What is Heat Treatment Oil?

Heat treatment oil is a specialized fluid used to control the cooling rate of steel heated to high temperatures. Its primary purpose is to prevent cracks and achieve a uniform micro structure during the heat treatment process.

Heat treatment typically involves heating steel to temperatures close to or above 1,000°C. If rapidly cooled without proper control, the steel can develop cracks. By carefully managing the cooling process using heat treatment oil and optimal conditions, manufacturers can produce strong, crack-resistant steel components.

Among various heat treatment oils, quenching oil is commonly used to rapidly cool austenitized steel to form a martensitic structure. In general, the term “heat treatment oil” encompasses all oils used in quenching, tempering, annealing, and other thermal processes. Simply put, heat treatment oil acts as a high-performance lubricant designed to harden and enhance the properties of steel components.

Let’s take a closer look at the two main categories of heat treatment fluids—water-soluble coolants and non-water-soluble oils—and their distinct characteristics.

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Water-Soluble Heat Treatment Coolants

Although often referred to as “water-soluble heat treatment oils,” the correct term is heat treatment coolant. These coolants pose a lower fire risk, are more environmentally friendly, and are easier to clean post-process. However, they must meet strict performance criteria:

1. Proper Cooling Performance
   The coolant must deliver optimal cooling performance based on concentration and temperature settings.
2. Ease of Cooling Performance Control
   It should be easy to monitor and adjust the cooling characteristics during use.
3. Thermal Stability
   It must resist degradation and maintain consistent quality over time.
4. Non-Putrefactive and Wastewater-Friendly
   The coolant should not decay or rot and must be easy to dispose of with minimal environmental impact.

When these conditions are met, water-based coolants can often outperform oils in versatility and offer a broader range of steel grades compatibility.

There are two types of water-based coolants:

• Non-film-forming
• Film-forming

This distinction is based on whether a protective film is formed on the surface of the quenched part.

Best Practices When Using Heat Treatment Coolants:

• Uniform cooling must occur simultaneously across the entire part.
• Temperature distribution should be consistent over time.
• The cooling process should remain gradual, especially in lower temperature ranges.

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Non-Water-Soluble Heat Treatment Oils (Quenching Oils)

Often referred to as quenching oils, these fluids are more cost-effective and do not rot like water-based coolants. However, they come with increased fire risk, environmental concerns, and more complex post-treatment requirements.

When selecting a heat treatment oil, it’s crucial to go beyond just the process requirements. Consider the following:

1. Type of heat treatment (quenching, atmospheric, salt bath, induction, flame, etc.)
2. Heating method (gas, electric, kerosene, diesel, etc.)
3. Equipment style (batch, pit, continuous)
4. Carburizing method (gas, liquid, solid)
5. Material, size, and tempering temperature of the steel
6. Tank capacity, agitation system, and cooling device specifications
7. Currently used fluids and existing issues

Heat treatment oils are classified according to KS (Korean Industrial Standards) and are commonly referred to by their intended use and treatment temperature: Cold, Semi-Hot, Hot, and Tempering Oils. Usage methods often remain proprietary to each company.

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Proper Oil Maintenance is Critical

Once selected, proper management of the heat treatment oil is essential. Regular monitoring of properties like flash point, acid value, insolubles, residual carbon, and moisture content is crucial.

Unlike general hydraulic, gear, or cutting oils, heat treatment oils require specialized handling. That’s why partnering with a reliable manufacturer is key—but not always easy.

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Why Dyna?

We’ve been a trusted supplier of industrial lubricants for over 30 years. We hold patents for water-soluble heat treatment coolants and serve a wide range of major corporations and small-to-medium-sized businesses across Korea.

If you’re considering switching your current heat treatment oil or coolant, feel free to reach out. We’ll analyze your needs and provide top-quality solutions at competitive prices.

For any inquiries about industrial lubricants, contact Dyna, your reliable partner in lubrication technology.

Dyna Co., Ltd.
Industrial Lubricant Solution
E-Mail : dyna@dynachem.co.kr
Web : dyna.co.kr/en/