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Iron  (basic element symbol: Fe)    Iron is the basis for the great bulk of our structural metals. The term "ferrous metal" means that the main element is iron. (Technically and from a scientific view, the ferrous metals include iron, cobalt (Co), and Nickel (Ni). Common practice in industry calls the iron alloys, only, as "ferrous".)

For recycling purposes, there are two categories of iron alloys: (1) cast iron ... usually, simply called "iron" and (2) steel. It is economical to separate these two forms since cast iron has a higher scrap price premium.  Both forms are magnetic, except the chromium-nickel stainless steels.  Cast iron items are easily identified by the rough finish (where not machined) and by the typically cast shape.

The forms of cast iron vary widely in alloy composition. Most cast iron is gray cast iron and is found in automobile engine blocks and machine bases. When broken (it is brittle), the exposed surface is gray with visible graphite.  The proportion of gray iron is dwindling although the total amount is still very important ... there's a lot of it around.   Ductile and alloy cast irons have increased strength and corrosion resistance and fill many applications which were formerly reserved for steel: crankshafts, chemical pumps, heat resistant parts. It is impossible to tell by visual examination, one type of cast iron from another. 

Most steel is plain carbon steel,  mainly because this form is cheap, easily worked, and weldable at the lower carbon content levels. The alloy steel scrap can command a higher scrap value if segregated and sold through a dedicated channel. There are many mini-steel mills which depend entirely on scrap and some of the most mundane carbon steels may contain unusual elemental components. (This writer, when browsing at an analysis of a plain carbon steel, was astonished to spot cobalt, molybdenum, and vanadium as components as trace elements. Some tool steel had been mixed into the scrap steel furnace feed!)

It is desirable to keep the scrap piles segregated and clean since the value drops due to unwanted debris and mixtures of scrap. 

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