Specifications of steels usedin the automobile industry

The motor body industry uses many different types of steel. Low-carbon steel is used for general constructional members. High-tensile steels are used for bolts and nuts which will be subjected to a heavy load. Specially produced deep-drawn steel including micro-alloyed steel is used for large body panels which require complex forming. Zinc-coated steel sheets are increasingly being specified for automobile production,both for body and chassis parts, as improved corrosion protection is sought. Stainless steel is used for its non-rusting,hard wearing and decorative qualities. The many different types of springs used in the various body fittings are produced from spring steel,while specially hardened steels make the tools of production. Drills,chisels, saws,hacksaws and guillotine blades are all pro- duced from special alloy steels,which are made from an appropriate mixture of metals and elements.
Steel varies from iron chiefly in carbon content; iron contains 3–4 per cent carbon while carbon steels may contain from 0.08 per cent to 1.00 per cent carbon. The chemical composition and mechanical properties of these carbon steels,especially when alloyed with other elements such as nickel, chromium and tungsten,have been gradually standardized over the years,and now the different types of steels used are produced to specifications laid down by the British Standards Institution. A British Standard specification defines the chemical composition and mechanical properties of the steel,and also the method and apparatus to be used when testing samples to prove that the mechanical properties are correct. The tensile strength,and in the case of sheet and strip steel the bend test,are the properties of most interest,but the British Standard specification also defines the elongation,the yield point and the hardness of the steel.
The steels used in the motor trade may be grouped as follows:

1.Cold forming steels
2.Carbon steels
3.Alloy steels
4.Free cutting steels
5.Spring steels
6.Rust-resisting and stainless steels.

As each group may contain many different specifications,some idea of the variety of steels may be gained. However,in the motor body industry the specifications which apply are those pertaining to cold forming steels,namely BS 1449:Part1:1983. The greatest percentage of steel used in motor bodies is in the form of coil,strip,sheet or plate. Sheet steel is a rolled product produced from a wide rolling mill (600mm or wider); to come under the heading of sheet steel,the steel must be less than 3mm thick. Steel 3–16mm thick comes under the heading of plate.
Tables 4.1,4.2 and 4.3 are the specifications for steel sheet strip and coil for the manufacture of motor body shells in the automobile industry.