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Forge welding (FOW), also called fire welding, is a solid-state welding process that joins two pieces of metal by heating them to a high temperature and then them together. It may also consist of heating and forcing the metals together with presses or other means, creating enough pressure to cause plastic deformation at the weld surfaces. Production Technology (Manufacturing Processes): Manufacturing Processes by P C Sharma -- S. Chand & Co. 2014 Page 369 The process, although challenging, has been a method of joining metals used since ancient times and is a staple of traditional . Forge welding is versatile, being able to join a host of similar and dissimilar metals. With the invention of electrical welding and gas welding methods during the Industrial Revolution, manual forge-welding has been largely replaced, although automated forge-welding is a common manufacturing process.
Welding processes can generally be grouped into two categories: melting and diffusion welding. Fusion welding involves localized melting of the metals at the weld interfaces, and is common in electric or gas welding techniques. This requires temperatures much higher than the melting point of the metal in order to cause localized melting before the heat can thermally conduct away from the weld, and often a filler metal is used to keep the weld from segregating due to the high surface tension. Diffusion welding consists of joining the metals without melting them, welding the surfaces together while in the solid state. Manual of Engineering Drawing: Technical Product Specification and documentation to British and International Standards by Colin H. Simmons, Dennis E. Maguire -- Elsevier 2009 Page 233
In diffusion welding, the heat source is often lower than the melting point of the metal, allowing more even heat-distribution thus reducing at the weld. In this method a filler metal is typically not used, but the weld occurs directly between the metals at the weld interface. This includes methods such as cold welding, explosion welding, and forge welding. Unlike other diffusion methods, in forge welding the metals are heated to a high temperature before forcing them together, usually resulting in greater plasticity at the weld surfaces. This generally makes forge welding more versatile than cold-diffusion techniques, which are usually performed on soft metals like copper or aluminum. Manual of Engineering Drawing: Technical Product Specification and documentation to British and International Standards by Colin H. Simmons, Dennis E. Maguire -- Elsevier 2009 Page 233
In forge welding, the entire welding areas are heated evenly. Forge welding can be used for a much wider range of harder metals and alloys, like steel and titanium. Manual of Engineering Drawing: Technical Product Specification and documentation to British and International Standards by Colin H. Simmons, Dennis E. Maguire -- Elsevier 2009 Page 233
The act of welding (joining two solid parts through diffusion) began with iron. The first welding process was forge welding, which started when humans learned to smelting iron from iron ore; most likely in Anatolia (Turkey) around 1800 BC. Ancient people could not create temperatures high enough to melt iron fully, so the bloomery process that was used for smelting iron produced a lump (bloom) of iron grains sintering together with small amounts of slag and other impurities, referred to as sponge iron because of its porosity.
After smelting, the sponge iron needed to be heated above the welding temperature and hammered, or "wrought." This squeezed out air pockets and melted slag, bringing the iron grains into close contact to form a solid block (billet).
Many items made of wrought iron have been found by archeologists, that show evidence of forge welding, which date from before 1000 BC. Because iron was typically made in small amounts, any large object, such as the Delhi Pillar, needed to be forge welded out of smaller billets. Welding by Richard Lofting -- Crowood Press 2013 Page 1 History of Humanity: From the seventh century B.C. to the seventh century A.D. by Sigfried J. de Laet, Joachim Herrmann -- Routledge 1996 Page 36--37
Forge welding grew from a trial-and-error method, becoming more refined over the centuries. Introduction to Welding and Brazing by R. L. Apps, D. R. Milner -- Pergamon Press 1994 Page xi Due to the poor quality of ancient metals, it was commonly employed in making composite steels, by joining high-carbon steels, that would resist deformation but break easily, with low-carbon steels, which resist fracture but bend too easily, creating an object with greater toughness and strength than could be produced with a single alloy. This method of pattern welding first appeared around 700 BC, and was primarily used for making weapons such as swords; the most widely known examples being Damascus steel, Japanese and Merovingian.
Titanium alloys are commonly forge welded. Because of titanium's tendency to absorb oxygen when molten, the solid-state, diffusion bond of a forge weld is often stronger than a fusion weld in which the metal is liquefied. Titanium: A Technical Guide, second edition by Matthew J. Donachie -- ASM International 2000 Page 76
Forge welding between similar materials is caused by solid-state diffusion. This results in a weld that consists of only the welded materials without any fillers or bridging materials. Forge welding between dissimilar materials is caused by the formation of a lower melting temperature eutectic between the materials. Due to this the weld is often stronger than the individual metals.
When Power hammer were developed, forge welding could be accomplished by heating the metal, and then placing it between the mechanized hammer and the anvil. Originally powered by , modern mechanical-hammers can also be operated by compressed air, electricity, steam, gas engines, and many other ways. Another method is forge welding with a die, whereby the pieces of metal are heated and then forced into a die which both provides the pressure for the weld and keeps the joint at the finished shape. Roll welding is another forge welding process, where the heated metals are overlapped and passed through rollers at high pressures to create the weld. Metal Casting and Joining by K. C. John -- PHI Learning 2015 Page 392 New Edge of the Anvil: A Resource Book for the Blacksmith by Jack Andrews --Shipjack Press 1994 Page 93--96
Modern forge-welding is often automated, using computers, machines, and sophisticated to produce a variety of products from a number of various alloys. Joining: Understanding the Basics by Flake C. Campbell ASM International 2011 Page 144--145 For example, steel pipe is often forge-welded during the manufacturing process. Flat stock is heated and fed through specially-shaped rollers that both form the steel into a tube and simultaneously provide the pressure to weld the edges into a continuous seam. Welding Fabrication & Repair: Questions and Answers by Frank M. Marlow -- Industrial press 2002 Page 43
Diffusion bonding is a common method for forge welding titanium alloys in the aerospace industry. In this process the metal is heated while in a press or die. Beyond a specific critical-temperature, which varies depending on the alloy, the impurities burn out and the surfaces are forced together. Titanium: A Technical Guide, second edition by Matthew J. Donachie -- ASM International 2000 Page 76
Other methods include flash welding and percussion welding. These are resistance forge-welding techniques where the press or die is electrified, passing high current through the alloy to create the heat for the weld. Titanium: A Technical Guide, second edition by Matthew J. Donachie -- ASM International 2000 Page 76 Shielded active-gas forge-welding is a process of forge welding in an oxygen-reactive environment, to burn out oxides, using hydrogen gas and induction heating. Subsea Pipeline Engineering by Andrew Clennel Palmer, Roger A. King -- PennWell 2008 Page 158
A primary requirement for forge welding is that both weld surfaces need to be heated to the same temperature and welded before they cool too much. When steel reaches the proper temperature, it begins to weld very readily, so a thin rod or nail heated to the same temperature will tend to stick at first contact, requiring it to be bent or twisted loose.
Care must be taken to avoid overheating the metal to the point that it gives off Ember from rapid oxidation (burning), or else the weld will be poor and brittle. New Edge of the Anvil: A Resource Book for the Blacksmith by Jack Andrews --Shipjack Press 1994 Page 93--96
To produce the right amount of hardness in the finished product, the smith generally begins with steel that has a carbon content that is higher than desired. In ancient times, forging often began with steel that had a carbon content much too high for normal use. Most ancient forge-welding began with hypereutectoid steel, containing a carbon content sometimes well above 1.0%. Hypereutectoid steels are typically too brittle to be useful in a finished product, but by the end of forging the steel typically had a high carbon-content ranging from 0.8% (eutectoid tool-steel) to 0.5% (hypoeutectoid spring-steel). The History of Hardening by Hans Berns -- Harterei Gerster AG 2013 Page 48--49
One of the most famous applications of forge welding involves the production of pattern welding blades. During this process a smith repeatedly draws out a billet of steel, folds it back and welds it upon itself. Another application was the manufacture of shotgun barrels. Metal wire was spooled onto a mandrel, and then forged into a barrel that was thin, uniform, and strong. In some cases the forge-welded objects are acid-etching to expose the underlying pattern of metal, which is unique to each item and provides aesthetic appeal.
Despite its diversity, forge welding had many limitations. A primary limitation was the size of objects that could be forge welded. Larger objects required a bigger heat source, and size reduced the ability to manually weld it together before it cooled too much. Welding large items like steel plate or girders was typically not possible, or at least highly impractical, until the invention of fusion welding, requiring them to be riveted instead. In some cases, fusion welding produced a much stronger weld, such as in the construction of boilers.
The oldest flux used for forge welding was fine silica sand. The iron or steel would be heated in a reducing environment within the coals of the forge. Devoid of oxygen, the metal forms a layer of iron-oxide called wüstite on its surface. When the metal is hot enough, but below the welding temperature, the smith sprinkles some sand onto the metal. The silicon in the sand reacts with the wustite to form fayalite, which melts just below the welding temperature. This produced a very effective flux which helped to make a strong weld. Iron and Steel in Ancient Times By Vagn Fabritius Buchwald -- Det Kongelige Danske Videnskabernes Selskab 2005 Page 65
Early examples of flux used different combinations and various amounts of iron fillings, borax, sal ammoniac, balsam of copaiba, cyanide of potash, and phosphate. The 1920 edition of Scientific American book of facts and formulae indicates a frequently offered trade secret as using copperas, saltpeter, common salt, black oxide of manganese, prussiate of potash, and "nice welding sand" (silicate).
''The History of Hardening'' by Hans Berns -- Harterei Gerster AG 2013 Page 48--49
''A History of Metallography'' by Cyril Stanley Smith -- MIT Press 1960 Page 3--5
This process was also common in the manufacture of tools, from wrought-iron with steel edges to iron with steel cutting surfaces. name = Berns/>
Materials
Many metals can be forge welded, with the most common being both high and low-. Iron and even some hypoeutectic can be forge welded. Some can also be forge welded. Principles of Welding: Processes, Physics, Chemistry, and Metallurgy by Robert W. Messler, Jr. -- Wiley VCH 2008 Page 102 Metals such as copper, bronze and brass do not forge weld readily. Although it is possible to forge weld copper-based , it is often with great difficulty due to copper's tendency to absorb oxygen during the heating. CDA Publication Issue 12 by the Copper Development Association -- CDA 1951 Page 40 Copper and its alloys are usually better joined with cold welding, explosion welding, or other pressure-welding techniques. With iron or steel, the presence of even small amounts of copper severely reduces the alloy's ability to forge weld. Alloying: Understanding the Basics by Joseph R. Davis -- ASM International 2001 Page 139 Joining of Materials and Structures: From Pragmatic Process to Enabling by Robert W. Messler -- Elsevier 2004 Page 333
Processes
The most well-known and oldest forge-welding process is the manual-hammering method. Manual hammering is done by heating the metal to the proper temperature, coating with flux, overlapping the weld surfaces, and then striking the joint repeatedly with a hand-held hammer. The joint is often formed to allow space for the flux to flow out, by beveling or rounding the surfaces slightly, and hammered in a successively outward fashion to squeeze the flux out. The hammer blows are typically not as hard as those used for shaping, preventing the flux from being blasted out of the joint at the first blow.
Temperature
Iron, different steels, and even cast-iron can be welded to each other, provided that their carbon content is close enough that the welding ranges overlap. Pure iron can be welded when nearly white hot; between and . Steel with a carbon content of 2.0% can be welded when orangish-yellow, between and . Common steel, between 0.2 and 0.8% carbon, is typically welded at a bright yellow heat. New Edge of the Anvil: A Resource Book for the Blacksmith by Jack Andrews --Shipjack Press 1994 Page 93--96
Decarburization
When steel is heated to an austenizing temperature, the carbon begins to diffuse through the iron. The higher the temperature; the greater the rate of diffusion. At such high temperatures, carbon readily combines with oxygen to form carbon dioxide, so the carbon can easily diffuse out of the steel and into the surrounding air. By the end of a blacksmithing job, the steel will be of a lower carbon content than it was prior to heating. Therefore, most blacksmithing operations are done as quickly as possible to reduce decarburization, preventing the steel from becoming too soft.
Applications
Forge welding has been used throughout its history for making most any items out of steel and iron. It has been used in everything from the manufacture of tools, farming implements, and cookware to the manufacture of fences, gates, and prison cells. In the early Industrial Revolution, it was commonly used in the manufacture of boilers and pressure vessels, until the introduction of fusion welding. It was commonly used through the Middle Ages for producing armor and weapons.
Flux
Forge welding requires the weld surfaces to be extremely clean or the metal will not join properly, if at all. Oxides tend to form on the surface while impurities like phosphorus and sulfur tend to migrate to the surface. Often a flux is used to keep the welding surfaces from oxidizing, which would produce a poor quality weld, and to extract other impurities from the metal. The flux mixes with the oxides that form and lowers the melting temperature and the viscosity of the oxides. This enables the oxides to flow out of the joint when the two pieces are beaten together. A simple flux can be made from borax, sometimes with the addition of powdered iron-filings. Bladesmithing with Murray Carter: Modern Application of Traditional Techniques by Murray Carter -- F+W Media 2011 Page 40
See also
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