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Steel Designers' Manual - 6th Edition (2003)
Fabrication effects and service performance 239
component or structure. In addition to the chemical composition and mechanical
properties, the test certificate should also record details of the steelmaking route
and any heat treatments applied to the material by the steel manufacturer.
It is not uncommon for some semi-finished products to be sold by the steel manufacturer
to other product finishers, or to stockholders. Unless these parties retain
careful records of the supply of the material it may be difficult to trace specific
details of the properties of steel bought from them subsequently, although some
stockholders do maintain such records.
Where products are manufactured from semi-finished steel and subsequently
given heat treatment for sale to the end user, the intermediate manufacturer should
produce his own test certificates detailing both the chemical analysis of the steel
and the mechanical properties of the finished product. For example, bolts used for
structural connections are manufactured from bar material and are normally
stamped with markings indicating the grade and type of bolt. Samples of bolts are
taken from manufactured batches after heat treatment and subjected to mechanical
tests to give reassurance that the correct strength of steel and heat treatment
have been used.
6.6 Fabrication effects and service performance
Basic steel products supplied from the steel manufacturer are rarely used directly
without some subsequent fabrication. The various processes involved in fabrication
may influence the suitability for service of the steel, and over the years established
procedures of good practice have been developed which are acceptable for particular
industries and applications.
6.6.1 Cutting, drilling, forming and drawing
Basic requirements in the fabrication of any steel component are likely to be cutting
and drilling. In thin sections, such as sheet material, steel can be cut satisfactorily
by guillotine shearing, and although this may form a hardened edge it is usually of
little or no consequence. Thicker material in structural sections up to about 15 mm
thickness can also be cut by heavy-duty shears, useful for small part pieces such as
gussets, brackets, etc. Heavier section thicknesses will usually have to be cut by cold
saw or abrasive wheel or by flame cutting. Cold saw and abrasive wheel cutting
produce virtually no detrimental effects and give good clean cuts to accurate dimensional
tolerances. Flame cutting is carried out using an oxyacetylene torch to burn
the steel away in a narrow slit, and this is widely used for cutting of thicker sections
in machine-controlled cutting equipment. The intense heating in flame cutting does
subject the edge of the metal to rapid heating and cooling cycles and so produces
the possibility of a hardened edge in some steels. This can be controlled by either
preheating just ahead of the cutting torch or using slower cutting speeds, or