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Steel Designers' Manual - 6th Edition (2003)
246 Applied metallurgy of steel
The steel must have the required strength, ductility and long-term service life in
the required environmental service conditions. For structural applications the steel
must also have adequate fracture toughness, this requirement being implemented
by standard Charpy test quality control levels.
Where the steel is to be fabricated into components or structures, its ability to
retain its required properties in the fabricated condition must be clearly established.
One of the most important factors in this respect for a number of industries is the
weldability of steel, and in this respect the chemical composition of the steel must
be controlled within tight limits, and the welding processes and procedures adopted
must be compatible with the material chosen.
The corrosion-resistance and potential fire-resistance/high temperature performance
of the steel may be important factors in some applications. A clear decision
has to be taken at the design stage as to whether resistance to these effects is to be
achieved by external or additional protection measures, or inherently by the chemical
composition of the steel itself. Stainless steels with high quantities of chromium
and nickel are significantly more expensive than ferritic carbon or carbon
manganese steels. Particular application standards generally specify the range of
material types which are considered suitable for their particular application.
Increased strength of steels can be obtained by various routes, including increased
alloying content, heat treatment, or cold working. In general as the strength
increases so does the cost and there may be little advantage in using high-strength
steels in situations where either fatigue or buckling are likely to be ruling modes of
failure. It should not be overlooked that although there is some increase in cost of
the basic raw material with increasing strength, there is likely to be a significant
increase in fabrication costs, with additional precautions necessary for the more
sophisticated types of higher-strength material.
Certain product forms are available only in certain grades of steel. It may not be
possible to achieve high strength in some product shapes and retain dimensional
requirements through the stage of heat treatment because of distortion problems.
Wherever possible, guidance should be sought on the basis of similar previous
experience or prototype trials to ensure that the particular material chosen will be
suitable for its required application.
6.7.2 Steel specifications and choice of grade
Structural steelwork, comprising rolled products of plate, sections and hollow
sections, is normally of a weldable carbon or carbon-manganese structural steel
to the new European based standard, BS EN 10025. Two strength grades are most
commonly used, grade S275 and grade S355, having yield strengths typically of
275 N/mm 2 and 355 N/mm 2 respectively. To help designers adjust from the old
BS 4360 deagnations, the Appendix Properties of steel contains a number of
tables which compare the old standard with the new European standards for
structural steels.
Further standards are cited in the Appendix British Standards for steelwork.