H13 hot work die steel is one of the most widely used chromium-molybdenum-vanadium based hot work tool steels, specified under ASTM (American Society for Testing and Materials) standards. It is celebrated for its exceptional combination of heat resistance, toughness, wear resistance, and thermal fatigue resistance, making it a preferred choice in industries where molds endure repeated high-temperature exposure and mechanical stress. Below is a comprehensive overview:
Chemical Composition
The typical chemical composition of H13 hot work die steel is as follows:
Carbon (C): 0.32–0.45% (contributes to hardness and strength through heat treatment)
Chromium (Cr): 4.75–5.50% (enhances oxidation resistance, heat resistance, and hardenability)
Molybdenum (Mo): 1.10–1.75% (improves high-temperature strength, toughness, and thermal fatigue resistance)
Vanadium (V): 0.80–1.20% (refines grain structure, increases wear resistance, and stabilizes carbides)
Silicon (Si): 0.80–1.20% (aids in deoxidation, improves heat resistance, and enhances toughness)
Manganese (Mn): 0.20–0.50% (boosts hardenability and reduces brittleness)
Phosphorus (P): ≤0.030% (minimized to prevent embrittlement)
Sulfur (S): ≤0.030% (controlled to avoid reduced toughness and machinability issues)
Key Properties
H13’s performance is defined by its ability to maintain stability under extreme thermal and mechanical conditions, making it a versatile choice for hot work applications:
Superior Thermal Fatigue Resistance
Excels in withstanding repeated cycles of heating (up to ~650°C) and cooling, minimizing the risk of cracking caused by thermal stress—critical for long mold life.
High Toughness and Ductility
Maintains excellent toughness even after heat treatment, reducing the likelihood of brittle fracture during heavy-duty operations like forging or die casting.
Excellent Wear Resistance
Resists abrasion and deformation under high-temperature friction, extending service life in applications involving contact with molten metals or hot workpieces.
Good Hardenability and Heat Treatment Stability
Achieves uniform hardness across thick sections with minimal distortion during heat treatment, ensuring dimensional precision in finished molds.
Oxidation Resistance
Forms a protective oxide layer at high temperatures, reducing scaling and degradation when exposed to air or industrial atmospheres.
Physical Properties
Density: ~7.85 g/cm³
Thermal Expansion Coefficient: ~11.0×10⁻⁶/K (at 20–500°C)
Thermal Conductivity: ~35 W/(m·K) (at room temperature)
Melting Point: ~1450–1500°C
Mechanical Properties (After Heat Treatment)
Hardness: Typically 42–48 HRC (adjustable via tempering; higher hardness for wear resistance, lower for enhanced toughness).
Tensile Strength (Rm): ~1200–1600 MPa
Yield Strength (Rp0.2): ~1000–1400 MPa
Elongation (A): ~10–15%
Impact Toughness (Charpy V-notch): ≥25 J/cm² (at room temperature, depending on heat treatment).
Heat Treatment Process
Proper heat treatment is essential to maximize H13’s performance. The process typically includes:
Annealing
Purpose: Soften the steel for machining, reduce internal stress, and improve machinability.
Process: Heat to 830–860°C, hold for 2–4 hours, then furnace cool slowly (≤50°C/hour) to below 500°C before air cooling.
Result: Hardness ≤235 HBW, ensuring ease of machining.
Quenching
Purpose: Harden the steel by transforming austenite to martensite.
Preheating: Two stages—first at 650–750°C, then at 850–900°C (to avoid thermal shock and ensure uniform heating).
Austenitizing: Heat to 1010–1050°C, hold for 30–60 minutes (depending on section thickness) to fully dissolve carbides.
Cooling: Quench in oil or compressed air (oil for deeper hardness; air for minimal distortion in large or complex parts).
Tempering
Purpose: Relieve quenching stress, reduce brittleness, and balance hardness with toughness.
Process: Temper at 500–650°C (common range for hot work), hold for 2–4 hours per 25mm thickness, then air cool. Double tempering is recommended to ensure complete transformation of retained austenite.
Result: Hardness adjusted to 42–48 HRC with optimal strength, toughness, and thermal stability.
Application Fields
H13’s versatility and robust performance make it indispensable in numerous high-temperature manufacturing sectors:
Die Casting Molds: Widely used for aluminum, magnesium, and zinc die casting (e.g., automotive engine components, electronic housings, and industrial parts).
Hot Forging Dies: Ideal for forging steel, brass, and aluminum alloys (e.g., crankshafts, gears, and structural automotive parts).
Extrusion Dies: Suitable for extrusion of aluminum, copper, and other non-ferrous alloys (e.g., window frames, heat sinks, and structural profiles).
Hot Stamping Tools: Applied in hot stamping processes for high-strength automotive steel components (e.g., door beams, bumpers).
Plastic Injection Molds: Used for high-temperature plastic molding (e.g., engineering plastics like PA, POM, or PEEK).
Industrial Furnace Parts: Employed in components requiring heat resistance, such as furnace liners or hot work fixtures.
H13’s reliability and adaptability have solidified its status as a benchmark hot work die steel, trusted across industries for demanding high-temperature applications.
