SAE 8620H (ASTM A304) Hardenability Steel
SAE 8620H (ASTM A304) Hardenability Steel for Automotive & Mechanical Tubular Components
Comprehensive material data for SAE 8620H according to ASTM A304, including chemical composition, mechanical properties (typical), physical and thermal characteristics, international equivalents, and application guidance for seamless tubes and pipes used in automotive and mechanical structures.
Hot forging, cold drawing, machining, carburizing, quenching & tempering, induction hardening, nitriding
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SAE 8620H Hardenability Steel Introduction
SAE 8620H is a low-carbon, nickel-chromium-molybdenum alloy steel designed to meet specified hardenability bands per ASTM A304. It is widely supplied as hot-rolled or cold-finished bars, and also processed into seamless tubes and pipes for structural and mechanical components. The 'H' designation ensures consistent core hardenability, making it ideal for carburized parts requiring high surface hardness and a tough, durable core. Typical applications include automotive transmission gears, shafts, pins, and steering components. The material exhibits good machinability in the normalized condition, excellent forgeability, and predictable heat treatment response. When used in tubular forms, it offers an optimal balance of strength, toughness, and fatigue resistance for rotating and load-bearing applications.
SAE 8620H Hardenability Steel Chemical Composition
The chemical requirements for SAE 8620H are established to produce a controlled hardenability band. Limits for carbon, manganese, and other austenite stabilizers are wider than for standard SAE 8620 to ensure consistent Jominy curve results. Residual elements such as copper, nickel, and chromium may be present but are below specified maxima when not intentionally added.
| Element | Content (%) | Remarks |
|---|---|---|
| Carbon (C) | 0.17–0.23 | Core hardenability is primarily affected by carbon content |
| Manganese (Mn) | 0.60–0.95 | Promotes hardenability and acts as a deoxidizer |
| Silicon (Si) | 0.15–0.35 | Typical deoxidation residual |
| Nickel (Ni) | 0.35–0.75 | Improves core toughness and hardenability |
| Chromium (Cr) | 0.35–0.65 | Increases hardenability and carburizing response |
| Molybdenum (Mo) | 0.15–0.25 | Prevents temper embrittlement and refines grain |
| Phosphorus (P) | ≤ 0.035 | Max; higher levels reduce toughness |
| Sulfur (S) | ≤ 0.040 | Max; controlled for machinability, typically 0.020–0.040 for improved machining |
| Iron (Fe) | Balance | Approx. 97.0–98.1% |
SAE 8620H Hardenability Steel Thermal & Electrical Physical Properties
Physical properties are typical for low-alloy Ni-Cr-Mo steel in the normalized and tempered condition. These values are influenced by microstructure and temperature. Data provided at room temperature unless otherwise indicated.
| Property | Typical Value | Unit | Condition / Temperature |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At 20 °C |
| Elastic Modulus (E) | 205 | GPa | At 20 °C |
| Shear Modulus (G) | 80 | GPa | Calculated, at 20 °C |
| Poisson's Ratio (ν) | 0.29 | – | At 20 °C |
| Thermal Expansion Coefficient (α) | 11.8 | 10⁻⁶/K | 20–100 °C |
| Thermal Expansion Coefficient (α) | 12.5 | 10⁻⁶/K | 20–200 °C |
| Thermal Expansion Coefficient (α) | 13.1 | 10⁻⁶/K | 20–400 °C |
| Thermal Conductivity (λ) | 46.7 | W/(m·K) | At 100 °C |
| Thermal Conductivity (λ) | 42.5 | W/(m·K) | At 200 °C |
| Thermal Conductivity (λ) | 38.0 | W/(m·K) | At 400 °C |
| Specific Heat Capacity | 475 | J/(kg·K) | At 20–100 °C |
| Electrical Resistivity (ρₑ) | 0.22 | μΩ·m | At 20 °C |
SAE 8620H Hardenability Steel Mechanical Properties
The mechanical properties of SAE 8620H depend heavily on heat treatment. In the 'as-rolled' or normalized condition the steel is relatively soft and ductile, suitable for machining and forming. After carburizing, quenching, and low-temperature tempering, the surface exhibits high hardness while the core retains good strength and toughness. The table below presents representative values for the most common conditions. Actual values shall meet the hardenability requirements of ASTM A304, not necessarily specific tensile limits.
| Property | Typical Value | Unit | Test Condition / Heat Treatment |
|---|---|---|---|
| Yield Strength (ReH) | ≥ 345 | MPa | Normalized (870 °C, air cool) |
| Yield Strength (ReH) | 550–700 | MPa | Quenched (860 °C, oil) and tempered (540 °C, water) – core properties |
| Tensile Strength (Rm) | ≥ 585 | MPa | Normalized (870 °C, air cool) |
| Tensile Strength (Rm) | 750–900 | MPa | Quenched (860 °C, oil) and tempered (540 °C) – core properties |
| Elongation (A, 50 mm) | ≥ 23 | % | Normalized (870 °C, air cool) |
| Elongation (A, 50 mm) | 18–22 | % | Quenched and tempered (540 °C) – core properties |
| Reduction of Area (Z) | ≥ 50 | % | Normalized |
| Reduction of Area (Z) | 45–60 | % | Quenched and tempered (540 °C) |
| Hardness | 160–190 | HBW | Normalized (approx.) |
| Hardness | 220–260 | HBW | Quenched and tempered (540 °C) – core |
| Surface Hardness | 58–63 | HRC | Carburized (0.8–1.2 mm case), quenched, tempered at 180 °C |
| Charpy Impact (KV) | ≥ 40 | J | Normalized, at room temperature |
| Charpy Impact (KV) | ≥ 60 | J | Quenched & tempered (540 °C), at room temperature |
| Bend Test | No cracks | – | 180° bend, diameter = 3t, normalized condition (typical acceptance) |
SAE 8620H Hardenability Steel Fully Equivalent Material Standards & Alternative Designations
| Country/Region | Standard | Designation | Remarks |
|---|---|---|---|
| USA | ASTM A304 | 8620H | Original hardenability band steel |
| International | ISO 683-11 | 20NiCrMo2-2H | Chemically equivalent H-steel for carburizing, with same hardenability band |
| Europe | EN 10084 | 20NiCrMo2-2H (1.6523H) | European H-steel with identical hardenability requirements |
| Germany | DIN 17210 / DIN EN 10084 | 20NiCrMo2-2H (1.6523H) | Superseceded DIN, now EN |
| UK | BS 970 Part 3 | 805M20H | Hardenability band version of 805M20 (similar chemistry) |
| Japan | JIS G4052 | SCM420H (partially) | Chromium-molybdenum H-steel, lower nickel but sometimes used as alternative, verify hardenability |
SAE 8620H Hardenability Steel Application Introduction
SAE 8620H in tube form combines the benefits of a hollow section with a deep-hardening, wear-resistant case after carburizing. It is extensively used in powertrain and driveline components where rotating or sliding contact demands high surface fatigue strength and a ductile core. The predictable hardenability minimizes distortion and ensures consistent mechanical properties across batches. The material can be machined in the normalized state, welded with low-hydrogen procedures, and successfully induction hardened or nitrided for specific surface requirements.
Product Applications: Seamless mechanical tubing per ASTM A519, Drawn-over-mandrel (DOM) precision tubes, Hollow bar stock for machining ring gears and sleeves, Forged and bored tubular blanks for gear blanks, Cylinder liners (thin-walled, carburized)
Processed into products: Automotive transmission gears (input/output shafts as hollow design), Differential side gears and pinions, Steering knuckles (tubular design for weight reduction), Drive shafts and half shafts, Pinion shafts for power tools, Oil pump drive sleeves, Roller bearing races (where through-hardening is not required), Hydraulic cylinder rod guides, Precision bushings for heavy machinery
Application industries: Automotive (passenger cars, commercial vehicles, motorcycles), Agricultural Machinery (tractor transmissions, PTO shafts), Construction & Mining Equipment (axle shafts, pivot pins), Oil & Gas (drill stem subs, reciprocating pump shafts), Wind Energy (pitch & yaw drive gears, bearing spacers), General Engineering (hydraulic cylinder bushings, structural hollow shafts)
SAE 8620H Hardenability Steel Similar/Comparable Materials & Near-Equivalent Recommendations
| Country/Region | Standard | Designation | Remarks |
|---|---|---|---|
| USA | ASTM A29/SAE | 8620 (non-H) | Standard non-hardenability controlled version; may exhibit wider hardenability variation |
| USA | ASTM A304 | 8617H / 8622H | Alternative H-steels with slightly lower/higher carbon for different core hardness |
| Europe | EN 10084 | 20MnCr5 (1.7147) | Manganese-chromium carburizing steel, lower nickel, similar case hardness but lower core toughness |
| Europe | EN 10084 | 18CrNiMo7-6 (1.6587) | Higher alloyed carburizing steel for heavier sections, more hardenability |
| Japan | JIS G4052 | SCr420H | Chromium carburizing H-steel, no molybdenum, used for lightly stressed parts |
| China | GB/T 5216 | 20CrNiMoH | Similar Ni-Cr-Mo hardenability steel, close match in China market |
Notes:
Hardenability is mandatory: For SAE 8620H the Jominy curve at J 1.6 mm (1/16 in) shall be 70–84 HRC, J 3.2 mm (2/16 in) 65–81 HRC, J 4.8 mm (3/16 in) 61–77 HRC, J 6.4 mm (4/16 in) 56–73 HRC, J 8.0 mm (5/16 in) 52–69 HRC, J 9.5 mm (6/16 in) 48–64 HRC, J 12.7 mm (8/16 in) 41–57 HRC, and J 16.0 mm (10/16 in) 36–50 HRC. Material must meet the full band. Heat treatment: Typical carburizing at 900–930 °C, quench in oil (or polymer), temper at 150–200 °C for surface hardness, or temper at 500–550 °C for core toughness. Welding: Preheating to 150–260 °C and post-weld stress relief is recommended when welding in the hardened condition. Machinability: Rated at approximately 65% compared to AISI 1212, best in the normalized or spheroidize annealed condition.
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