The electrode is composed of two parts: the welding core and the coating. The electrode is applied uniformly and centrally to the metal core by applying coating (coating) to the core. Different types of electrodes, welding core is also different. The welding core is the metal core of the electrode. To ensure the quality and performance of the weld, there are strict regulations on the content of various metal elements in the welding core, especially on the content of harmful impurities (such as sulfur, phosphorus, etc.), there should be strict restrictions, which is better than the base material. The composition of the weld core directly affects the composition and performance of the weld metal, so the harmful elements in the weld core should be minimized.

Welding carbon steel and low alloy steel welding core, generally use low carbon steel as the welding core, and filled with manganese, silicon, chromium, nickel and other components (see the welding wire national standard GB1300-77). The reason for the use of low carbon is on the one hand, when the carbon content is low, the steel wire plasticity is good, the welding wire drawing is relatively easy, on the other hand, it can reduce the reducing gas CO content, reduce splash or porosity, and increase the temperature of the weld metal solidification, which is beneficial to the over-head position welding. The addition of other alloying elements is mainly to ensure the comprehensive mechanical properties of the weld, and also has a certain effect on the welding process performance and the removal of impurities.

High alloy steel and aluminum, copper, cast iron and other metal materials, in addition to the requirements of the welding core composition like the metal to be welded, the content of impurities should also be controlled, and some specific alloying elements are often added according to the process requirements.