié
- How thick is the carburized layer on AISI 8620?
Typical layers are 0.5–1.2 mm thick—adjusted by carburizing time (4 hours = ~0.5 mm; 12 hours = ~1.2 mm). For parts like gears, a 0.8–1.0 mm layer balances wear resistance and flexibility; for shafts, 0.5–0.7 mm avoids surface cracking. - Can AISI 8620 be used without carburizing?
Yes—but it’s not ideal. Non-carburized AISI 8620 has low strength (600 traction MPa) et résistance à l'usure, so it’s only used for low-load parts (par ex., parenthèses). Carburizing unlocks its full potential for wear and impact. - Is AISI 8620 suitable for low-temperature applications?
Yes—its nickel content maintains impact toughness à -30 °C (even after carburizing). For temperatures below -30 °C (par ex., arctic machinery), choose AISI 8640 (higher nickel) for extra low-temperature toughness.