Carbon dioxide gas shielded welding (CO2 gas shielded welding) is a method of welding mainly conducted in an atmosphere of carbon dioxide gas, and is widely used in industry. It is one of the standard processes of automatic welding, and accounts for about 90% of the total world welding consumable expenditure. Different types of carbon dioxide gas shielded welding are according to the different welding properties of the welding current and the welding wires.
GBT 8110-87 is a national standard for carbon dioxide protective welding steel wires in China, established by the Ministry of Machinery Industry of the People’s Republic of China on 1987-06-01. This standard defines the requirements, test methods and quality grades of carbon dioxide protective welding steel wires used in carbon dioxide welding.
The main characteristics of welded steel wire can be characterized in terms of their chemical compositions, mechanical properties and weldability. The chemical composition of gas shielded welding steel wire should be close to the heat resisting steel of the same series; and so that the mechanical properties meet the requirements of the welding technology and economics. The mechanical properties of gas shielded welding produced by carbon dioxide welding steel wire are mainly determined by the welding current and the welding wire. The welding current is mainly related to the melting and deposition behavior of the welding wire, and the weldability is mainly determined by the mechanical properties of the deposited welds.
The requirement of the protective welding layer quality and deposit performance of carbon dioxide protective gas shielded welding wire is to ensure that the deposited weld has good fusion, low porosity and high mechanical strength, sufficient toughness, suitable welding speed and good welding performance. The welding quality and stability of carbon dioxide protective welding steel wire can be improved by means of controlling the chemical composition, surface characteristics and mechanical properties of the steel wire.
The chemical composition of carbon dioxide protective gas shielded welding steel wire shall be in conformity with the stipulated requirements. The chemical composition of the steel wire must meet the requirements of the base steel and the weldability requirements. The amount of deoxidizers in the steel wire shall be sufficient to ensure that there is no excessive oxidized inclusions in the deposited welds. The concentration of alloy elements in the steel wire should meet the specified range, in order to control the hardenability and prevent the body of the weld joint from cracking.
The surface characteristics of the carbon dioxide gas shielded welding steel wire has a great influence on the welding performance and welding quality. The surface of steel wire shall be clean and free from rust, slag and dirt. The surface oxide layer of the steel wire shall be removed and the surface of the steel wire shall remain smooth during feed, welding and storage.
The mechanical properties of the carbon dioxide gas shielded welding steel wire are mainly determined by the welding current and the welding wire. The welding current should be as small as possible, so that the maximum power intake of the electrode does not exceed the rated value of the welding machine, for otherwise high temperature would easily produce cracks in the welds due to a too large welding current. The welding wire should have suitable wire diameter and surface characteristics, so that the deposition performance of the electrode is good and the weld is full, tight and even. The mechanical properties of the deposited welds should meet the strength requirements of the materials and structures.
To sum up, according to GBT 8110-87, carbon dioxide protective welding steel wire can be characterized in terms of their chemical composition, mechanical properties and weldability. It is necessary to control the chemical composition, surface characteristics and mechanical properties of the steel wire in order to improve the welding quality and stability of the carbon dioxide protective welding.
