An Introduction to Steel Making

plate rollingOne of our offshore customers asked about our production facilities this week so I’m going to tell you a tiny bit about how our steel is made.

Dillinger is an integrated steel mill. This means that the mill makes its own iron, transforms it to steel slabs and then rolls it into plates. The reason for this is that it gives Dillinger very precise control over the quality of the finished product.

Iron Making

To start with the iron ore and coke are put into the blast furnace. This melts everything down to pig iron a glowing reddish yellow white liquid that is poured into a special railway tank (or torpedo car) that will keep the metal hot as it is transported.

The torpedo car is then unloaded and the liquid iron poured into the 170 tonne ladle. It’s at this point that all the work is done on getting the chemical composition of the steel right.

Steel Making

The first step is to reduce the sulphur to as low a level as possible. This is because Iron Sulphide is very brittle and severely impacts the final strength of the steel.

The next step is to stir the molten pig iron with a lance of oxygen. This transforms the iron into steel and some scrap steel is also added at this stage. The Phosphorous content is also reduced.

The result of this stage is a steel that has the approximate chemical qualities of the final grade and this is where many steel plants stop.

What happens at Dillinger next is known at the secondary metallurgy. Through a variety of processes the steel is cleaned to create an ultra-low sulphur steel, with minimal quantities of non-metallic oxides and a very low carbon content. This is key to the later performance of the steel plates.

Slab Casting

Once the liquid steel meets the stringent quality requirements it is poured into the worlds largest continuous caster (by cross section) which is able to produce 450mm thick by 2000mm wide slabs. Further tests are done on the slabs at this point.

When the steel is poured into the caster physics means that the ends of the slab don’t achieve the same purity at the centre portion. Unlike many mills Dillinger doesn’t accept this and cuts the ends off the slabs to ensure that the quality is consistent throughout (there is very little variability in test results across the finished slab at Dillinger compared to some other mills).

Finally the slabs are chopped to standard sizes and sent to the rolling mill.

Plate Rolling

The rolling mill at Dillingen is one of the most efficient in the world and is the second reason for the extremely high quality of Dillinger plate. It is able to produce plates up to 36m long, 5m wide and 450mm thick (though not all at once).

Making top quality plate requires the application of a vast amount of force in a precisely controlled manner. The first step is to heat the slab up to 1200C and remove the oxide coating.

The slabs are then passed through the two rolling stands repeatedly as the thickness is reduced and the final plate dimension is achieved. This process deforms the steel crystals, making them smaller and finer. The smaller and finer they are, the stronger the steel.

When you make thin plates this is relatively easy as you reduce a thick slab from 400mm to 10mm. When you are making thick plate it’s a lot harder as you may only be reducing from 400mm to 200mm but you still need the same level of deformation to get a consistent microstructure to avoid cracks and imperfections in the slab.

This is why Dillinger is preferred over Korean and Chinese steel plates because the power and process control means that you get a very strong, reliable plate.

Finishing and Testing

There are then a number of finishing processes that deliver the plates to customers specific requirements. These include levelling, which ensure the plate are entirely even, cooling for quench and tempering, heat treatment, and a whole range of integrated testing and certification facilities.

Finally, the plates are cut into the final size and stamped

I hope that this has given some insight into how steel is made at Dillinger and why it is different, and better, than many other steels. Do feel free to ask us any questions about the process.

Oakley Steel Requirements

Do send us your purchasing enquiries this week. We specialise in thick carbon steel plate (40 – 100mm ++) in:

  • A516 60/70
  • HIC and SSC Resistant plate
  • S355
  • S690QL
  • EH36 / DH36
  • 400/500HB

All plates are from Germany and come with 3.1 or 3.2 certificate.

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