What are the hardness fluctuation standards for H13 material after tempering?

Following tempering, the following hardness fluctuation requirements apply to H13 material: A single workpiece within the same batch should have a hardness range of <=2 HRC, and the batch's average hardness should be steady between 48 and 52 HRC. If this range is exceeded, there is a quality hazard and the process is deemed out of control.

 

1. Acceptance Criteria for Hardness Fluctuation

<=2 HRC

the greatest variation in hardness between various measurement locations on the same workpiece, which may indicate uneven microstructure or cooling.

48–52 HRC

This range should be the focus of all workpiece measurements. A warning is necessary if the divergence from the average value is more than 1 HRC.

<=1.5 HRC range

The average hardness fluctuation should be less when several batches are constantly produced, indicating process stability.

Practical Application: After tempering H13 hot runner nozzles, a Wuhan firm mandates that the hardness range of five measuring sites per piece be <=1.8 HRC. Products that don't meet standards are promptly separated for further examination.

 

2. Dangers and Repercussions of Excessive Variations2 HRC: Shows the existence of localized soft spots or places that are not properly tempered, which might result in stress concentration during service and possibly early deformation or breaking;

<48 HRC: Shows insufficient strength and vulnerability to wear and collapse due to over-tempering or incomplete quenching;52 HRC: Shows excessive brittleness, high residual stress, inadequate tempering, and a markedly elevated risk of rapid fracture;

Unstable process control is indicated by large batch dispersion, which may have an impact on the uniformity of mold life.

Case Study: A batch of H13 manifolds showed hardness dispersion ranging from 46 to 53 HRC as a result of irregular temperature control in the tempering furnace. After three days of use, two pieces cracked.

 

3. Crucial Steps to Guaranty Uniform Hardness

Utilize a PID temperature-controlled furnace: Keep a full furnace temperature curve for every furnace and keep the temperature differential within the furnace between ±5℃;

Pre-inspect raw materials: To prevent material fluctuations from influencing the tempering reaction, use XRF to confirm that the Cr, Mo, and V compositions meet specifications.