The austenitic stainless steel heat exchange tube has good corrosion resistance and oxidation resistance, but it still appears brittle fracture during use. What is the reason?
The so-called brittleness refers to the performance of engineering components such as steel and steel when the toughness and plasticity index values are low. Brittle failures often have no signs, but the hazards are often catastrophic. Just like stainless steel heat exchange tubes, once brittle fracture occurs, It is easy to cause internal leakage of the heat exchanger, and even serious economic losses to the enterprise. Therefore, when we use stainless steel heat exchange tubes in our daily use, we should pay attention to its use and try to avoid brittle fracture of the stainless steel heat exchange tubes.
Stress is certain. The effective stress that produces stress corrosion is tensile stress. It is the superposition of engineering stress, residual stress and assembly stress. Residual stress will be generated during the production process and assembly process of stainless steel heat exchange tubes.
In many cases Below, residual stress alone is sufficient to produce stress corrosion; stress corrosion also has stress concentration sources. Stainless steel heat exchange tubes may form micro-cracks, bumps and scratches during assembly and use. These are all stress corrosion stresses. Centralized source
A very small amount of Cl- (Cl- content exceeding 25mg/L) can cause stress corrosion and cracking of austenitic stainless steel heat exchange tubes. Cl- can cause stress corrosion to austenitic stainless steel heat exchange tubes, first of all in stress concentration. Pitting corrosion occurs at the location, which penetrates along the grain boundary or through the grain direction. When it penetrates to a certain depth, brittle fracture occurs under tensile stress; in addition, H2S causes stress corrosion damage to austenitic stainless steel heat exchange tubes The stress corrosion mechanism is that FeS generated at high temperature interacts with humid air to produce polythionic acid, which is easy to cause intergranular stress corrosion fracture in the heat-affected zone of austenitic stainless steel welding.
It is worth noting that the brittle fracture of the stainless steel heat exchange tube may be related to the heat treatment of the stainless steel heat exchange tube, especially in some cases, in a certain tempering temperature range, the change curve of the toughness index with the tempering temperature.
There is a trough, showing brittleness; therefore, the stainless steel heat exchange tube produced by Dongyan Company adopts reasonable material selection and strict heat treatment process to suppress and prevent the generation of temper brittleness, thereby ensuring the heat exchange work of the stainless steel heat exchange tube.