How to perform bright quenching heat treatment on screws

Performing bright quenching heat treatment on screws is a technical process that requires precise control of process parameters. Its purpose is to achieve high hardness and good mechanical properties while maintaining a bright and oxidation-free surface on the screws.

I. Specific steps for bright quenching

• Pre-treatment

Cleaning: Thoroughly remove oil stains, rust, and impurities from the surface of the screws. This can be achieved through ultrasonic cleaning, alkaline cleaning, or solvent cleaning.

Drying: Ensure that the screws are completely dry to prevent surface defects caused by water evaporation during the heating process.

• Selection of protective atmosphere

Controlled atmosphere: By precisely controlling the composition of the furnace atmosphere (such as CO, H₂, N₂, etc.), a stable carbon potential or nitrogen potential can be achieved to prevent oxidation and decarburization.

Vacuum: Heating in a vacuum environment completely avoids oxidation and is suitable for screws with high precision and surface quality requirements.

Inert gas: Using nitrogen or argon as a protective gas is suitable for medium- to low-temperature bright quenching.

• Heating

Heating rate: Control the heating rate according to the material and size of the screws to avoid overheating or deformation.

Temperature control: Precisely control the quenching temperature to ensure complete austenitization of the material. For example, the quenching temperature for carbon steel screws is typically 820-860°C, and may be higher for alloy steel screws.

Holding time: Determine the appropriate holding time based on the effective thickness of the screws to ensure uniform transformation of the microstructure.

• Quenching

Cooling medium: Select an appropriate quenching medium, such as fast quenching oil, polymer aqueous solution, or gas quenching (e.g., nitrogen). The cooling rate should be fast enough to obtain a martensitic structure, but not so fast as to cause cracking.

Cooling method: Immersion quenching, spray quenching, or fluidized bed quenching can be used to ensure uniform cooling of the screws.

• Tempering (optional)

Purpose: Eliminate quenching stresses, improve toughness, and adjust hardness.

Temperature and time: Select appropriate tempering temperature and time based on the material and performance requirements of the screws. For example, the tempering temperature for carbon steel screws is typically 150-400°C, and the tempering time is determined by the size of the screws.

II. Application examples

• Automotive fasteners: High-strength bolts, nuts, and other parts that need to withstand high loads can have their surface hardness and wear resistance improved through bright quenching.

• Electronic equipment: Micro screws need to maintain a bright surface to avoid oxidation affecting conductivity.

• Aerospace: High-precision screws need to be quenched in a vacuum or controlled atmosphere to ensure stable performance.

III. Precautions

• Safe operation: Quenching media (such as fast quenching oil) are flammable, and strict safety operating procedures must be followed.

• Environmental requirements: Quenching waste liquid must be treated before discharge to avoid environmental pollution.

• Process optimization: Continuously optimize heat treatment process parameters based on the specific requirements of the screws to improve product quality and production efficiency.