How to choose suitable welding rods

Selection principles

The selection of welding rods must ensure the safety and feasibility of the welding structure. After comprehensive examination of the chemical composition, mechanical properties, plate thickness and joint form of the welded materials, welding structure characteristics, stress state, structural use conditions and weld performance requirements, welding construction conditions and technical and economic benefits, welding rods should be selected in a targeted manner. If necessary, weldability tests should be carried out.

Selection points

① Consider the mechanical properties and chemical composition of the weld metal. For ordinary structural steel, the weld metal is usually required to have the same strength as the parent material. Welding rods with a tensile strength equal to or slightly higher than the parent material should be selected. For alloy structural steel, the alloy composition is sometimes required to be the same or close to that of the parent material. In unfavorable conditions where the welded structure is rigid, the joint stress is high, and the weld is prone to cracks, welding rods with lower strength than the parent material should be considered. When the content of carbon, sulfur, phosphorus and other elements in the parent material is high, cracks are likely to occur in the weld. Alkaline low-hydrogen welding rods with good crack resistance should be selected.
② Consider the performance and working conditions of welded components. For weldments that bear loads and impact loads, in addition to meeting the strength requirements, the weld metal should be guaranteed to have high impact toughness and plasticity. Low-hydrogen electrodes with high plasticity and toughness indexes can be selected. For weldments that contact corrosive media, stainless steel electrodes or other corrosion-resistant electrodes should be selected according to the properties of the medium and the corrosion characteristics. For weldments working under high temperature, low temperature, wear resistance or other special conditions, corresponding heat-resistant steel, low-temperature steel, surfacing or other special-purpose electrodes should be selected.
③ Consider the characteristics of welding structure and stress conditions. For thick and large welded parts with complex structural shapes and high rigidity, due to the large internal stress generated during welding, it is easy to cause cracks in the weld. Alkaline low-hydrogen electrodes with good crack resistance should be selected. For weldments with low stress and difficult to clean welding parts, acidic electrodes that are not sensitive to rust, scale and oil should be selected. For weldments that cannot be turned over due to conditions, electrodes suitable for all-position welding should be selected.
④ Consider construction conditions and economic benefits. Under the condition of meeting the performance requirements of the product, acidic electrodes with good processability should be selected. In narrow or poorly ventilated places, acidic electrodes or low-dust electrodes should be used. For structures with large welding workload, high-efficiency electrodes should be used as much as possible, such as iron powder electrodes, high-efficiency gravity electrodes, etc., or special electrodes such as bottom electrodes and vertical downward electrodes should be used to improve welding productivity.