What are the common defects after tempering H13 material?

After tempering H13 material, common flaws include uneven hardness, excessively high or low hardness, microstructure coarsening, excessive residual stress, and surface decarburization. These flaws can have a major impact on the mold's longevity and service performance.

 

1. Principal Types and Causes of Defects

A flaw

Particular Expression

Primary Cause

Hardness Variability (Range > 2 HRC)

significant variations in hardness throughout different parts of the same object, creating hard or soft regions.

Inconsistent cooling, uneven furnace stacking, and uneven tempering temperature

Low Hardness (less than 48 HRC)

decreased strength and wear resistance, as well as insufficient overall hardness.

over-tempering brought on either an overly high tempering temperature or an overly lengthy holding period.

High Hardness (> 52 HRC)

high brittleness and early cracking risk.

incomplete tempering due to inadequate holding time or tempering temperature.

Microstructure Coarsening

coarse carbide agglomeration, matrix cutting, and toughness reduction.

secondary carbide precipitation brought about by an overly high tempering temperature or an overly extended tempering period.

High Residual Stress (> 100 MPa)

wire cutting cracking, deformation during machining, and rapid thermal fatigue crack propagation.

tempering just once or cooling too quickly.

Decarburization of the Surface

decreased hardness, wear resistance, and surface carbon content.

uncleaned surface prior to tempering or inadequate management of the furnace environment.

Real-world example: A batch of H13 mold cores showed a hardness dispersion of 46–53 HRC due to a tempering furnace temperature control malfunction, which caused three cracking incidences in a single week of operation.

 

2. Techniques for Defect Identification and Verification

Hardness Testing: Determining the individual item range and batch standard deviation by multi-point measurements with a portable hardness tester;

Metallographic Analysis: Determining whether the microstructure is homogenous tempered martensite + scattered carbides by looking at it under a 400× microscope;

X-ray diffraction (XRD) is used to detect residual stress, with a pass standard of ≤100 MPa;

Compositional Analysis: XRF verifies that there is no surface decarburization (normal C content) and that criteria are met for Cr, Mo, V, and other elements.

The combination of "data verifiable, microstructure reliable, process controllable" is the most dependable safety principle.

 

3. Measures for Prevention and Control

Conduct two rounds of tempering: In order to fully release stress, the furnace must air cool to room temperature following the initial tempering.

Accurate temperature control: Make sure the temperature differential inside the furnace is ≤±5°C by using a PID temperature control furnace that is set at 580°C.

Standardized furnace loading: To increase the consistency of thermal circulation, use tooling racks, eliminate stacking, and keep a minimum of 5 cm between workpieces.

Process documentation: To achieve traceability, record operator information, hardness data, and temperature curves for each furnace cycle.

Wuhan Heat Treatment Plant and Jingmo Technology are suggested service providers; both have CQI-9 certification, guaranteeing more reliable process control.