Voltage annealing

Stress Relief Annealing.

The process of stress-relief annealing involves heating the material to a temperature below the recrystallization point, usually between 450°C and 650°C (for steel), depending on the material. This moderate heating allows the metal’s atomic lattice to rearrange without significant phase changes. This reduces residual stresses built up during earlier machining steps.

The microstructure of the material remains largely unchanged, but the heat treatment redistributes dislocations within the crystal lattice. This reduces internal stresses without significantly changing the hardness or strength of the material. The cooling rate must be controlled, often by slow air cooling, to prevent new stresses from forming.

In stress-relief annealing, protective gas environments such as nitrogen or argon are sometimes used to prevent oxidation, especially in materials prone to surface contamination. The equipment used includes furnaces with precise temperature control, cooling chambers and sometimes protective gas environments to ensure high quality of the final product.

Types & Variations of Tension Arm Annealing

There are several variations of stress-relief annealing, depending on the material and the specific requirements of the part:

• Standard Stress Arm Annealing: This is the most common form, applied to ferrous metals such as steel, cast iron and alloys. Parts are heated to a temperature between 500°C and 650°C, followed by slow cooling in air.
• Subcritical Annealing: This is a lower-temperature variant, typically performed below 450°C, and often used for aluminum and copper alloys. This treatment reduces residual stresses without significantly affecting the mechanical properties of the material.
• Post-Weld Heat Treatment (PWHT): This is a specific form of stress-relief annealing after welding operations to reduce residual stresses caused by local heating and cooling. It is especially important in pressure vessels, pipelines and other welded structures.

Each variant addresses different material properties and stress levels. Choosing the right variant ensures that the parts maintain their desired mechanical properties and eliminate unwanted residual stresses.

Material suitability & Preparation

Stress-relief annealing is suitable for a wide range of metals, including:

• Steel and Cast Iron: These materials often undergo stress relief annealing to prevent distortion and improve dimensional stability after operations such as welding or machining.
• Aluminum and Aluminum Alloys: Aluminum is susceptible to residual stresses during machining and forming. Stress-relief annealing helps eliminate internal stresses without drastically altering the soft nature of the material.
• Copper alloys: For copper alloys, stress-relieved annealing is performed at lower temperatures, allowing the material to retain its ductility while reducing internal stresses.

Before a part undergoes low-tension annealing, it must be thoroughly cleaned to remove surface contaminants such as oils, oxides or scale. This prevents defects during heat treatment. In addition, complex geometries may require special fixings to ensure uniform stress reduction and prevent distortion.

Performance Enhancements & Benefits

The main advantages of low-tension annealing are the significant reduction of internal stresses in materials. This leads directly to:

• Improved Dimensional Stability: Parts are less susceptible to deformation, especially in precision applications.
• Improved Machinability: After low-tension annealing, materials are often easier to machine, leading to reduced tool wear and improved surface condition in subsequent machining operations.
• Extended Fatigue Life: Parts that have undergone low-tension annealing are more resistant to fatigue failure, making them suitable for dynamic and load-bearing applications.
• Reduced Risk of Cracking: By eliminating internal stresses, the risk of cracking during use, especially on welded parts, is greatly reduced.

These performance improvements make stress-relief annealing essential for components exposed to thermal and mechanical loads in their operational environments.

Applications & Relevance in Industry

Stress-relief annealing is widely used in various industries:

• Aerospace: Critical parts such as turbine blades, structural frames and engine components are stress-annealed to ensure dimensional accuracy and fatigue resistance.
• Automotive: Gears, axles and other high-performance parts in vehicles are stress-annealed to prevent premature failure and increase wear resistance.
• Construction and Heavy Machinery: Large welded structures such as cranes, bridges and pipelines undergo stress low annealing to reduce stresses created during fabrication, ensuring long-term durability and performance.
• Defense and Maritime Industries: Components used in military vehicles, submarines and ships benefit from stress-relief annealing to withstand harsh conditions and high mechanical loads.

Compliance with industry standards such as AMS 2750 (for aviation) ensures that stress-relief annealing meets the stringent requirements of specific industries. Certification and compliance with such standards demonstrate our commitment to providing high-quality and reliable heat treatment services.

Customization & Process Optimization

We offer customized stress annealing treatments tailored to the specific requirements of each project. Our team works closely with customers to customize temperature profiles, holding times and cooling rates to ensure the process is optimized for the specific material and application. We also offer:

• Controlled Atmospheres: To prevent oxidation or contamination, we offer low-tension annealing in inert gas environments such as nitrogen or argon.
• Custom Made Cooling Profiles: Depending on the material and geometry of the part, we adjust cooling rates to prevent new stresses from forming during the cooling phase.

This level of customization ensures that each treated component meets or even exceeds performance standards.