AISI 8630 / 8630 mod, 1.6591 Low Alloy Nickel-Chrome-Moly Steel

Product Description

AISI 8630 / 8630 mod, 1.6591 is a premium low alloy steel featuring a carefully balanced composition of nickel, chromium, and molybdenum, specifically engineered for critical applications requiring exceptional toughness, strength, and hardenability. This versatile alloy is distinguished by its optimized carbon content (0.28-0.33%) combined with carefully controlled amounts of nickel (≤1.00%), chromium (0.85-1.50%), and molybdenum (0.35-0.65%) that together provide an outstanding combination of mechanical properties. AISI 8630 is particularly valued for its deep hardenability, exceptional toughness at low temperatures, and excellent wear resistance in the quenched and tempered condition. The modified version (8630 mod) features refined chemistry and processing, delivering enhanced mechanical properties and improved low-temperature impact toughness. With consistent performance across heavy sections and large forgings, this sophisticated alloy has become the material of choice for some of the most demanding components in the oil and gas, power generation, and heavy equipment industries.

Applications

AISI 8630 / 8630 mod, 1.6591 low alloy steel is specifically designed for applications requiring high strength, toughness, and excellent hardenability, particularly in large section sizes. Its primary applications include:

• Oil and gas equipment including wellhead components and subsea connectors
• Hub connectors and subsea manifolds for offshore applications
• Large and critical forgings for power generation equipment
• Heavy-duty gears and gearboxes for industrial machinery
• Shafts and rotors for high-torque applications
• High-strength fasteners and bolting for critical applications
• Pinions and gears for mining equipment
• Drive components in heavy equipment
• Compressor and turbine components
• Marine propulsion components and shafting
• Large-diameter pipeline fittings and components
• High-strength structural components for critical load-bearing applications

The exceptional combination of mechanical properties and deep hardenability makes AISI 8630 / 8630 mod, 1.6591 particularly valuable for applications requiring both strength and toughness in large section sizes where other alloys might not achieve consistent properties throughout the cross-section.

Standards and Specifications

AISI 8630 / 8630 mod, 1.6591 low alloy steel complies with the following international standards and specifications:

• ASTM A29/A29M – Standard Specification for Steel Bars, Carbon and Alloy, Hot-Wrought
• ASTM A473 – Standard Specification for Stainless Steel Forgings
• ASTM A508/A508M Grade 4A – Standard Specification for Quenched and Tempered Vacuum-Treated Carbon and Alloy Steel Forgings for Pressure Vessels
• ASTM A519 – Standard Specification for Seamless Carbon and Alloy Steel Mechanical Tubing
• ASTM A646 – Standard Specification for Premium Quality Alloy Steel Blooms and Billets for Aircraft and Aerospace Forgings
• SAE J1268 – Standard for 86xx Series Alloy Steels
• German Standard: DIN 1.6591 (approximate equivalent)
• API 6A – Specification for Wellhead and Tree Equipment
• API 16A – Specification for Drill-through Equipment
• NACE MR0175/ISO 15156 – Materials for use in H₂S-containing Environments in Oil and Gas Production

Modified versions (8630 mod) often feature additional requirements for chemistry, cleanliness, heat treatment, and mechanical properties beyond the standard specifications to meet specific industry or customer requirements.

Chemical Composition and Grade Comparison

Chemical Composition (in %)

Element	C	Si	Mn	P	S	Cr	Mo	Ni	V	Cu
Min	0.28	0.15	0.75	≤	≤	0.85	0.35	≤	≤	≤
Max	0.33	0.45	1.00	0.025	0.025	1.50	0.65	1.00	0.06	0.25

Grade Equivalents

Standard	Designation
AISI/SAE	8630
German DIN	1.6591 (approximate)
UNS	G86300
EN	30CrNiMo8 (similar)
Chinese GB	30CrNiMo

Comparison with Similar Grades

Property	AISI 8630 / 1.6591	AISI 4130	AISI 4340
Chemical Composition	0.3C-0.9Cr-0.5Mo-0.8Ni	0.3C-0.9Cr-0.2Mo	0.4C-0.8Cr-0.25Mo-1.8Ni
Hardenability	Excellent	Good	Excellent
Tensile Strength (typical)	655-860 MPa	655-790 MPa	760-1280 MPa
Toughness	Very Good	Good	Good
Weldability	Good	Very Good	Fair
Key Advantage	Balance of properties	Better weldability	Higher strength

Mechanical Properties

AISI 8630 / 8630 mod, 1.6591 offers excellent mechanical properties in the quenched and tempered (QT) condition:

Mechanical Properties in Quenched and Tempered (QT) Condition

Property	Value
0.2%-Offset-Yield Strength Rp0.2 in MPa (ksi)	≥ 517 (75)
Tensile Strength Rm in MPa (ksi)	≥ 655 (95)
Elongation L0 = 4 d (A5) in %	≥ 18
Reduction of Area (Z) in %	≥ 35
Impact Toughness (Charpy-V at 23 °C) in J (ft-lbs)	≥ 54 (40)
Impact Toughness (Charpy-V at -60 °C) in J (ft-lbs)	≥ 27 (20)
Hardness in BHN (HRC)	207 – 234 (19 – 22)

Physical Properties

Property	Value
Density	7.85 g/cm³ at 20°C
Elastic modulus at 20°C	205 GPa
Thermal conductivity at 20°C	42 W/m·K
Specific heat capacity at 20°C	470 J/kg·K
Electrical resistivity at 20°C	0.22 μΩ·m
Thermal expansion coefficient (20-100°C)	11.9 × 10⁻⁶ /K
Magnetic permeability	Ferromagnetic

Available Dimensions

SHUNFU METAL supplies AISI 8630 / 8630 mod, 1.6591 low alloy steel in the following dimensions:

• Round Bars: Diameter range from 25 mm to 500 mm (1″ to 20″)
• Forged Blocks: Up to 1000 mm thickness (40″) according to customer specifications
• Custom Forgings: According to customer drawings and specifications
• Rings and Seamless Rolled Rings: Up to 3000 mm (118″) diameter with varied wall thicknesses
• Plates: Thickness from 10 mm to 300 mm (0.394″ to 11.8″)
• Tubes and Hollow Bars: Various dimensions according to customer requirements

Materials can be supplied in the annealed, normalized, or quenched and tempered condition. Custom dimensions and specifications are available upon request to meet specific project requirements. All products are fully tested and certified to meet or exceed relevant industry standards.

Heat Treatment

AISI 8630 / 8630 mod, 1.6591 achieves its optimal properties through a carefully controlled heat treatment process:

• Normalizing: 870-925°C (1600-1700°F) followed by air cooling
• Austenitizing: 830-870°C (1525-1600°F) followed by oil or water quenching
• Tempering: 540-675°C (1000-1250°F) depending on desired mechanical properties
• Stress Relieving: 550-650°C (1020-1200°F) for 1 hour per 25 mm of thickness

For critical applications, vacuum degassing, special melting practices, and controlled cooling rates may be employed to ensure optimal cleanliness, grain structure, and mechanical properties. Heat treatment parameters can be customized to achieve specific property requirements for specialized applications.

Tempering Chart

Tempering Temperature	Approximate Yield Strength MPa (ksi)	Approximate Tensile Strength MPa (ksi)	Approximate Hardness (HRC)
540°C (1000°F)	724 (105)	862 (125)	28-32
595°C (1100°F)	620 (90)	758 (110)	24-28
650°C (1200°F)	517 (75)	655 (95)	19-22
675°C (1250°F)	448 (65)	586 (85)	17-20

Enhanced Properties of 8630 mod

The modified version of AISI 8630 (8630 mod, 1.6591) typically incorporates several enhancements over the standard grade:

• Refined Chemistry: More stringent controls on residual elements and microalloying additions
• Improved Cleanliness: Reduced inclusion content through advanced melting and refining practices
• Enhanced Low-Temperature Toughness: Specialized heat treatment processes to optimize grain structure and toughness
• Superior Through-Hardenability: Consistent properties throughout large cross-sections
• Better Hydrogen Sulfide (H₂S) Resistance: Meeting requirements of NACE MR0175/ISO 15156 for sour service applications
• Refined Microstructure: Optimized tempered martensite/bainite structure for improved toughness and strength balance

These enhancements make 8630 mod particularly suitable for critical applications in the oil and gas industry, especially for subsea components and equipment exposed to harsh environments.

Fabrication Characteristics

AISI 8630 / 8630 mod, 1.6591 offers the following fabrication characteristics:

• Machinability: Good machinability in the annealed or normalized condition. Approximately 65-70% of free-cutting steels (B1112).
• Weldability: Good weldability with proper procedures. Preheating to 200-300°C (390-570°F) is recommended. Post-weld heat treatment is typically required for heavy sections.
• Formability: Good hot formability at 900-1150°C (1650-2100°F). Limited cold formability in the annealed condition.
• Surface Treatments: Excellent response to nitriding, carburizing, and other surface hardening treatments.
• Heat Treatment Response: Excellent response to heat treatment with predictable and consistent mechanical properties.

For critical applications, SHUNFU METAL can provide detailed fabrication guidelines and technical support to ensure optimal results.

Why Choose SHUNFU METAL for AISI 8630 / 8630 mod, 1.6591

When sourcing AISI 8630 / 8630 mod, 1.6591 low alloy steel for your critical applications, SHUNFU METAL delivers superior quality and service. Our inventory of 8630 / 8630 mod meets the most stringent industry standards and undergoes comprehensive quality control to ensure consistent performance. We provide complete material traceability and certification, including:

• Material test reports (MTR) documenting chemical composition
• Mechanical property certification including impact testing at specified temperatures
• Heat treatment documentation
• Non-destructive testing results including ultrasonic, magnetic particle, and other inspections as required
• Microstructure evaluation and grain size determination
• API and NACE compliance certification where applicable
• Positive material identification (PMI) testing reports

Our technical experts can assist you in selecting the optimal heat treatment condition of AISI 8630 / 8630 mod for your specific application requirements, ensuring the ideal balance of strength, toughness, and other mechanical properties. With competitive pricing, reliable global shipping, and responsive customer service, we aim to be your trusted partner for specialty steel solutions.

Contact us today with your AISI 8630 / 8630 mod, 1.6591 requirements. Our team is ready to provide detailed quotations and technical support to help you select the ideal material specification for your critical components in oil and gas, power generation, heavy equipment, or other demanding applications.