Basic principles of welding material selection
1. Consider the physical properties, mechanical properties and chemical composition of the weldment materials:
(1) For welding of structural steels, the principle of equal strength is generally considered, and a welding material that meets the mechanical properties of the joint is selected.
(2) For dissimilar steel welding joints between low-carbon steel and low-alloy steel, welding materials corresponding to steels with lower strength grades are generally selected.
(3) For the welding of heat-resistant steel and stainless steel, in addition to considering the strength, it is also necessary to consider that the main chemical composition of the weld metal is close to the chemical composition of the base metal.
(4) When harmful impurities such as carbon, sulfur, and phosphorus are high in the chemical composition of the base metal, a welding material with strong crack resistance should be selected. Such as low hydrogen welding materials.
2. Consider the working conditions and performance of the weldment:
(1) In the case of welding parts under dynamic and impact loads, in addition to ensuring tensile strength and yield strength, there are higher requirements for impact toughness and plasticity. At this time, low-hydrogen welding materials should be selected.
(2) When the weldment works in corrosive medium, it is necessary to distinguish the type, concentration, working temperature and type of corrosion (general corrosion, intergranular corrosion, stress corrosion, etc.) of the medium, so as to select the appropriate stainless steel welding material.
(3) When the weldment works under abrasion conditions, it is necessary to distinguish between general wear or impact wear, intermetal wear or abrasive wear, wear at normal temperature or wear at high temperature. Consideration should also be given to working in corrosive media to select the appropriate surfacing material.
(4) Weldments that work at low or high temperature should be selected from welding consumables that can guarantee the mechanical properties at low or high temperature.
3. Consider the complexity and structural characteristics of the weldment, the type of welding joints, etc .:
(1) Weldments with complicated shapes or large thicknesses are prone to cracks due to the large internal stress generated by the weld metal during cooling and shrinking. Therefore, it is necessary to use welding materials with good crack resistance, such as low hydrogen electrode and high toughness electrode.
(2) For some joints with small bevels or joints with strict control of root penetration, welding consumables with greater penetration or penetration capacity should be selected.
(3) When it is difficult to clean some welding parts due to restrictions, we should consider using welding materials that are not sensitive to rust, scale and oil pollution, such as acid welding electrodes, so as to avoid defects such as porosity.
4. Consider the spatial position of the weld:
Some welding materials are only suitable for welding at one position, and the results are poor when welding at other positions. Some welding materials can be welded in various positions. When selecting, consider the characteristics of the welding position:
5. Consider the welding working conditions and operating environment:
(1) Where there is no DC welding machine, AC and DC welding materials should be used.
(2) Certain steel materials (such as pearlite heat-resistant steel) need to be subjected to post-weld stress relief heat treatment, but cannot be carried out due to equipment conditions or their own structural limitations. Austenitic stainless steel welding materials), which can be exempted from post-weld heat treatment.
(3) Welding materials shall be reasonably selected according to the construction site conditions, such as field operation and welding work environment.
(4) Where both acid and alkaline electrodes can be satisfied, in view of the high requirements for operating technology and construction preparation of alkaline electrodes, acid electrodes should be used as much as possible.
6. Consider the economics of welding:
(1) On the premise of ensuring the use performance, try to choose a cost-effective welding consumable.
(2) Different welding materials can be used for the primary and secondary welds with different performance requirements. Do not pursue the comprehensive performance of the welding material one-sidedly.
7. Consider welding efficiency:
For structures with heavy welding workload, high-efficiency welding materials should be used as much as possible, such as welding wire, iron powder electrodes, high-efficiency stainless steel electrodes, etc.
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