A full guide of h11 tool steel heat treatment

Acero para herramientas H11 heat treatment’s purpose is to transform the soft, annealed microstructure, consisting mainly of ferrite and alloy carbides, into a hardened and tempered martensitic structure with beneficial carbides that provide the desired cutting or working properties. This multi-stage process typically involves preheating, hardening, quenching, and tempering.

So, what is H11 tool steel? H11 is a popular 5% chromium hot-work tool steel. It is widely utilized in high-temperature applications such as die casting molds, hot rolling, hot extrusion, hot forging, and even for structural components in aerospace technology, like helicopter rotor shafts.

Below, we introduce the steps for the heat treatment of H11 steel.

1. Precalentamiento y Alivio del estrés

Preheating has three functions: it reduces thermal shock (which can cause distortion or cracking), increases equipment productivity by reducing high-heat furnace time, and minimizes carburization/decarburization if the high-heat furnace atmosphere is not neutral.

The preheating temperature for H11 is 650°C (1200°F), and it is kept at this temperature for 10-15 minutes. For parts with severe cross-sectional changes, or for large or intricate tools, it’s safer to slowly heat the furnace to the preheat temperature, or place the part on top of the furnace to remove chill before placing it inside. For atmosphere or vacuum heat treatment, a single preheat between 790 and 845 °C (1450 and 1550 °F) is typically used¹.

Although preheating can relieve some stresses, conventional stress relieving is more effective. High-temperature tempering of H11 steel can significantly relieve stress. Stress relieving aims to reduce internal stresses that can cause distortion or cracking during subsequent heat treatment or service. A stress-relief temper is highly recommended after substantial machining, grinding, welding, or electrical discharge machining (EDM) operations. The stress relief temperature is generally 14–28 °C (25–50 °F) lower than the previous tempering temperature. The tempering temperature will be mentioned below.

2. Austenitización (endurecimiento)

This is the second critical step, where the steel is heated to a high temperature to dissolve various complex alloy carbides and transform the ferrite-pearlite structure into austenite. The austenitizing temperature range for H11 steel is 995 to 1025°C (1825 to 1875°F). Soaking times range from 20 minutes plus an additional 5 minutes for each 25 mm (1 inch) of section thickness. For H13, austenitizing temperatures are generally higher, ranging from 1050 to 1180 °C (1920 to 2155 °F). Find more H11 vs H13 steel.

3. Enfriamiento

Enfriamiento is the process of rapidly cooling a material from the austenitizing temperature to transform austenite into a hard martensitic structure. H11 steel is an air-hardening steel, which minimizes residual stress and dimensional changes when cooled in air. H11 steel is cooled in air to 52–65 °C (125–150 °F) before undergoing further tempering treatment.

Generally speaking, all hot-worked tool steels cannot be water quenched, as water quenching carries a high risk of cracking.

4. Templado

Templado is performed after quenching. The purpose is to increase the steel’s toughness and relieve the high internal stresses that make the as-quenched martensitic structure very susceptible to cracking. H11 is a secondary hardening steel. The performance of H11 reaches its optimal state after two tempering processes. The tempering temperature for H11 steel is 510°C (950°F), and the holding time for both tempering processes is two hours. After quenching, H11 steel must be tempered immediately when it reaches the recommended temperature to prevent cracking.

5. Recocido

Recocido is performed to soften the steel, making it suitable for machining, and to produce microstructural uniformity for subsequent hardening treatments. Forged H11 parts should be slowly cooled to room temperature after forging and then fully annealed. 870–900 °C (1600–1650 °F), soaking for approximately 1 hour per inch (2.4 min/mm) of thickness, and then slow cooling at a rate of 14 °C (25 °F) per hour down to 482 °C (900 °F) before air cooling to room temperature. This process results in a maximum annealed hardness of approximately 220 HB.

The above are the common heat treatment steps for H11 steel, which are based on our own experience and professional literature. We hope this information will be helpful to users of H11 steel. If you need H11 steel materials, please feel free to contact us.

1. ASM International. (1989). Manual de ASM, Volumen 16: Mecanizado (p. 120). ASM International. ↩︎