Steels_ Metallurgy and Applications, Third Edition

Engineering steels 253

argon shrouding of the molten stream was adopted which prevented reoxidation,
leading to a further reduction in the non-metallic inclusion content. In the mid-
1970s, many steelmakers introduced vacuum induction melting and vacuum arc
remelting (VIM, VAR) to produce exceptionally clean steels. However, dramatic
improvements in cleanness have also been obtained in bulk steelmaking processes
for bearing grades, particularly with the introduction of secondary steelmaking
facilities. Davies et al. 27 have described the facilities that have been installed at
Stocksbridge Engineering Steels for the production of beating steels and these are
summarized in Table 3.12. Steels from a 100 t electric arc furnace are processed
via a vacuum arc degassing (VAD) unit while melts from a 150 t furnace are
transferred to a ladle furnace (LF), equipped with argon stirring, arc heating and
alloying facilities. Care is also taken to minimize the inclusion content with the
use of high alumina and graphitized magnesia refractories.
The SAM count rating for alumina (Type B) and globular oxides (Type D)
on casts of SAE 52100, produced by Stocksbridge Engineering Steels between
1984 and 1986, have been monitored by Hampshire and King. 2~ These data are
shown in Figure 3.35. The major decrease in Type D inclusions in April 1985
coincides with the introduction of the ladle steelmaking facility and it is reported
that individual Type D SAM counts since that time have rarely exceeded a value
of 3. On the other hand, the introduction of ladle steelmaking did not have a
dramatic effect on the incidence of Type B alumina inclusions, the SAM count
being between 3 and 8 over the period shown. Mean oxygen contents of less than
about 10 ppm can now be obtained via the ladle refining route, i.e. approaching
that produced by vacuum arc remelting.

Table 3.12 Facilities for the production of clean steels at Stocksbridge Engi-
neering Steels

Process route element B Furnace route C Furnace route

Slag-free tapping

Ladle stirring

Slag control

Reheating

Degassing

Alloying

Ladle refractories

Ingot teeming shroud

Ingot holloware

CC ladle to tundish a

CC tundish

CC tundish to mould

Submerged taphole

Argon through sidewall

plug

Specific synthetic slags

Arc heating in VAD

Integral part of VAD

via 13 alloy hoppers

75-85% A1203 walls and

bottom 92% MgO slag line

Inert gas

60% A1203

Graphitized A1203 shroud

700-mm deep, MgO-lined

Graphitized A1203

submerged entry shroud and

flux, or inert gas

Submerged taphole

Argon through sidewall

and bottom plugs

Specific synthetic slags

Arc heating in LF

Separate tank degasser

via 13 alloy hoppers

82-85% A1203 walls and

bottom 96% MgO slag line

Inert gas

60% AI203

Not applicable

Not applicable

Not applicable

aCC = continuous caster.

After Davies et al. 27