What is the effect of tempering time on H13 material?

The microstructure stability, consistent hardness, and residual stress release of H13 material are all significantly impacted by tempering time. A duration that is too short will result in insufficient stress release, whereas a duration that is too lengthy will result in carbide coarsening. The recommended holding time is two hours or more each time; for thicker sections, the duration must be increased in accordance with the thickness.

 

1. The connection between performance and tempering time

Range of Time

Effects on Performance and Microstructure

Less than two hours

High hardness and brittleness, incomplete martensite tempering, inadequate residual stress release, and a markedly elevated risk of cracking

≥2 hours (Suggested)

Complete transformation of martensite into tempered martensite, consistent precipitation of carbides, stabilization of hardness at 48–52 HRC, and ideal toughness

Too much time (>4 hours)

Although flexibility somewhat increases, overall performance declines as carbides start to coarsen and agglomerate, the matrix softens, and strength and wear resistance decline.

Practical Use: In Wuhan's mold factories, 580℃×2h×2 tempering is a well-established method that guaranties microstructure stability and full stress release.

 

2. Principles of Time Adjustment for Thick Workpieces

Standard Thickness (≤25mm): Heat treatment for two hours is adequate.

Thick Workpieces (>25mm): Increase the heat treatment duration by 30 minutes for each extra 25mm of thickness.

Common Examples:

50 mm thick plate → heat treatment for three hours;

100 mm thick mold core → five hours of heat treatment to avoid inadequate core tempering.

Case Study: For just 2.5 hours, a company heat-treated an H13 manifold plate that was 80 mm thick. Testing showed that the surface hardness was 49.8 HRC and the core hardness was 53.1 HRC, both of which were beyond the permitted range. Four hours was chosen as the new treatment duration.

 

3. Tempering cycles and time have a synergistic effect.

Two cycles of tempering are required: cool to room temperature following the first tempering, and then do a second tempering, both of which call for enough holding time.

Mechanism

First tempering: This process starts the microstructural alteration and releases the majority of the quenching stress.

Second tempering: Ensures total microstructural stabilization by removing fresh stresses created during the initial tempering.

Safety Standards: "Timely completion, guarantyd number of tempering cycles, and data archiving." To guaranty traceability, complete holding records and furnace temperature curves are kept for every furnace.