The mother slabs fr om NLMK are first checked for dimension, weight and marking before they are cut into baby slabs weighing between 1.5 and 35 tons - varying in thickness fr om 100 to 360 mm.
Before reheating, the baby slabs are prepared by flame scarfing at the slabs storage facility and marked with a identification number that ensures traceability through out the production. Having been cut into baby slabs, the basic materials are transported to natural gas fired furnaces, where they are reheated up to a rolling temperature of 1200° C. The reheating is computer controlled and the maximum temperature is 1325° C
Even if the slabs are heated up in a low-oxygen atmosphere, which keeps oxidation of the surface to a minimum, scale is formed. This hard and thin layer of scales might damage the surface of the plates when rolled in the mill. The scales are removed by "descaling" - spraying water at 200 bar pressure on the surface - just before rolling.
The scale is - like all by-products - reused in various productions
Fr om descaling the slab is transported to the rolling stand. The slab temperature is now about 1180° C. The slab is rolled under up to 8000-ton pressure to produce a plate of the required width and thickness.
The stand is a so-called "four-high" rolling stand, wh ere 2 working rolls with a diameter of 1.000 mm, are supported by two backup rolls with a diameter of 2.000 mm.
NLMK DanSteel A/S also carries out controlled rolling of plates, wh ere temperature and mechanical deformation are controlled to yield specific mechanical properties of the plates after rolling. Depending on the rolling process, this leads to normalized or thermomechanically rolled plates, resulting in improved mechanical properties.
NLMK DanSteel A/S can produce steel plates from 5 to 220 mm in thickness, 4050 mm wide and more than 20 metres long. The warm mechanical processing in rolling might cause some non-flatness of the plate. The newly rolled plates are therefore levelled in a hot leveller at temperatures between 700 and 1000° C.The nine rollers in the hot leveller straighten the plate before it is transferred to the cooling bed.
The plates are cooled for about half an hour so that the temperature reaches approximately 500° C. Thicker plates are placed in stacks and cool slowly to about 200° C to avoid hydrogen cracks.
In some cases, either to reach certain mechanical properties, or as per norms, standards or customer requirements, a heat treatment is needed after rolling. This process called normalizing is done by reheating the plates to about 900° C in a natural gas fired furnace. The temperature is kept at this temperature in a few minutes. To meet the expanding demand for normalized plates, NLMK DanSteel A/S has invested in new and bigger capacity. NLMK DanSteel A/S now has a normalizing capacity of 80 % of the total plate volume.
After Normalizing the plates are levelled in the cold leveler before being cut to ordered size.
Even if some plates are sent directly to storage halls without cutting, the majority of the plates first have to be cut at both sides in the double shear before being cut in the final length. At this time also a test sample is cut and sent to our laboratory for testing. For thicker plates NLMK DanSteel A/S uses flame cutters to cut the plates into dimensions according to customer specifications.After cutting, the dimension, geometry, surface, and marking are inspected.
Around 20% of the production is shot blasted and primed as a protection against corrosion. The process included drying of the plates, shot blasting and paint application. The paint is a special durable anti-corrosion compound.
All plates are sorted and stacked in our big storage halls.
The plates are loaded on lorries or railway wagons with magnet cranes for transport to the costumers or loaded on internal units for transport to our harbour wh ere they are loaded in ships.
70 pct. of the production is sent by ships, 15 pct. by lorries, and 15 pct. by railway.
NLMK DanSteel production process