How to Determine if H13 Material Has Been Sufficiently Tempered

Combining hardness testing, metallographic analysis, and residual stress testing to thoroughly verify the structural stability and performance compliance of H13 material is the main technique for figuring out whether it has been adequately tempered.

 

1. Hardness Testing Technique (Often Employed in the Field)

Indicators

Performance Tempering

Justification

Range of Hardness

48–52 HRC

Over-tempering is indicated by an HRC below 48, and under-tempering is indicated by an HRC above 52.

Range of Single Pieces

≤2 HRC

Multiple point measurements (center, edge, thickness boundary); the material is more uniform if the range is less.

Stability of Batches

Average change in value ≤±1 HRC

Data that is consistent across several furnaces indicates a controlled process.

For instance, an H13 manifold plate's hardness at five different testing sites is 49.8, 50.1, 50.3, 49.9, and 50.0 HRC, with a variation of just 0.5 HRC, suggesting adequate and consistent tempering.

 

2. Verification of Metallographic Structure (Key Criterion) A fully tempered microstructure should have the following features when viewed under a 400× microscope:

Matrix Structure: Dispersed fine carbides plus uniform tempered martensite;

Absence of Abnormal Structure: absence of network carbides, untempered martensite, and oxidation of grain boundaries;

Microstructure Consistency: A "hard surface, soft interior" appearance is avoided by having no discernible changes in microstructure across thick and thin sections.

Sampling Recommendation: Take at least 5% of each batch, focusing especially on thick or difficult sections.

 

3. Identification of Remaining Stress (High-Requirement Situations)

X-ray diffraction (XRD) is the detection method;

Residual stress ≤100 MPa is the acceptance criterion.

Significance: Machining cracking or early service failure can result from excessive stress.

Application Scenarios: Applied to high-reliability parts like precision mold cores and hot runner nozzles.

 

4. Process Proof The following process records can be utilized to infer the process even in the absence of metallographic or stress testing:

Double Tempering: Allow the first tempering to cool to room temperature before beginning the second tempering;

Precise Temperature Control: Make use of a PID temperature-controlled furnace with a furnace temperature differential of ≤±5°C and a setting of 580°C±5°C;

Adequate Holding Time: ≥2 hours for each holding period, plus an extra 30 minutes for thick parts that are 25 mm thick;

Keeping Furnace Temperature Curves: To guaranty traceability, keep thorough heating and cooling records for every furnace.

Safety Principles: The most dependable strategy combines "data archiving, organizational reliability, and performance compliance".