1. Consider physical properties, mechanical properties and chemical composition of weldments.
(1) In the welding of structural steels, the principle of equal strength is generally considered, and the welding materials which meet the mechanical properties of the joints are selected.
(2) For dissimilar steel welded joints between low-carbon steel and low-alloy steel, the welding material corresponding to the steel with lower strength grade is generally selected.
(3) For the welding of heat-resistant steel and stainless steel, besides considering the strength, the main chemical composition of the weld metal should be considered to be close to that of the base metal.
(4) When the harmful impurities such as carbon, sulfur and phosphorus are high in the chemical composition of the base metal, the welding material with strong crack resistance should be selected. Such as low hydrogen type welding materials.
2, consider the working conditions and performance of weldments:
(1) Under the condition of dynamic load and impact load, weldments have higher requirements for impact toughness and plasticity besides ensuring tensile strength and yield strength. Low hydrogen type solder should be used at this time.
(2) When welding in corrosive medium, it is necessary to distinguish the type of medium, concentration, working temperature and corrosion type (general corrosion, intergranular corrosion, stress corrosion, etc.), so as to select the appropriate stainless steel welding material.
(3) When welding parts are working under abrasive conditions, it is necessary to distinguish between general wear or impact wear, intermetallic wear or abrasive wear, wear at room temperature or wear at high temperature. It is also necessary to consider whether to work in corrosive medium so as to select suitable surfacing material.
(4) Welding materials which can guarantee the mechanical properties at low or high temperature should be selected for the weldments working at low temperature or high temperature.
3, consider the complexity and structural features of weldments, the type of welded joints and so on.
(1) The weldments with complex shapes or large thicknesses are prone to cracks because of the large internal stress produced by the cooling shrinkage of the weld metal. Therefore, welding materials with good crack resistance, such as low hydrogen electrode and high toughness electrode, must be used.
(2) For some joints with small groove, or joints with strict root penetration control, welding materials with greater penetration or penetration should be selected.
(3) When it is difficult to clean up some welding parts due to the limitation of conditions, it should be considered to select welding materials which are not sensitive to rust, oxide scale and oil stain reaction, such as acid electrode, so as to avoid porosity and other defects.
4. Consider the spatial location of weld:
Some welding materials are only suitable for one position of the welding, other positions of the welding effect is poor, and some welding materials are various positions can be welded, the selection should consider the characteristics of the welding position:
5. Considering welding conditions and operating environment:
(1) when there is no DC welding machine, AC and DC welding materials should be selected.
(2) Some steels (such as Pearlite Heat-resistant steel) need post-weld stress relief heat treatment, but can not be carried out due to the limitation of equipment conditions or its own structure, should choose different chemical composition of the base metal welding materials (such as austenitic stainless steel welding materials), can avoid post-weld heat treatment.
(3) reasonable welding materials should be selected according to the conditions of the construction site, such as field operation and welding working environment.
(4) Where both acidic and alkaline electrodes can be satisfied, acidic electrodes should be used as far as possible in view of the high requirements of alkaline electrodes for operation technology and construction preparation.
6, consider the economics of welding:
(1) in order to ensure the performance, we should try to choose cost-effective welding materials.
(2) For primary and secondary welds with different performance requirements, different welding materials can be used instead of one-sidedly pursuing the overall performance of the welding materials.
7. Consider welding efficiency:
For structures with large welding workload, high efficiency welding materials, such as welding wire, iron powder electrode and high efficiency stainless steel electrode, should be adopted when conditions permit.