How to solve the hardness difference after tempering of H13 material?

Precise temperature control, standardized furnace loading, two tempering processes, and bolstering the pre-inspection of raw materials to guaranty the uniformity of microstructure transformation from the source are the key to resolving the hardness difference after tempering of H13 material.

 

1. Fundamental Approach

The underlying cause

The answer

Impact

Inconsistent Temperature

To confirm that the real temperature difference is ≤±5°C, set a PID temperature-controlled furnace to 580°C±5°C and set up several temperature measurement locations (top, middle, bottom, and corners).

Avoid abnormally high or low hardness due to localized overheating or cold regions.

Variations in Cooling

To increase the consistency of thermal circulation, keep workpieces at least 5 cm apart, refrain from stacking, and make use of tooling racks.

Remove "shading areas" to guaranty that thick and thin sections are heated consistently.

Inadequate Tempering Cycles

It takes two cycles of tempering. Prior to the second tempering, let the air settle to room temperature following the initial tempering.

Release any remaining stress completely to avoid microstructure rebound.

Variations in Raw Materials

Use XRF to determine whether the Cr (5.0%~5.5%), Mo (1.1%~1.75%), and V (0.8%~1.2%) content satisfies the requirements prior to tempering.

Removing Inconsistent Reactions Caused by Deviations in Alloy Elements

Practical Case Study: By improving the temperature control system and furnace loading technique, Jingmo Technology decreased the hardness range of H13 manifold plates from 3.1 HRC to 1.4 HRC, raising the batch pass rate to 99.2%.

 

2. Data Closed-Loop and Process Control

Multi-point Inspection per item: Each item is measured at three to five locations (center, edge, thickness boundary), and the range is computed to guaranty ≤2 HRC;

Verification of Metallographic Sampling: ≥5% of the batch is sampled to ensure that the microstructure consists of scattered carbides and homogenous tempered martensite;

Maintaining Furnace Temperature Curves: To ensure process traceability, comprehensive heating and cooling data are maintained for every furnace;

Creating Quality Archives: To facilitate problem review, hardness data, operators, and equipment numbers are documented.

Advice: To quickly spot trend deviations (like a steady decline in average hardness), control charts can be created using data from several successive batches.

 

3. Suggestions for On-Site Optimization

Give priority to service suppliers who comply, such Wuhan Heat Treatment Plant and Jingmo Technology, who facilitate prompt delivery and comprehensive reports;

Steer clear of high-temperature measurements: To avoid thermal softening influencing the reading, cool the workpiece to room temperature (<50°C) prior to measurement;

Before using the device, calibrate it. To prevent systematic variations, make sure the inaccuracy is ≤±1 HRC on a standard block.