WHY USE WROUGHT IRON?

To the naked eye there is no visible difference between forged bars of Wrought Iron & Mild Steel (its modern day corresponding) though Wrought Iron is not distinguished by its looks but by its working properties and its resistance to corrosion. Wrought Iron is softer to forge, as it is workable at a higher heat than Mild Steel making it more ‘malleable’ below the hammer. Though it is Wrought Iron’s superior weathering properties   that are most notable.

While Wrought Iron does, in common with all ferrous metals corrode in certain circumstances, (see maintenance), prove of its durability and long life expectancy is commonplace in our towns and countryside. Victorian town house railings – Wrought Iron two hundred years ancient. Vast showy gateways to eighteenth century fantastic houses – Wrought Iron three hundred years ancient. Stone cramps on Tudor bridges – Wrought Iron five hundred years ancient. The simple fact that so much Showy Wrought Ironwork survives, regularly with small or no maintenance, speaks volumes for the material.

Problems with the rapid corrosion of Mild Steel in comparison with Wrought Iron were well known by the beginning of the twentieth century and this prompted Matthew Truth, in USA to investigate. He concluded that the carbon in Steel is responsible for its corrodibility; leading to the theory that removing the carbon removes the problem of corrosion. His efforts to produce pure iron resulted, not in a metal which was proven to have any resistance to corrosion, but which was very tough and malleable and found favour in the emerging markets for mass-produced cold pressings; ARMCO iron.  No convincing prove was ever produced to back up claims of the non-corrodibility of pure iron and in fact Pure Iron manufacturers themselves make no claims to its corrosion resistance. In fact these same manufacturers offer other materials known as ‘Weathering Steel’ in Britain, or ‘Corten Steel’ in the USA, for which they do make such claims.  One of the chief uses for Pure Iron in today’s industry is as sacrificial anodes to protect steelwork tanks and ships as it has been found to corrode preferentially to mild steel.

Truth’s examination of puddled wrought iron and mild steel was a chemical analysis, which appears to have overlooked the presence of the slags. During the manufacturing process, wrought iron does not become molten, as do more highly refined metals, so that impurities are included in the matrix of the iron rather than being separated and disposed of.   At these high temperatures the impurities are turned to glass, and are commonly known as ’slag’ consisting of carbides and silicates which give Wrought Iron its fibrous structure; approximately 250,000 siliceous fibres appear in each cross-sectional square inch of excellent quality wrought iron. A specific test is required to find out slag of which Wrought Iron contains up to 5% though it is this slag which provides wrought iron its corrosion resistant properties.