Basic principles for selecting electrodes

1) Equal strength principle

Generally used for welding low carbon steel and low alloy steel. For workpieces or structures subjected to static or general loads, electrodes with the same tensile strength as the base metal are usually used. This is the principle of equal strength. For example, welding 20, Q235 and other low carbon steel or steel with tensile strength of about 400 MPa can use E43 series welding rod. For welding steel with 16Mn, 16Mng and other tensile strengths in the range of 500MPa, E50 series welding rods are used (1MPa is equal to 10kg force).

Some people think that it is wrong to use a welding rod with high tensile strength to weld materials with low tensile strength. The concept of steel with high tensile strength is generally poor, and the tensile strength of the weld metal is purely pursued. It reduces its plasticity and is often not necessarily beneficial.

2) Principle of the same component

Generally used for welding metal materials such as heat-resistant steel and stainless steel. Welding workpieces or structures working in special environments, such as abrasion resistance, corrosion resistance, and high mechanical properties at high or low temperatures, shall be selected to ensure that the properties of the deposited metal are similar or similar to those of the parent metal. This is the principle of equality. For welding stainless steel, stainless steel welding rod should be used; when welding heat-resistant steel, heat-resistant steel welding rod should be used.

3) Conditional principle

   Choose the most according to the working conditions and characteristics of the workpiece or welded structure. For example, for welding workpieces that need to withstand dynamic loads or impacts on tea, low-hydrogen alkaline electrodes with high impact toughness of deposited metal should be used. Conversely, when welding the general structure, an acid electrode should be used. Although the welding site should also consider the power supply situation of the construction site, site equipment conditions, economy and welding efficiency, but this is a relatively minor issue and should be decided according to the actual situation.

4) Principle of crack resistance

Use a crack-resistant alkaline electrode to avoid cracks in the joint during welding and use. It is generally used for welding structures with high welding rigidity, complex shape and dynamic load during use.

5) Anti-porosity principle

Due to the limitation of welding process conditions, such as oil stains and rust on the joint parts of the weldment, it is necessary to use an acid electrode with strong resistance to pores, so as to prevent gas from staying in the weld during the welding process and forming pores.

6) Low cost principle

Under the premise of meeting the requirements of use, try to select the electrode with good process performance, low cost and high efficiency.

7) The principle of equal resilience

That is, the weld metal and the base material are tough or similar, because in practice, the fear of the welded structure is mostly not due to insufficient strength, but insufficient toughness. Therefore, the strength of the electrode is slightly lower than that of the base metal, and the toughness is the same or similar. This is also the low toughness of high-strength steel welding.