Forge welding - it is a process of permanently joining heated pieces of metal using external pressure. It is also called forge welding. Steel, when heated to certain temperatures, becomes doughy. Pieces of such steel, tightly pressed together, weld quite well.
This technology has been known since ancient times.. For making spears and swords, as well as sickles and scythes, ancient craftsmen used small amounts of valuable and rare high carbon steel to make a sharp point or blade, and then insert it into softer and cheaper iron. Then all this was heated to a high temperature and carefully hammered until a single whole product was obtained..
Ancient iron, even before the Bessemer process, called wrought iron, because it was obtained by forging, that is, essentially the same forge welding, from several small pieces of so-called puddling iron.
Until recently, forge welding was widely used in rural and collective farm forges for the repair of agricultural machinery..
Forge butt welding, overlap and girth
The ends to be welded are thickened in order to, in order to bring the cross-section to the specified size of the ring cross-section during forging after welding. Most often, forge welding is performed butt-weld, overlap or girth (picture 1). In all cases, the ends have a convex shape. This is necessary in order, so that the slag, which is formed during welding, squeezed out.
Forge welding is used, eg, in the manufacture, rings (drawings 2 and 3).
Other methods of forge welding are split welding and welding using so-called checkers..
Forge Split Welding
Split welding is used, when it is necessary to make from strip steel, eg, steel tires for cart. Before welding, the ends of the strip are pulled back and cut (picture 3). Then the ends are connected with overlap, heated to welding temperature and forged. Due to the large surface of the joint, such welding is quite strong..
Forge welding with checkers
Stick welding is used to connect large parts, usually rings. The ends of the part are forged with an inclination of 30-40º (picture 5). Insert parts - checkers are forged from the same steel and with the same inclination. The place of welding is heated to the welding temperature and forged under a hammer.
Forge welding temperature of steel
For forge welding, the part is heated to a temperature, close to melting point: steel containing 0,1 % carbon - up to 1400-1450 ºS, steel with 0,4 % carbon - up to 1320-1370 ºS. It is important to determine these temperatures as accurately as possible., so insufficient heating will lead to lack of fusion, and excessive heating - to burnout or even melting.
Experienced blacksmiths detect the right temperature by the color of the heat: near 1300 ºС - bright yellow color, and about 1400 ºС - already bright white. When the desired temperature is reached, you must immediately start forging., so prolonged exposure can lead to overheating of steel.
The use of flux in forge welding
Heating the steel causes it to oxidize and it becomes scaled., which interferes with welding. Therefore, the ends to be welded are usually sprinkled with flux.. Quartz sand mixed with borax and table salt is used as a flux in rural smithies.. At high temperatures, the flux combines with the scale and forms a slag layer, which protects the welding surface from oxidation. With low carbon content in steel fluxes are often not used, since the melting point of such steel is higher, than its oxide.
Before starting welding, the slag is removed with a steel brush., and the remnants are squeezed out during subsequent forging. For good welding, the welded place is well forged with hammer blows.
Steel for blacksmith forging
Usually only mild steels are forged.. Steel welds very well with carbon content up to 0,2 %, satisfactory - steel with carbon content up to 0,5 %. Other steels are welded using conventional welding methods - electric or gas.
1) A. A. Shapiro Rural Blacksmith's Handbook, 1967.
2) J. DeLaRonde Blacksmithing: Basics for Homestead, 2008