1. Indledning
Over the past century, 8620 alloy steel has earned a reputation as a workhorse in industries requiring case-hardened, high-toughness components—from automotive gears to heavy machinery shafts.
First developed in the mid-20th century, 8620 falls under the SAE J403 nomenclature system (often paralleled by ASTM A681 eller AISI classifications) as a low-alloy, carburizing grade stål.
Its balanced chemistry—moderate carbon content augmented by nickel, Krom,
and molybdenum—enables deep-case carburizing and subsequent quench/temper cycles that produce a hard external case atop a ductile, tough core.
Følgelig, Aisi 8620 steel appears in applications that demand slidstyrke on the surface without sacrificing impact resilience internally.
This article explores 8620 from multiple vantage points—metallurgical, mechanical, forarbejdning, and economic—to provide a thorough, professional, and credible resource.
2. Chemical Composition of 8620 Legeringsstål
| Element | Typisk rækkevidde (wt %) | Role / Effect |
|---|---|---|
| Kulstof (C) | 0.18 – 0.23 | – Provides hardenability after carburizing – Forms martensitic case during quench – Low core carbon ensures a tough, ductile core |
| Mangan (Mn) | 0.60 – 0.90 | – Acts as a deoxidizer during melting – Promotes austenite formation, improving hardenability – Increases tensile strength and toughness |
| Silicium (Og) | 0.15 – 0.35 | – Serves as a deoxidizer and sulfur modifier – Enhances strength and hardness – Improves tempering response |
| Nikkel (I) | 0.40 – 0.70 | – Increases core toughness and impact resistance – Deepens hardenability for uniform core martensite – Improves corrosion resistance slightly |
Krom (Cr) |
0.40 – 0.60 | – Promotes hardenability and wear resistance in the case – Forms alloy carbides that enhance surface hardness – Contributes to tempering stability |
| Molybdæn (Mo) | 0.15 – 0.25 | – Increases hardenability and depth of hardness – Improves high-temperature strength and creep resistance – Refines grain size |
| Kobber (Cu) | ≤ 0.25 | – Acts as an impurity – Slightly improves corrosion resistance – Minimal effect on hardenability or mechanical properties |
| Fosfor (S) | ≤ 0.030 | – Impurity that increases strength but reduces toughness – Kept low to avoid brittleness in the core |
| Svovl (S) | ≤ 0.040 | – Impurity that improves machinability by forming manganese sulfides – Excessive S can cause hot shortness; controlled to maintain ductility |
| Jern (Fe) | Balance | – Base matrix element – Carries all alloying additions and determines overall density and modulus |
3. Physical and Mechanical Properties of 8620 Legeringsstål
Below is a table summarizing key physical and mechanical properties of 8620 alloy steel in its normalized (core) and case-hardened (carburized + quenched + tempered) betingelser:
| Ejendom | Normalized (Core) | Carburized Case | Noter |
|---|---|---|---|
| Densitet (ρ) | 7.85 g/cm³ | 7.85 g/cm³ | Same base density in all conditions |
| Termisk ledningsevne (20 ° C.) | 37–43 W/m·K | 37–43 W/m·K | Typical for low-alloy steels |
| Specific Heat (cₚ) | 460 J/kg·K | 460 J/kg·K | Values change negligibly after heat treatment |
| Elastic Modulus (E) | 205–210 GPa | 205–210 GPa | Remains essentially constant |
| Koefficient for termisk ekspansion (20–100 °C) | 12.0–12.5 × 10⁻⁶ /°C | 12.0–12.5 × 10⁻⁶ /°C | Unaffected by surface treatments |
Trækstyrke (UTS) |
550–650 MPa | 850–950 MPa | Core (normalized) vs.. case (surface) after carburize + quench + temper |
| Udbyttestyrke (0.2% offset) | 350–450 MPa | 580–670 MPa | Core yield in normalized condition; case yield after Q&T |
| Forlængelse (in 50 mm gage) | 15–18% | 12–15% | Core retains higher ductility; case slightly lower but still ductile around hardened layer |
| Hårdhed (Hb) | 190–230 HB | — | Normalized hardness before carburizing |
| Case Surface Hardness (HRC) | — | 60–62 HRC | Measured at immediate surface after Q&T |
| Core Hardness (HRC) | — | 32–36 HRC | Measured ~ 5–10 mm beneath surface after Q&T |
Effective Case Depth |
— | 1.5–2.0 mm (50 HRC) | Depth at which hardness falls to ~ 50 HRC |
| Charpy V-Notch Impact (20 ° C.) | 40–60 J | Core: ≥ 35 J; Case: 10–15 J | Core toughness remains high; case is harder and less tough |
| Rotating Bending Fatigue Limit (R = –1) | ~ 450–500 MPa | ~ 900–1,000 MPa | Case-hardened surface greatly improves fatigue resistance |
| Compressive Strength | 600–700 MPa | 900–1,100 MPa | Case compression ~3× core tensile; core compression ~3× core tensile |
| Slidstyrke | Moderat | Fremragende | Surface hardness of ~60 HRC provides high wear resistance |
Noter:
- All values are approximate and depend on exact processing parameters (F.eks., tempering temperature, quench medium).
- Normalized properties represent the un-carburized, annealed state. Carburized case values reflect typical gas-carburizing (0.8–1.0 % C case), oil/quench + temper (180 ° C.) cycles.
- Fatigue and impact values assume standard test specimens; real-world components may vary due to residual stresses and geometry.
4. Heat Treatment and Surface Hardening of 8620 Legeringsstål
Common Heat Treatment Cycles
Austenitizing
- Temperaturområde: 825–870 °C, depending on section size (higher for thicker sections to ensure full austenitization).
- Hold Time: 30–60 minutes, ensuring uniform austenite grain formation.
- Considerations: Too high a temperature or excessive hold can cause grain coarsening, reducing toughness.
Quenching
- Medium: Oil of medium viscosity (F.eks., ISO 32–68) or polymer-based quenchants to reduce distortion, especially in complex geometries.
- Target Core Hardness: ~32–36 HRC after tempering.
Temperering
- Temperaturområde: 160–200 °C for carburized parts (to preserve a hard case), or 550–600 °C for through-hardened requirements.
- Hold Time: 2–4 hours, followed by air cooling.
- Result: Balances hardness with toughness—higher temp temper (550 ° C.) yields more ductile core but softer surface.
Carburizing Procedures
Pack Carburizing
- Procedure: Encasing parts in charcoal-based packs at 900–930 °C for 6–24 hours (depending on desired case depth), then quench.
- Pros/Cons: Low-cost equipment, but variable case uniformity and greater distortion.
Gas Carburizing
- Procedure: Controlled atmosphere furnaces introduce carbon-bearing gases (methane, propane) at 920–960 °C; case depth often 0.8–1.2 mm in 4–8 hours.
- Fordele: Precise carbon potential, minimal distortion, repeatable case depths.
Vacuum Carburizing (Low-Pressure Carburizing, LPC)
- Behandle: Carburizing under low-pressure, high-purity process gases at 920–940 °C, followed by rapid high-pressure gas quench.
- Fordele: Excellent case uniformity (±0.1 mm), reduced oxidation (“white layer” minimized), and tight distortion control, at higher equipment costs.
Microstructural Changes during Carburizing, Quenching, and Tempering
- Carburizing: Introduces a carbon gradient (surface ~0.85–1.0% C down to core ~0.20% C), forming an austenitic case layer.
- Quenching: Transforms the carburized case to Martensite (60–62 HRC), while the core converts to a mixed martensite-tempered martensite or bainite (depending on quench severity).
- Temperering: Reduces residual stresses, converts retained austenite, and allows carbide precipitation (Fe₃C, Cr-rich carbides) to improve toughness.
The ideal temper cycle (180–200 °C for 2 timer) yields a case with fine carbide distribution and a ductile core.
Advantages of Case Hardening versus Through-Hardening
- Surface Hardness (60–62 HRC) resists wear and pitting.
- Core Toughness (32–36 HRC) absorbs impact and prevents catastrophic brittle failure.
- Residual Stress Management: Proper tempering reduces quench-induced stresses, leading to minimal part distortion and high fatigue life.
Distortion Control and Residual Stress Management
- Quench Medium Selection: Oil vs. polymer vs. gas quench—each produces different cooling curves.
Polymeric quenchants (F.eks., 5–15% polyalkylene glycol) often reduce warping relative to oil. - Fixture Design: Uniform support and minimal restraint during quench reduce bending or twisting.
- Multiple Tempering Steps: A first low-temperature temper stabilizes martensite, followed by a higher-temperature temper to reduce residual stress further.
5. Corrosion Resistance and Environmental Performance
Atmospheric and Aqueous Corrosion
As a low-alloy steel, 8620 exhibits moderate corrosion resistance in atmospheric conditions. Imidlertid, unprotected surfaces can oxidize (rust) within hours in humid environments.
In aqueous or marine environments, corrosion rates accelerate due to chloride attack.
A typical as-quenched and tempered surface (32 HRC) in 3.5% NaCl at 25 °C shows ~0.1–0.3 mm/year uniform corrosion.
Følgelig, protective coatings (phosphate, paint, or electroplated Zn/Ni) often precede service in corrosive settings.
Stress-Corrosion Cracking Susceptibility
8620’s moderate toughness post-carburizing helps resist stress-corrosion cracking (SCC) better than high-carbon steels, but caution is required in chloride-rich or caustic environments combined with tensile stress.
Testing indicates that thin carburized sections (< 4 mm) are more vulnerable if not fully tempered. pH-controlled inhibitors and cathodic protection mitigate SCC in critical applications.
Protective Coatings and Surface Treatments
- Phosphate Conversion Coatings: Iron-phosphate (FePO₄) applied at 60 °C for 10 minutes yields a 2–5 µm layer, improving paint adhesion and initial corrosion resistance.
- Pulverbelægning / Wet Painting: Epoxy-polyester powders cured at 180 °C provide 50–80 µm of barrier protection, ideal for outdoor or mildly corrosive environments.
- Electroplated Zinc or Nickel: Tynd (< 10 µm) metal layers applied after acid pickling—zinc provides sacrificial protection, whereas nickel enhances wear and corrosion resistance.
High-Temperature Oxidation and Scaling
In continuous service above 300 ° C., 8620 can form thick oxide (scale) layers, leading to weight loss of up to 0.05 mm/year at 400 ° C..
Molybdenum additions somewhat improve oxidation resistance, but for prolonged high-temperature use (> 500 ° C.), stainless or nickel-based alloys are preferred.
6. Weldability and Fabrication of 8620 Legeringsstål
Preheat, Interpass, and PWHT Recommendations
- Preheating: 150–200 °C prior to welding reduces thermal gradients and slows cooling to prevent martensite in the heat-affected zone (Haz).
- Interpass Temperature: Maintain 150–200 °C for multi-pass welds to minimize HAZ hardness.
- Post-Weld Heat Treatment (PWHT): A stress-relief temper at 550–600 °C for 2–4 hours ensures HAZ toughness and reduces residual stresses.
Almindelige svejseprocesser
- Shielded Metal Arc Welding (SMAW): Using low-hydrogen electrodes (F.eks., E8018-B2) yields tensile strengths of 500–550 MPa in weld metal.
- Gas Metal Arc Welding (GMAW/MIG): Flux-cored (ER80S-B2) or solid wires (ER70S-6) produce high-quality welds with minimal spatter.
- Gas Tungsten Arc Welding (GTAW/TIG): Offers precise control, especially for thin sections or stainless overlays.
Weld Metal Selection
Preferred filler metals include 8018 eller 8024 serie (SMAW) og ER71T-1/ER80S-B2 (GMAW).
These have matching hardenability and tempering characteristics, ensuring weld and HAZ do not become brittle after PWHT.
7. Applications and Industry Use Cases
Automotive Components
- Gears and Pinions: Carburized case (0.8–1.2 mm depth) with core stress-relieved yield surface wear resistance og core shock absorption—ideal for transmissions.
- Steering Shafts and Journals: Benefit from high fatigue life and toughness, ensuring safety in steering systems.
Heavy Machinery and Construction Equipment
- Track Roller Shafts and Bushings: High surface hardness (> 60 HRC) combats abrasive wear in harsh conditions.
- Bucket Pins and Hinge Pins: Core toughness prevents catastrophic failure under high-impact loads.
Oil and Gas Drilling Tools
- Drill Collars and Subs: Require rotating bending fatigue resistance; 8620’s carburized surface reduces wear in drilling mud environments.
- Couplings and Threaded Connections: Benefit from corrosion-resistant coatings and case-hardened threads for high-pressure service.
Bearings, Forklift Masts, and Pivots
- Bearing Races: Carburized 8620 resists pitting and spalling under high-rpm conditions.
- Mast Slide Blocks: High core ductility absorbs shock, while hardened surfaces reduce galling.
8. Comparisons with Other Carburizing Alloys
When specifying a carburizing-grade steel, engineers often evaluate multiple alloys to balance cost, Mekanisk ydeevne, hardness depth, og sejhed.
Under, we compare 8620 alloy steel—one of the most widely used case-hardening grades—with three common alternatives: 9310, 4140, og 4320.
| Criterion | 8620 | 9310 | 4140 | 4320 |
|---|---|---|---|---|
| Alloy Content | Moderate Ni/Cr/Mo | High Ni (1.65–2,00%), higher Mo | Cr/Mo, no Ni, higher C | Similar to 8620, tighter S/P controls |
| Case Depth (til 50 HRC) | ~ 1.5–2.0 mm | ~ 3–4 mm | N/A (through-hardening to ~40 HRC) | ~ 1.5–2.0 mm |
| Core Toughness (Q&T) | UTS 850–950 MPa; Charpy 35–50 J | UTS 950–1,050 MPa; Charpy 30–45 J | UTS 1,000–1,100 MPa; Charpy 25–40 J | UTS 900–1,000 MPa; Charpy 40–60 J |
| Surface Hardness (HRC) | 60–62 HRC (carburized) | 62–64 HRC (carburized) | 40–45 HRC (through-hardening) | 60–62 HRC (carburized) |
Bearbejdningsevne (Normalized) |
~ 60–65% of 1212 | ~ 50–60% of 1212 | ~ 40–45% of 1212 | ~ 55–60% of 1212 |
| Distortion Control | Moderat, polyquench quench recommended | Good with LPC or gas quench | Higher distortion in large sections | Better than 8620 in large weldments |
| Koste (Raw Material Basis) | Base price | +15–25% over 8620 | Similar to 8620 | +5–10% over 8620 |
| Typical Use Cases | Automotive gears, aksler, general parts | Aerospace gears, wind turbine pinions | Crankshafts, dies, heavy machine parts | Oliefeltudstyr, large welded parts |
Selecting the Right Alloy
When choosing between these carburizing alloys, consider:
Case Depth Requirements:
- If deep cases (> 3 mm) are essential, 9310 eller LPC-processed 8620 become candidates.
- For moderate case depth (1.5–2.0 mm), 8620 eller 4320 are more economical.
Core Strength and Toughness:
- 8620 meets most moderate-duty needs with UTS ~ 900 MPa in the core.
- 9310 eller 4320 offer enhanced toughness in large sections or welded assemblies.
Through-Hardening vs. Case Hardening:
- When a uniform HRC 40–45 is sufficient, 4140 is often more cost-effective, eliminating carburizing steps.
- If slidstyrke on working surfaces is critical, 8620/9310/4320 provide superior surface hardness.
Cost and Availability:
- In high-volume automotive applications, alloy steel 8620 dominates because of its cost-to-performance balance.
- 9310 is justified in rumfart og defense where performance supersedes raw material cost.
Weldability and Fabrication Needs:
- 4320’s tighter impurity control makes it preferable in large welded structures.
- 8620 is easier to weld than 9310, which requires stricter preheat and interpass controls due to higher hardenability.
9. Konklusion
8620 alloy steel continues to rank among the most versatile case-hardening steels available.
From its balanced low-carbon, multi-alloyed chemistry to its proven performance in carburized, quenched, and tempered condition,
8620 meets the exacting requirements of modern industries—automotive, rumfart, tungt maskiner, olie og gas, and beyond.
By understanding alloy steel 8620’s metallurgy, Mekanisk opførsel, processing parameters, and evolving technologies,
Engineers can confidently specify and design high-performance components that meet today’s evolving demands—and anticipate tomorrow’s challenges.
DEZE Offers High-Quality 8620 Alloy Steel Components
På DENNE, we specialize in producing precision-engineered components made from alloy steel, a trusted material known for its exceptional combination of surface hardness and core toughness.
Thanks to its excellent carburizing capabilities, our 8620 parts deliver outstanding slidstyrke, fatigue strength, og dimensional stability, even in demanding mechanical applications.
Our advanced heat treatment processes, strict quality control, og in-house machining capabilities ensure that each component meets the highest industry standards.
Whether you’re sourcing for Automotive, rumfart, tungt maskiner, eller industrial drivetrain systems.
Why Choose DEZE’s 8620 Alloy Steel Parts?
- Superior case hardening up to 60–62 HRC
- Excellent toughness and fatigue resistance
- Custom machining and surface treatments available
- Fully compliant with ASTM, SAE, and AMS standards
- OEM and volume production support
From gears and shafts til camshafts and specialty mechanical parts, DENNE delivers dependable, high-performance solutions tailored to your needs.
Kontakt os today to learn more or request a quote.
FAQs – 8620 Legeringsstål
Why is 8620 steel suitable for carburizing?
8620 has a relatively low carbon content in the core (ca.. 0.2%), which maintains ductility, while its alloying elements enable deep case hardening up to 60–62 HRC.
This makes it ideal for surface wear resistance without sacrificing core strength.
What heat treatments are typically applied to 8620 alloy steel?
Typical treatments include carburizing, followed by quenching and tempering. This process hardens the surface layer while maintaining a softer, more ductile core.
Normalizing and annealing may also be used prior to carburizing for improved machinability or grain refinement.7.
Is 8620 easy to machine and weld?
In the annealed condition, 8620 exhibits good machinability. Imidlertid, post-carburizing machining should be limited to avoid tool wear.
It can be welded in the annealed or normalized state but requires preheating and post-weld stress relief to prevent cracking.
What standards cover 8620 alloy steel?
Common specifications for 8620 omfatte:
- ASTM A29 / A29M – General requirements
- SAE J404 – Chemical composition
- Ams 6274 / Ams 6276 – Aerospace quality grades
