Selection of stainless steel welding materials in pressure vessels

In terms of the selection of austenitic stainless steel welding materials, the selection principle of austenitic stainless steel welding materials is to ensure that the corrosion resistance and mechanical properties of the weld metal are basically equivalent to or even higher than the base metal without cracks. , usually requiring that its alloy composition roughly matches the composition of the parent metal. For corrosion-resistant austenitic stainless steel, it is usually hoped to contain a certain amount of ferrite structure, which can ensure excellent crack resistance and relatively good corrosion resistance. However, in some special media, such as the weld metal of urea equipment, the presence of ferritic stainless steel is prohibited, otherwise its corrosion resistance will be reduced. For heat-resistant austenitic stainless steel, control of the ferrite content in the weld metal should be considered. For austenitic stainless steel weldments that operate in high temperature environments for a long time, the ferrite content in the weld metal cannot exceed 5%.
In terms of the selection of ferritic stainless steel welding materials, there are three main types of ferritic stainless steel welding materials. The first is welding materials whose composition basically matches the base metal; the second is austenitic welding materials; and the third is nickel-based alloy welding materials. , because its price is relatively high, so it is rarely used.
Ferritic stainless steel welding consumables can use materials that are equivalent to the base metal, but when the degree of restraint is high, cracks can easily occur. Heat treatment can be used after welding to restore corrosion resistance and improve joint plasticity. The use of austenitic welding consumables eliminates the need for preheating and post-weld heat treatment, but for various steels that do not contain stabilizing elements, sensitization of the heat-affected zone still exists. Types 309 and 310 chromium-nickel austenitic welding consumables are commonly used. For Cr17 steel, 308 type welding materials can also be used. Welding materials with high alloy content are beneficial to improving the plasticity of welded joints. Austenitic or austenitic-ferritic weld metal is basically as strong as the ferritic base metal, but in some corrosive media, the corrosion resistance of the weld may be very different from that of the base metal. Pay attention when selecting welding consumables.
In terms of the selection of martensitic stainless steel welding materials, among stainless steels, martensitic stainless steel can use heat treatment to optimize its performance. Therefore, in order to ensure that the performance meets the corresponding requirements, especially for heat-resistant martensitic stainless steel, the weld composition The composition should be as close as possible to the base material. In order to avoid cold cracks, austenitic welding materials can also be used. At this time, the weld strength is definitely lower than the base metal.
When the composition of the weld is similar to that of the base metal, the weld and the heat-affected zone will harden and become brittle at the same time, and a tempering softening zone will appear in the heat-affected zone. In order to avoid cold cracking, components with a thickness of more than 3 mm usually need to be preheated and heat treated after welding to enhance the joint performance, because the thermal expansion coefficients of the weld metal and the base metal are basically the same. After heat treatment, there is It is possible to completely eliminate welding stress.