High temperature fatigue refers to the process in which
stainless steel plates are damaged or even broken due to repeated stress changes at high temperatures. The results of the research show that in a certain high temperature range, the high temperature fatigue strength of 10 to the 8th power is half of the high temperature tensile strength at that temperature.
Thermal fatigue refers to the fact that during the heating and cooling process, when the temperature changes and is subject to external constraints, stress is formed inside the material corresponding to its own expansion and contraction deformation, causing damage to the material. When heated and cooled repeatedly rapidly, the stress becomes impactful, and the resulting stress is greater than normal. At this time, some stainless steel plates will show brittle failure. This phenomenon is called a shock. Thermal fatigue and thermal shock are similar phenomena, but the former is mainly accompanied by large fluctuations in plastic strain, while the damage of the latter is mainly brittle failure.
The composition and heat treatment conditions of stainless steel plates have a direct impact on high temperature fatigue strength. Especially when the carbon content increases, the high-temperature fatigue strength will increase significantly, and the solution heat treatment temperature also has a significant impact. Generally speaking, ferritic stainless steels will have good thermal fatigue properties. Among austenitic stainless steels, stainless steel grades that are high in silicon and have excellent elongation at high temperatures have excellent thermal fatigue properties.
The lower the thermal expansion coefficient, the lower the strain under the same thermal cycle, the smaller the deformation resistance and the higher the fracture strength, and the longer the service life will be. It can be said that the fatigue life of martensitic stainless steel 1Cr17 is the longest, while the fatigue life of austenitic stainless steel such as 0Cr19Ni9, 0Cr23Ni13 and 2Cr25Ni20 is the shortest. In addition, castings are more susceptible to damage due to thermal fatigue than forgings. At room temperature, the fatigue strength of 10 to the power 7 is half the tensile strength. Compared with the fatigue strength at high temperatures, it can be seen that the fatigue strength does not differ greatly in the temperature range from room temperature to high temperature.
