Could you provide the hardness curve of H13 after tempering?

The hardness of H13 is stable at 48–52 HRC within the tempering temperature range of 550–600°C, according to the hardness curve after tempering. Two tempering operations can produce the best microstructure and characteristics.

1. Standard Tempering Procedure and Correlation with Hardness

Applicable Scenarios for Tempering Temperature (°C) Hardness Range (HRC) Microstructure

550 50~52 Dispersed carbides and tempered martensite Brittleness control and high wear resistance requirements are essential.

580 (Suggested) 49–51 Fine carbides combined with uniform tempered martensite Mainstream procedure, best overall performance

600 48–50 Enhanced hardness and slight softening Moderate softening is permissible under high impact circumstances.

Actual Data: The H13 hot runner nozzle had a service life of more than 500,000 cycles and a measured hardness of 49.8 HRC after tempering at 580°C for two hours for two cycles.

2. Tempering Times' Impact on Hardness

Single tempering: Unstable microstructure, perhaps high hardness (>52 HRC), insufficient release of residual stress;

Two cycles of tempering: complete release of tension, hardness falls to 48–52 HRC, range ≤2 HRC, stable performance;

Three or more tempering cycles: There is no discernible benefit, but the risk of grain coarsening and energy consumption are increased.

Important Note: To prevent thermal stress accumulation that could cause cracking, the furnace needs to be air-cooled to room temperature prior to the second tempering cycle.

3. Process Control Points to Guaranty Reproducibility of Curves

Precise Temperature: To guaranty a furnace temperature difference of ≤±5°C, use a PID temperature-controlled furnace set to 580°C±5°C with several temperature readings;

Sufficient Time: For thicker pieces, add 30 minutes for every 25 mm of thickness; each holding time must be at least two hours;

Process Archiving: For traceability management, keep entire furnace temperature curves and test data for every furnace cycle.

"Precise temperature, sufficient number of cycles, and data archiving" are safety precepts that guaranty uniform hardness curves for every batch.