How to Determine the Stability of H13 Material

The main technique for assessing the stability of H13 material is to thoroughly assess its metallographic consistency, heat treatment process traceability, and hardness uniformity. When combined, these three elements create a closed loop that determines material stability.

1. Quick On-Site Evaluation of Hardness Uniformity Testing

Testing Procedure: Measure three to five important points (such as the center, edge, and thickness boundary) on each workpiece using a portable hardness tester.

Acceptance criteria: batch average hardness consistent between 48 and 52 HRC; single-piece hardness range ≤ 2 HRC.

Abnormality Warning: Unstable material characteristics can be caused by uneven cooling or insufficient tempering if the range is more than 3 HRC.

Practical Advice: 100% testing of important workpieces; sampling rate of at least 10% per batch.

2. Metallographic Analysis (Basis for Authoritative Judgment)

Stable Performance of Microstructure Features Unreliable Performance

Matrix Structure: Dispersed carbides plus uniform tempered martensite Network carbides, coarse martensite, or leftover ferrite

No oxidation, no microcracks, and a clear grain boundary state Microcracks (overheating), remelting spheres, and oxidation at the grain interface

Network dispersion, homogenous precipitation aggregation, fine carbide distribution, and decreased toughness

Testing Requirements: Use a metallographic microscope with a magnification of 400× or greater after sampling and processing. Sampling at least five percent of each batch is advised.

3. Closed-Loop Quality Assurance (Process Traceability)

Furnace Temperature Profile: Verify that the temperature during the tempering process is steady at 550–600°C, with appropriate heating and cooling rates, and that there are no disruptions or variations;

Batch Report: Provide operation logs, testing staff details, and comprehensive hardness testing data;

Service Provider Qualification: Give preference to heat treatment facilities with CQI-9 certification, whose procedures are uniform and their documentation is comprehensive.

"Data traceability, organizational credibility, and process controllability" are essential safety principles.