The selection of welding rod shall be based on the chemical composition, mechanical properties, thickness and joint form of the material to be welded, the characteristics of the welding structure, the state of force and the conditions of use of the structure, on the premise of ensuring the safety and practicability of the welding structure. , Welding construction conditions and technical and economic benefits comprehensive examination, the selection of welding rod, if necessary, the need for weldability test.
First, the same kind of steel welding electrode selection points
1, consider the weld metal mechanical properties and chemical composition
For ordinary structural steel, usually require the strength of the weld metal and base metal, welding metal should be selected tensile strength equal to or slightly higher than the base metal welding rod. For alloy structural steel, it is also sometimes required that the alloy composition be the same as or close to the base metal. Welding structure in the rigid, high joint stress, weld cracks easily unfavorable circumstances, should consider the use of lower strength than the base metal welding rod. When the content of carbon, sulfur, phosphorus and other elements in the parent metal is high, cracks easily occur in the weld, alkaline low hydrogen type electrode with good crack resistance should be used.
2, consider the use of welding components performance and working conditions
To withstand the load and impact load weldment, in addition to meet the strength requirements, the main weld metal should ensure that the higher the impact toughness and plasticity, the choice of plastic, toughness indicators of the higher low hydrogen type electrode. Contact with the corrosive media welding, should be based on the nature of the medium and corrosion characteristics of stainless steel welding electrodes or other selection. In the high temperature, low temperature, wear-resistant or other special conditions of welding work, should be the appropriate choice of heat-resistant steel, low temperature steel, welding or other special purpose welding rod.
3, consider the welding structure and stress conditions
On the structure of complex shape, large rigid large welding parts, due to the welding process has a lot of internal stress, easy to crack the weld, should be used good alkaline cracking performance of low hydrogen electrode. On the force is not large, difficult to clean the welding parts clean weldment should be used on the rust, scale, oil is not sensitive to acidic electrodes. Welders that can not be flipped by the conditions should be selected for welding electrodes in all positions.
4, consider the construction conditions and economic benefits
In the case of product performance requirements to meet the conditions should be good acidity of the electrode. In narrow or poor ventilation conditions, should be used acidic or low-dust electrode. Welding large workload on the structure, the conditions should try to use high efficiency electrodes, such as iron powder electrode, high efficiency gravity electrode, or use the bottom electrode vertical electrode like special electrode to improve the welding productivity.
Second, dissimilar steel welding electrode selection points
1, different levels of carbon steel low alloy steel (or low alloy steel low alloy high strength steel)
The general requirements of weld metal or joint strength of not less than the minimum strength of the two kinds of metal to be welded, the choice of electrode deposited metal strength should be able to ensure the strength of the weld and joint is not less than the strength of 铡 base material strength, At the same time the plasticity of the weld metal and impact toughness should not be less than the higher strength and poor plastic 铡 base metal properties. Therefore, according to the strength of both the lower level of steel selection electrode. However, in order to prevent weld cracking, the welding process shall be determined by the steel grades with higher strength and poor weldability, including welding specifications, preheating temperature and post-weld heat treatment.
2, low alloy steel austenitic stainless steel
Should be in accordance with the chemical composition of the deposited metal to limit the value of the selected electrode, the general use of high chromium and nickel content, better plasticity and crack resistance Cr25-Ni13-type austenitic steel electrode to avoid brittle hardened Tissue-induced cracks. But should be less weldability of stainless steel to determine the welding process and specifications.
3, stainless steel composite plate
Should consider the grass-roots, multi-layer, transition layer welding requirements of the use of three different performance of the electrode. The grassroots (carbon steel or low alloy steel) welding, the choice of the corresponding intensity level of structural steel electrode; cladding directly with the corrosive media contact, the corresponding composition should be selected austenitic stainless steel electrode. The key is the transition layer (that is, the interface between the cladding layer and the base layer), we must consider the dilution of the matrix material should be selected Cr25-Ni13-type austenitic steel electrode with higher chromium and nickel content, good plasticity and crack resistance