Aobo Steel supplies H11 steel for your project

3. Heat Treatment for H11 Tool Steel

H11 (a variant with slightly higher carbon) is a 5% Chromium hot-work tool steel known for its excellent performance in demanding applications. Understanding the correct heat treatment is essential to achieve the desired properties. As specialists in tool steel with over 20 years of forging experience, we provide this guide based on established practices.

3.1 Understanding H11 Hardenability

A key feature of H11 is its deep air-hardenability. This means even large sections can be hardened uniformly by simply cooling in air. The major advantage here is minimal residual stress after hardening, which significantly reduces the risk of distortion or cracking during use.

3.2 Recommended Heat Treatment Procedures

3.2.1 Normalizing (If Required)

If you need to homogenize the steel’s microstructure, follow this process:

• Heat to approximately 1065°C (1950°F).
• Hold at the temperature for 1 hour for every 25 mm (1 inch) of thickness.
• Air cool to room temperature.
• Immediately anneal the steel.
• Caution: Be aware of the potential for cracking during this process, especially if the surface is decarburized.

3.2.2 Hardening

H11 is an air-hardening steel.

• Austenitize by heating typically within the range of 980-1070°C (1800-1960°F). (Consult specific data sheets for precise temperatures based on desired properties.)
• Cool in the air.
• An as-quenched hardness of around 61 HRC can be anticipated for H11.

3.2.3 Tempering

H11 is secondary hardening steel. Optimal properties are achieved by tempering above the secondary hardening peak (around 510°C / 950°F).

1. Benefits: Tempering at these higher temperatures provides significant stress relief and stabilizes the steel’s properties for use at elevated temperatures.
2. Flexibility: Heat-treated parts can often undergo warm working or preheating for welding up to 55°C (100°F) below the tempering temperature without losing significant properties.
3. Example Properties:
   
   • Tempered at 510°C (950°F): Approx. 2120 MPa Tensile Strength, 1710 MPa Yield Strength, 56.5 HRC.
   • Tempered at 540°C (1000°F): Approx. 2005 MPa Tensile Strength, 1675 MPa Yield Strength, 56.0 HRC.
4. Selection: Choose the tempering temperature based on the required balance of strength, toughness, and hardness for your specific application.

3.2.4 Stress Relief

While the high tempering temperatures provide substantial stress relief, an additional stress relief cycle can be performed if needed.

• Heat the steel to a temperature below the final tempering temperature.
• Hold for a suitable duration.
• Cool slowly.
• This process aims to reduce remaining stresses without significantly changing hardness or microstructure.

4. Forging H11

If forging H11 components:

• Preheat: Heat uniformly to 790-815°C (1450-1500°F).
• Forging Temperature: Forge within the range of 1120-1150°C (2050-2100°F).
• Minimum Temperature: Stop forging if the temperature drops below 925°C (1700°F). Reheat if necessary.
• Cooling (Critical): Due to its air-hardening nature, slow cooling after forging is essential to prevent stress cracks. Transfer the part to a furnace at approximately 790°C (1450°F), equalize the temperature, and then cool slowly in the furnace (with the furnace switched off) or by burying it in an insulating material, such as lime, mica, or ash.
• Annealing: Anneal the forging after it has cooled slowly.