8407 Hot Work Mold Steel
8407 is a high-performance hot work tool steel renowned for its exceptional thermal fatigue resistance, high-temperature strength, and versatility in demanding hot-forming applications. Developed to withstand extreme heat, pressure, and cyclic thermal stress, it is widely used in industries such as die casting, hot forging, and plastic injection molding of high-temperature resins.
Basic Information
Definition: 8407 is a chromium-molybdenum-vanadium alloy hot work steel designed to maintain mechanical stability at temperatures up to 600–700°C. It excels in resisting heat checking, oxidation, and plastic deformation under repeated heating and cooling cycles, ensuring long service life in harsh environments.
Corresponding Standards: Originating from Sweden (SSAB), 8407 is equivalent to international grades such as DIN 1.2344 (Germany), AISI H13 (USA), and GB 4Cr5MoSiV1 (China). It is often recognized as a premium variant of H13 with tighter composition controls for enhanced performance.
Key Characteristics: Superior thermal fatigue resistance, excellent high-temperature toughness, good wear resistance, and uniform hardenability across thick sections.
Chemical Composition
8407’s composition is precisely balanced to optimize hot-work performance, with key elements as follows:
Element Content Range Role in the Steel
Carbon (C) 0.38–0.42% Provides a foundation for hardness and carbide formation, balancing strength and toughness at high temperatures.
Chromium (Cr) 4.80–5.20% Enhances oxidation resistance, hardenability, and thermal stability; forms protective chromium oxides to resist scaling at high temperatures.
Molybdenum (Mo) 1.20–1.50% Boosts high-temperature strength, creep resistance, and thermal conductivity; reduces temper brittleness.
Vanadium (V) 0.80–1.20% Refines grain structure, improves wear resistance via hard vanadium carbides, and enhances resistance to heat-induced cracking.
Silicon (Si) 0.80–1.20% Improves oxidation resistance and high-temperature strength; acts as a deoxidizer for purity.
Manganese (Mn) 0.30–0.50% Enhances hardenability and machinability without compromising high-temperature performance.
Phosphorus (P) ≤0.015% Strictly controlled to minimize brittleness, especially under thermal stress.
Sulfur (S) ≤0.005% Ultra-low content to avoid reducing toughness and causing hot cracking.
Physical Properties
Density: Approximately 7.85 g/cm³ (consistent with most high-alloy hot work steels).
Melting Point: Around 1450–1500°C.
Thermal Conductivity: ~38–42 W/(m·K) at room temperature; maintains stable heat dissipation at high temperatures.
Coefficient of Thermal Expansion: ~11.0×10⁻⁶/°C (20–500°C), minimizing distortion during rapid heating/cooling cycles.
Elastic Modulus: ~210 GPa at room temperature; retains ~80% of modulus at 600°C, ensuring structural integrity under heat.
Mechanical Properties
8407’s mechanical properties are optimized for durability in high-temperature environments, with performance tailored to resist heat, wear, and fatigue:
Annealed State (for Machining)
Hardness: ≤235 HB (easily machinable with conventional tools).
Tensile Strength: ~700–800 MPa.
Elongation: ~18–22% (good ductility for complex mold shaping).
After Hardening + Tempering (for Hot-Work Use)
Tempering Temperature Hardness Tensile Strength (20°C) High-Temp Strength (600°C) Impact Toughness (Charpy V-Notch)
500°C (932°F) 48–52 HRC ~1600–1800 MPa ~1000–1100 MPa ~35–45 J
550°C (1022°F) 45–48 HRC ~1400–1600 MPa ~900–1000 MPa ~45–55 J
600°C (1112°F) 40–45 HRC ~1200–1400 MPa ~800–900 MPa ~55–65 J
Thermal Fatigue Resistance: Exceptional—resists microcracking from repeated thermal cycles, critical for long die life in die casting.
Wear Resistance: Good at high temperatures, thanks to vanadium and chromium carbides, ensuring durability in abrasive conditions.
Heat Treatment Process
Proper heat treatment unlocks 8407’s full potential for hot-work applications:
Annealing
Purpose: Soften the steel for machining and ensure a uniform microstructure.
Process: Heat to 850–880°C, hold 2–4 hours, then cool slowly (≤30°C/hour) to 500°C, followed by air cooling. Results in hardness ≤235 HB with spheroidal carbides.
Austenitizing
Temperature: 1020–1050°C (1868–1922°F).
Hold Time: 30–60 minutes (based on thickness) to dissolve carbides and form uniform austenite.
Quenching
Cooling: Oil quenching (standard) or high-pressure gas quenching for complex parts. Ensures full hardening with minimal distortion.
Result: As-quenched hardness of 50–55 HRC (martensitic structure).
Tempering
Temperature: 500–600°C (932–1112°F), with 2–4 hours holding time (double tempering required to eliminate retained austenite and reduce stress).
Effect: Optimizes high-temperature strength, toughness, and thermal fatigue resistance. Higher temperatures prioritize toughness over hardness.
Processing Performance
Machinability: Excellent in the annealed state (≤235 HB) with carbide or high-speed steel tools. Tight control of inclusions ensures smooth machining surfaces.
Weldability: Moderate—requires preheating to 300–400°C and post-weld tempering to avoid cracking. Suitable for mold repair and modification.
Formability: Limited cold formability; hot forming is possible at 1000–1100°C, followed by annealing to restore machinability.
EDM Performance: Superior—produces a smooth recast layer with minimal defects, ideal for intricate mold details like cooling channels.
Application Fields
8407 is the material of choice for high-precision hot-work applications demanding reliability under extreme conditions:
Die Casting:
Molds for aluminum, zinc, and magnesium die casting (withstands molten metal contact and rapid cooling cycles).
Core pins, ejector pins, and inserts in high-pressure die casting (HPDC) systems.
Hot Forging & Extrusion:
Forging dies for automotive components (e.g., crankshafts, gears) and industrial machinery parts.
Extrusion dies for non-ferrous metals and high-temperature alloys.
Plastic Injection Molding:
Molds for high-temperature resins (e.g., PEEK, LCP) and engineering plastics requiring elevated mold temperatures.
Other Hot-Work Tools:
Hot shear blades, rolling mill rolls, and glass molding tools (endures continuous high-heat exposure).
In summary, 8407 hot work mold steel sets a high standard for performance in hot-forming processes, offering a unique blend of thermal fatigue resistance, toughness, and wear resistance. Its consistent quality and global recognition make it a top choice for critical applications in automotive, aerospace, and industrial manufacturing.