Contents
D6AC Alloy Steel: Properties, Processes, Applications
- John
SteelPro Group supplies D6AC alloy steel bars, a high-strength material designed for aerospace and defense. This post explores its main characteristics, manufacturing techniques, and uses, guiding you in selecting the ideal material for challenging conditions.
What Is D6AC Steel?
D6AC steel is a durable, medium-carbon, low-alloy metal with exceptional strength. It reaches up to 280 ksi tensile strength while maintaining toughness. Its deep-hardening properties make it suitable for large cross-sections without sacrificing strength. Vacuum arc remelting (VAR) ensures purity and uniformity. The alloy can undergo heat treatment, be precisely machined, and welded, making it perfect for use in aerospace and defense industries.
D6AC Steel Specifications
D6AC meets stringent aerospace and defense standards, including:
- AMS 6431: Defines heat-treated bars for high-strength structural components.
- MIL-S-8949: Specifies material requirements for aircraft and missile parts.
- AMS 2300: Ensures cleanliness for premium-grade VAR-processed steel.
- Other Certifications: ASTM A579 (Class 23), FMS-1011 (General Dynamics), GM-1013 (Grumman), and Lockheed-specific standards (STM-05-500, LCM-05-2190).
Our D6AC stock is traceable to these certifications, guaranteeing compliance with global aerospace, defense, and industrial OEM requirements.
D6AC Alloy Steel Properties Overview
- Exceptional strength-to-mass balance for aviation and military uses.
- Excellent fracture toughness and fatigue resistance.
- Superior hardenability for large-section applications.
- Retains mechanical properties at elevated temperatures.
D6AC Steel Chemical Composition
| Element | Content |
| Carbon (C) | 0.46% |
| Silicon (Si) | 0.25% |
| Manganese (Mn) | 0.75% |
| Chromium (Cr) | 1.10% |
| Nickel (Ni) | 0.60% |
| Molybdenum (Mo) | 1.00% |
| Vanadium (V) | 0.10% |
| Iron (Fe) | As Balance |
D6AC Steel Mechanical Properties
| Property | Condition | |
| 600°F (316°C) | 950°F (510°C) | |
| Tensile Strength | 280 ksi (1931 MPa) | 228 ksi (1572 MPa) |
| Yield Strength | 250 ksi (1724 MPa) | 195 ksi (1345 MPa) |
| Elongation | 7% | 7% |
| Reduction of Area | 23% | 25% |
| Hardness (HRC) | 53 | 46 |
D6AC Steel Physical Properties
| Property | Value (Imperial) | Value (Metric) |
| Density | 0.284 lb/cu.in | 7.8 g/cm³ |
| Specific Heat Capacity | 0.116 Btu/lb·°F | 486 J/kg·K |
| Melting Point | 2600°F | 1427°C |
| Thermal Conductivity | 30 Btu·ft/(h·ft²·°F) | 51.9 W/(m·K) |
| Average Thermal Expansion | 7 µin/in·°F | 12.6 µm/m·°C |
| Elastic Modulus (Tensile) | 32,000 ksi | 220 GPa |
Thermal Expansion Coefficient
| Temperature Range | Imperial Value | Metric Value |
| 0 – 100°F (-18 – 38°C) | 7.38 µin/in·°F | 13.28 µm/m·°C |
| 0 – 600°F (-18 – 316°C) | 7.61 µin/in·°F | 13.70 µm/m·°C |
| 100 – 200°F (38 – 93°C) | 7.31 µin/in·°F | 13.16 µm/m·°C |
| 600 – 700°F (316 – 371°C) | 9.70 µin/in·°F | 17.46 µm/m·°C |
| 600 – 1300°F (316 – 704°C) | 8.95 µin/in·°F | 16.11 µm/m·°C |
D6AC Steel Bars Dimensions
SteelPro Group supplies precision-engineered D6AC steel bars. All products meet AMS 6431 and MIL-S-8949 specifications, with full traceability and certification.
| Product Type | Size Range (Imperial) | Size Range (Metric) |
| Round Bars | 0.5″ – 12″ Diameter | 12.7 mm – 304.8 mm Diameter |
| Hexagonal Bars | 0.5″ – 6″ Across Flats | 12.7 mm – 152.4 mm A/F |
| Square Bars | 1″ – 12″ Width | 25.4 mm – 304.8 mm Width |
| Billets (Forging Stock) | 6″ – 24″ Diameter | 152.4 mm – 609.6 mm Diameter |
D6AC Steel Applications
D6AC steel is extensively utilized in aviation, military, and manufacturing industries for its exceptional durability and superior mechanical strength.
- Aerospace: Used in landing gear, structural components, and high-stress airframe parts.
- Defense: Applied in armor, missile components, and weapon systems requiring impact resistance.
- Industrial: Suitable for high-strength shafts, pressure vessels, and tooling applications.
Its combination of strength, fracture resistance, and deep-hardening makes it ideal for critical load-bearing components.
D6AC Steel Forging
Forging is the first step in shaping D6AC steel, where the material is heated and formed into the desired component.
- Heating temperature: 2000-2250°F (1093-1232°C).
- Closed-die forging: Higher temperatures improve material flow.
- Final forging temperature: Should not drop below 1700°F (927°C) to prevent loss of ductility.
- Cooling cycle: After forging, the steel is placed in a furnace at 1200-1300°F (649-704°C), soaked as required, and then slowly cooled to 1000°F (538°C) before air cooling.
D6AC Steel Heat Treatment
1. Normalizing
To refine the grain structure and enhance mechanical properties, D6AC steel is first normalized by heating to 1700°F (927°C) followed by air cooling. This step improves toughness and prepares the material for subsequent hardening.
2. Hardening (Quenching)
For optimal strength and hardness, D6AC steel is typically hardened by heating to 1700°F (927°C) in a protective atmosphere to prevent surface oxidation. The quenching method depends on the section thickness:
- Thin sections (<1 inch / 25 mm): Air cooling is sufficient.
- Larger sections: Require oil quenching with controlled oil temperatures between 150-250°F (65-121°C).
- Alternative method: Salt quenching at 400-420°F (204-218°C), followed by air cooling, is sometimes used for more uniform hardness.
3. Tempering for Desired Strength
After quenching, tempering is crucial to balance hardness and toughness. The procedure includes raising the material to a set temperature, maintaining it for the necessary time, and then allowing it to cool.
- For 260 ksi tensile strength: Temper at 575°F (302°C) for 2 hours, then air cool. Double tempering is recommended.
- For 200 ksi tensile strength: Temper at 1100°F (593°C) for 2 hours, then air cool.
- For 180 ksi tensile strength: Temper at 1150°F (621°C) for 2 hours, then air cool.
Double tempering is frequently used to achieve consistent mechanical characteristics and reduce residual stress.
Tempering Data: Hardness vs. Temperature
| Tempering Temp. | Hardness (HRC) |
| 400°F (204°C) | ~60 |
| 600°F (316°C) | ~55 |
| 800°F (427°C) | ~50 |
| 1000°F (538°C) | ~45 |
| 1200°F (649°C) | ~40 |
4. Annealing (Softening for Machining)
If machining or forming is required before final heat treatment, annealing is performed by heating to 1500-1550°F (816-843°C), followed by furnace cooling at 50°F (28°C) per hour down to 1000°F (538°C) before air cooling. This results in a softer, more workable material.
D6AC Steel Machining
Once the material is heat-treated or annealed, machining operations can be performed. Because of D6AC steel’s exceptional toughness and durability, precision is essential during machining.
- Machinability rating: 50-55% of AISI B1112 screw stock.
- Recommended tools: Carbide or high-speed steel (HSS) tools for better wear resistance.
- Cutting fluids: Sulfurized or chlorinated oils help reduce tool wear and improve machining efficiency.
- Post-machining treatment: For components above 200 ksi tensile strength, stress relief treatment (800°F / 427°C for 3 hours) is advised.
D6AC Steel Welding
D6AC steel is weldable, but due to its high hardenability, strict control of preheating and post-weld heat treatment is necessary.
- Preheat temperature: 450-550°F (232-288°C) before welding.
- Welding methods:
- Thin sections: Tungsten Inert Gas (TIG) welding.
- Thicker sections: Gas Metal Arc Welding (GMAW) with matching filler metal.
- Post-weld heat treatment:
- Hold at 600°F (316°C) after welding, then air cool to 300°F (149°C).
- Immediately perform stress relief annealing at 1000°F (538°C) to prevent residual stresses.
- For critical applications, a full normalizing + tempering cycle is recommended.
D6AC Steel VS 4340 Steel
D6AC steel is stronger and tougher than 4340 steel.
While both are heat-treatable, D6AC requires stricter processing controls to maintain its ultra-high strength. 4340, on the other hand, is easier to machine and weld, making it a more versatile choice for automotive, industrial, and general aerospace components. If maximum strength, durability, and fatigue resistance are required, D6AC is the superior option.
Get High-Performance D6AC Steel from SteelPro Group
SteelPro Group offers certified D6AC alloy steel for aerospace, defense, and industrial applications. With precision-engineered stock, full traceability, and expert support, we ensure you get the right material for the job.
Contact us today to discuss your D6AC steel requirements. Our team is ready to assist with custom orders, technical support, and competitive pricing!
