Autogenous welding is applied to welds which are made by heating metals to such a temperature that they will fuse together on contact, without the application of pressure. The difference between forge welding and autogenous welding lies mainly in the difference in the temperature of the metals. In the autogenous weld, the metal is heated to a state of fluidity, and the two pieces flow together. This name is also applied to the process of adding molten metal to other metal pieces, thus building up or filling defects in the latter. There are different methods of autogenous welding - by the electric arc, by the oxyacety-lene flame, by the thermit method.