How to ensure uniform furnace temperature during tempering of H13 material

Implementing multi-point temperature measurement, standardizing furnace loading, and performing frequent furnace temperature uniformity tests (TUS) to control the temperature difference within the furnace to ≤±5°C are the key to ensuring uniform furnace temperature during tempering of H13 material. This ensures consistent performance of workpieces in the same batch.

 

1. Crucial Controls

Calculate

Particular Operation

Function

Verification of Multi-point Temperature Measurements

For real-time monitoring, place at least six temperature measurement points in the furnace's upper, middle, lower, front, rear, and corners.

Make sure the real temperature difference is ≤±5°C by accurately capturing the cold and hot zones.

Standardized Method for Furnace Loading

Workpiece spacing should be at least 5 cm; minimize stacking; and utilize fixtures that can withstand high temperatures.

Boost the effectiveness of hot air circulation and avoid uneven local heating.

Control of Segmented Heating

When the temperature is below 400°C, raise it gradually (≤150°C/h) to lessen thermal stress and temporary temperature variations.

Prevent the workpiece's surface and core from experiencing an extreme temperature differential that could cause asynchronous microstructure alteration.

Frequent TUS Examinations

Assess furnace temperature uniformity on a quarterly basis in accordance with AMS 2750.

Check the stability of the equipment and quickly spot any problems with aging or thermocouple drift.

Practical Example: Jingmo Technology used a multi-zone temperature-controlled furnace and fixture configuration to minimize the hardness differential of the H13 manifold from 2.8 HRC to 1.2. The batch pass rate at HRC increased to 99.2%.

 

2. Common signs of a failure in temperature uniformity:

Dispersed hardness distribution within the same workpiece or batch: Hardness difference > 2 HRC;

Inconsistent microstructure: Metallographic investigation reveals coarsened carbides in some places and untempered martensite in others;

Early service failure: Stress concentration in "soft spots" or "hard areas" causes localized cracking or accelerated wear.

Warning case: Due to damage to the furnace's bottom insulating layer, the bottom workpiece's temperature (which was supposed to be 580°C) was only 568°C. This resulted in a hardness as low as 47.8 HRC, which meant that the entire batch was rejected.

 

3. Mechanism for long-term guarantee

Create process archives: To facilitate traceability, complete heating and cooling curves and temperature measurement records are kept for every furnace.

Frequent equipment calibration: To guaranty data accuracy, thermocouples and temperature controllers are calibrated every three months;