H13 TOOL STEEL | 1.2344 | skd61

4. Heat Treatment

The heat treatment of H13 involves several critical steps to achieve the desired properties:

4.1 Forging and Post-Forging Cooling

It is easy to forge and is typically forged at temperatures between 1120 and 1150°C (2050 to 2100°F). Before forging, we recommend preheating the steel to 790 to 815°C (1450 to 1500°F), then uniformly heating it to the required forging temperature.

During forging, the material temperature must not drop below 925°C (1700°F). If it is about to fall below this temperature, it must be reheated to the required forging temperature.

This material is an air-hardening steel that must be cooled slowly to prevent stress cracking. After forging, the material must be placed in a furnace at 790°C (1450°F) and held until the temperature is uniform; then cooled slowly.

4.2 Annealing (Spheroidize Anneal)

Following the previous step, the H13 material should undergo spheroidizing annealing, which aims to eliminate stress, enhance the toughness and ductility, and form the required microstructure.

The specific details of the annealing process are as follows: heat the steel to 871°C (1600°F), hold for 1 hour per inch (25.4 mm) of thickness, then cool at a rate of 14°C (25°F) per hour down to 482°C (900°F), followed by air cooling to room temperature.

4.3 Normalizing (Generally Not Recommended)

Because of the risk of cracking, we generally do not recommend normalizing treatment for H13, especially when surface decarburization is not prevented by a controlled atmosphere furnace. However, this normalizing treatment can still improve the uniformity of the material. This step must be performed immediately after spheroidizing annealing.
The specific steps are as follows: preheat to approximately 790 °C (1450 °F), slowly and uniformly heat to 1040 to 1065 °C (1900 to 1950 °F), hold for 1 hour per 25 mm (1 inch) of thickness, and then air cool.

4.4 Hardening (Austenitizing and Quenching)

The hardening temperature is around 1030 °C (1885 °F). Other sources suggest a range of 1010-1040 °C (1850-1900 °F), or specifically 1025 °C (1875 °F).

H13 is an air-hardening steel, and we recommend performing a preheating treatment.  The preheating temperature is 815 °C (1500 °F). For a 1” (25mm) cube, it should be preheated to 650 °C (1200 °F) and held for 10 to 15 minutes before setting the furnace for the soaking step. For delicate parts, an additional preheat may be necessary.

After preheating, raise the furnace temperature to its austenitizing temperature of 1010 °C (1850 °F). The soaking process then begins, with the soaking time calculated from the moment the material’s temperature is the same as the furnace temperature. Specific details are as follows: For parts thicker than 1“ (25mm), the soak time is typically half an hour per inch of the smallest cross-section. For smaller parts, specific soak times are provided: 1/8” (3.175mm) for 10-15 minutes, 1/4” (6.350mm) for 15 minutes, 1/2“ (12.70mm) for 20 minutes, 3/4” (19.05mm) for 25-30 minutes, and 1” (25mm) for 30 minutes.

Air quenching can minimize residual stress and reduce thermal shock. While air quenching is the most common method for H13, oil quenching is also used in practice. The hardness after quenching is 52-54 HRC. During the quenching cycle of the material, the next step of tempering should be performed immediately at a temperature no lower than 66°C/150°F to prevent cracking.

4.5 Tempering

We recommend tempering H13 twice or even three times to achieve optimal toughness and extend tool life. The first tempering temperature is 565°C (1050°F), the second tempering temperature is 550°C (1025°F), with each cycle lasting 2 hours per inch (25mm) of thickness.

After tempering, the hardness varies with the tempering temperature. For example, as-quenched H13 has a hardness of 52-54 HRC. Tempering at 204°C (400°F) results in 51-53 HRC, while tempering at 538°C (1000°F) yields 47-48 HRC, and at 621°C (1150°F) it can be 36-38 HRC. Common tempering temperatures range from 540-620°C (1000-1150°F), producing a stable microstructure that makes the material most suitable for high-temperature applications.

It is essential to avoid tempering H13 at around 500°C (930°F), as this temperature yields the lowest toughness.