Faster Pickling of Alloy Steels and High Carbon Steels
EPS FOR OTHER 'TOUGH TO PICKLE' STEELS
EPS mechanical pickling is gaining experience with other grades of steel that are difficult to pickle through conventional acid pickling:
Electrical Steel, also known as Silicon Steel due to its high Si content (up to 6%) which improves the electrical resistivity of the material, is notoriously difficult to pickle with hydrochloric acid. This difficulty stems from the presence of silica or silicate on the strip surface. The pickling line must be slowed significantly to achieve full scale removal, but 'over-pickling' can cause corrosion of the steel at grain boundaries and degrade its electrical properties.
EPS, being a mechanical process, is indifferent to the presence of silicates of the surface and can descale electrical steel at roughly the same speed as low carbon steel with no danger of degrading the electrical properties of the strip.
Harder steels – high carbon and alloy steels – have a different composition of mill scale that is more difficult to remove by acid pickling. This means the pickling line must be slowed considerably to achieve full scale removal – up to 75% slower than when running low carbon strip.
The slow line speed not only hurts economics, it increases the risk of the acid eroding some of the steel substrate, so inhibitors must be added to the pickle liquor – another factor that makes acid pickling of harder steels more difficult and more expensive than low carbon steel.
With EPS 'mechanical pickling' there is no line speed decrease when running high carbon or alloy steels. The EPS process is largely unaffected by the composition of the scale. Production experience shows that higher carbon steels (grade 1018 to 1074) and series 41XX, 51XX and 61XX alloy steels can be run on
an EPS line at about the same speed as low carbon
strip. The determining factor in line speed for EPS is the
thickness of the strip – thicker material entails a thicker
layer of scale – and not the composition of the scale.
EPS Lowers The Costs To Pickle
High Alloy Steels
With no need to decrease line speed when running high carbon or alloy steels, the primary economic advantage of EPS processing is obvious:
higher throughput. But another EPS economic advantage applies in
• Some mills can employ special measures to produce high
carbon hot roll steel with lower levels of magnetite and
hematite, specifically to improve acid pickling performance
This inefficient, expensive practice is not needed if the pickling
will be done by the EPS process.
Recoiling EPS-processed strip at Stripco