How to Prevent Deformation and Cracking in Quenching Furnace Processing

Workpiece deformation and cracking are the most common and harmful quality defects in quenching furnace processing. Due to unreasonable process parameters, non-standard operation, equipment parameter deviation and material characteristics, metal workpieces are prone to thermal stress and structural stress imbalance during high-temperature heating and rapid cooling, resulting in warping, bending, dimensional deviation, edge cracking and internal penetrating cracking. These defects directly lead to workpiece scrapping, increased production costs and delayed orders. Mastering targeted prevention methods is the key to stabilize quenching processing quality.

1. Optimize Quenching Furnace Heating Curve to Reduce Thermal Stress

Excessively fast heating speed is the primary cause of workpiece cracking and deformation. Rapid high-temperature heating leads to inconsistent temperature rise on the workpiece surface and core, producing huge thermal stress and causing structural distortion and cracking. To solve this problem, professional quenching furnaces should adopt multi-stage slow heating programs: set low-temperature preheating stage (200–400°C) to fully eliminate workpiece residual stress and moisture; adopt gradient temperature rise to avoid instantaneous thermal shock; extend soaking time appropriately according to workpiece thickness to ensure uniform temperature of surface and core, reducing temperature difference stress. For thin plates, strips and irregular precision parts, low-speed heating parameters must be strictly implemented.

2. Select Matching Cooling Medium and Control Cooling Speed

Unreasonable cooling mode is the main cause of quenching deformation and cracking. Different steel materials have different stress tolerance limits: high-carbon steel and tool steel have poor toughness and are prone to cracking under rapid water quenching, so medium-speed oil quenching should be adopted to balance hardening effect and stress release; medium-carbon structural steel can use water-oil composite quenching, with fast initial cooling to ensure hardness and slow later cooling to avoid cracking; precision thin parts adopt gas quenching to realize uniform slow cooling and completely eliminate deformation risks. It is necessary to avoid unified cooling parameters for all workpieces and formulate targeted cooling schemes according to material and structure.

3. Standardize Workpiece Placement and Fixture Auxiliary Fixing

Unbalanced workpiece placement and free deformation during heating are important causes of irregular deformation. During furnace loading, workpieces should be placed flat and evenly, avoiding unilateral stress and overlapping extrusion. For easily deformed parts such as long shafts, thin plates and arc-shaped parts, special high-temperature resistant fixtures and brackets must be used for fixed clamping to limit thermal deformation space. Batch processing should control single-batch loading density to ensure smooth hot gas circulation in the furnace and uniform heating of each workpiece, avoiding local overheating and uneven stress distribution.

4. Strictly Control Quenching Temperature and Soaking Time

Over-temperature heating and excessive soaking time will cause steel grain coarsening, increased material brittleness and reduced crack resistance. Long-term low-temperature heating leads to insufficient phase transformation and uneven internal structure, resulting in inconsistent stress release and deformation. It is necessary to strictly implement material-specific standard quenching temperature parameters, avoid over-temperature and under-temperature processing, and match soaking time according to workpiece thickness. Thick workpieces extend soaking time appropriately, while thin precision parts shorten heat preservation time to prevent grain growth and structural deterioration.

5. Optimize Post-Quenching Transfer and Subsequent Tempering Process

Too fast workpiece transfer speed from furnace to cooling medium will cause local temperature sudden drop and stress concentration. It is necessary to standardize transfer operation to ensure stable and uniform cooling of workpieces. In addition, timely tempering treatment after quenching is essential. Complete low-temperature or medium-temperature tempering within 24 hours after quenching can completely eliminate quenching residual stress, stabilize workpiece size and effectively prevent delayed cracking during storage and use.

By comprehensively optimizing furnace heating parameters, cooling process, operation specifications and post-processing procedures, factories can reduce quenching deformation and cracking defective rate by more than 90%, greatly improving product qualification rate and production economic benefits.