What is the optimal tempering time for H13 material with a hardness of 48-52 HRC?

For H13 material with a hardness of 48–52 HRC, the ideal tempering period is ≥2 hours each tempering cycle, repeated twice. For every 25 mm of effective thickness, the tempering time for thicker parts should be extended by 30 minutes.

 

1. The connection between performance and tempering time

Setting the Time

Effect on Efficiency

Justification

≥2 hours (Suggested)

guaranties consistent carbide precipitation and adequate martensite tempering.

High hardness and poor toughness are the results of incomplete tempering caused by insufficient time.

Extended Tempering for Heavy Components

For every 25 mm of thickness, increase by 30 minutes.

prevents a "soft inside, hard outside" appearance by guaranteeing a homogeneous alteration of the core structure.

Just One Tempering

Residual stress is not fully released, making it vulnerable to cracking while in use.

There must be two tempering cycles; the air must drop to room temperature prior to the second.

Practical Application: The standard procedure in Wuhan is 580°C × 2h × 2 tempering cycles. The hot runner nozzle life can exceed 500,000 cycles, and the measured hardness is steady at 49–51 HRC.

 

2. Crucial Elements of Time Management

The first tempering needs to be done right away: To avoid cracking due to residual stress, tempering should be done as soon as possible after quenching (recommended ≤4 hours);

Cooling to room temperature is crucial: In order to prevent thermal stress buildup, air cooling to less than 50°C is necessary in between tempering cycles;

Holding time should be computed from the moment the workpiece reaches the predetermined temperature; consistent preheating should occur prior to timing in order to avoid partial core austenitization;

Maintain furnace temperature profiles: To guaranty process traceability, each furnace should have comprehensive heating and cooling records.

Case Study: After just three days of operation, a company's H13 mold core hardness reached 53.2 HRC as a result of a tempering time of just 1.5 hours, leading to brittle breakage.

 

3. Quality Assurance and Process Verification

Test three to five places on each item (center, edge, thickness boundary) for hardness, making sure the range is ≤2 HRC and the average value is 48–52 HRC;

Metallographic Sampling: Verify that the microstructure is composed of scattered carbides and homogenous tempered martensite, free of coarse or network carbides;

Process Recording: For simple problem evaluation, note holding time, temperature, and operators.

"Precise temperature, sufficient number of tests, and adequate time" are three essential safety principles.