For welded tubes of special materials, heat treatment must be carried out before and after welding, which is very important to the welding quality. The pre-heating of welded pipes made of special materials can not only slow down the cooling rate after welding, but also help hydrogen diffuse and escape from the weld metal to avoid hydrogen-induced cracking. At the same time, the degree of hardening of the weld seam and the heat-affected zone is reduced, and the crack resistance of the welded joint is improved.
It can also reduce the welding stress, uniform local or overall preheating, and reduce the temperature difference between the weldments in the welding area, so that on the one hand, the welding stress is reduced, and on the other hand, the welding strain rate is reduced, which is beneficial to avoid welding cracks. It can reduce the degree of restraint of the welded structure, especially for reducing the degree of restraint of the fillet joints. As the preheating temperature increases, the incidence of cracks decreases.
The selection of preheating temperature and interlayer temperature for welded pipes of special materials is not only related to the chemical composition of steel and welding rods, but also related to the stiffness of the welded structure, welding method, and ambient temperature. It should be determined after comprehensive consideration of these factors. In addition, the thickness direction of the steel and the uniformity of the preheating temperature in the weld zone have an important impact on reducing the welding stress.
The post-weld heat treatment of welded pipes with special materials has three purposes, namely, hydrogen elimination, welding stress relief, and improvement of weld structure and comprehensive performance. The main function of post-weld hydrogen elimination treatment is to accelerate the escape of hydrogen in the weld and heat, which is extremely effective in preventing welding cracks in low alloy steel.
Stress relief heat treatment is to reduce the yield strength of the welded workpiece at high temperature, so as to relax the welding stress. There are two common methods: one is overall high temperature tempering, and the other is local high temperature tempering. After heat treatment, the metallographic structure of the welded joint is improved, the plasticity and toughness of the welded joint are improved, and the comprehensive mechanical properties of the welded joint are improved.
It can also reduce the welding stress, uniform local or overall preheating, and reduce the temperature difference between the weldments in the welding area, so that on the one hand, the welding stress is reduced, and on the other hand, the welding strain rate is reduced, which is beneficial to avoid welding cracks. It can reduce the degree of restraint of the welded structure, especially for reducing the degree of restraint of the fillet joints. As the preheating temperature increases, the incidence of cracks decreases.
The selection of preheating temperature and interlayer temperature for welded pipes of special materials is not only related to the chemical composition of steel and welding rods, but also related to the stiffness of the welded structure, welding method, and ambient temperature. It should be determined after comprehensive consideration of these factors. In addition, the thickness direction of the steel and the uniformity of the preheating temperature in the weld zone have an important impact on reducing the welding stress.
The post-weld heat treatment of welded pipes with special materials has three purposes, namely, hydrogen elimination, welding stress relief, and improvement of weld structure and comprehensive performance. The main function of post-weld hydrogen elimination treatment is to accelerate the escape of hydrogen in the weld and heat, which is extremely effective in preventing welding cracks in low alloy steel.
Stress relief heat treatment is to reduce the yield strength of the welded workpiece at high temperature, so as to relax the welding stress. There are two common methods: one is overall high temperature tempering, and the other is local high temperature tempering. After heat treatment, the metallographic structure of the welded joint is improved, the plasticity and toughness of the welded joint are improved, and the comprehensive mechanical properties of the welded joint are improved.
