How to Determine if H13 Material is Fully Hardened

Metallographic analysis and cross-sectional hardness gradient testing are the main techniques used to determine whether H13 material is fully hardened. In order to determine whether the quenching depth satisfies the requirement, it is essential to establish that the core structure has fully changed into martensite.

 

1. Cross-sectional hardness testing is the most dependable method of determination.

Testing Procedure: Measure the hardness every two to three millimeters from the surface to the core after cutting the workpiece along its centerline.

Acceptance Criteria:

48–52 HRC is the surface hardness;

Complete hardening is indicated by core hardness > 90% of surface hardness (i.e., ≥ 43 HRC);

"Incomplete hardening" is a possibility if the core hardness is less than 40 HRC.

Use a portable Leeb hardness tester (conversion required) or a Rockwell hardness tester (HRC).

Assure the stability of the service.

 

2. Metallographic Analysis (Basis for Authoritative Judgment)

Hardened/Unhardened Appearance of the Location

Surface: homogeneous carbides plus fine, needle-like tempered martensite same as on the left

Tempered martensite with a uniform core Coarse martensite or a mixture of ferrite and pearlite

Transition Zone: There are no visible soft bands, the structure is continuous, the hardness abruptly changes, and it is prone to cracking

Testing Requirements: Use a metallographic microscope at 400x magnification after sample, polishing, and etching with 4% nitric acid alcohol.

 

3. Supplementary Judgment Techniques

Verification of Process Parameters:

if the quenching temperature falls between 1020 and 1050 °C;

if the holding time is computed as one hour for every 25 mm thickness;

If the cooling medium has a water concentration of less than 0.5%, is it qualified quenching oil?

Furnace Temperature Curve Verification: To guaranty adequate austenitization of the core, make sure all heating, holding, and cooling records are complete.

Initial Magnetic Assessment: Because martensite is ferromagnetic, the hardened area shows significant magnetism; however, this should not be the main foundation for judgment.

Risk Alert: Under high pressure, workpieces with acceptable surface hardness but insufficient core hardening are vulnerable to abrupt fracture.