If you’re designing parts that need a tough coreE a hard, superficie resistente all'usura, come gli ingranaggi automobilistici, alberi industriali, or aerospace fasteners—you need a material that balances ductility and surface strength.AISI 8620 acciaio legato is the perfect solution: come nichel-cromo-molibdeno a basso tenore di carbonio (Ni-Cr-Mo) lega, è ideale per la cementazione (un trattamento termico che indurisce solo la superficie), delivering a hard outer layer (fino a 60 HRC) and a tough inner core. Questa guida ne analizza le proprietà, applicazioni del mondo reale, processo di produzione, and material comparisons to help you solve “tough core + hard surface” design challenges.
1. Material Properties of AISI 8620 Acciaio legato
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 booststenacità, chromium enhances surface hardenability, and molybdenum improveslimite di fatica. Let’s explore its key properties in detail.
1.1 Composizione chimica
AISI 8620 adheres to ASTM A29/A29M standards, with elements optimized for carburizing. Below is its typical composition:
| Elemento | Simbolo | Gamma di contenuti (%) | Key Role |
|---|---|---|---|
| Carbonio (C) | C | 0.18 – 0.23 | Low enough to keep the core ductile; reacts with carbon during carburizing to harden the surface |
| Nichel (In) | In | 0.40 – 0.70 | Core toughness booster; maintainsimpact toughness at low temperatures (-30 °C) |
| Cromo (Cr) | Cr | 0.40 – 0.60 | Enhances surface hardenability; miglioraresistenza alla corrosione of the carburized layer |
| Molibdeno (Mo) | Mo | 0.15 – 0.25 | Raiseslimite di fatica; prevents brittleness in the carburized surface |
| Manganese (Mn) | Mn | 0.70 – 0.90 | Refines grain structure; aumentaresistenza alla trazione without reducing ductility |
| Silicio (E) | E | 0.15 – 0.35 | Aids deoxidation; supports stability during carburizing |
| Fosforo (P) | P | ≤ 0.035 | Minimized to avoid brittle fracture in the carburized layer |
| Zolfo (S) | S | ≤ 0.040 | Controlled to balancelavorabilità e qualità della superficie (lower S = smoother carburized surfaces) |
| Vanadium (V) | V | ≤ 0.03 | Trace element; refines grains for uniform surface hardening |
| Rame (Cu) | Cu | ≤ 0.30 | Trace element; adds mild atmospheric corrosion resistance for outdoor parts |
1.2 Proprietà fisiche
These traits make AISI 8620 ideal for carburized parts across industries:
- Densità: 7.85 g/cm³ (same as standard steels)—simplifies weight calculations for gears, alberi, or fasteners
- Punto di fusione: 1,420 – 1,450 °C (2,588 – 2,642 °F)—compatible with carburizing and forging processes
- Conducibilità termica: 42.0 Con/(m·K) A 20 °C; 38.0 Con/(m·K) A 300 °C—ensures even carbon diffusion during carburizing (no uneven surface hardness)
- Coefficiente di dilatazione termica: 11.5 × 10⁻⁶/°C (20 – 100 °C)—minimizes distortion during carburizing and quenching
- Proprietà magnetiche: Ferromagnetic—enables non-destructive testing (NDT) like magnetic particle inspection to check surface cracks after carburizing.
1.3 Proprietà meccaniche
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:
| Proprietà | Metodo di misurazione | Non-Carburized (Annealed) | Carburized (0.8–1.0% Surface C) |
|---|---|---|---|
| Surface Hardness | HRC | 18 – 22 HRC | 58 – 60 HRC |
| Core Hardness | HRC | 18 – 22 HRC | 30 – 35 HRC |
| Resistenza alla trazione | MPa (ksi) | 600 MPa (87 ksi) | 1,100 MPa (159 ksi) |
| Forza di snervamento | MPa (ksi) | 350 MPa (51 ksi) | 800 MPa (116 ksi) |
| Allungamento | % (In 50 mm) | 28 – 32% | 12 – 15% |
| Resistenza all'impatto | J (A -30 °C) | ≥ 90 J | ≥ 45 J (core toughness) |
| Fatigue Limit | MPa (rotating beam) | 300 MPa | 650 MPa |
1.4 Altre proprietà
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.
- Formabilità: Great—soft in the annealed condition (18–22 HRC), so it can be bent, forged, or stamped into complex shapes (per esempio., spazi vuoti degli ingranaggi) before carburizing.
- Lavorabilità: Excellent—annealed AISI 8620 cuts easily with HSS or carbide tools; carburized parts require grinding for final shaping.
- Resistenza alla corrosione: Moderate—chromium in the carburized layer resists mild rust; per ambienti difficili, add zinc plating or epoxy coating.
- Surface Wear Resistance: Outstanding—carburized surface (58–60HRC) resists metal-to-metal wear, extending part life by 3–4x vs. non-carburized steels.
2. Applications of AISI 8620 Acciaio legato
AISI 8620’s carburizing advantage makes it ideal for parts that need to resist wear while absorbing impact. Here are its key uses:
- Ingranaggi: Ingranaggi di trasmissione automobilistici, industrial gearbox gears, and helicopter rotor gears—hard surface resists tooth wear; tough core absorbs shock from gear meshing.
- Alberi: Drive shafts, alberi a camme, and axle shafts—hard surface resists abrasion; tough core handles torque and bending.
- Cuscinetti: Bearing races and bushings—smooth, hard surface minimizes friction; tough core prevents cracking from heavy loads.
- Parti automobilistiche: Pinions, sprockets, and clutch hubs—withstand engine heat and repeated contact; carburized surface resists wear from daily use.
- Macchinari industriali: Chain links, rulli trasportatori, and fasteners—hard surface resists dirt/abrasion; tough core handles impact from material handling.
- Componenti aerospaziali: Landing gear pins, engine accessory gears, and fasteners—carburized surface resists wear; tough core tolerates takeoff/landing stress.
3. Manufacturing Techniques for AISI 8620 Acciaio legato
Producing AISI 8620 focuses on carburizing to create a “hard surface + tough core” structure. Here’s the step-by-step process:
- Produzione dell'acciaio:
- AISI 8620 is made using an Forno ad arco elettrico (EAF) (recycles scrap steel) O Fornace ad ossigeno basico (BOF). Nichel (0.40–0.70%), cromo (0.40–0.60%), and molybdenum (0.15–0.25%) are added during melting to ensure uniform alloy distribution.
- Rotolamento & Forgiatura:
- The steel is Laminato a caldo (1,100 – 1,200 °C) into bars, piatti, or tubes—hot rolling makes it easy to form. Per parti complesse (per esempio., spazi vuoti degli ingranaggi), suo Hot Forged to shape, then annealed to soften (18–22 HRC) per la lavorazione.
- Lavorazione:
- Annealed AISI 8620 is machined into near-final shapes (per esempio., gear teeth blanks) using turning, fresatura, o perforazione. HSS tools work well for most cuts; carbide tools are used for tight tolerances.
- Carburazione (Critical Step):
- Gas Carburizing: Parts are heated to 880–920 °C in a carbon-rich gas (per esempio., 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).
- Tempra: 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.
- Temperamento: Parts are reheated to 180–220 °C for 1–2 hours, then air-cooled. This reduces surface brittleness without lowering hardness.
- Trattamento superficiale:
- Rettifica: Carburized parts are ground to smooth the surface (removes oxidation) and achieve final tolerances (per esempio., gear tooth precision).
- Placcatura: Zinc plating (resistenza alla ruggine) per parti esterne; cromatura (extra wear resistance) for high-friction parts.
- Pallinatura: Optional—blasts the surface with small metal balls to reduce residual stress and boost limite di fatica.
- Controllo qualità:
- Chemical Analysis: Spectrometry verifies nickel, cromo, and molybdenum levels (per ASTM A29/A29M).
- Hardness Testing: Rockwell testing checks surface (58–60HRC) and core (30–35 HRC) durezza.
- Microstructural Analysis: Optical microscopy confirms a uniform carburized layer (no gaps or uneven carbon distribution).
- NDT: Ultrasonic testing checks for internal defects; magnetic particle inspection finds surface cracks from carburizing.
4. Casi di studio: AISI 8620 in Action
Real projects show how AISI 8620 solves “wear + impact” challenges.
Caso di studio 1: Automotive Transmission Gears (Germania)
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 ingranaggi. 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%.
Caso di studio 2: Industrial Conveyor Shafts (NOI.)
A warehouse had to replace conveyor shafts every 2 years due to surface wear and bending cracks. They used AISI 8620 alberi, carburized to 58 HRC and shot-peened. I nuovi alberi durarono 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 contro. Other Materials
How does AISI 8620 compare to other carburizable and wear-resistant steels?
| Materiale | Similarities to AISI 8620 | Differenze chiave | Ideale per |
|---|---|---|---|
| AISI 4140 | Cr-Mo alloy steel | Higher carbon (0.38–0.43%); not ideal for carburizing (core too hard); 15% più economico | 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 (per esempio., truck gears) |
| AISI 1018 | Acciaio a basso tenore di carbonio | No alloying; poor carburized surface strength; 30% più economico | Low-wear, low-load carburized parts |
| 52100 Cuscinetto in acciaio | High-carbon steel | Better wear resistance; no nickel (poor toughness); 20% pricier | Precision bearings (no impact) |
| Acciaio inossidabile 410 | Resistente alla corrosione | Carburizable; better rust resistance; 3× pricier | Wet-environment carburized parts |
Yigu Technology’s Perspective on AISI 8620 Acciaio legato
Alla tecnologia 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, alberi, e dispositivi di fissaggio. We supply AISI 8620 in bars, forged blanks, or machined components, with custom carburizing (0.5–1.2 mm layer thickness) e pallinatura. 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 Acciaio legato
- 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 MPa a trazione) e resistenza all'usura, so it’s only used for low-load parts (per esempio., parentesi). Carburizing unlocks its full potential for wear and impact. - Is AISI 8620 suitable for low-temperature applications?
Yes—its nickel content maintains impact toughness A -30 °C (even after carburizing). For temperatures below -30 °C (per esempio., arctic machinery), choose AISI 8640 (higher nickel) for extra low-temperature toughness.