Carbs

Carburizing – Overview of the Heat Treatment Process

Carburization works by diffusing carbon atoms into the steel surface at high temperatures (about 850°C to 950°C). The steel is exposed to a carbon-rich environment, usually gaseous (e.g., methane), liquid (oil) or solid (charcoal or carbon powder). At these temperatures, carbon atoms penetrate the surface of the steel, changing the chemical composition of the outer layer.

During cooling, the surface microstructure changes from a low-carbon ferritic phase to a high-carbon martensitic phase, while the core remains low-carbon and retains its softer, ductile properties. The cooling process, often by quenching (quenching), locks the carbon in the outer layer, resulting in a significant increase in hardness (usually between 55 and 65 HRC).

The depth of the carbon-enriched layer, called the case depth, is determined by the duration and temperature of the carburization process. Higher temperatures and longer exposure times result in a deeper case layer, while lower temperatures create a thinner but equally hard surface.

Types & Variants of Carbs

There are several variations of the carburetion process, each suitable for different applications and material requirements:

• Pack Carburizing: A traditional method in which steel parts are packed in a carbon-rich solid medium (such as charcoal) and sealed in a container. When heated, the carbon diffuses into the surface, creating a hard outer layer.
• Gas carburizing: In this modern process, steel is placed in a furnace containing a carbon-containing gas, such as methane or propane. Gas carburizing offers precise control over case depth and uniformity.
• Liquid carburizing: This involves immersing steel in a molten salt bath containing carbon. This method provides rapid transfer of carbon to the surface and is ideal for specific depth and hardness requirements.
• Vacuum Carburizing: An advanced technique that takes place in a controlled environment without oxygen. This prevents oxidation and allows for precise carbon intrusion, making this method suitable for applications such as aviation.

Each variant has specific advantages depending on the size, complexity and performance requirements of the part. Gas and vacuum carburetors are often used in modern industrial applications because of their precision and consistency.

Suitable Materials & Preparation

Carburizing is primarily applied to low-carbon steels (typically less than 0.2% carbon), as this low carbon content provides a significant improvement in surface hardness without affecting the core. Common steels suitable for carburizing include:

• 1018 and 1020 Steel: These low-carbon steels respond well to carbon inputs and achieve high surface hardness while the core remains ductile.
• Alloy steels (e.g., 8620, 9310): These steels contain alloying elements such as chromium, nickel and molybdenum, which improves carburizing response and provides additional toughness and fatigue resistance.

Before carburizing can take place, the parts must be thoroughly cleaned to remove surface contaminants that could impede carbon diffusion. In some cases, parts are preheated to ensure even temperature distribution during carburizing, which is essential for consistent case depth and hardness.

Performance Enhancements & Benefits

Carburizing offers several important advantages that make it indispensable for critical, heavily loaded components:

• Increased Surface Hardness: Carburizing significantly increases the hardness of the steel surface, with values as high as 65 HRC, depending on the carbon content and quenching process. This hardness is essential for wear resistance, especially in high friction environments.
• Enhanced Fatigue Strength: The process creates a compressive stress layer at the surface, which increases resistance to fatigue failure. This is especially important for parts such as gears and shafts subjected to repeated loads.
• Toughness of the Core: A unique advantage of carburizing is that only the surface is hardened, while the core remains soft and tough. This allows the part to absorb shock without breaking.

In quantitative terms, carburized parts can show up to 200% improvement in wear resistance and a 50% increase in fatigue life compared to untreated parts.

Applications & Industry Relevance

Carburizing is indispensable in many industries, especially where parts require high surface durability and core toughness:

• Automotive: Carburized parts such as gears, camshafts and crankshafts are essential to engines and transmission systems. These parts must withstand significant wear and fatigue without failing under continuous load.
• Aviation industry: Components such as landing gear components and turbine wheels are carburized to withstand the extreme conditions during flights, including high friction and cyclic loading.
• Construction equipment: Heavy equipment such as bulldozers and excavators use carbureted components to ensure that gears and bearings maintain their integrity under harsh conditions, extending the life of the machines.

These industries require compliance with strict quality and performance standards, such as AMS 2759/7 for case hardening, to ensure that carbureted parts meet required specifications for hardness, case depth and surface finish.

Customization & Process Optimization

Our carburetion process is fully customizable to meet the specific requirements of each project. We adjust temperature profiles, carbon potential, case depth and cooling methods to achieve the desired characteristics. For example:

• Custom Case Depth: By controlling exposure time and temperature during carburizing, we can customize case depth to meet the needs of each application. Thin case depths (0.5-1.0 mm) are suitable for smaller, precision components, while deeper case layers (up to 3 mm) are used for larger, heavily loaded components.
• Quenching media: We offer several quenching options-oil, water or inert gases-depending on the desired final hardness and microstructure. Each quenching medium affects the cooling rate, which is critical for locking in the desired surface properties.

Our expertise in optimizing these parameters ensures that each carbureted component meets the specific mechanical and performance requirements needed for the application.