H11 hot work die steel is a widely used chromium-molybdenum-vanadium based hot work tool steel, primarily specified under ASTM (American Society for Testing and Materials) standards. Renowned for its excellent balance of heat resistance, toughness, and wear resistance, it is a staple in industries requiring molds to withstand repeated exposure to high temperatures and mechanical stress. Below is a detailed overview:
Chemical Composition
The typical chemical composition of H11 hot work die steel is as follows:
Carbon (C): 0.32–0.45% (provides hardness and strength through heat treatment)
Chromium (Cr): 4.75–5.50% (enhances oxidation resistance and heat resistance)
Molybdenum (Mo): 1.10–1.60% (improves high-temperature strength and toughness)
Vanadium (V): 0.80–1.20% (refines grain structure and boosts wear resistance)
Silicon (Si): 0.80–1.20% (aids in deoxidation and improves heat resistance)
Manganese (Mn): 0.20–0.50% (enhances hardenability)
Phosphorus (P): ≤0.030% (minimized to avoid brittleness)
Sulfur (S): ≤0.030% (controlled to prevent reduced toughness)
Key Properties
H11’s performance is defined by its ability to maintain mechanical stability under high-temperature conditions, making it ideal for hot working applications:
Heat Resistance & Thermal Fatigue Resistance
Excels in resisting softening at elevated temperatures (up to ~600°C) and withstands repeated thermal cycling (heating and cooling), reducing the risk of cracking from thermal stress.
Toughness & Ductility
Offers high toughness even after heat treatment, minimizing the chance of brittle fracture during heavy-duty operations.
Wear Resistance
Good wear resistance under high-temperature friction, extending mold service life in applications like forging or extrusion.
Hardenability & Heat Treatment Stability
Achieves uniform hardness through heat treatment with minimal distortion, ensuring dimensional precision in finished molds.
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 (after quenching and tempering, adjustable based on application needs).
Tensile Strength (Rm): ~1200–1500 MPa
Yield Strength (Rp0.2): ~1000–1300 MPa
Elongation (A): ~10–15%
Impact Toughness (Charpy V-notch): ≥20 J/cm² (at room temperature)
Heat Treatment Process
Proper heat treatment is critical to unlock H11’s optimal performance:
Annealing
Purpose: Soften the steel for machining and reduce internal stress.
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.
Quenching
Purpose: Harden the steel by forming martensite.
Preheating: 650–750°C (first stage) and 850–900°C (second stage) to avoid thermal shock.
Austenitizing: 1000–1050°C, hold for 30–60 minutes (depending on section thickness).
Cooling: Quench in oil or air (oil quenching for deeper hardness; air quenching for minimal distortion).
Tempering
Purpose: Relieve quenching stress, improve toughness, and stabilize hardness.
Process: Temper at 500–650°C (common range for hot work applications), hold for 1–2 hours per 25mm thickness, then air cool. Repeat tempering for large parts to ensure uniformity.
Result: Adjusts hardness to 42–48 HRC with optimal balance of strength and toughness.
Application Fields
H11’s versatility makes it suitable for a wide range of high-temperature manufacturing processes:
Hot Forging Dies: Used for forging steel, aluminum, or other metals (e.g., automotive crankshafts, gears).
Die Casting Molds: Ideal for aluminum and magnesium die casting (e.g., engine blocks, automotive components).
Extrusion Dies: Suitable for extrusion of aluminum, copper, and other non-ferrous alloys.
Hot Stamping Tools: Applied in hot stamping processes for high-strength steel components in automotive manufacturing.
Industrial Furnace Components: Used for parts requiring heat resistance and structural stability in high-temperature environments.