Low-carbon structural steels 163However, at the industrial site (Kearny, New Jersey), copper exerts a more
powerful effect and would be promoted to a higher ranking than that shown
above.
Very similar results have also been obtained by Hudson and Stanners 15 and
Larrabee and Coburn l~ and it is generally acknowledged that phosphorus produces
a marked and progressive benefit up to at least 0.1%. However, phosphorus is very
detrimental to both toughness and weldability and therefore it is not included in
some grades of weathering steel, with some loss in corrosion resistance. Copper
is regarded as an essential constituent in weathering steels but little benefit is
gained by increasing the copper content above about 0.3%. Elements such as
silicon and chromium are mildly beneficial and the greatest benefit is obtained at
levels up to about 0.25% and 0.6% respectively. As indicated earlier, manganese
can be regarded as being neutral in its effect on corrosion resistance, whereas
sulphur is detrimental.
Steel spec~cations
Following the withdrawal of BS4360: 1990, a European standard was intro-
duced for weathering grades, namely BS EN 10155:1993 Structural steels with
improved atmospheric corrosion resistance. The chemical compositions of these
grades are shown in Table 2.7 which includes two high phosphorus compositions
and specific ranges for chromium and copper.
The mechanical properties of these grades are shown in Table 2.8. BS EN
10155:1993 offers a wider range of grades than the former British standard,
extending the requirements for both tensile and impact properties.
Clean steels and inclusion shape control
In parallel with developments in micro-alloy steels and thermomechanical
processing, major attention has also been given to methods of producing steels
which are isotropic with regard to tensile ductility and impact strength. Initially,
the need for these steels was precipitated by the incidence of lamellar tearing
in which plate material separates along planar arrays of non-metallic inclusions
under the forces generated in highly restrained welds. However, the need for
higher levels of impact strength in structural steels and the requirement for better
cold formability in strip products have also focused attention on the development
of cleaner steels and inclusion shape control.
The practice of adding calcium to steels for the reduction of sulphide and
oxide inclusions is now used world-wide and has the added benefit of modi-
fying the shape and size of these inclusions. One of the pioneers in this field
was Thyssen Niederrhein in Germany and the practice is described by Pircher
and Klapdar. 17 After tapping, calcium in the form of calcium silicide or calcium
carbide is injected deep into the ladle by means of a refractory lined lance,
using argon as a carder. The calcium vaporizes and as it bubbles through the
molten bath it combines with sulphur and oxygen in the steel. In either case,
the reaction products are carried into the slag. The steel is generally deoxidized