Tempering temperature has a significant impact on the hardness of H13 material: At temperatures below 550℃, the hardness is high but brittle; at temperatures above 600℃, the hardness decreases significantly. The ideal tempering temperature is 550~600℃, which stabilizes the hardness within the safe service range of 48~52 HRC.
1. Relationship between Tempering Temperature and Hardness
|
Tempering Temperature Range |
Hardness Change Trend |
Impact on Microstructure and Properties |
|
<550℃ |
High hardness (>52 HRC) |
Insufficient residual stress release, incomplete martensite tempering, high brittleness, high risk of cracking |
|
550~600℃ (Recommended) |
Stable hardness at 48~52 HRC |
Uniform microstructure, fully released stress, combining high strength and good toughness |
|
>600℃ |
Rapid decrease in hardness (<48 HRC) |
Carbide coarsening, matrix softening, impaired strength and wear resistance |
Practical Application: Tempering at 580℃±5℃×2h×2 times is a mature process widely used by mold factories in Wuhan, with measured hardness stable at 49~51 HRC.
2. Impact of Temperature Fluctuations on Batch Consistency
A deviation of ±10℃ can cause a hardness change of 1~2 HRC, affecting the consistency of mold life;
A temperature difference in the furnace > ±10℃ can easily cause excessive hardness differences (>2 HRC) within the same batch of workpieces, resulting in localized soft spots or hard areas;
Uncontrolled heating and cooling rates can lead to uneven microstructure transformation, causing internal stress concentration.
Case Study: Due to a drift in the temperature control sensor of a tempering furnace, the actual temperature was 15℃ lower than expected, resulting in an average hardness of 53.2 HRC for a batch of H13 manifold plates. Two pieces cracked within 5 days of operation.
3. Optimization Suggestions and Control Points
Use a PID temperature-controlled furnace: Ensure the deviation between the set temperature and the actual temperature is ≤ ±5℃;
Multi-point temperature measurement verification: Arrange temperature measurement points at different locations within the furnace to confirm temperature uniformity;
Perform two tempering cycles: After the first tempering, cool to room temperature before performing the second tempering to prevent stress rebound;
Maintain furnace temperature curves: Retain complete heating and cooling records for each furnace to achieve process traceability.
Safety principles: "Accurate temperature, sufficient number of cycles, and data archiving" to ensure the reliable performance of each batch of H13 workpieces.
