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On the premise of ensuring the safety and feasibility of the welding structure, the selection of welding rod shall be carried out in accordance with the chemical composition, mechanical properties, plate thickness and joint form of the welded material, the characteristics of the welding structure, the stress state, the requirements of the structure use conditions on the weld performance, the welding construction conditions and the technical and economic benefits, and the welding test shall be carried out if necessary.

(1) Key points of electrode selection for dissimilar steel welding

① Different strength levels of carbon steel low alloy steel (or low alloy steel low alloy high strength steel)

Generally, the strength of weld metal or joint is required to be not less than the * * low strength of the two welded metals. The strength of the deposited metal of the selected electrode should be able to ensure that the strength of the weld and joint is not less than the strength of the base metal with lower strength. At the same time, the plasticity and impact toughness of the weld metal should not be less than the performance of the base metal with higher strength and poorer plasticity. Therefore, the welding rod can be selected according to the steel with lower strength level among the two. However, in order to prevent welding cracks, the welding process should be determined according to the steel grade with high strength and poor weldability, including welding specifications, preheating temperature and post-weld heat treatment.

② Stainless composite steel plate

Should consider the base layer, multi-layer, transition layer welding requirements to choose three different performance of the electrode. For the welding of the base layer (carbon steel or low alloy steel), the structural steel electrode with corresponding strength grade shall be selected; for the clad layer in direct contact with corrosive medium, the austenitic stainless steel electrode with corresponding composition shall be selected. The key is the welding of the transition layer (I. e. the interface between the multi-layer and the base layer), the dilution effect of the base material must be considered, and the Cr25-Ni13 austenitic steel electrode with high chromium and nickel content, good plasticity and crack resistance should be selected.

③ Low alloy steel austenitic stainless steel

The electrode should be selected according to the value of the chemical composition of the deposited metal. Generally, the Cr25-Ni13 austenitic steel electrode with high chromium and nickel content and good plasticity and crack resistance should be selected to avoid cracks caused by brittle hardening organization. However, the welding process and specifications shall be determined according to the stainless steel with poor weldability.

(2) Key points of electrode selection when welding the same kind of steel

① Consider the performance and working conditions of welded components

For weldments bearing load and impact load, in addition to meeting the strength requirements, the weld metal should be guaranteed to have high impact toughness and plasticity, and low hydrogen type electrodes with high plastic and toughness indicators can be selected. For weldments in contact with corrosive media, stainless steel electrodes or other corrosion-resistant electrodes shall be selected according to the nature and corrosion characteristics of the media. Welding parts working under high temperature, low temperature, wear resistance or other special conditions shall be made of corresponding heat-resistant steel, low temperature steel, surfacing or other special purpose electrodes.

② Consider the mechanical properties and chemical composition of weld metal

For ordinary structural steel, the weld metal and base metal are usually required to have equal strength, and the electrode with the tensile strength of the deposited metal equal to or slightly higher than the base metal should be selected. For alloy structural steel, the alloy composition is sometimes required to be the same as or close to the base metal. In the welding structure rigidity, joint stress is high, the weld is easy to produce cracks in the adverse circumstances, should consider the choice of lower than the base metal strength of the electrode. When the content of carbon, sulfur, phosphorus and other elements in the base metal is high, cracks are easy to occur in the weld, and the basic low hydrogen type electrode with good crack resistance should be selected.

③ Consider construction conditions and economic benefits

In the case of meeting the performance requirements of the product, the acid electrode with good processability should be selected. In the narrow or poor ventilation conditions of the occasion, should choose acid electrode or low dust electrode. For structures with large welding workload, high-efficiency welding rods, such as iron powder welding rods, high-efficiency gravity welding rods, etc., or * * welding rods such as vertical downward welding rods should be used when conditions permit, so as to improve welding productivity.

④ Consider welding structure characteristics and stress conditions

For thick and large welded parts with complex structure and large rigidity, due to the large internal stress generated during the welding process, it is easy to cause cracks in the weld, so alkaline low-hydrogen electrode with good crack resistance should be selected. For weldments with little stress and difficult to clean up welding parts, acid electrodes insensitive to rust, oxide skin and oil should be selected. For weldments that cannot be turned over due to conditions, electrodes suitable for all-position welding shall be selected.