SAE 8620 steel
Nickel-chromium-molybdenum case-hardening steel: chemistry, supplied condition, case/core requirements and procurement limits.
Tags: materials, steel, alloy-steel, case-hardening
On this page
Identity and intended use
Interlloy's typical 8620 core data after carburizing and oil quenching at 840°C give 785 MPa yield at 11 mm, 590 MPa at 30 mm and 490 MPa at 63 mm. The entries sit in a typical table despite the “min” label. Verify the actual section, case and core separately for the finished part. Interlloy carburized core table
SAE 8620 is a low-carbon nickel-chromium-molybdenum alloy steel used for carburized components that need a wear-resistant surface supported by a tougher core. Encore lists gears, pinions, splined shafts and piston pins among its applications. Its 2016 Product Manual, page 31, distinguishes carburized use from uncarburized heat-treated use and describes hot-rolled/as-rolled supply, with larger diameters hot forged/as forged. Those are supplier descriptions, not a guarantee that every item sold as 8620 arrives in one condition. Encore Metals, 2016 Product Manual
Chemistry and designation boundaries
Metallus's Practical Data for Metallurgists, nineteenth edition, copyright 2024, lists the following composition ranges for standard alloy steel 8620. These are mass percentages, not nominal additions or finished-part mechanical properties. Metallus, standard alloy steel tables
| Element | Listed range, mass % |
|---|---|
| Carbon | 0.18–0.23 |
| Manganese | 0.70–0.90 |
| Chromium | 0.40–0.60 |
| Nickel | 0.40–0.70 |
| Molybdenum | 0.15–0.25 |
This abbreviated table omits other limits; use the full governing specification for acceptance. SAE's public description of J404_200901, revised January 27, 2009, distinguishes heat composition from permitted check-analysis variations under J409. It covers specified alloy-steel product forms and directs sheet/strip and mechanical tubing to separate ASTM specifications. “SAE 8620” therefore does not by itself identify a universal product specification or dimensional tolerance. SAE J404_200901
Keep 8620 and 8620H separate in structured records. Atlas's April 2006 8620H sheet explicitly associates the H suffix with guaranteed hardenability and publishes Jominy bands. It also lists different composition ranges for its H-grade product. Do not infer that a chemistry-only 8620 certificate meets a specified hardenability band. Atlas 8620H, pages 1–2
Voestalpine Australia's product page labels DIN and BS designations as nearest standards. Treat such cross-references as comparison leads: verify chemistry, hardenability, product requirements and certification before approving substitution. The page has no verified technical revision date. Voestalpine HPM Australia, AISI 8620
Supplied steel versus finished case and core
Separate three states in a drawing or database:
- Incoming stock: dimensions, surface finish, annealed/as-rolled condition and acceptance hardness.
- Carburized and hardened component: surface hardness, case-depth definition and core requirements.
- Finished component: remaining case after grinding, dimensional accuracy and surface condition.
Atlas's historical supply example is annealed, maximum 212 HB, typically 170–200 HB. Cooling-medium selection depends on geometry, desired properties and hardenability. Atlas 8620H, page 1
Carburizing and quench/temper are distinct operations. Encore's historical example gives approximately 63 HRC case hardness after tempering at 150 °C and approximately 58 HRC after tempering at 232 °C. These are process-dependent examples, not two interchangeable grade ratings. The manual's treatment is not a production recipe for an arbitrary section or furnace. Encore Metals, 2016 Product Manual, page 31
Specify where hardness is measured and how case depth is defined. A surface indentation, a cross-section hardness traverse and a core tensile specimen answer different questions. Record the test method, acceptance location and sampling arrangement; do not silently store all three as a single “hardness” property.
Bounded section-size example
Interlloy's primary supplier table is headed typical mechanical properties for core—carburized and oil quenched at 840 °C. It shows the following section dependence. Although individual cells say “min”, the enclosing table remains typical guidance, not a universal delivery guarantee. No issue date was verified; the source's related-specification list includes older editions. Interlloy, 8620 case-hardening steel
| Test section | Core tensile strength | Core yield strength, listed minimum |
|---|---|---|
| 11 mm | 980–1270 MPa | 785 MPa |
| 30 mm | 780–1080 MPa | 590 MPa |
| 63 mm | 690–930 MPa | 490 MPa |
For a comparison only, the listed 30 mm yield value is 195 MPa below the 11 mm value: 785 − 590 = 195 MPa, about 24.8% of 785 MPa. This arithmetic does not predict an intermediate diameter or a gear tooth's local properties. The same source reports that uncarburized 8620's low carbon content limits its response to flame/induction hardening; changing surface-hardening route requires separate qualification. Interlloy, core table and introductory guidance
Process planning and acceptance
Use the following as an engineering review sequence, rather than a generic heat-treatment instruction:
- Establish load, wear location, geometry and required core support before selecting final properties.
- Agree stock condition and machining allowances with the material supplier and heat treater.
- Define case-depth criterion, hardness locations, protected surfaces and dimensional acceptance after finishing.
- Qualify the complete carburize/harden/temper/finish route on representative geometry.
- Retain heat identity and process/test records with the accepted component.
Joining also needs its own procedure. Atlas's historical sheet places welding before carburizing and calls for controlled preheat, low-hydrogen practice and cooling. Its numbers should not be copied into a repair instruction for a finished carburized part. Obtain a procedure addressing the actual condition, section and subsequent treatment. Atlas 8620H, page 3
Keep test basis, units and source edition with the value.