How to determine if the hardness of H13 material meets the standard after tempering

The primary criterion for evaluating whether the hardness of H13 material satisfies the requirement following tempering is that the hardness value falls between 48 and 52 HRC, with a single piece falling between ≤2 HRC. It is feasible to precisely determine whether it satisfies the service requirements by combining auxiliary verification with on-site testing.

1. Standards for Hardness Testing

An indicator

Typical Range

Justification

Hardness Average

48–52 HRC

Too high (>52) denotes strong brittleness; too low (<48) denotes insufficient strength.

Range of Single Pieces

≤2 HRC

The greatest variation across the same piece's several testing locations, indicating consistency

Stability of Batches

Average change in value ≤±1 HRC

Multiple pieces' average value deviates from the standard by no more than one HRC.

For instance, an H13 hot runner nozzle was found to be totally compliant when the hardness of five testing points was 49.8, 50.1, 50.3, 49.9, and 50.0 HRC, with a range of only 0.5 HRC.

2. Crucial Elements of On-Site Testing

Test Point Layout: Choose three to five crucial points (center, edge, thickness boundary) on each item that cover regions that are susceptible to uneven cooling.

Before using the instrument, check it on a standard block to ensure that the error is within ±1 HRC.

Cooling to Room Temperature: To avoid measurements being impacted by heat-induced softening, the workpiece temperature must be less than 50°C before testing.

Data Recording: To guaranty quality traceability, mark the workpiece with the serial number, furnace number, and testing staff.

Note: To guaranty precise measurement, the portable hardness tester should be examined every three months.

3. Supplementary Verification Techniques (High-Requirement Situations)

Metallographic analysis involves sampling and determining if the microstructure consists of distributed carbides and homogenous tempered martensite, devoid of network or coarse carbides;

Verification of the Furnace Temperature Curve: Determining whether the tempering process is uninterrupted and free from local temperature variations at 550–600°C;

Composition Analysis: Verify that the contents of Cr (5.0%~5.5%), Mo (1.1%~1.75%), and V (0.8%~1.2%) satisfy the requirements using XRF.