8418 is a premium high-performanceperformance hot-performance hot work tool steel renowned for its exceptional thermal fatigue resistance, high-temperature strength, and toughness. Developed for demanding hot forming applications, it excels in environments with repeated heating and cooling cycles, making it a preferred choice for die casting, forging, and extrusion tools.
Basic Information
Definition: 8418 is a chromium-molybdenum-vanadium alloy hot work steel designed to withstand extreme thermal stress, abrasion, and mechanical loads at elevated temperatures (up to 650°C). Its microstructure is optimized to resist heat checking (thermal cracking) and maintain dimensional stability during prolonged use.
Corresponding Standards: Developed by Swedish steel producers, it aligns with international hot work steel specifications. Equivalents include:
German: 1.2367 (similar properties but with slight compositional variations)
American: H13 (with improved toughness and thermal fatigue resistance)
Key Characteristics: Superior thermal fatigue resistance, excellent hardenability, high toughness at elevated temperatures, and good weldability for mold repair.
Chemical Composition
The precise alloying of 8418 balances strength, toughness, and heat resistance:
Element Content Range Role in the Steel
Carbon (C) 0.38–0.42% Provides a foundation for hardness and carbide formation, ensuring high-temperature strength.
Chromium (Cr) 5.00–5.50% Enhances oxidation resistance, hardenability, and thermal stability; forms chromium-rich carbides for wear resistance.
Molybdenum (Mo) 2.20–2.40% Boosts high-temperature strength and creep resistance; reduces temper brittleness.
Vanadium (V) 0.40–0.60% Refines grain structure, improves toughness, and forms hard vanadium carbides for wear resistance.
Silicon (Si) 0.30–0.50% Enhances oxidation resistance and high-temperature strength; acts as a deoxidizer.
Manganese (Mn) 0.30–0.60% Improves hardenability and strength without compromising toughness.
Physical Properties
Density: ~7.85 g/cm³ (consistent with most tool steels).
Melting Point: ~1450–1500°C.
Thermal Conductivity: ~35 W/(m·K) at room temperature; maintains stable heat transfer at high temperatures.
Coefficient of Thermal Expansion: ~11.0×10⁻⁶/°C (20–600°C), minimizing thermal distortion during cyclic heating.
Elastic Modulus: ~210 GPa at room temperature; retains ~80% of modulus at 600°C, ensuring structural stability under load.
Mechanical Properties
8418’s properties are optimized for hot work applications, with a focus on high-temperature performance:
Property Hardened & Tempered (550°C) High-Temp Performance (600°C)
Tensile Strength (Rm) 1400–1600 MPa ~900–1000 MPa
Yield Strength (Rp0.2) 1200–1300 MPa ~800–900 MPa
Elongation (A) 12–15% ~8–10%
Hardness 42–45 HRC ~38–40 HRC
Impact Toughness (Akv) ≥45 J (at 20°C) ≥30 J (at 600°C)
Thermal Fatigue Resistance: Exceptional—resists microcracking from repeated heating (to 650°C) and cooling cycles, extending mold life.
Wear Resistance: Good at high temperatures due to vanadium and chromium carbides, suitable for abrasive materials like aluminum or steel billets.
Heat Treatment
Proper heat treatment is critical to maximize 8418’s performance:
Annealing
Purpose: Soften for machining and ensure uniform microstructure.
Process: Heat to 850–870°C, hold 2–4 hours, cool slowly (≤30°C/hour) to 600°C, then air cool. Results in hardness ≤220 HB.
Austenitizing (Hardening)
Temperature: 1020–1050°C, held 1–2 hours (depending on section thickness).
Cooling: Oil quenching to 50–100°C, achieving as-quenched hardness of 50–55 HRC.
Tempering
Temperature: 520–580°C (typically 550°C), with 2–3 hours holding time (double tempering recommended).
Result: Balances hardness (42–45 HRC) and toughness, with maximum resistance to thermal fatigue.
Processing Performance
Machinability: Good in the annealed state (≤220 HB) using carbide tools. Proper cutting parameters prevent work hardening.
Weldability: Excellent for mold repair—preheating to 300–400°C and post-weld tempering at 550°C minimizes cracking and restores properties.
Formability: Hot working is possible at 1050–1150°C, followed by annealing to restore machinability. Cold formability is limited due to high strength.
Polishability: Can be polished to a smooth finish, suitable for molds requiring good surface quality in cast or forged parts.
Application Fields
8418 is ideal for high-stress hot work applications requiring resistance to thermal cycling and abrasion:
Die Casting:
Molds for aluminum and magnesium alloys (e.g., automotive components, aerospace parts) subjected to high pressure and cyclic heating.
Hot Forging:
Dies for forging steel, stainless steel, and non-ferrous metals (e.g., crankshafts, gears, structural parts).
Extrusion Tools:
Dies and mandrels for hot extrusion of aluminum, copper, and steel profiles.
Other Hot Work Applications:
Hot shear blades, pressure casting molds, and tooling for glass forming (resists thermal shock).
Advantages and Limitations
Advantages
Superior Thermal Fatigue Resistance: Outperforms H13 in cyclic heating/cooling environments, extending mold life by 30–50% in many applications.
High-Temperature Toughness: Maintains ductility at 600°C, reducing the risk of sudden fracture.
Excellent Hardenability: Uniform properties even in thick sections (up to 200mm), critical for large molds.
Good Weldability: Facilitates mold repair, reducing replacement costs.
Limitations
Higher Cost: More expensive than standard hot work steels (e.g., H13) due to advanced alloying.
Machining Challenges: Hardened material (42–45 HRC) requires specialized tooling for post-heat treatment machining.
Comparison with H13 Steel
Property 8418 H13
Thermal Fatigue Resistance Excellent Good
Toughness at 600°C Higher Moderate
Wear Resistance Similar Similar
Cost Higher Lower
Ideal Use Case High-cyclic hot forming (aluminum die casting) General hot work applications
In summary, 8418 hot mold steel is a premium material for demanding hot work applications, offering unmatched thermal fatigue resistance and high-temperature toughness. Its ability to withstand repeated thermal stress makes it a cost-effective choice for high-volume production, where mold longevity directly impacts manufacturing efficiency.