When 316 stainless steel pipe is welded with acid-resistant stainless steel, the defects in its welded joints are not as serious as when welding alloy structural steel, but hot cracks often occur when welding acid-resistant stainless steel. The common forms of thermal cracks include vent cracks, heat-affected zone cracks, and longitudinal and transverse weld cracks. The main cause of hot cracks is the influence of low melting point impurities on the austenite grain boundaries. In the later stage of the cooling crystallization process, the low melting point impurities on the grain boundary are in a liquid state, and thermal cracks are easily formed under the action of stress. The main way to solve the hot cracks of acid-resistant stainless steel is to take measures from metallurgical factors. 316 stainless steel pipes infiltrate some ferrite forming elements such as chromium, molybdenum, vanadium, etc. into the weld metal, so that the weld metal does not have a certain amount of ferrite. It becomes a dual-phase structure of austenite-ferrite, which can well prevent the weld metal from generating hot cracks.

This is because the low melting point impurities on the austenite grain boundaries are dispersed and separated by ferrite, which prevents the low melting point impurities from being distributed in a continuous network, thereby improving the thermal crack resistance. Therefore, it is generally believed that increasing the content of chromium, or containing a certain amount of molybdenum, tungsten, ancestors, and alloying elements, can play a role in preventing thermal cracks. When welding 18-8 stainless steel, if the ratio of chromium to nickel in the welding wire is less than 1.61, cracks will occur; when their ratio reaches 2.3-3.2, the generation of hot cracks can be prevented. Of course, it is also beneficial to reduce the sulfur and phosphorus content in the weld metal to resist thermal cracks. In Austen’s stainless steel weld metal, if the content of silicon is controlled within a certain range, the tendency of hot cracks in 316 stainless steel pipes can also be reduced.
The above requirements are mainly guaranteed by welding materials (welding rod, welding wire, flux). At present, many molten metals of 18-8 type stainless steel electrodes can obtain austenite-ferrite duplex structure. To reduce the occurrence of thermal cracks in 316 stainless steel pipes, the following measures can also be taken from the process:
(1) Change the welding slope or welding method to reduce the proportion of the base metal in the weld metal. This is because Sanyu has added anti-cracking elements to the components of the fli bonding material (welding wire, welding rod, flux), and reduced the harmful impurities of sulfur and phosphorus, which is better than the chemical composition of the base material, and minimize the base material The amount melted into the weld pool.
(2) Take the fastest welding speed possible. In multi-layer welding, wait for the first layer of welding seam to cool before welding the next layer to avoid overheating of the welding seam.
(3) When the welding is over or interrupted, the arc should be slowed down and the arc crater should be filled to prevent the formation of vent cracks. (4) Choose a reasonable welding structure and welding sequence to minimize the welding stress and also The occurrence of thermal cracks.