Why can't stainless steel be welded with carbon steel electrode

Why stainless steel can't be welded with carbon steel electrode is because it will cause intergranular corrosion of stainless steel. What is intergranular corrosion? It is a kind of local corrosion. The carbon content of stainless steel is too much, and the carbon expands faster than chromium along the stainless steel grains, and internal expansion towards the stainless steel grains, and forms chromium carbide compound at the grain boundary with chromium. The chromium content near the grain boundary drops sharply, forming a chromium-poor area, which loses its corrosion resistance under the action of corrosive medium, resulting in intergranular corrosion. The intergranular corrosion greatly reduces the mechanical strength and mechanical properties of stainless steel, and makes it unable to bear the gentle knocking, which is a very dangerous corrosion type. It is carbon that corrodes stainless steel intergranular. In general, carbon steel has higher carbon content than stainless steel, which is the reason why intergranular corrosion easily occurs when stainless steel is welded with carbon steel electrode. Therefore, low-carbon or even ultra-low-carbon stainless steel electrodes should be selected for stainless steel welding. On the other hand, acid electrode should not be used for important structures with high requirements on impact toughness and crack resistance. The so-called acid electrode refers to the electrode whose coating contains a large amount of acid oxides (such as silicon dioxide, titanium dioxide, etc.). This is mainly because: (1) the oxide in the acid electrode makes it more oxidizing, and at the same time, the weld metal contains more oxygen, which makes the alloy elements burn more; ② The coating of acid electrode contains more silicon dioxide, and a part of silicon exists in the weld in the form of silicon oxide inclusions, which leads to poor mechanical properties of the weld, especially lower plasticity and impact toughness than that of alkaline electrode; ③ The coating of acid electrode does not contain fluorite (CaF2), and its dehydrogenation ability is low. The weld metal has high hydrogen content and poor cold crack resistance, and the desulfurization element manganese content in the weld is low, and the desulfurization effect is poor; Steel bar welding of stainless steel water tank is widely used in construction engineering, just like binding joint. Flash butt welding, resistance spot welding, arc welding, electroslag pressure welding and submerged arc pressure welding are generally used in the welding process of hot rolled steel bars. Flash butt welding or arc welding is generally used for steel bar joints with a diameter of 10 mm; Electroslag pressure welding should be adopted for longitudinal reinforcement in reinforced concrete structures such as structures, chimneys, silos and dams; Resistance spot welding is often used for cross-type (honeycomb plane) plate members with diameter of 12mm and cold-drawn high carbon steel wire reinforcement. The building reinforcement is connected with thick steel plate in T-shape, and submerged arc pressure welding or arc welding is most appropriate. 1. Cold-drawn steel bars should be welded to the connector first, and then cold-drawn. 2. Flash butt welding and arc welding cannot be used for cold-drawn low carbon steel wires. 3. The distance between welded joint and bend of reinforcement shall not be less than 10 times of the diameter of reinforcement. 4, axial tension and small axial tension members of the steel bar, should be butt welding. 5. Immediately bear the stressed steel bars in the bearings of medium and heavy duty cranes, and welding joints should not be adopted. 6. Welded joints arranged in the same support shall be separated from each other. Within the road section with 30 times the diameter of the stressed steel bar (not less than 500mm), a steel bar cannot have two connectors (the full-length steel bar of the member should be provided with welded joints). The percentage of the total cross-sectional area of the steel bar with connectors to the total cross-sectional area of the steel bar is not limited. For non-prestressed steel bars, the connection points between the stressed area and fabricated structure are not restricted. Prestressed reinforcement: the tensile area should not exceed 25%; When flash butt welding is selected, the quality can be expanded to 50%, and the stress zone and post-tensioned screw end rod are not limited.