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.
James Menzies
Production
Leonard Powell
Technical Planner
David Wright
Production Director
Mark Barron
Business Development Manager
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