Lexicon
Steel
Steel is an alloy of iron and carbon (the amount of carbon can vary between 0.005% to 2% by weight) to which a certain number of elements like chrome, molybdenum, nickel and titanium can be added in variable amounts to make it weakly or strongly alloyed.
Special steels owe their name to their chemical composition, differentiating them from more common less alloyed steels because they contain generally more of the alloying elements but above all because the mechanical characterisitcs are controlled to guarantee the required service characteristics.
Tool steels
Tool steels are designed to be worked by contact, under mechanical constraints (and at times thermic constraints) that are normally demanding in a prolonged and repetitive way.
Improved machinability steels
Steels for cold working have their machinability improved by the addition during steel manufacture of small amounts of certain metals or metallic substances and by the control of inclusions.
Nitriding steels
Nitriding is a surface heat treatment which consists of a surface enrichment of nitrogen allowing an improvement of hardness (wear resistance) and the tribology characteristics. All steels can be nitrided. However, so-called nitriding steels contain alloying elements that allow nitrogen to become soluble or that contribute to hardening.
Direct hardening/carbo-nitriding
Direct hardening is a surface heat treatment which consists of the surface enrichment of carbon in the steel. Enrichment by carbon and nitrogen in the steel is called carbo-nitriding. Direct hardening, nitriding and carbo-nitriding are all heat treatments achieved in the hot condition and are generally followed by a temper or by a temper and harden, except the nitriding in order to obtain the required surface characteristics.
Method of Production
Electric arc furnace
The steel is produced from scrap* melted in an electric arc furnace, then refined (made to specification by appropriate addition of alloying elements) in a ladle furnace. The four steel works of Ascometal have electric arc furnaces.
* Scrap ' recycled steel from demolition of used products (vehicles, household appliances ... ), or from new arisings (steel works, forgers, machinists). Scrap is graded in accordance with its shape and composition, allowing the steel works to choose different scrap mixes to produce a given quality of steel.
Secondary metallurgy
Once out of the electric arc furnace, the steel must still be modified by ladle steelmaking or secondary metallurgy to obtain the requisite characteristics for the final product. The level of alloying elements is adjusted and the amount of impurities optimised. Amongst the main operations of secondary metallurgy are deoxidation, desulphurisation, dephosphorisation and decarburisation.
Ingot
Liquid steel is cast in an ingot mould. The product, once cooled and stripped from the mould, is called an ingot.
Continuous casting
Liquid steel is cast in a suspended base-free mould that is very strongly cooled. At the start of the casting operation a moveable base blocks the mould; once the base and the walls of the mould are sufficiently cooled, the moveable base and the liquid steel as it solidifies are withdrawn continuously between rollers. The product, on exiting the continuous casting machine, is cut into blooms.
Products
Bloom
Product of large section (round, square or rectangle). The term bloom is normally used when the section is greater than a square having sides of 160mm.
Billet
Product of smaller section than bloom (round, square or rectangle).
Continuously cast bloom or billet
Product (round, square or rectangle) produced by a continuous caster.
Continuously cast blooms are most often destined for rolling, in order to produce bars or wire rod.
Rolled bloom or rolled billet
Product the result of rolling an ingot or a bloom.
Bar
Product the result of rolling blooms or billets.
Wire rod and wire
Wire rod is a rolled product that is coiled while hot, having a dimension greater or equal to 5mm.
The product obtained by drawing or cold rolling of rod is called wire.
Cold conversion
Bar and Wire Drawing
Operation of cold conversion without the production of swarf consisting of passing wire rod (or bar) through dies so as to achieve large reductions in section. The products obtained are precision gauged, but their mechanical characteristics are equally modified
Finishing
The steel product can be delivered as it is after rolling or it can submit to various other operations called finishing. Here are some examples of finishing operations:
Straightening
The rolled bar is passed between guides (or rollers) in order to make it straight.
Facing
A rolled bar that has been sheared or cropped will have its ends deformed by shearing or by a burr after cropping. Facing is a machining operation that produces a straight and clean end.
Chamfering of ends
Grinding or machining of the bar ends in order to eliminate burr from cropping.
Peeling
Cold machining operation on bars via swarf removal. The machines used allow products with an excellent surface finish to be produced: shiny aspect, decarburisation and scale removed.
Grinding
Cold material removal to high precision (very tight tolerances) to obtain an excellent surface.
Cutting to length
Cutting of bars (mostly peeled) into usable pieces, in other words, of a defined length.
Heat treatment
Succession of operations through which steel is submitted to thermic cycles to obtain a change in their properties and/or structure.Two main types of heat treatment can be distinguished:
- Annealing treatments designed to soften the steel or to obtain a favourable microstructure to allow machining or other cold transformation
- Annealing treatments designed to soften the steel or to obtain a favourable microstructure to allow machining or other cold transformation.
