Specific operational steps for re-quenching and standardized tempering:

To assure microstructure reconstruction and performance recovery, the particular operational methods for re-quenching and standardized tempering involve heating to 1020–1050℃, holding at that temperature, quenching, and then carrying out two tempering processes at 550–600℃, each holding for at least two hours.

 

1. Requenching

Heat the workpiece gradually to 1020–1050℃. Segmented preheating (e.g., 600℃, 850℃)

advised to avoid cracking or distortion brought on by heat stress.

For every 25 mm of thickness, hold for at least 30 minutes. Make sure the core has been adequately austenitized.

Use high-pressure air cooling (vacuum furnace) or oil cooling (N32/N46 machine oil recommended).

achieve a fine, homogeneous martensitic structure.

<60°C is advised).

 

2. Conventional Tempering

After quenching, hold at a temperature of 550–600℃ (580℃ is ideal) for at least two hours.

releases the majority of residual tension and starts the change of the microstructure.

After tempering, it must be air-cooled to room temperature (<50°C); fast cooling is not allowed.

stops fresh thermal stress from developing.

Maintaining a constant temperature and duration, repeat the initial tempering procedure.

enhances microstructure stability and totally removes stress rebound.

Special Note: Hardness and toughness will not be stable if only one tempering stage is carried out.

 

3. Verification and Post-Remedial Testing

48–52 HRC on average;

Range <=2 HRC for a single piece.

Metallographic sampling: at least 5% of samples are extracted from every batch to verify that the microstructure is composed of scattered carbides and homogenous tempered martensite;

Furnace temperature profile retention: For traceable management, temperature records are kept for the duration of the process.