Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which gives it a "grain" resembling wood that is visible when it is etched or bent to the point of failure. Wrought iron is tough, malleable, ductile, corrosion resistant, and easily welded.
Before the development of effective methods of steelmaking and the availability of large quantities of steel, wrought iron was the most common form of malleable iron. It was given the name wrought because it was hammered, rolled or otherwise worked while hot enough to expel molten slag. The modern functional equivalent of wrought iron is mild steel, also called low-carbon steel. Neither wrought iron nor mild steel contain enough carbon to be hardenable by heating and quenching.
Wrought iron is highly refined, with a small amount of slag forged out into fibres. It consists of around 99.4% iron by mass. The presence of slag is beneficial for blacksmithing operations, and gives the material its unique fibrous structure. The silicate filaments of the slag also protect the iron from corrosion and diminish the effect of fatigue caused by shock and vibration.
52100 is a relatively simple steel with 1% carbon and 1.5% chromium, and small amounts of Mn and Si. 52100 steel has been in use since at least 1905 . It was developed for use in bearings. High carbon steels (0.8-1.0% C) were primarily used until the late 1800’s or early 1900’s, after which chromium additions to bearing steels were being made. 1% Cr steels have been used in bearings since at least 1903. These early chromium-alloyed bearing steels were produced in Germany by Fichtel & Sachs and by Deutsche Waffen- und Munitionsfabrik. French-produced chromium steels were also used in bearings in a similar time period. 52100 continues to be the most used bearing steel, so the steel design has certainly stood the test of time.