How to ensure the consistency of hardness in H13 material

Precise control of tempering process parameters, standardized furnace loading techniques, the use of two tempering processes, and a combination of raw material pre-inspection and full-process data monitoring are the main strategies for guaranteeing the consistency of hardness in H13 material, thereby achieving hardness stability between batches and within individual pieces.

 

1. Important Process Control Points

Control Object

Particular Measures

Function

Controlling the Temperature

Accurately set at 550–600°C; 580°C +/- 5°C is advised.

Precise temperature control is essential since a temperature variation of ±10°C can result in a hardness shift of 1~2 HRC.

The quantity of rounds of tempering

It needs to be tempered twice. Before the second tempering, allow the first to cool to room temperature.

to enhance microstructure stability and stop residual stress rebound.

Keeping Time

≥2 hours every time. Add thirty minutes for every twenty-five millimeters of thickness.

to prevent surface and interior irregularities and to guaranty adequate tempering of the core.

Cooling Technique

cooling by air to room temperature. Cooling with water or oil is not allowed.

to stop localized quenching or the development of subsequent stress.

Use a tempering furnace that has multi-point temperature measurement and PID temperature control. The furnace's temperature differential should be kept between ±5°C.

 

2. Optimizing Thermal Circulation and Furnace Loading

Reasonable Spacing: To prevent stacking and guaranty consistent hot air circulation, keep a minimum of 5 cm between workpieces.

Optimal Positioning: To avoid uneven cooling brought on by localized obstruction, alternate between thick and thin parts.

Use Tooling Racks: To secure workpieces and enhance heat transfer consistency, use supports that can withstand high temperatures.

Enhanced Convection: To increase temperature consistency, turn on forced convection or furnace fans.

Case Study: By maximizing furnace loading density, Jingmo Technology decreased the hardness difference of H13 manifold plates after tempering from 3.1 HRC to 1.4 HRC.

 

3. Closed-loop Process Monitoring and Quality

Furnace Temperature Curve Recording: To guaranty regulated and traceable temperatures, full heating and cooling curves are recorded for every furnace.

100% Hardness Testing: Following tempering, a portable hardness tester with a range of ≤2 HRC is used to assess hardness at three or more locations per piece.

Verification of Metallographic Sampling: To ensure that the microstructure is uniform tempered martensite + scattered carbides, ≥5% of the batch is sampled.

Raw Material Pre-inspection: XRF is utilized to verify that the Cr (5.0%~5.5%), Mo (1.1%~1.75%), and V (0.8%~1.2%) components satisfy the requirements prior to tempering.

"Precise temperature, sufficient number of tests, and data archiving" are the safety principles that guaranty complete process traceability and reproducibility.