8620 steel (G86200): properties, composition, equivalents
8620 steel (AISI/SAE 8620, UNS G86200): 0.20 % C, 0.55 % Ni, 0.5 % Cr, 0.2 % Mo case-hardening steel. Carburized case 58–62 HRC over 800–1000 MPa core. Composition, heat treatment, 8620 vs 4140/1018, 21NiCrMo2/SNCM220/20CrNiMo equivalents.
What is 8620?
AISI 8620 is the American standard case-hardening alloy steel: 0.20 % carbon with 0.55 % nickel, 0.5 % chromium and 0.2 % molybdenum, UNS G86200. The triple alloying is 'lean' — no single element above 0.7 % — but together they give enough hardenability for a 25 mm gear to develop a 58–62 HRC carburized case over a tough 30–35 HRC core, plus the nickel toughness that lets gear teeth take shock without spalling. It is the default steel for automotive and truck transmission gears, differential ring and pinion gears, camshafts, piston pins, splined shafts, kingpins, chain sprockets and, in the through-hardened condition, for medium-strength bolts and pins.
8620 is normally bought as 8620H (hardenability-guaranteed band) for gears, machined in the annealed or normalized state, then carburized at 900–930 °C, quenched in oil and tempered at 150–200 °C. Core properties depend strongly on section size — the table gives typical values at 25 mm.
EN 20NiCrMo2-2 (1.6523, ex 21NiCrMo2), JIS SNCM220, GB 20CrNiMo and BS 805M20/EN362 are the same steel; European gear practice more often uses 16MnCr5 or 18CrNiMo7-6, which are functional substitutes.
8620 chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | 0.18 – 0.23 | |
| Mn | 0.7 – 0.9 | |
| P | ≤ 0.035 | |
| S | ≤ 0.04 | |
| Si | 0.15 – 0.35 | |
| Ni | 0.4 – 0.7 | |
| Cr | 0.4 – 0.6 | |
| Mo | 0.15 – 0.25 |
SAE J404 / ASTM A29 (G86200). 8620H (H86200) hardenability band: J1.5 = 41–48 HRC, J9 ≈ 24–36 HRC. Compare EN 21NiCrMo2 (1.6523): C 0.17–0.23, Ni 0.40–0.70, Cr 0.35–0.70, Mo 0.15–0.25 — the same steel; 20NiCrMo2-2 (1.6523) in EN 10084 is the current name.
8620 mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| Annealed (860 °C, furnace cool) — typical | ≈ 385 (≈ 55.8) | ≈ 540 (≈ 78.3) | 31 | ≈ 149 HB |
| Normalized (915 °C, air) — typical | ≈ 360 (≈ 52.2) | ≈ 635 (≈ 92.1) | 26 | ≈ 183 HB |
| Cold drawn — typical | ≈ 550 (≈ 79.8) | ≈ 690 (≈ 100.1) | 15 | ≈ 200 HB |
| Carburized 925 °C, direct oil quench, temper 150 °C — core, 25 mm — typical | ≈ 690–800 (≈ 100.1–116.0) | ≈ 900–1050 (≈ 130.5–152.3) | 15 | ≈ 280–320 HB (core) |
| Carburized, single reheat quench (845 °C), temper 150 °C — core — typical | ≈ 640 (≈ 92.8) | ≈ 850 (≈ 123.3) | 17 | ≈ 260 HB (core) |
| Carburized — surface (0.8–1.0 % C case) | — | — | — | 58–62 HRC (case), depth 0.5–2.0 mm |
| Through-hardened (oil, 845 °C), tempered 200 °C — typical, ≤ 15 mm | ≈ 900 (≈ 130.5) | ≈ 1100 (≈ 159.5) | 12 | ≈ 40 HRC |
Typical values (ASM); AISI grades carry no property minimums. Core hardness after carburizing depends on section: ≈ 40 HRC at 12 mm, 30–35 HRC at 25 mm, 25 HRC at 50 mm. Charpy (core) ≈ 50–80 J.
Impact toughness
8620 requires a minimum Charpy V-notch energy of 60 J at 20 °C (typical, carburized core). Nickel gives the core high toughness — 8620 gears survive shock loading that cracks plain carbon-steel cases.
8620 equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| 805M20 (EN362) | BS (superseded British) | Identical | BS 970 805M20: C 0.17–0.23, Ni 0.35–0.75, Cr 0.35–0.65, Mo 0.15–0.25. |
| 20NiCrMo2-2 | EN (European) | Identical | 1.6523 (EN 10084; formerly 21NiCrMo2): C 0.17–0.23, Ni 0.40–0.70, Cr 0.35–0.70, Mo 0.15–0.25. |
| 20CrNiMo | GB/T (China) | Identical | GB/T 3077 20CrNiMo: C 0.17–0.23, Ni 0.35–0.75, Cr 0.40–0.70, Mo 0.20–0.30. |
| SNCM220 | JIS (Japan) | Identical | JIS G4053 SNCM220: C 0.17–0.23, Ni 0.40–0.70, Cr 0.40–0.65, Mo 0.15–0.30. |
| 8615 / 8617 / 8622 | AISI / SAE | Near | Carbon steps of the 86xx family (0.15, 0.17, 0.22 % C) for lighter or heavier cores. |
| 20KhGNM / 20KhN2M | GOST (Russia/CIS) | Near | GOST 4543 20KhGNM (C 0.18–0.23, Ni 0.40–0.70, Cr 0.40–0.70, Mo 0.15–0.25) is the closest Russian match. |
| 4320 / 18CrNiMo7-6 | AISI / SAE | Functional | Higher-Ni grades (1.8 / 1.5 % Ni) for larger, more heavily loaded gears. |
| 1018 / C15 | AISI / SAE | Functional | Unalloyed case-hardening steels for small, lightly loaded parts. |
| 16MnCr5 | EN (European) | Functional | European Mn-Cr case-hardening steel with similar hardenability, no Ni — the usual EU substitute in gear practice. |
Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for 8620 →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| G86200 / H86200 | UNS | 8620H = hardenability-guaranteed version, standard for gears. |
| 21NiCrMo2 / 20NiCrMo2-2 / 1.6523 | EN 10084 / DIN 17210 | European twin. |
| 805M20 / 805A20 / EN362 | BS 970 | EN362 still used in the UK/India. |
| SNCM220 | JIS G4053 | Formerly SNCM21. |
| 20CrNiMo | GB/T 3077 | Chinese twin. |
Product forms and tolerance standards
Product forms: hot-rolled and cold-finished bar (ASTM A29, A322, A108), forgings and forged gear blanks (A29 / A788), seamless tube (A519), plate (limited), wire and cold-heading stock, pre-machined gear blanks.
Dimensional tolerances: bar: ASTM A29 / A108; forgings: ASTM A788; aerospace: AMS 6274 / 6276.
Key property values
8620 core strength after carburizing
Direct oil quench from 925 °C + 150 °C temper, 25 mm section: ≈ 690–800 MPa yield / 900–1050 MPa tensile (100–150 ksi), core ≈ 280–320 HB (30–35 HRC). Single reheat quench: ≈ 640 / 850 MPa. Larger sections give lower core hardness (≈ 25 HRC at 50 mm).
8620 surface hardness
Carburized case 58–62 HRC (≈ 700–750 HV) at 0.8–1.0 % surface carbon; effective case depth (550 HV) typically 0.5–2.0 mm. Carbonitrided: 60–64 HRC at shallower depth.
8620 annealed / normalized properties
Annealed ≈ 385 MPa yield / 540 MPa tensile, ≈ 149 HB; normalized ≈ 360 / 635 MPa, 183 HB; cold-drawn ≈ 550 / 690 MPa, 200 HB.
Heat treatment
Anneal 855–885 °C, furnace cool. Normalize 900–925 °C (1650–1700 °F), air. Carburize 900–930 °C (1650–1700 °F); direct quench in oil from 845–870 °C, or reheat-quench from 845 °C for core refinement; temper 150–200 °C (300–400 °F) 1–2 h. Through-harden (if used un-carburized) 845–870 °C oil → ≈ 40 HRC in thin sections. Ac1 ≈ 730 °C, Ac3 ≈ 830 °C, Ms ≈ 395 °C (core). Jominy 8620H: J1.5 = 41–48, J9 = 24–36 HRC.
Machinability
≈ 65 % of B1112 annealed/normalized — good; machine before carburizing, leaving 0.1–0.3 mm grinding stock on gear flanks. Cold drawn 8620 machines slightly better.
Physical properties
Density 7.85 g/cm³, E = 205 GPa, expansion 11.3 × 10⁻⁶/K, conductivity 46.6 W/m·K.
Weldability
Fair weldability in the annealed/normalized state (CE ≈ 0.45–0.50): preheat 100–200 °C for sections > 12 mm, low-hydrogen consumables (E7018 / ER70S-6 or ER80S-D2), post-weld stress relief 550–650 °C. Never weld carburized surfaces; mask or machine off the case first.
Machining, forming and heat treatment
Turning, hobbing, shaping, broaching and drilling in the annealed or normalized condition are all good; consistent hardness (149–183 HB) gives predictable tool life. Cold heading and cold extrusion are possible after spheroidizing. Hot forging 1200–950 °C then normalize. After carburizing only grinding, honing and lapping; distortion is moderate and predictable with 8620H.
Typical applications
- Transmission and differential gears, ring and pinion sets (automotive, truck, off-highway)
- Camshafts, rocker arms, piston pins, kingpins, universal-joint crosses
- Splined shafts, spline couplings, chain sprockets and roller-chain pins
- Bearing races and rollers for large sizes (as 8620 or 4320 carburized)
- Hydraulic pump gears, planetary carriers, drive pinions
- Medium-strength fasteners, pins and bushings (through-hardened or carburized)
- Firearm components (bolt carriers, receivers), tooling blanks
Frequently asked questions
What is 8620 steel used for?
Mainly carburized gears, shafts, pins and cams that need a hard, wear-resistant surface (58–62 HRC) over a tough core — transmission and differential gears, camshafts, sprockets, splines. Un-carburized it serves as a medium-strength machining and fastener steel.
What is the difference between 8620 and 4140?
8620 is a case-hardening steel (0.20 % C): soft, tough core with a carburized hard skin. 4140 is a through-hardening steel (0.40 % C): uniform 28–50 HRC throughout. Use 8620 for gears and wear surfaces needing shock resistance, 4140 for shafts, bolts and parts needing strength through the section.
How hard can 8620 get?
Carburized surface 58–62 HRC (up to 64 HRC carbonitrided); core 30–40 HRC depending on section. Through-hardened without carburizing it reaches only about 40–45 HRC in thin sections.
What is 8620H?
8620 with a guaranteed Jominy hardenability band (H86200: J1.5 = 41–48 HRC, J9 = 24–36 HRC). Gear manufacturers specify 8620H so the core hardness after carburizing is predictable from heat to heat.
What is 8620 equivalent to in EN?
EN 20NiCrMo2-2 (1.6523, formerly 21NiCrMo2) is identical. European gear shops often substitute 16MnCr5 or 20MnCr5 (Mn-Cr, no Ni) or step up to 18CrNiMo7-6 for heavier gears.
Can 8620 be welded?
Yes in the annealed or normalized condition with 100–200 °C preheat for thicker sections and low-hydrogen filler; stress-relieve afterwards. Do not weld after carburizing.
Related grades
Verified against ASTM A29/A29M-20 (SAE J404 chemistry); ASTM A29/A29M-20 Table 2 (G86200); SAE J1268 (8620H hardenability); ASM Handbook Vol. 1 and Vol. 4; EN 10084:2008 (20NiCrMo2-2 comparison). Last checked: September 2026.