Hot-rolled steels are driven by Quality Standards or Constructors sprecifications, and they are classified according to Mechanical characteristics, as Yield-, Tensile-strength and Elongation, as well as Chemical composition. The variety of grades is as wide as uses are: Mild-steels, for standard cold-forming processes and manufactures; Structural steels in Mechanical and Building industries; Dual-Phase steels, the very best compromise between resistance and drawability; High strength, low alloy steels (HSLA), characterized by low carbon and alloy element contents giving them excellent functional properties, are particularly used when a weight reduction is required; Steels for Gas containers, particularly deep-drawable, offering an outstanding life-time and maintaining optimum safety characteristics; Special steels, having a particularly strong hardness and providing high mechanical strengths; High Resistant steels, the very best compromise between high resistance and weight-reducing needs. Hot Rolled steels are differentiated according to surface finishing, “Black” as mill-finished or “Pickled and Oiled”; they may be processed (cut, formed, welded) and possibly coated according to Standards or Steel mill recommendations.
Basically, Cold rolled steels are Hot rolled steels which thicknesses have been further reduced trough mechanical cold process; they are particularly destined to forming processes, as profiling, bending, drawing in Automotive industry or General Manufacture. Cold rolled steels may be supplied as “mild” non-alloyed, micro-alloyed (LA), Boron, Phosphorus, Bake Hardening steels. Currently, the cold rolled steels that NLMK Europe Strip Products produces are priory destined to its Galvanizing facility.
Galvanized steels are Hot rolled or Cold rolled steels, annealed and roll-coated through a 450°-melting bath of Zinc or Zinc-alloy. Zinc coating protects steel from corrosion. Depending on substrate' end-use and thickness, Zinc layer varies from 70 up to 450 gr/m2 - double side. Galvanized steels are used in General industry and Automotive sector.
Galvanized steels are in compliance with European Standard EN 10346, or eventually with automotive manufacturer's specifications, and they have same grade and processing ability as their steel substrates.
Organic coated or prepainted steels are Galvanized steel coated with a painting system consisting of a primer paint layer and a “finishing” paint layer. They are called "precision coating" or "front coating", and protected occasionally by a removable plastic fi lm. Paint results from the complex mix of 4 components: Resins, giving paint its properties; Pigments and loads, giving the color, modulating gloss, hardness and permeability; Solvents, liquids dissolving resins et reducing (diluting) the viscosity of the paint and Additives, influencing the drying, hardness, sliding.
Finishing layers vary from Polyester to PVDF, possibly containing leads of polyamide or additionally varnish-coated; the upper side coat varies from 15 up to 55 microns whilst reverse side is always and at least primer coated. Criteria or constraints for choosing the adequate organic coated steel are: Aesthetic, Process, Quality in use, Storage and Legislations.