Cryogenic Treatment - Selection and Precautions of Quenching Oil 

Cryogenic Treatment - Selection and Precautions of Quenching Oil

1. Ordinary Quenching Oil (Oil Temperature Below 60°C)
Ordinary quenching oil is primarily suitable for ferrous alloys with good hardenability, such as small-sized bearing steels and tool/mold steel components. In the past, mechanical oils of different grades were commonly used as quenching oils in China. In the early 1980s, to enhance cooling performance, thermal oxidative stability, and rust resistance, additives such as cooling accelerators, antioxidants, and rust inhibitors were incorporated into mechanical oils, developing ordinary quenching oils of various grades with superior performance compared to mechanical oils.

Applications:

Suitable for general quenching processes in salt bath furnaces, box furnaces, and pit furnaces.
Not recommended for mixing with other oils.
Thoroughly clean the oil tank before oil replacement.
Precautions:

Optimal operating temperature: 50–80°C.
Maximum operating temperature: ≤80°C (to avoid compromising service life).
Install agitation or oil circulation systems to improve cooling uniformity and ensure consistent cooling of workpiece surfaces.
Regularly replenish with fresh oil.
2. Bright Quenching Oil (Oil Temperature Below 70°C)
Bright quenching oil is a cooling medium for parts heat-treated in controlled atmospheres, ensuring a bright surface finish post-quenching. It is mainly used for small components that do not require secondary machining, such as precision instrument/watch parts and small cutting tools.

Features:

Prevents the formation of large colloidal aggregates from oxidation products on part surfaces.
Displaces insoluble residues already adhering to parts, maintaining surface brightness.
Applications:

Ideal for protective atmosphere furnace quenching of small-to-medium bearing steels, tool/mold steels, and instrument/gauge steels.
Suitable for non-protective atmosphere furnaces quenching highly hardenable steels.
Precautions:

Optimal operating temperature: 60–80°C.
Strictly control moisture content (>200 μg/g severely impairs brightness; oil treatment may be required).
3. Rapid Bright Quenching Oil (Oil Temperature Below 80°C)
Designed for protective atmosphere quenching, this oil offers faster cooling rates than bright quenching oil. It is tailored for materials with poor hardenability and larger components.

Applications:

Primarily used in automotive, tractor, bearing, and textile machinery industries for protective atmosphere quenching.
Suitable for carburizing and carbonitriding quenching of automotive gears, as well as cooling medium for other steels in protective/non-protective atmosphere furnaces.
Precautions:

Maximum operating temperature: ≤100°C (to ensure long-term cooling stability and brightness).
Avoid moisture contamination and mixing with other oils (even trace moisture degrades surface finish).
Strictly control carbon black and sulfur content in protective atmospheres (impacts post-quenching quality).
4. Vacuum Quenching Oil (Oil Temperature Below 80°C)
Vacuum quenching oil is essential for specialized industries where conventional heat treatments fail to meet requirements, such as aerospace. It is suitable for quenching large/medium-sized structural steels, bearing steels, tool/mold steels, and other alloys.

Precautions:

Initial Use: Pre-pump at 66×10³ Pa for 10–20 minutes to remove entrained air, preventing oil carryover into pipelines/vacuum systems.
Key Requirements:

Low Saturation Vapor Pressure:
Minimizes evaporation to reduce furnace contamination and maintain vacuum efficiency.
Excellent Cooling Performance:
Maintains high cooling capacity across a wide pressure range, compensating for reduced boiling intensity under vacuum conditions.
Superior Brightness and Thermal Stability:
Resists reactions with residual carbon, sulfur, oxygen, moisture, and acids to ensure part brightness and thermal stability.
Applications:

Enables oxidation-free, decarburization-free, and carbon-free processing with minimal distortion, extending component life and reducing environmental impact.