8620 Steel:Key Specs, Heat Treatment & Uses
8620 is a low-carbon nickel-chromium-molybdenum steel designed to become two materials in one: a hard, wear-resistant carburized case over a tougher load-carrying core. This guide separates grade chemistry from heat-treatment condition, explains the much-quoted 530 MPa and 26% figures, and shows what engineers and buyers must actually specify.
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Carburized wear components
Gears, pins, bushings, shafts and similar parts that need a hard surface without turning the entire section into a brittle high-hardness body.
~0.20% C + Ni-Cr-Mo
Low base carbon helps preserve core toughness. Nickel, chromium and molybdenum improve the hardening response and strength potential.
Up to about 62 HRC
Commercial data sheets report carburized, hardened and tempered case hardness up to roughly 62 HRC. The drawing must still define the real target and depth.
Properties are condition-specific
“8620 tensile strength” is incomplete without section, specimen, prior condition and heat-treatment history. Never mix numbers from unrelated data rows.
What is 8620 steel?
SAE 8620 is a low-carbon Ni-Cr-Mo alloy steel commonly used for carburized components. Carbon is diffused into the surface, followed by hardening and tempering, so the finished part can combine a high-hardness case with a more damage-tolerant core. The grade is commonly associated with UNS G86200 and standards such as SAE J404 and ASTM A322, but the purchase specification must match the actual product form.
The “20” in 8620 points to a nominal carbon level near 0.20%; it does not describe hardness. A raw or annealed bar is not the finished engineering system. Final performance depends on carburized carbon profile, effective case depth, section size, hardenability, quench severity, tempering, retained austenite, residual stress, finishing and inspection.
Do 530 MPa and 26% elongation describe the same 8620?
Not safely. Both values appear in commercial reference data, but they may belong to different product sizes or supply conditions. Combining them into one universal material card can corrupt a design or supplier comparison.
| Published example | Condition / specimen | Tensile strength | Yield strength | Elongation | How to use it |
|---|---|---|---|---|---|
| Annealed data example | Specific small round specimen | About 530 MPa | About 385 MPa | About 31% | Reference only Use for context, not as a purchase guarantee. |
| Commercial product-guide example | Supply-condition dataset | About 92 ksi / 634 MPa | About 52 ksi / 359 MPa | About 26% | Different row Do not combine its elongation with another row's tensile value. |
| Carburized test example | One defined carburize, quench and temper cycle | About 1,157 MPa | About 833 MPa | About 14.3% | Process-specific It demonstrates condition sensitivity, not a universal result. |
A property value is usable only when its grade, product form, specimen location, section size, prior condition, heat treatment and test method match your design basis. For released parts, use the material test report and required post-heat-treatment evidence.
What stays stable—and what changes dramatically.
Physical constants such as density and elastic modulus move far less than hardness, strength, ductility and fatigue response. A useful material model keeps these categories separate.
Typical steel density used for mass estimates.
Typical room-temperature stiffness; heat treatment does not create a high-modulus case.
A commercial upper capability, not an automatic acceptance target.
Surface hardness without effective case depth is an incomplete requirement.
Common SAE 8620 chemistry and what each element does.
The ranges below are commonly published for SAE 8620. Limits can vary slightly by governing standard and product route, so the current specification and heat analysis control the order.
Keeps the base steel relatively low carbon for core toughness and machinability before carburizing.
Supports toughness and hardenability, especially important to the load-carrying core.
Improves hardenability and wear response, working with the carbon-enriched case.
Supports hardenability and tempering response while helping resist softening.
Assists hardenability and deoxidation while contributing to strength response.
Acts mainly as a deoxidizer and contributes modestly to strength.
Usually restricted because excessive phosphorus can reduce toughness and increase segregation concerns.
Controlled because inclusions can affect fatigue, toughness and directional properties.
Its chromium content is far below stainless grades. Bare 8620 can corrode and normally needs oil, coating, plating or another approved protection system when the service environment requires it.
Is 8620 a logical starting point?
This selector organizes the material conversation; it does not replace the governing drawing, stress analysis, heat-treatment qualification or supplier approval.
Describe the part
Choose the closest condition. The recommendation updates instantly.
Strong 8620 candidate
A carburized wear surface with a tough core is exactly the property architecture 8620 was designed to deliver.
Carburizing does not simply “make 8620 harder.”
It creates a carbon concentration gradient. After quenching, the carbon-enriched surface can transform into a high-hardness structure, while the lower-carbon interior retains a different strength and toughness balance. The transition is continuous, so inspection must define how depth is measured.
Total case depth versus effective case depth
- Total case depth follows the metallurgical or chemical influence of carburizing to its practical limit.
- Effective case depth is measured to a specified hardness criterion. The criterion, test method, location and tolerance must be stated.
- Core hardness is not inferred from surface hardness. It depends on section size, hardenability and the thermal cycle.
- Residual stress and retained austenite can affect dimensional stability, contact fatigue and finishing behavior.
Specify outcomes, not a copied furnace recipe.
Temperature, carbon potential and time are only part of the process. Furnace loading, atmosphere uniformity, prior microstructure, section, quench transfer, oil condition, agitation and tempering all change the final profile and distortion.
Machine and plan allowances
Rough-machine the part in a suitable soft condition. Provide stock for finishing and identify distortion-sensitive features, sharp transitions, thin walls and masked surfaces.
Carburize to a controlled profile
Control atmosphere, temperature and time to develop the required carbon gradient. Case depth cannot be guaranteed from hours alone without process capability evidence.
Quench and temper
Select the hardening route for case structure, core response and dimensional risk. Tempering relieves stress and sets the usable hardness/toughness balance.
Finish and inspect
Grind or finish critical features, then verify effective case depth, case/core hardness, microstructure where required, dimensions, cracks and surface integrity.
Atmosphere and thermal control matter.
A controlled furnace is part of a qualified system, but the released requirement is the verified part result.
Image: S zillayali / Wikimedia Commons, CC BY 3.0.
Microstructure validates the route.
This is an illustrative martensitic micrograph from another quenched-tempered structural steel—not a certified 8620 case.
Image: Melancholia~itwiki / Wikimedia Commons, CC BY-SA 4.0.Model the part as a gradient when the case matters.
For simple elastic deflection, one steel modulus may be adequate. For contact fatigue, local yielding, crack initiation or grinding allowance, one homogeneous property set can hide the real mechanism.
Elastic stiffness is not the same as strength
Carburizing can change hardness and strength dramatically without turning the case into a material with a dramatically higher Young's modulus. A designer who increases the modulus in the surface layer to represent hardness is changing the wrong parameter.
Use depth-dependent evidence where failure starts at the surface
Gear tooth pitting, rolling contact fatigue and wear are driven by surface and subsurface stresses. When these limit the design, use the actual hardness/carbon profile, effective case depth, core response, residual-stress assumptions, surface finish and inclusion quality needed by the analysis.
Core properties depend on section size
Commercial 8620 data show different core tensile ranges for different section sizes after carburizing and oil quenching. This is a hardenability issue: a small pin and a thick gear hub may not develop the same center structure even when their surfaces reach the same case hardness.
At minimum, connect the reading to case depth, test position, core hardness, dimensional results and the qualification plan. Fatigue-critical designs may also need metallography, retained-austenite limits, residual-stress control, cleanliness requirements and process capability data.
8620 vs 4140, 1018, 9310 and 8620H.
The right comparison begins with the required property architecture. “Stronger steel” is not a complete selection objective.
| Grade / route | Core idea | Where it can fit | Why not automatically choose it |
|---|---|---|---|
| SAE 8620 | Low-carbon Ni-Cr-Mo carburizing steel | General-purpose gears, pins, bushings and shafts needing hard case + tough core. | Requires controlled case hardening; large sections or extreme fatigue duty may need stronger hardenability or quality controls. |
| 8620H | 8620 chemistry with a specified hardenability band | When center response and heat-treatment consistency need tighter control. | The H does not mean “higher hardness.” The required Jominy band, method and section response still must be specified. |
| 4140 | Medium-carbon Cr-Mo steel, commonly quenched and tempered | Parts where bulk strength through the section is more important than a deep carburized case. | It does not provide the same low-carbon core / high-carbon case architecture without a different surface-hardening strategy. |
| 1018 | Plain low-carbon steel | Lower-cost, lightly loaded parts and simpler case-hardening needs. | Lower hardenability limits reliable core response and depth capability in demanding sections. |
| 9310 | Higher-nickel premium carburizing steel | High-duty gears or demanding fatigue/toughness requirements under an approved specification. | Higher material and quality cost; its value must be justified by load, life and certification requirements. |
Machine before carburizing. Treat welding as an engineered exception.
8620 is often friendly to fabrication in a soft condition, but the finished case-hardened part behaves very differently. Process planning should follow the final material state.
Machining and finishing
- Start from a defined incoming condition. Annealed hardness and microstructure affect tool life and chip behavior.
- Rough-machine before carburizing. Preserve stock for grinding, honing or hard finishing.
- Plan distortion. Thin sections, keyways, splines and asymmetric mass can move during quenching.
- Protect the case. Excessive grinding can remove useful case depth or create grinding burn and tensile residual stress.
- Verify after unclamping. Runout and size can change when residual stress is released.
Welding and repair
- Weld before final case hardening where possible. A carburized high-hardness surface raises cracking and local property risks.
- Use a qualified low-hydrogen procedure. Preheat, filler, heat input, cooling and any post-treatment depend on thickness, restraint and condition.
- Do not publish a universal preheat. An arbitrary temperature may be too low for one repair and damaging for another.
- Define post-weld acceptance. HAZ hardness, cracks, dimensions and final thermal treatment must match the design authority's requirements.
- Protect traceability. Repair approval should identify the heat, part, procedure, operator and inspection results.
Where 8620 steel is commonly used.
Application lists identify the design pattern—not automatic approval. Load spectrum, section, case-depth target, lubrication, finish, cleanliness and reliability class determine whether 8620 is sufficient.
Hard tooth flanks resist wear and contact stress while the core supports bending and shock loads.
Carburized engagement surfaces can combine wear resistance with a machinable pre-treatment route.
Surface durability and a tougher interior can suit repeated contact and impact.
Case hardness supports sliding or rolling contact when geometry, lubrication and finish are controlled.
Localized surface wear resistance can be paired with a less brittle core.
Repeated engagement benefits from a qualified case/core profile and dimensional control.
What to put on an 8620 purchase order and heat-treatment drawing.
The grade name alone buys chemistry, not a finished gear property system. Include only requirements that the supplier can measure and that the design actually needs.
SAE 8620 / UNS G86200, product form, dimensions, quantity and the applicable current material specification.
State a hardenability-controlled grade and required band only when the core response requires it.
As-rolled, normalized, annealed or another defined condition, including an incoming hardness range if necessary.
Heat analysis, product analysis when required, material test report, heat/lot traceability and revision level.
Effective case depth target and tolerance, hardness criterion, test method, measurement location and surface-hardness range.
Core hardness or mechanical property, location, section basis and any hardenability evidence.
Microstructure, retained austenite, carbide network, grain size, cleanliness, decarburization or other limits only where justified.
Distortion allowance, masked areas, grind stock, final dimensions, runout and surface-finish requirements.
Hardness traverse, metallographic coupon location, crack inspection, ultrasonic testing or macroetch as applicable.
Define who can approve material substitution, reheat treatment, repair welding, case-depth deviation or rework.
Commercial tables often list 20NiCrMo2-2 / 1.6523 and SNCM220-family grades as related or nearest equivalents. Chemistry, hardenability, cleanliness, testing and product standards can differ. Approve substitution through the drawing authority after a clause-by-clause comparison.
Validate the real 8620 condition before production.
For laser cleaning, welding or marking, the grade name is not enough. Oceanplayer can review the actual condition, case state, coating, contamination, geometry and acceptance criteria, then use representative samples to identify a practical process window.
- 8620 specification, MTR and current condition
- Carburized case state or heat-treatment route
- Part thickness, geometry and critical surfaces
- Coating, oxide, oil or contamination
- Laser cleaning, welding or marking objective
- Visual, dimensional and metallurgical acceptance
8620 steel FAQ
Short answers to the questions engineers, machinists, heat treaters and buyers ask most often.
What is 8620 steel used for?
8620 is commonly used for carburized gears, pinions, pins, bushings, shafts, camshafts, splines, drive wheels and other parts that need a hard wear-resistant surface over a tougher core.
What is the chemical composition of 8620 steel?
Common published SAE 8620 ranges are about 0.18–0.23% carbon, 0.70–0.90% manganese, 0.40–0.70% nickel, 0.40–0.60% chromium, 0.15–0.25% molybdenum and 0.15–0.35% silicon, with phosphorus and sulfur limited. Confirm the current governing standard and MTR.
What is the tensile strength of 8620 steel?
There is no single 8620 tensile strength. Annealed commercial datasets commonly show values around the mid-500 MPa range, while a defined carburize/quench/temper condition can exceed 1,100 MPa. Section, specimen and heat treatment must accompany the value.
Does 8620 steel have 26% elongation?
Some commercial supply-condition datasets report about 26% elongation, but other annealed datasets report different values. Do not combine 26% with a tensile or yield value taken from another condition. Use a complete certified property set.
How hard can 8620 steel get?
Commercial manufacturer data report carburized, hardened and tempered case hardness up to roughly 62 HRC. The usable target depends on case depth, fatigue, toughness, grinding allowance, retained austenite and the governing heat-treatment specification.
What is the difference between 8620 and 8620H?
8620H is hardenability controlled to a specified band, commonly assessed by an end-quench method. The H does not mean extra hard. It is useful when center response and lot-to-lot heat-treatment consistency need tighter control.
Is 8620 steel stronger than 4140?
Neither grade is universally stronger. 8620 is optimized for a carburized case with a lower-carbon core. 4140 is commonly quenched and tempered for bulk section strength. The better choice depends on where hardness, strength, toughness and wear resistance are needed.
Can 8620 steel be welded?
8620 can be welded in a suitable soft condition using a qualified low-hydrogen procedure. Welding a carburized or hardened part is much riskier because the high-carbon surface and hard HAZ can crack or lose the intended case/core properties. Use an approved WPS and inspection plan.
Is 8620 easy to machine?
It is commonly machined successfully before case hardening. Tooling and cutting data must match the incoming hardness and operation. After carburizing, hard turning, grinding or honing may be required, with controls for grinding burn and case removal.
Does 8620 steel rust?
Yes. 8620 is an alloy steel, not stainless steel. Bare parts can corrode and may need oil, phosphate, paint, plating or another approved protection system.
What is the equivalent of AISI 8620?
Tables commonly list 20NiCrMo2-2 / 1.6523 and JIS SNCM220-family grades as related or nearest equivalents. They are not automatically interchangeable. Compare chemistry, hardenability, product standard, cleanliness and test requirements before substitution.
What should an 8620 heat-treatment drawing specify?
Define effective case depth and tolerance, hardness criterion and location, case and core hardness, metallurgical limits where necessary, masking, distortion and grind stock, final dimensions, crack inspection, traceability and the authority for deviations or rework.
Continue from alloy selection to process validation.
Use the resource that matches your next decision: equipment selection, surface-screening or representative sample evidence.
Standards and primary references.
The article prioritizes active standards, steelmaker data and condition-specific reference datasets. Confirm current revisions and project requirements before release.
- SAE J404: chemical compositions of SAE alloy steels and grade designation context.
- ASTM A322-24: standard-grade hot-wrought alloy steel bars.
- ASTM A29/A29M-20: general requirements for hot-wrought steel bars.
- ASTM A304-20: alloy-steel bars subject to end-quench hardenability requirements.
- ASTM A255-20a: methods for determining steel hardenability.
- Hillfoot — 8620 material datasheet: chemistry, associated standards and general case-hardening application context.
- Interlloy — 8620 case-hardening steel: case-hardness capability, section-sensitive core properties and typical applications.
- ASM MatWeb — AISI 8620 annealed condition: condition-specific mechanical and physical reference data.
- MatWeb — carburized 8620 example: one defined carburized, quenched and tempered property set demonstrating condition sensitivity.
- Online Metals — 8620 product guide: commercial supply-condition property and composition reference.