How to test the hardness of H13 material after tempering?

A portable hardness tester must be used to measure the hardness of H13 material several times at different locations on the workpiece following tempering. This guaranties that important areas are covered by the data, and range analysis and standard deviation are used to evaluate the uniformity. This is the main technique for confirming the heat treatment's quality.

 

1. Standard Practice for Hardness Testing on-Site

Procedures

Important Points

Justification

① Selection of Test Points

Each workpiece should have three to five test points marked on its surface, edges, center, and thickness joints.

To increase representativeness, cover areas that are susceptible to uneven cooling.

② Surface Care

To get rid of oxide coatings or oil stains, lightly sand the test points with sandpaper.

To prevent reading discrepancies, make sure the probe makes good contact.

③ Measuring Hardness

Use a portable Rockwell (HRC) or Leeb (HL) hardness tester in converted mode.

To increase data dependability, measure three times at each location and calculate the average result.

④ Data Capturing

Note the hardness values at each location, then compute the standard deviation and range (highest value minus minimum value).

Check to see if the variation is within a manageable range.

Acceptance criteria: batch average stable between 48 and 52 HRC, single piece range ≤ 2 HRC.

 

2. Evaluation and Reaction to Test Results

Range of Fluctuation

Judgment Outcome

Suggestion

≤1 HRC

Great, reliable procedure

Direct use is possible.

1-2 HRC

Normal variation, acceptable

Boost the monitoring of processes

2–3 HRC

There are possible issues that need be looked at.

Metallographic study and sampling to confirm microstructure homogeneity3 HRC

There are unqualified, soft places, or untempered areas.

Rework or discard the whole batch

For instance, a business examining an H13 hot runner nozzle discovered that a portion of it had a local hardness of 46.8 HRC, with a range of 3.3 HRC, while the remainder was 50.1 HRC. Uneven cooling was found to be the cause of this soft area issue.

 

3. Additional Verification Techniques

Metallographic Sampling Analysis: To verify the existence of untempered martensite, retained austenite, or microstructure coarsening, samples of workpieces with unusual hardness are prepared for examination;

Furnace Temperature Curve Verification: Determine whether there are any disruptions or localized temperature variations during tempering, and whether the temperature stays constant between 550 and 600°C;

Composition Pre-inspection and Comparison: By removing the impact of material variations, XRF is utilized to verify the consistency of Cr, Mo, and V content in the raw materials.