Welding process of commonly used heat resistant steel

Heat-resistant steel refers to steel that has both thermal stability and thermal strength under high temperature conditions. Thermal stability refers to the ability of steel to maintain chemical stability (corrosion resistance, non-oxidation) under high temperature conditions. Thermal strength means that steel has sufficient strength at high temperatures. The heat resistance is mainly guaranteed by alloy elements such as chromium, molybdenum, vanadium, titanium, niobium, etc. Therefore, the selection of welding materials should be determined according to the alloy element content of the base metal. Heat resistant steel is widely used in the construction of petroleum and petrochemical industrial installations. We can often come into contact with pearlitic heat resistant steel with low alloy content, such as 15CrMo, 1Cr5Mo, etc. Weldability of chromium-molybdenum heat resistant steel Chromium and molybdenum are the main alloy elements, pearlite heat-resistant steel significantly improve the high temperature strength and high temperature oxidation resistance of metals, but they make metal welding performance, welding seam and heat affected zone in which has a high tendency, quenching in air cooling after welding is easy to produce the hard and brittle martensite structure, not only affects the mechanical properties of welded joint, and produce a lot of stress, resulting in a cold cracking tendency. Therefore, the main problem of heat-resistant steel welding is crack, and the three elements forming crack are: organization, stress and the amount of hydrogen in the weld, so it is particularly important to develop a reasonable welding process. Welding process of pearlitic heat-resistant steel 2.1 groove The machining of groove usually uses flame or plasma cutting process. When necessary, the cutting should be preheated, and the PT test should be done after grinding clean to remove the cracks on the groove. V-shaped groove is usually selected, groove Angle is 60°, from the point of view of preventing cracks, groove Angle is more favorable, but increase the amount of welding, at the same time the groove and the inside of both sides of the grinding clean, remove oil, rust and moisture and other dirt (to hydrogen, to prevent pores). 2.2 set on Requirements can not be forced to group, to prevent internal stress, because of the chromium molybdenum heat resistant steel crack tendency is larger, so in the welding seam restraint degree can not be too large, so as not to cause too much stiffness, especially in the thick plate welding, hinder the free contraction of the weld reinforcement, fixtures and fixtures should be avoided as far as possible. 2.3 Selection of welding methods At present, the commonly used welding methods of pipeline welding in petroleum and petrochemical installation units are argon tungsten arc welding backing, electrode arc welding filling cover, other welding methods include MIG welding, CO2 gas shielded welding, electro-slag welding and automatic submerged arc welding. 2.4 Selection of welding materials The principle of selecting welding materials, the alloy composition and strength properties of the weld metal should basically be consistent with the corresponding index of the base metal or should reach the lowest performance index proposed by the technical conditions of the product. And in order to reduce the hydrogen content should be with alkaline low hydrogen type electrode, electrode or flux should be in accordance with the provisions, drying technology, along with it, put them in electrode increases with the increasing use in heat insulation barrels, electrode inside the insulation barrel shall not be more than 4 hours, otherwise should resume drying, drying times shall not be more than three times, in the process of concrete construction, have detailed provisions. Austenitic stainless steel electrode, such as A307 electrode, can also be used in hand arc welding of chromium molybdenum heat-resistant steel, but it still needs to be preheated before welding. This method is suitable for the situation that the weldment can not be heat treated after welding. 2.5 preheating Preheating is an important technological measure to eliminate cold cracks and stress during welding of pearlite heat-resistant steel. In order to ensure welding quality, it is necessary to preheat and maintain a certain temperature range whether in spot fixation welding or welding process. 2.6 Slow cooling after welding Slow cooling after welding is the principle that welding chromium-molybdenum heat-resistant steel must strictly follow, even in hot summer, this must be done, generally immediately after welding with asbestos cloth cover weld and near seam area, small welding parts can be placed in asbestos cloth slow cooling. 2.7 Post-welding heat treatment Heat treatment should be carried out immediately after welding, its purpose is to prevent delayed crack generation, eliminate stress and improve the structure.铜焊丝,Copper Welding Rods,铝焊丝,aluminium welding wire,镍焊条,Nickel electrode,药皮焊条,Flux Coated Brazing Welding Rods