If you’re designing parts that need a tough coreet un dur, wear-resistant surface—like automotive gears, arbres industriels, or aerospace fasteners—you need a material that balances ductility and surface strength.AISI 8620 acier en alliage is the perfect solution: as a low-carbon nickel-chromium-molybdenum (Ni-Cr-Mo) alliage, it’s ideal for carburizing (a heat treatment that hardens only the surface), delivering a hard outer layer (jusqu'à 60 HRC) and a tough inner core. This guide breaks down its properties, Applications du monde réel, processus de fabrication, and material comparisons to help you solve “tough core + hard surface” design challenges.
1. Propriétés matérielles de l'AISI 8620 Acier en alliage
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 improvesfatigue limit. Explorons ses principales propriétés en détail.
1.1 Composition chimique
AISI 8620 adheres to ASTM A29/A29M standards, with elements optimized for carburizing. Ci-dessous est sa composition typique:
| Élément | Symbole | Plage de contenu (%) | Rôle clé |
|---|---|---|---|
| Carbone (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; maintainsrésistance à l'impact at low temperatures (-30 ° C) |
| Chrome (Croisement) | Croisement | 0.40 - 0.60 | Enhances surface hardenability; améliorerrésistance à la corrosion of the carburized layer |
| Molybdène (MO) | MO | 0.15 - 0.25 | Raisesfatigue limit; prevents brittleness in the carburized surface |
| Manganèse (MN) | MN | 0.70 - 0.90 | Affine la structure des grains; augmentationrésistance à la traction without reducing ductility |
| Silicium (Et) | Et | 0.15 - 0.35 | Aids deoxidation; supports stability during carburizing |
| Phosphore (P) | P | ≤ 0.035 | Minimized to avoid brittle fracture in the carburized layer |
| Soufre (S) | S | ≤ 0.040 | Controlled to balancemachinabilité 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 Propriétés physiques
Ces traits font de l'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 Avec(m · k) à 20 ° C; 38.0 Avec(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
- Propriétés magnétiques: Ferromagnetic—enables non-destructive testing (NDT) 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 (Recuit) | Carburé (0.8–1.0% Surface C) |
|---|---|---|---|
| Surface Hardness | HRC | 18 - 22 HRC | 58 - 60 HRC |
| Dureté de base | HRC | 18 - 22 HRC | 30 - 35 HRC |
| Résistance à la traction | MPA (ksi) | 600 MPA (87 ksi) | 1,100 MPA (159 ksi) |
| Limite d'élasticité | MPA (ksi) | 350 MPA (51 ksi) | 800 MPA (116 ksi) |
| Élongation | % (dans 50 MM) | 28 - 32% | 12 - 15% |
| Résistance à l'impact | J (à -30 ° C) | ≥ 90 J | ≥ 45 J (ténacité de base) |
| Fatigue Limit | MPA (rotating beam) | 300 MPA | 650 MPA |
1.4 Autres propriétés
AISI 8620’s traits solve “tough core + hard surface” challenges:
- Soudabilité: 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 exemple, Gear Blanks) before carburizing.
- Machinabilité: 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 des environnements durs, 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 de l'AISI 8620 Acier en alliage
AISI 8620’s carburizing advantage makes it ideal for parts that need to resist wear while absorbing impact. Here are its key uses:
- Engrenages: Automotive transmission gears, industrial gearbox gears, and helicopter rotor gears—hard surface resists tooth wear; tough core absorbs shock from gear meshing.
- Arbres: Arbres d'entraînement, 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: Pignon, 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. Techniques de fabrication pour AISI 8620 Acier en alliage
Producing AISI 8620 focuses on carburizing to create a “hard surface + tough core” structure. Voici le processus étape par étape:
- Acier:
- AISI 8620 is made using an Fournaise à arc électrique (EAF) (recycles scrap steel) ou Fournaise de base à l'oxygène (BOF). Nickel (0.40–0,70%), chrome (0.40–0,60%), et molybdène (0.15–0,25%) are added during melting to ensure uniform alloy distribution.
- Roulement & Forgeage:
- The steel is Chaud roulé (1,100 - 1,200 ° C) into bars, assiettes, or tubes—hot rolling makes it easy to form. Pour des pièces complexes (Par exemple, Gear Blanks), c'est Hot Forged to shape, then annealed to soften (18–22 HRC) pour l'usinage.
- Usinage:
- AISI recuit 8620 is machined into near-final shapes (Par exemple, gear teeth blanks) using turning, fraisage, or drilling. HSS tools work well for most cuts; carbide tools are used for tight tolerances.
- Carburisant (Étape critique):
- Gas Carburizing: Parts are heated to 880–920 °C in a carbon-rich gas (Par exemple, methane) for 4–12 hours (longer = thicker hard layer). Le carbone se diffuse dans la surface (0.8–1,0% c), while the core remains low-carbon (0.18–0.23% C).
- Éteinte: Après le carburateur, parts are cooled to 830–850 °C, held briefly, puis éteint dans l'huile. This hardens the surface to 58–60 HRC and the core to 30–35 HRC.
- Tremper: 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 exemple, gear tooth precision).
- Placage: Placage de zinc (résistance à la rouille) for outdoor parts; placage chromé (extra wear resistance) for high-friction parts.
- Coup de feu: Optional—blasts the surface with small metal balls to reduce residual stress and boost fatigue limit.
- Contrôle de qualité:
- Analyse chimique: Spectrometry verifies nickel, chrome, et les niveaux de molybdène (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).
- NDT: Vérification des tests à ultrasons pour les défauts internes; magnetic particle inspection finds surface cracks from carburizing.
4. Études de cas: AISI 8620 en action
Real projects show how AISI 8620 solves “wear + impact” challenges.
Étude de cas 1: Automotive Transmission Gears (Allemagne)
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 HRC) prevented tooth pitting, and the tough core (32 HRC) 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. The new shafts lasted 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 en frais de remplacement.
5. AISI 8620 contre. Autres matériaux
Comment AISI 8620 compare to other carburizable and wear-resistant steels?
| Matériel | Similarities to AISI 8620 | Différences clés | Mieux pour |
|---|---|---|---|
| AISI 4140 | Cr-Mo alloy steel | Carbone plus élevé (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 | Carbone plus élevé (0.28–0,33%); harder core after carburizing; 10% pricier | Heavy-load carburized parts (Par exemple, 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 de roulement | En acier à haute teneur en carbone | Better wear resistance; Pas de 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 |
Perspective de la technologie Yigu sur AISI 8620 Acier en alliage
À la technologie Yigu, 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, and fasteners. We supply AISI 8620 dans les bars, forged blanks, or machined components, with custom carburizing (0.5–1.2 mm layer thickness) and shot peening. 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 sur AISI 8620 Acier en alliage
- 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. - Peut-on aisi 8620 be used without carburizing?
Yes—but it’s not ideal. Non-carburized AISI 8620 has low strength (600 MPa tensile) et porter une résistance, so it’s only used for low-load parts (Par exemple, supports). Carburizing unlocks its full potential for wear and impact. - Est aisi 8620 suitable for low-temperature applications?
Yes—its nickel content maintains résistance à l'impact à -30 ° C (even after carburizing). For temperatures below -30 ° C (Par exemple, arctic machinery), choose AISI 8640 (higher nickel) for extra low-temperature toughness.
