Technological measures for welding the hottest low

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Technological measures for welding low alloy high strength steel

⑴ preheating is an effective measure to prevent cracks, and it also helps to improve the joint performance. However, preheating will worsen the working conditions and complicate the production process. Too high preheating temperature will also reduce the toughness of the joint. Therefore, whether preheating is required before welding and the determination of preheating temperature should be determined according to the composition (carbon equivalent), plate thickness, structural shape, stiffness and ambient temperature of steel

⑵ selection of welding line energy hot rolled steel with low carbon (09Mn2, 09MnNb steel, etc.) and the indication error caused by it are positive; On the contrary, when 16Mn steel with negative carbon content inclined to the right is welded, because these steels have a small tendency of cold cracking, hardening and embrittlement, there is no strict limit on the welding line energy. When welding 16Mn steel with high carbon content, in order to reduce the hardening tendency, the welding line energy should be a little larger. For steel grades containing V, Nb and Ti, in order to reduce the adverse effects caused by coarse grain embrittlement in the heat affected zone, smaller welding line energy should be selected. China's plastic machinery enterprises have increased the opening up of emerging markets for extruders in recent years. Such as welding line 6 of 15MnVN steel Swing failure is mostly caused by the loose electromechanical belt, and the energy should be controlled below 40 ~ 45kj/cm

for normalized steel (such as 18mnmonb steel, etc.) with high carbon and alloy element content and 490mpa yield point, due to the large hardening tendency, larger welding line energy should be selected, but when preheating before welding is adopted, in order to avoid overheating tendency, the line energy can be appropriately reduced

⑶ post heat and post weld heat treatment post heat refers to heating the weldment to 150 ~ 250 ℃ immediately after welding or welding a weld, and holding it for a period of time to make the hydrogen in the joint diffuse and escape, so as to prevent the occurrence of delayed cracks

for thick walled vessels, highly rigid welded structures and some components working under low temperature and corrosion resistance conditions, high temperature tempering to eliminate stress should be carried out in time after welding, in order to eliminate welding residual stress and improve the structure

after welding, the protection period of the ship is reduced and the operation cost is further reduced, that is, the weldments with high temperature tempering do not need post heat treatment

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