Process annealing involves the heating of a steel with less than 0.3%C to a temperature usually between 550 and 650°C. The purpose of this is to relieve any Stress from distorted grains caused by cold working or deformation. The ferrite grains will reform as unstressed grains, while the pearlite remains in the deformed state.

Full annealing involves heating either hypo-eutectoid steels or eutectoid steels into the austenite region at a temperature of about 40°C above the upper critical temperature (UCT)'. The steel is then cooled very slowly, usually in a furnace, with the result being a softer, coarser grained steel than previously existed. All grains will be in an unstressed state.

Normalising involves heating a steel up into the austenite region well above the UCT. When the structure is all austenite, it is then cooled in still air. The process takes less time than full annealing and produces a finer grained structure and hence a stronger steel.

For medium to high carbon steels the higher amount of cementite in the form of pearlite makes these steels more difficult to machine. Spheroidising involves heating the steel to between 650°C and 700°C and holding it there for an extended time. This causes the layers of cementite within the pearlite to form spheroids of cementite. These spheroids of cementite are much easier to machine than the lamellar structure of pearlite.

Forging may be defined as the shaping of a metal through the use of force. Forging may be carried out above the recrystallisation temperature (hot forging) or below it (cold forging or pressing). Forging can take a variety of forms, the simplest type being that which a blacksmith does against an anvil. Forging may draw out a metal while reducing its cross-sectional area (drawing); reduce its length while increasing its cross-sectional area (upsetting), or it may force the metal into dies to take the required shape, as in drop forging.

Rolling can be done either above the recrystallisation temperature, (hot rolling), or below the recrystallisation temperature, (cold rolling). The recrystallisation temperature is that temperature above which deformed (stressed) grains in metal will re-nucleate and grow into annealed grains (stress-free). Unstressed grains will not re-nucleate, but they will grow.

Extrusion comes in two forms; direct, where the ram pushes the metal into the die from the other side, and indirect, where the ram and die are the one part. Direct extrusion generally requires more effort so it is used with more ductile materials. Indirect extrusion is used in the extrusion of alloys with lower ductility, but, because the equipment required is more expensive, direct extrusion is used where possible. Both direct and indirect extrusion are hot working processes. Unlike the other types of extrusion, this is a cold forming process. Impact extrusion involves the use of a hammer impact to extrude a shape. The punch goes into a die and the material blank is forced from the die around the punch. Cans and short tubes are often made using this method.

Metal powder forming or powder metallurgy is a process that finds extensive use. The process involves first getting the metal into powder form. This may be done by mechanical disintegration such as grinding, atomizing the metal from liquid form by chemical means, or by electrolytic methods.

If we are welding cold rolled plate then in the HAZ the plate will exhibit unstressed grains, as the welding process will heat the plates near the weld above the material's recrystallisation temperature. Generally non-ferrous metals will be softened around the weld by the welding process. While mild steel is very easily welded it will also suffer grain growth near the weld, which will soften cold rolled plate. High carbon steels and some alloy steel are more challenging to weld and may need to be slow cooled to stop martensite forming. In some high carbon steels pre-heating may be necessary to stop martensite forming or cracks developing. Care must be taken when welding stainless steels, because at elevated temperatures (650-800°C) some of the chromium may react with carbon to form chromium carbides which means the passive chromium oxide layer cannot form. When welding is required stainless steel alloys with very low carbon are often chosen to lessen the chance of carbide formation.

Ferrite is a very soft, ductile phase, although it looses its toughness below some critical temperature.

Austenite is a soft, ductile phase that can be work hardened to high strength levels, particularly in the fully austenitic Hadfield manganese steels.

The retained austenite is white and lies between the plate martensite "needles." However, there are also a few white particles of cementite in the micrograph (arrows).

This type of polymer softens on the application of heat. It can also be re-melted and reformed. Thermoplastics have long linear chain structures, with the chains formed by covalent bonds. Weak van der Waal's forces hold the separate chains together. As a consequence, they are usually flexible and often transparent. When put under a tensile load, they stretch readily, as there is little resistance to the chains straightening or sliding over one another (refer to Volume 1, p 26). Examples are polyethylene. polystyrene, polytetrafluroethylene (PTFE), polymethylmethacrylate (acrylic), polypropylene, polyvinyl chloride (PVC) and acrylonitrile butadiene styrene (ABS). They find use in cable coating on bicycles and for car parts such as grilles, badges, door handles and window winders.

This type of polymer undergoes a chemical change when heat is applied. The change is not reversible so these polymers do not soften when they are reheated. Thermoplastics have network structures, with covalent bonds, along the chains and across the chains. They tend to be more rigid than thermosoftening polymers. When they are put under tension, the cross-linking resists deformation. This makes them less flexible than a linear polymer. Epoxy resins, silicone, polyurethane and polyester resins are examples of thermosetting polymers. Epoxy resins find use in the aireraft industry for joining panels, and the silicones are often used in gasket manufacture tor cars. Epoxy resin also find extensive use in bicycles and racing cars for use as the matrix in carbon fibre reinforced polymers.

Rubber is a natural polymer. In synthetic form it has great use in transport. The tyres for cycles and cars use a modified rubber, which is called vulcanised rubber. Rubber in its natural form is a linear polymer that is too flexible for use in a tyre. By adding around 5% sulphur to the rubber mix and heating it to about 150°C, a moderate level of cross-linking is achieved. The vulcanised rubber is more rigid, but still flexible. To increase rigidity, tyres are usually constructed from a composite of rubber with cotton strands, while radial tyres for cars use steel wire and polyester cord.

This is used to shape thermoplastics. A polymer tube is lowered into a mould, and air forces the tube to the shape of the mould. It is used to make polymer containers such as those used to store oils. A different form of blow moulding is used to make soft drink bottles, here injection moulding is used to create "pre-forms" that are then heated and blown using a blow moulding technique.

As for metals, polymers can be extruded, with the polymer taking the shape of the die through which it is extruded. The polymer granules are melted and the molten material is forced through the die. This process is only suitable for thermosoftening polymers. Polymer tubing is manufactured using this method. The outer covering of bicycle cables is coated with plastic in this way.

This process is used in the manufacture of various thermoplastic containers. Heated thermoplastic sheets are placed over dies to produce the required shape. The forming can be done using matching dies, a vacuum or air pressure. Often, special thermoplastic sheets are used for this process.

A thermoplastic is poured into a cavity between two rollers, and the plastic is squeezed through the rollers. The rollers may be embossed with patterns or they may be smooth. Tiles, films and curtains can be made this way.

The molten polymer is poured into a mould and the centrifugal force throws the polymer to the walls of the mould, forming a hollow article.

This is one of the most commonly used polymer forming procedures. Molten polymer is injected into a cavity in the shape of the finished article. When the polymer solidifies, it is ejected and the procedure starts again. Injection moulding lends itself readily to mass production. Many items are injection moulded and are often identified by the small remnants of the sprue on the item and a split line where the polymer was injected into the mould. They are used in the manufacture of small thermoplastic mouldings for cars and bicycles.