Iron based metal Cast iron Cast iron usually refers to grey cast iron, but identifies a large group of ferrous alloys, which harden with a eutectic. In metal identification iron accounts for more than 95%, while the main alloy elements are carbon and silicon. The quantity of carbon in cast irons is the range 2.1 - 4%, as ferrous alloys with less are denoted carbon steel by definition. Cast irons be full of appreciable amounts of silicon, normally 1 - 3%, and consequently these alloys should be considered ternary Fe-C-Si alloys. Even though this, the principles of cast iron solidification are understood from the binary iron-carbon phase diagram, where the eutectic point lies at 1154 °C and 4.3 wt% carbon. Since cast iron has nearly this composition, its melting temperature of 1150 to 1200 °C is about 300 degrees lower than the melting point of pure iron. Cast iron tends to be brittle, unless the name of the particular alloy suggests otherwise. The color of a fracture surface can be used in metal identification to identify an alloy: carbide impurities allow cracks to pass straight through, follow-on in a smooth, “white” surface, while graphite flakes deflect a passing crack and initiate countless new cracks as the material breaks, resulting in a rough surface that appears grey. By means of its low melting point, good fluidity, castability, excellent machinability and wear resistance, cast irons have become an engineering substance with a wide range of applications, including pipes, machine and car parts.

Wrought iron Wrought iron is commercially pure iron, having a very small carbon content (not more than 0.15 percent), but frequently containing some slag. It is tough, malleable, and ductile and is easily welded. However, it is too soft for blades and swords, at least for their cutting edges, which are usually made of steel with a high carbon content. Wrought iron is so named since it is “wrought” or worked from a “bloom” of porous iron mixed with slag and other impurities. The word “wrought” is an archaic past tense of the verb to work. As irregular past-tense forms in English have traditionally been phased out over extensive periods of time, wrought became worked. Wrought iron in metal identification literally means worked iron. Wrought iron has been used for thousands of years, and represents the “iron” that is referred to throughout western history. It is a fibrous material with many strands of slag mixed into the metal. These slag inclusions give it a “grain” resembling wood, with distinct appearance when etched. Also due to the slag, it has a leathery look when broken or bent past its failure point. Wrought iron has been replaced to a very great extent by mild steel. It is, therefore, hardly produced at all today. It was used where a tough material is required. Wrought iron, at present, is used for rivets, chains, ornamental iron work, railway couplings, water and steam pipes, raw material for manufacturing of steel, bolts and nuts, horse shoe bars, handrails, straps for timber roof trusses, boiler tubes, roofing sheets, etc. Ornamental ironwork is often referred to as “wrought iron,” even though today it is more likely to be made from mild steel.

Ductile iron Ductile iron, also called ductile cast iron or nodular cast iron, is a type of cast iron invented in 1942 by Keith Millis While most varieties of cast iron are brittle, ductile iron is much more ductile, as the name implies. Cast iron is an iron alloy characterized by its relatively high carbon content (usually 2% to 4%). When molten cast iron solidifies, some of the carbon precipitates as graphite forming tiny, irregular flakes within the crystal structure of the metal. While the graphite enhances the desirable properties of cast iron (improved casting and machining propertes, better thermal conductivity), the flakes disrupt the crystal structure and precipitate cracks, leading to cast iron’s characteristic brittleness. For metal identification ductile iron the graphite forms into spherical nodules rather than flakes, thus inhibiting the creation of cracks and providing the enhanced ductility that gives the alloy its name. The formation of nodules is achieved by addition of “nodulizers” (for example, magnesium or cerium) into the melt. Yttrium has also been studied as a possible nodulizer. A recent development in ductile iron metallurgy is austempered ductile iron where the metallurgical structure is manipulated through a sophisticated heat treating process.