Temp

Tempering Process: Heat Treatment of Metals

The scientific foundation of tempering revolves around manipulating the microstructure of the metal. After hardening, where the metal takes on a martensitic structure (hard but brittle), tempering helps relieve internal stresses created during the hardening process by diffusing atoms within the metal structure.

When a hardened metal is reheated during tempering, it causes the breakdown of martensite to more stable phases such as ferrite and cementite, depending on the temperature used. These phase changes result in reduced hardness but improved toughness and ductility.

Precise control of temperature is crucial here. Typical tempering temperatures range between 150°C and 650°C. Lower temperatures (150-300°C) retain more hardness, while higher temperatures (400-650°C) provide more toughness but lower hardness.

The cooling medium used during tempering can range from air cooling to more controlled methods such as furnace cooling, depending on the desired properties of the material. Industrial furnaces with precise temperature control are often used for this process.

Different Types of Tempering

There are several forms of tempering, each aimed at achieving specific material properties:

• Low-temperature tempering (150-300°C): this method retains a higher degree of hardness and reduces brittleness to a lesser degree. It is often applied to tools and cutting equipment that need to retain their sharpness.
• Medium-temperature tempering (300-500°C): this method provides a balance between hardness and toughness, making it suitable for structural parts in the automotive and construction industries.
• High-temperature tempering (500-650°C): At these temperatures, the material loses some hardness, but gains significant toughness and impact resistance. This type of tempering is often used for large, heavily loaded parts such as gears and shafts.

Each form of tempering is designed to tailor a material’s properties to specific industrial applications to achieve the right balance of mechanical properties.

Suitability of Materials & Preparation

Tempering is most commonly applied to steels and steel alloys, especially those previously hardened by tempering. High carbon steels benefit significantly from tempering because it reduces the brittleness of martensitic structures. Low-alloy steels, tool steels and stainless steels can also be tempered, but the exact procedure and results depend on the alloy composition.

Prior to tempering, metals must be properly prepared. This includes cleaning the surface to remove contaminants that may affect heat transfer during the process. In addition, hardening often precedes tempering because it provides the initial hardness needed for many steel components.

While tempering is effective in many cases, challenges can arise with certain alloys. Alloys with high amounts of alloying elements, such as chromium or vanadium, for example, require more precise temperature management to achieve the desired microstructural changes.

Performance Enhancements & Benefits

The tempering process significantly improves the overall performance of metals by balancing strength and toughness. Important benefits of tempering include:

• Increased Toughness: Tempering reduces brittleness, making parts less likely to break or crack under impact or stress.
• Improved Wear Resistance: Tempering at medium and high temperatures increases wear resistance, extending the life of components such as gears and shafts.
• Optimized Hardness: By selecting the appropriate tempering temperature, manufacturers can control the final hardness of the metal to make it suitable for the intended application.
• Improved Fatigue Resistance: Tempering reduces internal stresses, which improves fatigue resistance of components under varying loads, such as springs or load-bearing beams.

Hardened and tempered steel can reach a hardness value between 30-60 HRC (Rockwell hardness), depending on the tempering temperature and composition of the steel.

Applications & Importance to Industry

Tempering is essential in industries where parts must endure heavy loads, repeated stress or high wear. Common applications include:

• Automotive: Components such as crankshafts, camshafts and gears are tempered to ensure they can withstand the constant stress and wear in engines and transmissions.
• Aviation: Aircraft components, such as landing gear and engine components, are tempered to achieve a balance between weight reduction and high strength requirements.
• Tooling and Manufacturing Industry: Cutting tools, molds and dies are often tempered to achieve the necessary hardness for precision machining while maintaining sufficient toughness to prevent breakage.
• Construction: Structural components, such as beams and supports, are tempered to carry heavy loads without deforming or failing.

In these industries, tempering helps meet stringent standards, such as ASTM A229 (for high-strength spring steels) and AMS 2750 (pyrometry standards for aerospace applications).

Customization & Process Optimization

We offer custom options to achieve the specific mechanical properties required by each project. These options include adjustments in tempering temperatures, durations and cooling methods. Our engineers work closely with customers to ensure that the tempering process is tailored to their material and application requirements, whether for high wear resistance or optimal fatigue strength.

By using advanced furnaces with precise control systems, we can achieve uniform tempering results even for complex geometries and large batch productions.