How to test the consistency of hardness in H13 material

The main technique for determining the consistency of hardness in H13 material is to measure several points on the workpiece with a portable hardness tester, compute the workpiece range and batch standard deviation, and then use metallographic analysis to confirm the microstructure's uniformity. Soft spots and hard zones are examples of inconsistent locations that can be promptly identified using this method.

 

1. Hardness Testing Procedure on-site

Procedures

Important Points

Justification

① Selection of Measurement Points

Choose the surface, edge, center, and thickness transition zone as three to five crucial points for each piece.

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

② Surface Care

Oil stains and oxide layers can be removed by sanding with sandpaper until it has a shiny sheen.

To prevent low readings, make sure the probe makes good contact.

③ Calibration of Instruments

Before testing, make sure the inaccuracy is less than ±1 HRC by calibrating on a standard block.

Avoid systemic prejudice.

④ Multi-point Assessment

At each location, take three measurements, then average the results.

Adjacent indentations should be separated by at least 3 mm. Improve repeatability and decrease chance errors.

⑤ Analysis of Data

Determine the standard deviation and range (highest value minus minimum value).

ascertain the consistency of hardness.

Pass Criteria: Batch average between 48 and 52 HRC, single piece range < 2 HRC.

 

2. Criteria for Consistency Judgment

An indicator

Performance Consistency

Risk of Inconsistency

Range of a Single Component

≤2 HRC >3 HRC denotes inadequate tempering or inconsistent cooling.

Average of Batches

48–52 HRC

Warning is required for deviations greater than 1 HRC.

Standard Deviation for Batches

≤0.8 HRC

The procedure becomes increasingly unstable as the value increases.

For instance, five measuring points on an H13 manifold have hardness values of 50.1, 50.3, 49.8, 46.5, and 50.2 HRC, with a range of 3.7 HRC. This is considered a local soft area flaw that could crack while being used.

 

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: Verify whether there are any disruptions or localized temperature variations during tempering, and whether the temperature stays steady 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.

The safety principle "Data speaks for itself, multi-dimensional verification" guaranties controllable and traceable hardness consistency.