Annealing
Annealing is a heat treatment process used to alter the properties of materials such as metals and glass. By heating the material to a specific temperature and then slowly cooling it, annealing can relieve internal stresses, increase ductility, and improve the material's machinability. This process helps to refine the microstructure of the material, making it more uniform and stable.
4 Key excerpts on "Annealing"
eBook - ePub- W. Chapman(Author)
- 2019(Publication Date)
- Routledge(Publisher)
...The appear ance of the filament, as seen through the telescope, is shown alongside the diagram Fig. 28(c). Heat colours. The luminous colours corresponding to different furnace and metal temperatures are as follows: Reasons for heat treatment. Metal is heat-treated to give it certain desired properties. Some of the properties which may be required and the treatments necessary are as follows: To soften the metal— Annealing. To harden it to resist wear, or to enable it to cut other metals— Hardening. To remove some of the extreme brittleness caused by hardening— Tempering. To refine the structure after it has been distorted by hammering or working when in the cold state— Normalising. In addition there are various other treatments such as toughening the metal to better withstand shock, toughening soft steel so that it machines without tearing, treating special steels to increase their strength and so on. Annealing The purposes of Annealing are (1) to soften the steel so that it maybe more easily machined, (2) to relieve internal stresses which may have been caused by working the metal or by unequal contraction in casting. The process involves (a) heating slowly to the required temperature, (b) holding at that temperature for long enough to enable the internal changes to take place, (c) cooling slowly. We have seen that above the critical range steel consists of austenite. This is true whatever may have been the structural condition of the steel before heating. Furthermore, when austenite is cooled normally through the critical range, it changes to pearlite, mixed with ferrite or cementite, depending on the carbon content of the steel. This change occurs only if the cooling is slow. The true transformation to pearlite, therefore, is dependent on having true austenite to start with, and then allowing sufficient time for the metal to cool through the critical range for the soft pearlite to form...
eBook - ePubApplied Welding Engineering
Processes, Codes, and Standards
- Ramesh Singh(Author)
- 2011(Publication Date)
- Butterworth-Heinemann(Publisher)
...Various cooling curves can be superimposed on the I-T diagram. The full Annealing process consists of heating to the proper temperature and then cooling slowly, through the transformation range, in a furnace. Spheroidizing Annealing is performed to produce a spheroidal or globular form of carbide and so improve machinability. Tempering involves heating the steel to some temperature below the lower critical temperature and thus relieving the residual stresses and improving its ductility and toughness. Cold worked aluminum alloys acquire strain hardness, requiring the material to be annealed. Keywords Heat treatment, critical range, austenite, phase diagram, Isothermal Transformation diagram, cooling, Annealing, tempering, aluminum alloys. Heat treatment is the practical application of physical metallurgy discussed earlier in this book. The action is in most cases thermal, with the aim of modifying the structure of the material in order to obtain desired properties. Other approaches could include thermo-chemical and thermo-mechanical processes, both of which strive to reach the same goal as the plain controlled heating and cooling cycle that is generally understood by the term ‘heat treatment’. Heat treatment is defined as a combination of heating and cooling operations, timed and applied to a metal or alloy in the solid state in a way that will produce desirable properties. The first step in the heat treatment of steel is to heat the material to some temperature at or above the critical range in order to form austenite. Different heat treatments are based on the subsequent cooling and reheating of the austenitized material. To understand the heat treatment of steel – and for that matter any metal – it is important to fully understand the phase diagram of that metal. We have discussed phase diagrams in detail in Chapter 4 of this section, and now shall take the most common and most applied phase diagram of iron carbon to discuss the heat treatment of steel...
eBook - ePub- Roger Timings(Author)
- 2007(Publication Date)
- Routledge(Publisher)
...To anneal (soften the workpiece), you allow the hot metal to cool down as slowly as possible. Small components can be buried in crushed limestone or in ashes. Larger components and batches of smaller components will have been heated in furnaces. When the correct temperature has been reached, the component is ‘soaked’ at this temperature so that the temperature becomes uniform throughout its mass. The furnace is then shut down, the flue dampers are closed and the furnace is sealed so that it cools down as slowly as possible with the work inside it. Although such slow cooling results in some grain growth and weakening of the metal, it will impart maximum ductility. This results in the metal being in the correct condition for cold forming. However, because of its extreme softness and grain growth the metal will tend to tear and leave a poor surface finish if it is machined. Components to be machined should be normalized as described in Section 4.16.5. Stress-relief Annealing This process is reserved for steels with a carbon content below 0.4%. Such steels will not satisfactorily quench harden but, as they are relatively ductile, they will be frequently cold worked and become work hardened. Since the grain structure will have become severely distorted by the cold working, the crystals will begin to reform and the metal will begin to soften (theoretically) at 500°C. In practice, the metal is rarely so severely stressed as to trigger recrystallization at such a low temperature. Stress-relief Annealing is usually carried out between 630°C and 700°C to speed up the process and prevent excessive grain growth. Stress-relief Annealing is also known as: • Process Annealing since the work hardening of the metal results from cold-working (forming) processes. • Inter-stage Annealing since the process is often carried out between the stages of a process when extensive cold working is required...
eBook - ePub- R. E. Smallman, A.H.W. Ngan(Authors)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
...In that case, it is necessary to increase the temperature of the deformed metal above the strain ageing temperature before it recovers its original softness and other properties. 11.6.2 Three stages of Annealing The removal of the cold-worked condition occurs by a combination of three processes, namely, (i) recovery, (ii) recrystallization and (iii) grain growth. These stages have been successfully studied using light microscopy, transmission electron microscopy and X-ray diffraction. Mechanical properties, e.g. hardness, and physical properties, e.g. density, electrical resistivity and stored energy, have also been measured. Figure 11.8 shows the change in some of these properties on Annealing. During the recovery stage the decrease in stored energy and electrical resistivity is accompanied by only a slight lowering of hardness, and the greatest simultaneous change in properties occurs during the primary recrystallization stage. However, while these measurements are no doubt striking and extremely useful, it is necessary to understand them to correlate such studies with the structural changes by which they are accompanied. Figure 11.8 Rate of release of stored energy (Δ P), increment in electrical resistivity (Δ ρ) and hardness (VPN) for specimens of nickel deformed in torsion and heated at 6 K/min (Clareborough et al., 1955). 11.6.3 Recovery This process describes the changes in the distribution and density of defects with associated changes in physical and mechanical properties which take place in worked crystals before recrystallization or alteration of grain orientation occurs. From the previous section the structure of a cold-worked metal consists of dense dislocation networks, formed by the glide and interaction of dislocations, and, consequently, the recovery stage of Annealing is chiefly concerned with the annihilation and rearrangement of these dislocations to reduce the lattice energy and does not involve the migration of large-angle boundaries...
