Chemical composition

H11 tool steel equivalent grades and the compositions

Properties

Tool steel H11 possesses an exceptional combination of attainable hardness, red hardness (hot hardness), toughness, and wear resistance.

• Strength: It can be heat-treated to yield strengths of 0.2% well above 1380 MPa (200 ksi) and ultimate tensile strengths exceeding 2070 MPa (300 ksi). 
• Hardness: Normal working hardnesses typically range from 40 to 55 HRC. For applications such as aluminum die casting, a preferred hardness of 47 HRC is noted. In die casting, H11 dies can be hardened to 42–52 HRC; inserts and cores to 46–52 HRC; plungers to 46–50 HRC; slides to 46–52 HRC; shot sleeves to 44–48 HRC; and nozzles to 32–42 HRC. For hot forging punches and dies, hardness typically ranges from 44–48 HRC. Hot-rolling mill rolls (for short runs and low temperatures) are made of H11 at 40–48 HRC. Hot swaging dies are typically 48–52 HRC.
• Hot Hardness/Red Hardness: Good temper resistance, maintaining high hardness and strength at elevated temperatures. It resists softening during continuous exposure to temperatures up to 540 °C (1000 °F). While its hot hardness is lower than some other hot-work steels, such as H19 or H21, it still retains hardness better than other medium-alloy steels at higher temperatures. Hot Hardness/Red Hardness is a very important property for hot-work tool steels.
• Toughness and Ductility: Good ductility and impact strength. It has better resistance to brittle fracture than higher-alloy-content steels such as H14, H19, and H21. Electroslag remelting (ESR) or vacuum arc remelting (VAR) processes can significantly improve ductility and toughness.
• Fatigue Resistance: This material offers high fatigue resistance and thermal stability over a temperature range of 75 to 540°C (167 to 1000°F). Compared with 4340 steel that has undergone the same high-intensity heat treatment, H11 has better fatigue strength.
• Wear Resistance: Its wear resistance is lower than H13’s.
• Weldability: It is readily weldable, even in heavy sections. 
• Machinability: Good machinability, rated around 70% of a standard 1% carbon steel.
• Thermal properties: It has a relatively low coefficient of thermal expansion and a thermal conductivity of 26 W/m·K.
• Corrosion Resistance: Above-average resistance to oxidation and corrosion.
• Heat Checking Resistance: Good resistance to thermal fatigue (heat checking).

H11 Tool Steel Heat Treatment

Precise heat treatment of H11 tool steel is crucial to achieving optimal performance as a 5% chromium hot-work die steel and an ultrahigh-strength steel, similar to H11 Modified and H13. This process tunes the microstructure for demanding factory tooling. 

Forging

This steel is easily forged, with a suitable forging temperature range of 1120 to 1150°C (2050 to 2100°F). We recommend preheating the billet to 790-815°C (1450-1500°F), then uniformly heating it to the forging temperature. The forging temperature must NOT be lower than 925°C (1700°F). If the temperature drops near this level, it must be reheated before continuing the forging process.

Austenitizing

Austenitizing, the primary hardening step, involves heating to transform its structure into austenite. This allows uniform conversion and dissolution of alloying elements and carbides.

• Preheating: Preheat H11 to 760-815 °C (1400-1500 °F) before austenitizing to minimize thermal shock and cracking, especially for this high-alloy material.
• Austenitizing Temperatures and Soaking Times: The Austenitizing Temperature is 995-1025 °C (1825-1875 °F). The soaking time is 20 minutes + 5 minutes per 25 mm (1 inch) of thickness.

Holding at the austenitizing temperature ensures uniform transformation and dissolution.

Quenching

After austenitizing, H11 steel is rapidly quenched to form hard martensite. H11 is an air-hardening steel that provides uniform hardening throughout large sections with minimal residual stresses and dimensional changes. Air cooling is the standard and preferred method for H11 tool steel. While air cooling is standard, oil quenching from 995 °C (1825 °F) is a possible alternative. H11 and other hot-work tool steels must never be water-quenched, as this can lead to cracking.

Tempering

After hardening, tempering H11 tool steel by reheating to a lower temperature is crucial for improving toughness, relieving stress, and stabilizing properties. Steel H11 is a secondary hardening steel. It achieves its best performance when tempered at temperatures above 510°C (950°F). We recommend performing multiple tempering treatments on it to achieve optimal toughness and extend tool life. Allow the parts to cool to room temperature between tempering cycles to minimize residual austenite. 

Table of Hardness and Tempering Temperature for H11 Steel

Annealing 

The annealing temperature ranges from 845 to 900°C (1550-1650°F). The cooling rate is 22-40°C/h (40-75°F/h). The hardness after annealing is 192-229 HB.

Other Important H11 Heat Treatment Considerations

• Normalizing: This process is generally not recommended for H11 or H13 tool steels due to the high risk of cracking, particularly when surface decarburization occurs.
• Stress-Relief: After H11 has been processed, such as grinding, welding, or EDM (electrical discharge machining), we strongly recommend stress-relief treatment at 650°C. This treatment should be carried out at a temperature 14–28°C (25–50°F) lower than the previous tempering temperature. After stress relief, cool slowly at a maximum rate of 300°C/h to prevent the formation of new stresses.
• Cryogenic Treatment: Sub-zero treatment (e.g., -73°C / -100°F) can reduce retained austenite; however, H11’s high tempering temperatures usually make it unnecessary to achieve maximum secondary hardening.
• Surface Protection: Protecting its surfaces from oxidation and decarburization during high-temperature treatments, such as austenitizing and annealing, is vital. This is often achieved using controlled atmospheres, vacuum furnaces, or salt baths.

Applications

• Die Casting Dies
• Forging Dies
• Extrusion Tools
• Hot Shear Blades:
• Aerospace Components

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