Welding performance of butt welding flange

Toughening of butt welding flange welding HAZ

　　 Butt-welded flange welding HAZ is a non-uniform body in terms of structure and performance, especially the fusion zone and the coarse-grained zone are prone to embrittlement, which is the weak zone of the entire welded joint. Therefore, measures should be taken to improve the toughness of the welded HAZ. According to research, the toughening of HAZ can adopt the following two measures.

　　① Control the organization. For low-alloy steel, the carbon content should be controlled so that the alloying element system is a strengthening system of low-carbon traces of multiple alloying elements. In this way, under the cooling conditions of welding, the HAZ is distributed with dispersion-strengthened particles, which can obtain low-carbon martensite, lower bainite and acicular ferrite and other tough structures in the structure. In addition, the grain boundary segregation should be controlled as much as possible.

　　② Toughening treatment. For some important structures, post-weld heat treatment is often used to improve the performance of the joint. But for some large and complex structures, even local heat treatment is difficult. Reasonable formulation of the welding process, correct selection of welding heat input and preheating and post-heating temperatures are effective measures to improve welding toughness.

　　 In addition, there are many ways to improve the toughness of the HAZ. For example, fine-grained steel adopts a controlled process to further refine the ferrite grains, which will also improve the toughness of the material. Metallurgical refining technology can make the content of impurities (S, P, O, N, etc.) in steel extremely low. These measures make the sidewalk of the steel to be improved, thereby also improving the toughness of the welded HAZ.

Softening of butt welding flange welding HAZ

For metals or alloys strengthened by cold work hardening or heat treatment before welding, different degrees of vector strength will generally occur in the welding heat-affected zone. The most typical ones are high-strength steels that have been modulated and alloys with precipitation strengthening and dispersion strengthening. , The softening or vector strength produced in the heat-affected zone after welding.

　　 When welding quenched and tempered steel with butt welding flange, the softening degree of HAZ is related to the heat treatment state of the base material before welding. The lower the tempering temperature of the quenching and tempering treatment of the base metal before welding, the greater the degree of strengthening, the more severe the softening degree after welding. A large number of experimental studies have shown that under different welding methods and different welding heat input, the most obvious part of the softening in the HAZ is the section where the temperature is between A1-A3.