Intense Cooling Technology On TIG Dressed Layer

With the progress of science and technology, China's railway has entered the era of high-speed railway. During the high-speed traveling, the welded framework of bogie is bearing strong vibration and impact loading. The anti-fatigue properties and its reliabilities of the framework will affect the safety of train travel. Therefore, it is very necessary to study in-depth the postweld treatment technology to improve the fatigue strength of welded joints of the framework.Under normal circumstances, the weld root is no longer the weak part easy to form fatigue crack, but the weld toe becomes the fatigue crack initiation source for the welded joints in full penetration. To that end. the feasibility and effectiveness of the intense cooling technology after TIG dressing in the weld toe was investigated to improve the fatigue strength of the joints. Compared experiments were made on the mechanical properties, especially the fatigue strength of the welded joints for the weld toe in a state of as welded, TIG dressed and intense cooled treatment after TIG dressing so as to study the influence the intense cooling treatment on the welding residual stress state, fatigue strength, as well as the microstructures and conventional mechanical properties of the joints. The research results indicate through the intense cooling treatment for the TIG dressed weld toe that the residual stress reduces with the increase of temperature of TIG dressed zone. When the temperature of TIG dressed region was over 450℃, the residue tensile stresses in the weld toe were transformed into compressive stresses, The microstructures were fine in the TIG-dressed zone and its HAZ obviously, the strength, plasticity and compact toughness of the welded joints fulfilled technological requirements. At the same time, the smooth transition formed in the TIG dressed zones of the weld toe using this new postweld treatment technology, and the stress concentration factor was reduced, so that the fatigue strength.of the joint was increased greatly.