8620 Steel
Also: AISI 8620, SAE 8620, UNS G86200, 8620H, 20NiCrMo2-2 / 1.6523, SNCM220 (JIS, near), 805M20 / EN362 (BS 970, near), carburizing steel, case hardening steel, nickel-chrome-moly carburizing steel
8620 is the standard carburizing steel: machined soft, then carburized to a 58-63 HRC case over a tough core. Values annealed and carburized.
Sourcing 8620 parts or stock?
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At a glance
| Density | 7.85 g/cm³ (0.284 lb/in³) |
|---|---|
| Tensile strength | About 535 MPa (78 ksi) annealed; about 630 MPa (91 ksi) normalized; roughly 900-1,300 MPa (130-190 ksi) in a carburized and quenched core, section dependent |
| Yield strength | About 385 MPa (56 ksi) annealed; about 360 MPa (52 ksi) normalized; roughly 700-1,000 MPa (100-145 ksi) in a carburized and quenched core |
| Hardness | About 149 HB (about 80 HRB) annealed; about 183 HB normalized; carburized case 58-63 HRC over a core of about 25-40 HRC |
| Elongation | About 31% annealed; about 26% normalized; roughly 10-15% in a hardened core |
| Modulus of elasticity | 205 GPa (29.7 Msi) |
| Thermal | Melts at about 1,420-1,510 °C (2,590-2,750 °F); thermal conductivity ~46 W/m·K |
| Composition | Fe, 0.18-0.23% C, 0.70-0.90% Mn, 0.40-0.70% Ni, 0.40-0.60% Cr, 0.15-0.25% Mo, 0.15-0.35% Si |
Typical values, Annealed and normalized figures for bar as bought; case and core figures after carburizing, oil quenching and tempering at 150-200 °C (300-400 °F). Core values depend strongly on section size.. Confirm against the mill certificate and the purchase spec.
- MachinabilityGood
- About 65% of the 1212 benchmark annealed. Hot-rolled or dead-soft bar can be gummy and tear on threads; normalized or cold-drawn stock cuts cleaner. Finish soft; after carburizing only grinding or hard turning touches the case.
- WeldabilityGood
- Low carbon makes it easier than 4140: low-hydrogen filler and a modest preheat of about 100-200 °C (200-400 °F) on heavy sections. Weld before carburizing; a carburized case is effectively unweldable, so mask weld zones or machine the case off first.
- FormabilityGood
- Annealed bar and wire cold head and cold form well for pins and small parts; gear blanks are hot forged routinely.
- Corrosion resistancePoor
- Rusts like carbon steel. Carburized gears run in oil; exposed parts get black oxide, phosphate and oil, or plating.
8620 is a low-carbon nickel-chromium-molybdenum steel, about 0.20% carbon, made to be carburized. The part is machined in the soft annealed or normalized condition, then heated in a carbon-rich atmosphere so carbon diffuses into the surface. After quenching and a low temper, the surface is a 0.8% carbon case at 58-63 HRC that resists wear and contact fatigue, while the core stays a low-carbon, tough structure at roughly 25-40 HRC.
That case-and-core combination is what gears, pinions, ring gears, splined shafts, king pins, chain pins and cam followers need: a hard face that does not wear or pit, backed by a core that takes shock loads without cracking. The small nickel, chromium and molybdenum additions give 8620 enough hardenability that the core strengthens in moderate sections and the case hardens reliably in an oil quench, which plain carbon 1018 does not. It is the most widely used carburizing grade in U.S. gear and driveline work.
Design around the process. The case is only 0.5-1.5 mm (0.020-0.060 in) deep, so finish grinding must not remove too much of it; parts distort in the quench; and anything that must stay soft or be welded later, such as threads, has to be masked or machined off before hardening. Without carburizing, 8620 quenches only to the low-to-mid 40s HRC, so it is not a through-hardening steel; that is 4140.
Heat treatment
Bought annealed, normalized or cold drawn for machining; normalize at about 915 °C (1,675 °F) to refine forgings and gear blanks. Carburize at about 900-930 °C (1,650-1,700 °F) to an effective case depth, measured to 50 HRC, of typically 0.5-1.5 mm (0.020-0.060 in); then either direct quench in oil or cool, reheat to about 845 °C (1,550 °F) and quench for a finer case. Temper at 150-200 °C (300-400 °F) for a 58-63 HRC surface. Carbonitriding at lower temperature gives shallow cases on small parts, and low-pressure vacuum carburizing with a gas quench reduces distortion and avoids surface oxidation. Areas that must stay soft are masked with copper plate or stop-off paint, or left oversize and machined after carburizing but before hardening. Quenched without carburizing, 8620 reaches only the low-to-mid 40s HRC.
Tempers and conditions
- Hot rolled
- Annealed
- Normalized
- Cold drawn
- Carburized, hardened and tempered (case 58-63 HRC)
- Carbonitrided (shallow case)
Stock forms
- Round bar (hot rolled and cold drawn)
- Hex and flat bar
- Plate
- Forgings and gear blanks
- Seamless tube
- Wire and rod for cold heading
Relative cost
Tier 2 of 5. Close to 4140 per pound, roughly 1.5x 1018. The carburizing cycle, priced by furnace load and case depth, often costs more than the steel.
Typical applications
- Gears, pinions and ring gears
- Transmission and splined shafts, camshafts
- King pins, chain pins, pivot pins and bushings
- Ratchets, pawls and sprockets
- Cam followers, rollers and wear pads
- Carburized bearing rings and rollers
- Driveline and differential parts in trucks, tractors and off-highway equipment
Process compatibility
How 8620 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| Carburizing | ExcellentExcellent | What 8620 is for: a 58-63 HRC case 0.5-1.5 mm deep over a tough core; specify effective case depth to 50 HRC. Can 8620 steel be case hardened? |
| Gear Cutting | ExcellentExcellent | Hobbed or shaped soft, carburized, then ground or honed; the standard gear route. |
| CNC Machining | GoodGood | Machine to finish soft, leaving grind stock on precision features; mask or oversize areas that must stay soft. |
| CNC Turning | GoodGood | Pins and shafts turn well from normalized or cold-drawn bar; dead-soft stock can tear. |
| CNC Grinding | ExcellentExcellent | Grinds the case to size after hardening; keep total stock removal well inside the case depth. |
| Heat Treating | GoodGood | Normalize before machining and quench and temper after carburizing; alone, it hardens only to the 40s HRC. |
| Vacuum Heat Treating | GoodGood | Low-pressure vacuum carburizing with gas quench: less distortion and no intergranular oxidation on gear teeth. |
| Forging | ExcellentExcellent | Gear blanks, pinions and yokes forge easily; normalize after forging for consistent machining and carburizing. |
| Welding | GoodGood | Weld before carburizing with low-hydrogen filler and modest preheat; never weld a carburized case. |
| Shot Peening | GoodGood | Peening gear roots and fillets after carburizing adds bending-fatigue life. |
| Black Oxide | GoodGood | Common finish on carburized pins and small gears; oil it for storage protection. |
| Nitriding | FairFair | Takes a nitrided case, but the soft core supports it poorly under contact loads; carburizing is the better fit. |
| Induction Hardening | PoorPoor | At 0.20% carbon the surface only reaches the low to mid 40s HRC; carburize it, or use 4140 or 1045 for induction. |
Design and sourcing tips
- Specify the case completely: "Carburize, harden and temper: effective case depth 0.75-1.0 mm (0.030-0.040") to 50 HRC, surface 58-63 HRC, core 25-40 HRC", measured after final grind.
- Add grind stock to the case depth: if you grind 0.15 mm off a journal, carburize that much deeper so the finished case still meets the drawing.
- Mark areas that must stay soft (threads, weld zones, features machined later) and say how: copper mask, stop-off, or "leave oversize, machine after carburize, before harden".
- Allow for distortion: specify runout and flatness after heat treat, and grind or hone critical gear and bearing features.
- Use 8620 when the part needs a 60 HRC wear surface and impact toughness; use 4140 when it needs strength through the section more than a hard face.
Frequently asked questions
- How hard can 8620 steel get?
- Carburized, quenched and tempered, the surface reaches 58-63 HRC while the core stays at roughly 25-40 HRC depending on section size. Quenched without carburizing, 8620 only reaches the low to mid 40s HRC, because 0.20% carbon cannot form hard martensite.
- What is the difference between 8620 and 4140?
- 8620 is a low-carbon carburizing steel: you add carbon to the surface to make a hard case over a tough core, ideal for gears and pins. 4140 is a medium-carbon through-hardening steel: it hardens across the section to a uniform strength, and gets a harder surface by nitriding or induction hardening. Choose 8620 for wear plus impact, 4140 for strength through the part.
- Can 8620 be welded?
- Yes, before it is carburized. Its low carbon makes it easier to weld than 4140; use low-hydrogen filler and a modest preheat on heavy sections. A carburized case behaves like high-carbon steel and cracks when welded, so mask weld zones before carburizing or machine the case off.
- What is 8620 steel used for?
- Parts that need a very hard, wear-resistant surface over a tough core: gears, pinions, ring gears, splined and transmission shafts, king pins, chain pins, cam followers and some bearing rings. It is the most common carburizing steel in U.S. gear and driveline work.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM A29/A29M, ASTM A322 and ASTM A304 (8620H) bar specifications
- SAE J404 (chemistry) and SAE J1268 (hardenability bands)
- ASM Handbook Vol. 4 (heat treating, carburizing)
- Producer data sheets and Jominy hardenability data for 8620 and 8620H
