Research on Low Cycle Fatigue and Fracture Characteristics of 304 Stainless Steel

304 stainless steel is the most widely used chromium-nickel stainless steel. It has good corrosion resistance, heat resistance, low temperature strength and mechanical properties, as well as good processability and weldability. It is widely used in the production of equipment and parts that require good comprehensive performance (corrosion resistance and formability). It is widely used in machinery, aerospace and other fields, mainly in the production of oil and gas pipes, pressure vessels, etc., mostly in In a special working environment. Oil and gas pipelines, pressure vessels, etc. are subjected to a limited number of cycles throughout their life. For example, pressure vessels are sometimes only subjected to a few load cycles per day. In practical engineering applications, its static strength generally meets the requirements, so the research on its low-cycle fatigue fracture characteristics is of practical significance. Fatigue fractures of 304 stainless steel components occur from time to time, leading to serious consequences.

Under stress control, a tensile and compression fatigue test is carried out on 304 stainless steel specimens to study its low-cycle fatigue fracture characteristics. To process the test data, obtain the low cycle SN curve of 304 stainless steel under stress control and fit the expression of low cycle stress life; use the expression to calculate the fatigue limit of 304 stainless steel; analyze the relationship between strain and life under different stresses The relationship between and the relationship between the number of loading and the plastic strain energy; observe the fracture. The greater the load, the more fatigue sources, the smaller the distance between them, the faster the specimen fractures, the shorter the life, and the rougher the fatigue source area of ​​the fracture. This is because when the load is large, the source of cracks is easy to form on the surface of the test piece. The more the number of cracks, the easier it is for the test piece to break, and the friction on the surface of the fracture surface is less, which is rougher; the smaller the load, the more the test piece needs to be broken. The longer it is, the more severe the friction on the surface of the fracture surface, and the smoother it will be, relatively speaking.