Steels, as a family of materials, offer a wide range of characteristics that find uses in many and varied applications. This section concentrates on those materials,
normally aircraft grades, which can be considered for use in space and any precautions that shall be taken for their application.
Steels are used in structural items (e.g. rocket motor casings) and within engineering components (e.g. bearings and springs) in a variety of subsystems and devices.
Steels are based on alloys of iron and carbon (between 0,05 % and 2 %C). All contain some level of other elements, i.e. even plain carbon steels (up to 1,7 % C) contain manganese up to
about 1 % Mn. This results from excess Mn used for deoxidation and desulphurization during smelting. Impurity levels (e.g. phosphorus and sulphur) depend mainly on the smelting and melting processes used, although increased use of remelted scrap metal can introduce other problem elements such as copper. Alloy steels contain one or more additional alloying elements to improve properties and workability.
The tensile strength of plain carbon steels increases with carbon content up to
approximately 0,8 %C, reaching a theoretical maximum of about 900 MPa, with a corresponding decrease in ductility. Hardness increases progressively with C-content, so that low- (0,1 % C--0,3 % C) to medium-carbon steels (0,3 % C--0,6 %C) are used for various "engineering" components, whereas high-carbon steels (0,6 % C--0,9 %C) are used for applications requiring hardness and wear resistance.
Alloying additions to plain carbon steels produce a wide range of alloy steels with improved
performance. Alloying effects can be microstructure-related: for example, control of transformation effects, control of grain size, carbide precipita-tion; process-related: workability, heat-treatment, hardenability and weldability; corrosion-related: forming adherent oxide films on the surface . Depending on the level of additions, some elements have effect on all of these. |
