The receiver, not the trigger guard and backstrap.
Malleable iron or wrought iron for the receivers? I thought the receivers were forged wrought iron, not cast malleable iron.
BP 1st gen Colt's single-action Army revolvers used a malleable iron frame construction.
Malleable iron was a common material for the frames or receivers of most firearms during that era due to its strength and ability to be easily cast, forged and then machined, making it suitable for early production processes. True steel frames in Colt revolvers were introduced much later in the manufacturing process, becoming standard among most firearm makers in the early 20th century.
Cast iron is a class of brittle iron–carbon alloys with a carbon content of more than 2% and silicon content around 1–3%. Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its carbon appears: while cast iron has its carbon combined into the iron carbide compound cementite, which is very hard, but brittle, as it allows cracks to pass straight through.
Malleable iron is cast as white iron, the structure being a metastable carbide in a pearlitic matrix. Through an annealing heat treatment, the brittle structure as first cast is transformed into the malleable form. Carbon agglomerates into small roughly spherical aggregates of graphite, leaving a matrix of ferrite or pearlite according to the exact heat treatment used.
Malleable iron was used as early as the 4th century BCE, and archaeologists have found malleable iron artifacts made in China between 4th century BCE and 9th century CE. By the Tang dynasty, the use of malleable iron in China waned, although there are malleable iron artifacts dating to the 9th century. Malleable iron is first mentioned in England in a patent dating to the 1670s. Réaumur conducted extensive research on malleable iron in 1720. He discovered that iron castings which were too hard to be worked could be softened by packing them into iron ore or hammer slag and exposing them to extreme high temperature for a number of days. Creating malleable iron began in the United States in 1826 when Seth Boyden started a foundry for the production of harness hardware and other small castings.
Three basic types of malleable iron are recognized within the casting industry: blackheart, whiteheart, and pearlitic. malleable iron still has a legitimate place in the design engineer's toolbox. Malleable iron is a good choice for small castings or castings with thin cross sections (less than 0.25-inch, 6.35 mm).
Malleable iron also exhibits better fracture toughness properties in low temperature environments than other nodular irons, due to its lower silicon content. The ductile to brittle transition temperature is lower than many other ductile iron alloys. It is still often used for small castings requiring good tensile strength and the ability to flex without breaking (ductility). Uses include electrical fittings, hand tools, pipe fittings, washers, brackets, fence fittings, power line hardware, farm equipment, mining hardware, and machine parts.
The word "wrought" is an archaic past participle of the verb "to work", and so "wrought iron" literally means "worked iron". Wrought iron is a general term for the commodity, but is also used more specifically for rough finished iron goods, as usually manufactured by a blacksmith. It was used in that narrower sense in British Customs records, such manufactured iron was subject to a higher rate of duty than what might be called "unwrought" iron. Cast iron, unlike wrought iron, is brittle and cannot be worked either hot or cold.
Wrought iron is now accepted as a form of commercial iron containing less than 0.10% of carbon, less than 0.25% of impurities total of sulfur, phosphorus, silicon and manganese, and less than 2% slag by weight.
Wrought iron contains approximately 250,000 slag inclusions, or stringers, per square inch, giving it properties not found in other forms of ferrous or cast metal. A fresh fracture shows a clear bluish color with a high silky luster and fibrous appearance.
Wrought iron also lacks the carbon content necessary for hardening through heat treatment, Wrought iron can be melted and cast; however, the product is no longer wrought iron, since the slag stringers characteristic of wrought iron disappear on melting, so the product resembles impure, cast, Bessemer steel. There is no engineering advantage to melting and casting wrought iron, as compared to using cast iron or steel, both of which are cheaper.
For several years after the introduction of the Bessemer process and open hearth steel, there were different opinions as to what differentiated iron from steel; some believed it was the chemical composition and others that it was whether the iron heated sufficiently to melt and "fuse". Fusion eventually became generally accepted as relatively more important than composition below a given low carbon concentration. Another difference is that malleable iron and steel can be surface and core hardened by heat treating.
In historical contexts (pre-20th century), some early gun components, mostly barrels, were made from wrought iron. This was before modern steel alloys were widely available and understood. Early frames and receivers were often made of malleable iron (a form of cast iron that was heat-treated to make it more malleable). However, these materials were intended for lower-pressure black powder loads. The transition to steel for receivers did not fully occur until the early 1900s to accommodate the higher pressures of smokeless powder.
The use and demand for wrought iron reached its peak in the 1860s, being in high demand for ironclad warships and railway use. However, as advances in ferrous metallurgy improved the quality of malleable iron and steel, and as the Bessemer process and the Siemens–Martin process made mild steel and malleable iron much cheaper to produce, the use of wrought iron declined.
By the late 19th century, when metallurgists were finally able to better understand what properties and processes made good iron, iron in most use and in steam engines was being displaced by steel, whilst the old cylindrical boilers with fire tubes were displaced by inherently safer water tube boilers.
