Introduction

H11 tool steel is a chromium-based hot work steel belonging to the H-series according to AISI standards. It is widely known for its excellent combination of high toughness, good thermal conductivity, high fatigue strength, and moderate wear resistance. H11 is particularly valued for its ability to withstand both high temperatures and repeated heating/cooling cycles without significant distortion or cracking. It offers superb mechanical properties even at elevated temperatures and has superior impact resistance compared to most other hot work tool steels.

H11 is supplied in annealed, hardened, or tempered conditions depending on application requirements and is a preferred choice for applications involving high mechanical and thermal stresses.

  • High Toughness and Ductility
  • Good Resistance to Thermal Fatigue
  • Excellent Resistance to Cracking and Distortion
  • Moderate Wear Resistance
  • Good Strength Retention at Elevated Temperatures
  • Sufficient Hardness After Heat Treatment
  • Good Thermal Conductivity

Uses/Applications:

H11 tool steel is commonly used in various demanding applications such as:

Hot Work Applications:

  • Forging dies
  • Extrusion dies
  • Die-casting dies for aluminum, magnesium, and zinc
  • Plastic molds requiring high strength and toughness

Aerospace Components:

  • Aircraft landing gear parts
  • Structural parts subject to high stress

High-Temperature Applications:

  • Tool holders
  • Mandrels

Automotive Industry:

  • Dies and punches
  • Shafts and axles

Its excellent combination of strength, toughness, and heat resistance makes H11 versatile across multiple industries.

Heat Treatment:

H11 can be heat-treated to obtain the desired balance between hardness and toughness:

Annealing:

  • Heat slowly to 843°C – 871°C.
  • Hold for several hours.
  • Cool slowly in the furnace at 10°C/hour down to 538°C.
  • Then air cool.
  • Resulting hardness: Max 229 HB.

Hardening:

  • Preheat in two stages: 600°C–650°C, then 870°C–900°C.
  • Austenitize at 1000°C–1040°C.
  • Quench in still air or warm oil.

Tempering:

  • Temper immediately after quenching.
  • Temper at 537°C–649°C.
  • Double tempering recommended for maximum toughness.

Achieving proper hardness between 48–55 HRC ensures an optimal balance of toughness and wear resistance.

Chemical Composition:

Element Content (%)
Carbon (C) 0.32 – 0.42
Manganese (Mn) 0.20 – 0.50
Silicon (Si) 0.80 – 1.20
Chromium (Cr) 4.75 – 5.50
Molybdenum (Mo) 1.10 – 1.75
Vanadium (V) 0.30 – 0.60
Phosphorus (P) ≤ 0.03
Sulfur (S) ≤ 0.03

This chemical composition gives H11 its remarkable toughness, strength, and heat resistance properties.

Mechanical Properties:

Property Typical Value
Hardness (Annealed Condition) ≤ 229 HB
Hardness (After Hardening) 48 – 55 HRC
Tensile Strength 1,520 MPa (approximate)
Yield Strength 1,200 MPa (approximate)
Elongation at Break ~14%
Impact Toughness High

Note: Mechanical properties vary depending on the exact heat treatment process.

Physical Properties:

Property Typical Value
Density 7.8 g/cm³
Modulus of Elasticity (E) 215 GPa
Thermal Conductivity 24.6 W/m·K at 20°C
Specific Heat Capacity 460 J/kg·K
Coefficient of Thermal Expansion 12.5 × 10⁻⁶ /°C (20–100°C)

H11’s good thermal conductivity is crucial for resisting thermal shock in hot working conditions.

Forging:

Forging Temperature Range: 980°C to 1120°C.

Procedure:

  • Preheat slowly to around 750°C.
  • Raise to forging temperature and forge uniformly.
  • Do not forge below 980°C.
  • Slow cooling in furnace or insulating material after forging to prevent cracking.

Post-forging annealing is advised for stress relief and optimal properties.

Dimensional Tolerances:

Bright Bars:

  • Precision tolerance as per DIN/ASTM standards or customer specification.

Rolled and Forged Bars:

  • General tolerance based on diameter and length.

Machined Bars:

  • Tight tolerance for critical mold and die applications.

Accurate dimensional control is critical for tool-making applications.

Machinability:

Relative Machinability: About 70% of a mild steel benchmark.

Machining Recommendations:

  • Use rigid machines and carbide or HSS cutting tools.
  • Preheating during rough machining is advisable to avoid cracking.
  • Machining in the annealed condition is easier than after hardening.

Corrosion Resistance:

  • H11 tool steel is not inherently corrosion resistant.
  • Protective coatings (like nitriding or chrome plating) can be applied for enhanced corrosion resistance, especially when used in humid or chemically active environments.

Available Form:

H11 tool steel is available in various forms, including:

  • Bright Round Bars
  • Forged Bars
  • Flat Bars
  • Plates
  • Sheets
  • Blocks
  • Custom cut-to-size profiles

These forms can be customized based on dimensional and mechanical property requirements.

Weldability:

Good weldability with precautions:

  • Preheat before welding (~300°C–400°C).
  • Use compatible filler materials.
  • Post-weld heat treatment (stress relief) is mandatory to restore mechanical properties.
  • Slow cooling post-weld is required to prevent cracking.

Welding should be carried out by skilled personnel to ensure structural integrity.

Conclusion:

H11 tool steel is a highly versatile material prized for its excellent toughness, thermal fatigue resistance, and high-temperature strength. It is ideal for hot work applications such as extrusion dies, forging dies, and die-casting molds, while also serving crucial roles in aerospace and automotive industries. With its combination of performance characteristics, H11 remains a critical material solution for applications demanding strength, resilience, and thermal stability. Proper heat treatment and careful handling ensure that H11 delivers superior tool life, minimal downtime, and outstanding overall performance.

Related Products :   D2, DB6, DIN 1.2714, DIN 1.2080, DIN 1.2379, DIN 1.2343, DIN 1.2344, EN31, H11, H13, OHNS, HCHCR, M2, P20+S, P20, P20+Ni, K310, Maps