What Is AISI 8622H Steel?
01AISI 8622H is a low-alloy, nickel-chromium-molybdenum (Ni-Cr-Mo) case-hardening steel in the SAE 86xx series. Its UNS designation is G86220. The suffix "H" designates a guaranteed hardenability band per ASTM A304, making it the precision-specified alternative to standard SAE 8622 for components where consistent case depth is a hard engineering requirement.
The designation is governed by two interlocking standards. Chemical composition follows SAE J1268 (H-steel chemistry limits), while hardenability bands are defined and tested to ASTM A304 via the Jominy end-quench method (ASTM A255). Together they ensure that every production heat delivers consistent case depth and core hardness — something non-H grades fundamentally cannot guarantee.
Its quadruple alloy system — chromium for hardenability and carbide stability, nickel for core toughness and low-temperature impact resistance, molybdenum for hardenability and temper-brittleness suppression, and manganese for grain refinement — positions 8622H as the industry-standard material for transmission gears, ring gear forgings, and drive pinions operating under high-cycle contact fatigue loading per AGMA 2001 or ISO 6336.
The "H" suffix does not mean tighter chemistry. It means the steel mill is contractually required to test every production heat by the Jominy end-quench method and certify that the hardness at each standard distance falls within published minimum and maximum limits. This shifts quality assurance from chemistry compliance to functional performance — a far more direct predictor of heat treatment outcome. Specify 8622H (never just 8622) whenever a case depth or HRC requirement appears on the drawing.
Chemical Composition of AISI 8622H
02AISI 8622H chemistry is specified under two limits: the standard grade (non-H) per SAE J403, and the H-band grade per SAE J1268. The H-band permits wider elemental variation but mandates hardenability testing. The table below compares both.
SAE 8622 vs AISI 8622H — Chemistry Comparison Table
| Element | SAE 8622 (Standard / SAE J403) | AISI 8622H (H-Band / SAE J1268) | Role in Steel Performance |
|---|---|---|---|
| Carbon (C) | 0.20 – 0.25% | 0.17 – 0.25% | Controls core hardness and carburized case carbon potential |
| Manganese (Mn) | 0.70 – 0.90% | 0.60 – 0.95% | Increases hardenability; refines grain; acts as mild deoxidizer |
| Silicon (Si) | 0.15 – 0.35% | 0.15 – 0.35% | Primary deoxidizer; moderate solid-solution strengthener |
| Chromium (Cr) | 0.40 – 0.60% | 0.35 – 0.65% | Hardenability; carbide stability; case wear resistance |
| Nickel (Ni) | 0.40 – 0.70% | 0.35 – 0.75% | Core toughness; low-temperature Charpy impact resistance |
| Molybdenum (Mo) | 0.15 – 0.25% | 0.15 – 0.25% | Hardenability; suppresses temper brittleness in core |
| Phosphorus (P) | ≤ 0.035% | ≤ 0.035% | Controlled residual — excess causes grain boundary embrittlement |
| Sulfur (S) | ≤ 0.040% | ≤ 0.040% | Controlled residual — excess reduces ductility and fatigue life |
Source: SAE J403 (standard chemistry), SAE J1268 (H-band chemistry). The H-band intentionally allows wider elemental limits and compensates with mandatory Jominy testing per ASTM A304.
The carbon equivalent of AISI 8622H, calculated using the IIW formula CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15, is approximately 0.60–0.72 depending on actual heat chemistry within the H-band. This places 8622H in the medium-CE category requiring preheat for welding (175–230°C) and post-weld heat treatment for structural weld joints.
Mechanical Properties of AISI 8622H
03Mechanical properties of AISI 8622H depend on heat treatment condition and whether values apply to the carburized case or the core. The following tables cover the standard carburized and Q&T condition, plus physical and thermal properties.
Core Properties — Carburized + Quenched and Tempered at 150°C
| Property | Heat Treatment Condition | Typical Value | Unit |
|---|---|---|---|
| Tensile Strength (UTS) | Q&T at 150°C | 930 – 1,100 | MPa |
| Yield Strength (0.2% proof) | Q&T at 150°C | 680 – 850 | MPa |
| Elongation (A5) | Q&T at 150°C | 14 – 18 | % |
| Reduction of Area (Z) | Q&T at 150°C | 55 – 65 | % |
| Charpy Impact (CVN) | Q&T, room temperature | 55 – 80 | J |
| Brinell Hardness (annealed) | Soft annealed | ≤ 207 | HBW |
| Core Hardness (after carburizing) | Carburized + Q&T | 30 – 42 | HRC |
| Case Hardness (0.1 mm depth) | Carburized + Q&T | 58 – 63 | HRC |
| Effective Case Depth (ECD at 50 HRC) | Gas carburizing | 0.8 – 2.5 | mm |
| Density | Annealed | 7.85 | g/cm³ |
| Elastic Modulus (E) | Room temperature | 205 | GPa |
| Poisson's Ratio (ν) | Room temperature | 0.29 | — |
Physical and Thermal Properties
| Property | Temperature | Value | Unit |
|---|---|---|---|
| Thermal Conductivity | 20°C | 47.7 | W/(m·K) |
| Coefficient of Thermal Expansion | 20–200°C | 11.3 × 10⁻⁶ | /°C |
| Specific Heat Capacity (Cp) | 20°C | 477 | J/(kg·K) |
| Electrical Resistivity | 20°C | ~0.22 | μΩ·m |
| Magnetic Permeability | — | Ferromagnetic | — |
All values above are representative for small test bars (≤25 mm diameter). In actual forged components with section sizes above 75 mm, core hardness and tensile strength decrease due to reduced cooling rates during quenching — a phenomenon called "mass effect" or "section sensitivity." For forged 8622H parts with cross-sections above 100 mm, always specify and verify mechanical properties from the production heat's actual test coupon, not reference tables.
Hardenability — AISI 8622H Jominy H-Band Data
04The defining feature of the 8622H designation is the guaranteed hardenability band per ASTM A304, measured by the Jominy end-quench test per ASTM A255. Every production heat must be tested and its hardness results documented at standard distances from the quenched end. Results that fall outside the H-band limits represent a non-conformance.
Full Jominy End-Quench Hardenability Table — AISI 8622H (ASTM A304)
| Distance from QE (1/16 in.) | Distance (mm) | Min HRC | Max HRC | Band Midpoint HRC |
|---|---|---|---|---|
| J2 | 3.2 | 38 | 50 | 44 |
| J4 | 6.4 | 34 | 45 | 40 |
| J6 | 9.5 | 30 | 43 | 37 |
| J8 | 12.7 | 27 | 41 | 34 |
| J10 | 15.9 | 25 | 39 | 32 |
| J12 | 19.1 | 24 | 37 | 31 |
| J16 | 25.4 | 22 | 35 | 29 |
| J20 | 31.8 | 20 | 33 | 27 |
| J32 | 50.8 | 18 | 30 | 24 |
Source: ASTM A304 H-band for 8622H. Every production heat must fall within these min/max limits. Request the Jominy test report as part of the Mill Test Certificate (MTC EN 10204 3.1 or 3.2).
To determine whether a specific cross-section will achieve the required core hardness: (1) Calculate the equivalent Jominy distance for your section diameter using ASTM A255 Appendix A1 (D-equivalent charts). (2) Look up the H-band limits at that J-distance. (3) If the required core HRC falls within the band midpoint ± half the band width, specification is achievable. If you need >35 HRC at J16 (the limit for 8622H), consider upgrading to AISI 9310 or 4320H.
Heat Treatment of AISI 8622H
05AISI 8622H is designed for the carburized and case-hardened condition. The following five-step sequence is the industry standard for achieving 58–63 HRC at the surface with a tough 30–42 HRC core.
Heat Treatment Parameter Reference Table
| Operation | Temperature | Cooling Medium | Duration | Target Result |
|---|---|---|---|---|
| Normalizing | 870–900°C | Air | Per section | Refine forged grain structure; relieve residual stress |
| Soft Annealing | 790–830°C | Furnace cool | 2–4 hrs | ≤ 207 HBW for CNC machining before carburizing |
| Gas Carburizing | 900–940°C | Endothermic gas | 4–12 hrs | Case C: 0.8–1.0%; ECD at 50 HRC: 0.8–2.5 mm |
| Hardening Quench | 820–845°C | Oil (marquench for heavy sections) | — | Case: 58–63 HRC; Core: 30–42 HRC |
| Low Temperature Temper | 150–200°C | Air or oil | 1–2 hrs | Reduce quench residual stress; retain full case hardness |
| High Temper (core Q&T only) | 550–650°C | Air | 2 hrs | Core-only: 28–35 HRC for shaft and pin applications |
Oil quenching is the standard for 8622H. Water quenching is not recommended for sections above 25 mm — the high quench rate causes thermal gradients that produce quench cracks, particularly in forged parts with abrupt cross-section changes. For forged rings and shafts above 100 mm, marquenching in hot oil at 150–200°C reduces distortion and cracking risk while still achieving full 58–63 HRC case hardness.
Open Die Forging Parameters for AISI 8622H
06AISI 8622H has excellent hot-working behavior between 850°C and 1,250°C. As a Ni-Cr-Mo alloy steel, it responds well to open die forging with high forging ratios, which refine the prior cast microstructure into a dense, equiaxed grain structure that improves both fatigue performance and ultrasonic testing cleanliness.
| Parameter | Recommended Value / Range | Technical Notes |
|---|---|---|
| Forging Start Temperature | 1,150 – 1,250°C | Begin forging only after thorough soaking; verify with contact pyrometer. Above 1,280°C risks austenite grain coarsening. |
| Forging Finish Temperature | 850 – 950°C | Must not forge below 850°C — risk of adiabatic shear bands and intergranular cracking in the Ni-Cr-Mo matrix. |
| Minimum Forging Ratio | ≥ 3:1 (preferably 4:1) | Higher ratios break down cast dendritic structure, eliminate porosity, and improve ultrasonic cleanliness to EN 10228-3 Q4/Q5 levels. |
| Post-Forge Cooling | Slow cool in ash or sand | Prevents thermal shock and delayed hydrogen cracking, particularly in sections above 150 mm. Do not air blast or water cool. |
| Post-Forge Anneal | 790–830°C, furnace cool | Required before machining; achieves ≤207 HBW to allow standard carbide tooling without excessive wear. |
| Ultrasonic Testing Standard | ASTM A388 / EN 10228-3 | 100% volumetric UT on all gear blanks and shaft forgings. Specify quality class (Q3–Q5) on the engineering drawing. |
The 8622H designation is particularly effective for large forged ring blanks used as gear ring blanks and planetary carriers. The guaranteed hardenability band ensures that in cross-sections of 100–150 mm, the core achieves sufficient quenching response to meet the root bending fatigue requirements of AGMA 2001 or ISO 6336 gear ratings. This is its primary advantage over non-H SAE 8620 in large-section applications.
For ordering information — available sizes, tolerances, lead times, and pricing — visit the AISI 8622H Forging Parts product page.
Custom AISI 8622H Forged Parts — Factory Direct
Jiangsu Liangyi manufactures open die forgings and seamless rolled rings in AISI 8622H, 30 kg to 30,000 kg per piece. ISO 9001:2015 certified. MTC EN 10204 3.1/3.2. UT testing per ASTM A388 or EN 10228-3. Free RFQ response within 24 hours.
Machinability and Weldability
07Machinability of AISI 8622H
In the normalized or annealed condition (≤207 HBW), AISI 8622H machines well. Its machinability index is approximately 65–70% relative to AISI B1112 free-machining steel as the 100% baseline. This is adequate for standard CNC turning, milling, drilling, and broaching operations when appropriate tooling is selected.
| Operation | Cutting Speed | Feed Rate | Recommended Tooling |
|---|---|---|---|
| Turning — Rough | 80–100 m/min | 0.3–0.5 mm/rev | PVD-coated carbide insert P30–P40 |
| Turning — Finish | 120–160 m/min | 0.08–0.15 mm/rev | PVD carbide P15–P25; sharp edge geometry |
| Drilling | 20–35 m/min | 0.10–0.25 mm/rev | HSS-Co or solid carbide; flood coolant |
| Milling | 60–90 m/min | 0.05–0.12 mm/tooth | Carbide end m |
| Milling | 60–90 m/min | 0.05–0.12 mm/tooth | Carbide end mills, TiAlN coating |
| Grinding (after heat treatment) | 25–30 m/s (wheel) | 0.01–0.03 mm/pass | CBN wheel preferred; aluminum oxide acceptable |
Weldability of AISI 8622H
AISI 8622H has moderate weldability. Its carbon equivalent (CE, IIW formula) of approximately 0.60–0.72 requires preheat and post-weld heat treatment for structural weld joints. In most applications, 8622H components are not welded after carburizing because the carburized case would be destroyed. Pre-carburize welding is feasible with these precautions:
Preheat to 175–230°C. Use low-hydrogen electrodes (AWS E8018-C1). Interpass temperature below 315°C. Apply PWHT at 595–650°C for 1 hour per 25 mm of weld throat. Cool to below 95°C before carburizing.
AISI 8622H vs Competing Grades — Selection Matrix
08Use this matrix to determine when 8622H is the right choice versus its most common alternatives. The deciding factors are section size, hardenability requirement, and cost.
| Selection Criterion | SAE 8620 | AISI 8622H ✦ | AISI 9310 | AISI 4320H |
|---|---|---|---|---|
| Hardenability Guarantee | ✗ None | ✓ ASTM A304 | ✓ Wide band | ✓ ASTM A304 |
| Case Hardness (HRC) | 58–62 | 58–63 | 58–62 | 58–62 |
| Core Toughness | ||||
| Large Section (>100mm) | Poor | Good | Excellent | Good |
| Relative Cost | Lowest | Low–Moderate | Highest | Moderate |
| Heat-to-Heat Consistency | Variable | Guaranteed | Guaranteed | Guaranteed |
| Best Application | Small gears, shafts <50mm | Transmission gears, ring gear forgings, 50–150mm sections | Aerospace gears, highly loaded turbines | Large gears where 9310 cost is prohibitive |
Typical Applications of AISI 8622H Forgings
09Helical, spur, and bevel gears where AGMA 2001 or ISO 6336 specifies minimum case depth and surface hardness by drawing.
Forged ring blanks for planetary gearboxes and wind turbine drives; seamless ring rolling gives circumferential grain flow for superior tooth root bending fatigue.
Heavy-duty commercial vehicle and agricultural drivetrains requiring combined contact wear resistance and high torsional fatigue life.
Ball mill pinions, SAG mill drives, and conveyor drive shafts operating under high cyclic shock loads in abrasive mining environments.
Ship propulsion reduction gears and thruster drives where guaranteed case depth eliminates under-hardening risk in large 100–200mm ring gear cross-sections.
Main gearbox planetary carriers and output shafts; H-band hardenability guarantee supports compliance with IEC 61400-4 wind turbine gearbox design requirements in large cross-section forgings.
International Equivalents of AISI 8622H
10AISI 8622H does not have a perfect 1:1 equivalent in every national standard. The grades below share the same Ni-Cr-Mo alloying intent but none carry the ASTM A304 hardenability band guarantee. Always verify with the steel mill when substituting on a drawing that specifies 8622H.
SNCM220 (JIS) and EN 1.6523 share similar chemistry but carry no ASTM A304 H-band guarantee. If your drawing specifies 8622H, either procure 8622H with a Jominy report in the MTC, or formally re-qualify the substitute grade with documented hardenability testing.