Corrosion resistance of chromium-nickel steel
Working in production or doing serious business on a home farmstead, you often have to weld stainless steel. For example, to lengthen the pipe from stainless steel or weld stainless sheets to obtain a container. The problem is that we do not know how the welded joints will behave under load. It is about the durability of these compounds that we will talk about.
Factors affecting the occurrence of intergranular corrosion
It occurs in the place of welding of stainless steel, where the metal is melted. The dimensions of this corrosion depend on many factors. These include the thickness of the sheet, the method of welding, the chemical composition and structure of the metal, and the grain size. It is known that in gas welding — metal is more susceptible to destruction than with arc welding. Welding with a double-sided seam also expands the intergranular corrosion zone. The reason is an increase in the duration of the critical temperatures for the metal. When welding with a one-sided seam, this time is much less. The thicker the part, the longer the temperature effect, which contributes to the destruction of the metal structure and the appearance of intergranular corrosion. All these factors were determined by scientific experiments. The metal was of different thicknesses and was welded by various methods. The corrosion test was carried out using copper sulfate and sulfuric acid.
Types of welding.
Argon-arc welding proved to be the best, and, worst of all, acetylene-oxygen welding. Recall that the higher the welding speed, the less the tendency to intergranular corrosion. The influence of the time of exposure to high temperatures on the development of corrosion in multilayer welding was studied. We took 12 x 18n9t steel and welded it with the brand 08 x 18Н9. The amount of carbon in the electrodes was different. It was established that in the case of multilayer welding 12 x 18n9t steel did not always show a 100% resistance to intergranular corrosion. This result depended on the duration of the action on the metal of the critical temperature. If the first layer of the butt weld was subjected to a short thermal action, less than the critical time, then the welding site did not tend to intergranular corrosion. Welding with cross seams can also contribute to the development of fracture. This occurs if the metal that is closer to the weld seam has a coarse crystal structure. This structure is more susceptible to corrosion than fine-grained. To reduce intergranular corrosion to a minimum, appropriate steel grades and faster welding should be used.
When using such a welding, the time of heating of the metal in the zone of critical temperatures increases and there is a large heat absorption in the places of the welded seams. For this reason, the first weld is less prone to corrosion. The fusion of the following layers increases the possibility of the appearance of fracture due to an increase in the total rate. But there is the possibility of reducing the tendency to intergranular corrosion in multilayer welding. This can be achieved by the following actions. 1) Hardening of steel when heat occurs under high temperature and rapid cooling. 2) Decrease in the amount of carbon. 3) Introduction to the composition of titanium, niobium, tantalum. 4) Treatment at t ° 800−900 ° C. On which of these methods will stop, depends on the purpose of the equipment and the conditions under which intergranular corrosion begins to develop.
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