Heat Treatment / Annealing
- Annealing is a generic term covering a range of processes which can be carried out at a variety of temperatures.
- The primary purpose of annealing is to reduce the hardness of a material for subsequent machining. It also increases ductility and helps to eliminate residual stresses.
- For ferrous materials (steels, cast irons, etc) Keighley Labs offers two main processes which require long cycle times and very slow cooling. – Full Annealing at higher temperatures of 800°C to 980° C and Sub-Critical or Spheroidise Annealing at 650°C to 750°C.
- Controlled temperature and controlled cooling is necessary to ensure the correct material structure.
- For many aluminium alloys annealing is typically carried out at 320°C to 420°C
- Alternative combinations of annealing on offer include Isothermal which can be carried out at the customers’ request.
- The principal benefits of annealing depend on annealing process used.
- Annealing is commonly used after casting, forging or other material processing routes to soften materials and minimise residual stresses, improve machinability and increase ductility by carefully controlling the microstructure.
- High temperature annealing of non-stainless ferrous materials is usually done to homogenise, soften and stress relieve, aiding stability and machinability – and help limit problems in subsequent heat treatments particularly cracking risks.
- Sub-critical annealing is done for many of the same reasons – to soften and stress relieve, aiding stability and machinability.
- For stainless steels solution annealing is primarily used to provide an optimum corrosion resistant condition.
- For aluminium alloys it may be done to aid forming.
- Annealing applied to cast iron castings to remove chilling from founding is a high temperature process. This process may not be suited to all chilled irons (for example those containing chromium or other elements that cause or contribute to excess carbide chilling).
- Whilst most metallic materials can be “annealed” using an applicable process, commercial processes are more commonly limited to ferrous materials, aluminium alloys, copper alloys, nickel alloys and titanium alloys.
- For the most common range of ferrous materials KLL can often offer vertical or other special fixturing to minimise distortion – however, most distortion comes from the relief of uneven residual stresses and cannot be prevented.
- Annealing at KLL is normally carried out in open atmospheres with no control of surface oxidation and scaling. This is usually applicable to un-machined or proof machined components or materials with shot blasting often used to clean parts up for subsequent machining.
- Components up to 1120mm in diameter and 1730mm long can be treated vertically using special jigging. Maximum weight 2000Kg.
Keighley Laboratories Ltd
Registered Office:
Croft House
South Street
Keighley
West Yorkshire
BD21 1EG
Registered in England 164811
UK Tel: +44 (0)1535 664211
Email: info@keighleylabs.co.uk