8620 haluang metal na bakal: Deep Case, matigas na core, Carburizing steel

Mga Nilalaman ipakita ang

1. Panimula

Over the past century, 8620 haluang metal na bakal has earned a reputation as a workhorse in industries requiring Kaso matigas, 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 o AISI classifications) as a low-alloy, carburizing grade bakal na bakal.

Its balanced chemistry—moderate carbon content augmented by nickel, kromo,

and molybdenum—enables deep-case carburizing and subsequent quench/temper cycles that produce a hard external case atop a ductile, tough core.

Dahil dito, AISI 8620 steel appears in applications that demand Paglaban sa Pagsusuot on the surface without sacrificing impact resilience internally.

Ang artikulong ito ay nagsasaliksik 8620 from multiple vantage points—metallurgical, mekanikal, pagproseso ng, and economic—to provide a thorough, propesyonal, and credible resource.

2. Kemikal na komposisyon ng 8620 haluang metal na bakal

Elemento	Tipikal na saklaw (wt %)	Tungkulin / Epekto ng
Carbon (C)	0.18 – 0.23	– Provides hardenability after carburizing – Forms martensitic case during quench – Low core carbon ensures a tough, ductile core
Mga mangganeso (Mn)	0.60 – 0.90	– Acts as a deoxidizer during melting – Promotes austenite formation, improving hardenability – Increases tensile strength and toughness
Silicon (Si Si)	0.15 – 0.35	– Serves as a deoxidizer and sulfur modifier – Enhances strength and hardness – Improves tempering response
Nikel (Ni)	0.40 – 0.70	– Increases core toughness and impact resistance – Deepens hardenability for uniform core martensite – Improves corrosion resistance slightly
Chromium (Cr)	0.40 – 0.60	– Promotes hardenability and wear resistance in the case – Forms alloy carbides that enhance surface hardness – Contributes to tempering stability
Molibdenum (Mo)	0.15 – 0.25	– Increases hardenability and depth of hardness – Improves high-temperature strength and creep resistance – Refines grain size
Tanso (Cu)	≤ 0.25	– Acts as an impurity – Slightly improves corrosion resistance – Minimal effect on hardenability or mechanical properties
Posporus (P)	≤ 0.030	– Impurity that increases strength but reduces toughness – Kept low to avoid brittleness in the core
Sulfur (S)	≤ 0.040	– Impurity that improves machinability by forming manganese sulfides – Excessive S can cause hot shortness; controlled to maintain ductility
Bakal na Bakal (Fe)	Balanse	– Base matrix element – Carries all alloying additions and determines overall density and modulus

3. Pisikal at mekanikal na katangian ng 8620 haluang metal na bakal

Below is a table summarizing key physical and mechanical properties of 8620 alloy steel in its normalized (core) and case-hardened (na carburized ang mga + pinawi ang + tempered) mga kondisyon:

Pag-aari	Normalized na (Core)	Carburized Case	Mga Tala
Densidad ng katawan (ρ)	7.85 g/cm³	7.85 g/cm³	Same base density in all conditions
Thermal kondaktibiti (20 °C)	37–43 W/m·K	37–43 W/m·K	Karaniwan para sa mababang-haluang metal na bakal
Specific Heat (cₚ)	460 J/kg· K	460 J/kg· K	Values change negligibly after heat treatment
nababanat na modulus (E)	205–210 GPa	205–210 GPa	Remains essentially constant
Koepisyent ng Thermal Expansion (20-100 ° C)	12.0–12.5 × 10⁻⁶ /°C	12.0–12.5 × 10⁻⁶ /°C	Unaffected by surface treatments
Lakas ng Paghatak (Mga UTS)	550–650 MPa	850–950 MPa	Core (Normalized) mga bes. kaso (surface) after carburize + pawiin + pag-uugali
Yield Lakas (0.2% Offset)	350–450 MPa	580–670 MPa	Core yield in normalized condition; case yield after Q&T
Pagpapahaba (sa 50 mm gage)	15–18%	12–15%	Core retains higher ductility; case slightly lower but still ductile around hardened layer
Ang katigasan ng ulo (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 Epekto (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
Lakas ng Compressive	600–700 MPa	900–1,100 MPa	Case compression ~3× core tensile; core compression ~3× core tensile
Magsuot ng Paglaban	Katamtaman	Napakahusay	Surface hardness of ~60 HRC provides high wear resistance

Mga Tala:

All values are approximate and depend on exact processing parameters (hal., 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), langis / pag-quench + pag-uugali (180 °C) Mga Cycle.
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 haluang metal na bakal

Common Heat Treatment Cycles

Awteritisismo

Saklaw ng Temperatura: 825–870 °C, depending on section size (higher for thicker sections to ensure full austenitization).
Oras ng Hold: 30–60 minuto, ensuring uniform austenite grain formation.
Mga Dapat Isaalang alang: Too high a temperature or excessive hold can cause grain coarsening, Pagbabawas ng katigasan.

Pagpapawi

Katamtaman: Oil of medium viscosity (hal., ISO 32–68) or polymer-based quenchants to reduce distortion, lalo na sa mga kumplikadong geometries.
Target Core Hardness: ~32–36 HRC after tempering.

Paghina ng loob

Saklaw ng Temperatura: 160–200 °C for carburized parts (to preserve a hard case), or 550–600 °C for through-hardened requirements.
Oras ng Hold: 2-4 na oras, sinundan ng paglamig ng hangin.
Resulta: Balances hardness with toughness—higher temp temper (550 °C) yields more ductile core but softer surface.

Carburizing Procedures

Pack Carburizing

Pamamaraan: 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

Pamamaraan: 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.
Mga kalamangan: Precise carbon potential, minimal na pagbaluktot, repeatable case depths.

Vacuum Carburizing (Low-Pressure Carburizing, LPC)

Proseso: Carburizing under low-pressure, high-purity process gases at 920–940 °C, followed by rapid high-pressure gas quench.
Mga Benepisyo: Excellent case uniformity (±0.1 mm), reduced oxidation (“white layer” minimized), and tight distortion control, at higher equipment costs.

Microstructural Changes during Carburizing, Pagpapawi, and Tempering

Carburizing: Introduces a carbon gradient (surface ~0.85–1.0% C down to core ~0.20% C), forming an austenitic case layer.
Pagpapawi: 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).
Paghina ng loob: 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 mga oras) yields a case with fine carbide distribution and a ductile core.

Advantages of Case Hardening versus Through-Hardening

Tigas ng Ibabaw (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 (hal., 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 mababang-haluang metal na bakal, 8620 exhibits moderate corrosion resistance in atmospheric conditions. Gayunpaman, unprotected surfaces can oxidize (kalawang na) 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) sa 3.5% NaCl sa 25 °C shows ~0.1–0.3 mm/year uniform corrosion.

Dahil dito, protective coatings (phosphate, pintura, 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 para sa 10 minutes yields a 2–5 µm layer, improving paint adhesion and initial corrosion resistance.
Palabok na patong / 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: Manipis na manipis (< 10 M) 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 (skala ng 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 haluang metal na bakal

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).
Temperatura ng Interpass: 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.

Mga Karaniwang Proseso ng Welding

Shielded Metal Arc Welding (SMAW): Using low-hydrogen electrodes (hal., 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 o 8024 serye ng mga (SMAW) at 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

Mga Bahagi ng Automotive

Gears and Pinions: Carburized case (0.8–1.2 mm depth) with core stress-relieved yield surface wear resistance at 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.

Mga bearing, 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 gastos, mekanikal na pagganap, hardness depth, at tigas na tigas.

Sa ibaba, we compare 8620 alloy steel—one of the most widely used case-hardening grades—with three common alternatives: 9310, 4140, at 4320.

Pamantayan	8620	9310	4140	4320
Alloy Content	Moderate Ni/Cr/Mo	High Ni (1.65–2.00%), higher Mo	Cr/Mo, no Ni, higher C	Katulad ng 8620, tighter S/P controls
Case Depth (sa 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
Tigas ng Ibabaw (HRC)	60–62 HRC (na carburized ang mga)	62–64 HRC (na carburized ang mga)	40–45 HRC (through-hardening)	60–62 HRC (na carburized ang mga)
Machinability (Normalized na)	~ 60–65% of 1212	~ 50–60% of 1212	~ 40–45% of 1212	~ 55–60% of 1212
Pagbaluktot Control	Katamtaman, polyquench quench recommended	Good with LPC or gas quench	Higher distortion in large sections	Better than 8620 in large weldments
Gastos (Raw Material Basis)	Base price	+15–25% over 8620	Katulad ng 8620	+5–10% over 8620
Typical Use Cases	Automotive gears, mga shaft, general parts	Aerospace gears, wind turbine pinions	Mga Crankshaft, namamatay na, heavy machine parts	Oilfield equipment, large welded parts

8620 Mga Serbisyo sa Machining ng Alloy Steel CNC

Selecting the Right Alloy

When choosing between these carburizing alloys, Isipin ang:

Case Depth Requirements:

Kung deep cases (> 3 mm) ay mahalaga, 9310 o LPC-processed 8620 become candidates.
For moderate case depth (1.5–2.0 mm), 8620 o 4320 are more economical.

Core Strength and Toughness:

8620 meets most moderate-duty needs with UTS ~ 900 MPa in the core.
9310 o 4320 offer enhanced toughness in large sections or welded assemblies.

Through-Hardening vs. Kaso Hardening:

When a uniform HRC 40–45 is sufficient, 4140 is often more cost-effective, eliminating carburizing steps.
Kung Paglaban sa Pagsusuot on working surfaces is critical, 8620/9310/4320 provide superior surface hardness.

Gastos at Availability:

In high-volume automotive applications, haluang metal na bakal 8620 dominates because of its cost-to-performance balance.
9310 is justified in aerospace at pagtatanggol 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. Pangwakas na Salita

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 na carburized ang mga, pinawi ang, and tempered kalagayan,

8620 meets the exacting requirements of modern industries—automotive, aerospace, mabigat na makinarya, langis at gas, at sa kabila ng.

By understanding alloy steel 8620’s metallurgy, mekanikal na pag uugali, 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

Sa DEZE, we specialize in producing precision-engineered components made from haluang metal na bakal, 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 Paglaban sa Pagsusuot, lakas ng pagkapagod, at dimensional na katatagan, even in demanding mechanical applications.

Our advanced Mga proseso ng paggamot ng init, strict kontrol sa kalidad, at in-house machining capabilities ensure that each component meets the highest industry standards.

Whether you’re sourcing for automotive, aerospace, mabigat na makinarya, o industrial drivetrain systems.

Why Choose DEZE’s 8620 Mga Bahagi ng Bakal na Alloy?

Superior case hardening up to 60–62 HRC
Mahusay na katigasan at paglaban sa pagkapagod
Custom machining and surface treatments available
Fully compliant with ASTM, SAE, and AMS standards
OEM and volume production support

Mula sa gears and shafts sa camshafts and specialty mechanical parts, DEZE delivers dependable, high-performance solutions tailored to your needs.

Makipag ugnay sa amin today to learn more or request a quote.

FAQs – 8620 haluang metal na bakal

Why is 8620 steel suitable for carburizing?

8620 has a relatively low carbon content in the core (mga approx. 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 haluang metal na bakal?

Typical treatments include carburizing, na sinusundan ng pagpapawi at pagtitimpi. 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.

Ay 8620 easy to machine and weld?

Sa kondisyon ng annealed, 8620 exhibits good machinability. Gayunpaman, 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 haluang metal na bakal?

Common specifications for 8620 isama mo na:

ASTM A29 / A29M – General requirements
SAE J404 – Chemical composition
AMS 6274 / AMS 6276 – Aerospace quality grades