How does tempering temperature affect the hardness of H13 material?

The hardness of H13 material is greatly affected by temperature: at temperatures below 550°C, the hardness is high yet brittle; at temperatures beyond 600°C, the hardness dramatically drops. In order to stabilize the hardness within the safe service range of 48–52 HRC, the optimal tempering temperature is 550–600°C.

 

1. The connection between hardness and tempering temperature

Temperature Range Tempering

Trend of Hardness Change

Effects on Properties and Microstructure

<550°C

High hardness (>52 HRC)

High brittleness, partial martensite tempering, inadequate residual stress release, and a high cracking risk

550–600°C (Suggested)

Hardness stability at 48–52 HRC

High strength and strong toughness combined with a uniform microstructure and fully released stress above 600°C

Hardness rapidly decreases (<48 HRC)

Reduced strength and wear resistance, matrix softening, and carbide coarsening

Practical Application: Wuhan mold factories utilize a well-established method called tempering at 580℃±5℃×2h×2 times, with measured hardness steady at 49~51 HRC.

 

2. Temperature Variations' Effect on Batch Consistency

The consistency of mold life can be impacted by a hardness shift of 1~2 HRC caused by a difference of ±10°C;

Localized soft spots or hard areas can develop from extreme hardness variances (>2 HRC) within the same batch of workpieces caused by a temperature fluctuation in the furnace more than ±10°C;

Internal stress concentration can result from unequal microstructure alteration brought on by uncontrolled heating and cooling rates.

Case Study: A batch of H13 manifold plates had an average hardness of 53.2 HRC because the actual temperature was 15°C lower than anticipated due to a drift in the temperature control sensor of a tempering furnace. Within five days of operation, two pieces cracked.

 

3. Control Points and Optimization Recommendations

When using a PID temperature-controlled furnace, make sure the difference between the actual and set temperatures is less than or equal to ±5°C.

Multi-point temperature measurement verification: To ensure temperature uniformity, set up temperature measurement points at various sites inside the furnace;

Do two rounds of tempering: To avoid stress rebound, cool to ambient temperature after the first tempering;

Maintain furnace temperature curves: To establish process traceability, keep thorough heating and cooling data for every furnace.

"Accurate temperature, sufficient number of cycles, and data archiving" are safety standards that guaranty each batch of H13 workpieces operates dependably.