What methods can be used to stabilize the hardness of H13 material?

To ensure that the hardness consistently falls within the range of 48~52 HRC and the range of individual pieces is ≤2 HRC, the main strategies for stabilizing the hardness of H13 material include precise control of the tempering process, standardized furnace loading, implementation of two tempering processes, and enhanced pre-inspection of raw materials and process monitoring.

 

1. Crucial Controls

Description of the Measure

Precise Tempering Temperature Control: Maintain a strict temperature range of 550–600°C, with a recommended range of 580°C to 5°C. A hardness shift of 1~2 HRC can occur for every ±10°C change.

Double Tempering: To avoid residual stress rebound, cool to room temperature following the initial tempering.

Standardized Furnace Loading Method: To prevent stacking and guaranty consistent hot air circulation, keep workpieces at least 5 cm apart.

Pre-inspection of Raw Material Composition: Determine whether Cr (5.0%~5.5%), Mo (1.1%~1.75%), and V (0.8%~1.2%) satisfy the requirements using XRF.

PID Temperature Controlled Furnace + Multi-point Temperature Measurement: Keep a full furnace temperature curve for every furnace and regulate the temperature differential within the furnace within ±5°C.

Practical Case: By maximizing furnace loading density and temperature control, Jingmo Technology lowered the hardness range of H13 manifold plates from 3.1 HRC to 1.4 HRC.

 

2. Data Closed Loop and Process Monitoring

Piece-by-Piece Multi-Point Inspection: Determine the range by measuring three to five points per piece (center, edge, thickness boundary) using a portable hardness tester.

Verification of Metallographic Sampling: ≥5% of each batch should be sampled to ensure that the microstructure consists of scattered carbides and homogenous tempered martensite.

Creating Quality Records: To accomplish traceability management, furnace temperature curves, hardness data, and operator information are recorded for every batch.

Plotting control charts for several consecutive batches to spot consistent changes or increases in dispersion is known as trend analysis and early warning.

For instance, a manufacturer found that tempering furnace temperature control drift caused the average hardness of three consecutive batches to drop from 49.6 → 48.1 → 47.3 HRC.

 

3. Suggestions for On-Site Optimization

Give local compliance service providers priority, such as Wuhan Heat Treatment Plant and Jingmo Technology, who facilitate prompt delivery and comprehensive reporting;

Steer clear of high-temperature environment measurements: To avoid thermal softening influencing readings, let workpieces cool to room temperature (<50°C) before measuring;

Before using the device, calibrate it. Make sure the inaccuracy is ≤±1 HRC on a standard block to prevent systematic deviations.

"Accurate temperature, sufficient number of tests, and data archiving" are the safety principles that enable complete process control and reproducibility.