26 Sep,2023
Tip: Why cannot stainless steel be welded with carbon steel electrodes?
Why stainless steel cannot be welded with carbon steel electrodes is because doing so can cause intergranular corrosion in stainless steel.
What is intergranular corrosion?
Intergranular corrosion is a type of localized corrosion that extends inward along the boundaries between metal grains. Due to differences in chemical composition between the surface and interior of grains, as well as the presence of impurities or internal stresses at grain boundaries, the bonding between grains can be disrupted, greatly reducing the mechanical strength of the metal, deteriorating its mechanical properties, and being unable to withstand impact, it is a very dangerous form of corrosion.
Carbon is the main element causing intergranular corrosion, and the carbon content of carbon steel is usually higher than that of stainless steel. This is why welding stainless steel with carbon steel electrodes is prone to intergranular corrosion. Therefore, for stainless steel welding, low-carbon or even ultra-low-carbon stainless steel electrodes should be selected, such as Ao102, Ao132, Ao002, etc.
In addition, for important structures that require high impact toughness and crack resistance, acidic welding rods should not be used. The so-called acidic welding rod refers to a welding rod that contains a large amount of acidic oxides (such as silicon dioxide, titanium dioxide, etc.) in the coating.
This is because the oxides in the first acidic welding rod make it highly oxidizing, and at the same time, the weld metal has a high oxygen content, resulting in significant burning loss of alloy elements; The second acidic electrode coating contains a large amount of silicon dioxide, and a portion of silicon exists in the form of silicon oxide inclusions in the weld seam, resulting in poor mechanical properties of the weld seam, especially lower plasticity and impact toughness compared to alkaline electrodes; The third acidic electrode coating does not contain fluorite (CaF2) and has low dehydrogenation ability; The weld metal has a high hydrogen content, poor cold cracking resistance, and a low manganese content in the desulfurization element in the weld, resulting in poor desulfurization effect.
In summary, acidic welding rods should not be used for important welding structures, but rather alkaline welding rods with low oxygen content, high alloy transition coefficient, and low sulfur and hydrogen content in the weld metal should be used.
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