Effects Of Different Strain Strengthening Methods On Fatigue Properties Of S30408 Austenitic Stainless Steel

S30408 austenitic stainless steel has excellent characteristics such as high strength,low temperature resistance and corrosion resistance,and is widely used in the manufacturing process of low temperature tank trucks.Because of its low yield strength ratio,strain strengthening technology is usually used to pretreat S30408 to increase the yield strength and thereby reduce the pressure vessel wall thickness.With the widespread application of low-temperature liquefied gas and the large-scale development of liquefied gas storage tanks,the lightweight design of pressure vessels is becoming increasingly important.In this thesis,a series of research works were S30408 as the research object and conducts on its fatigue performance after strain strengthening.The main contents are as follows:(1)Based on the fatigue test results at room temperature and-163 °C,the fatigue properties of S30408 are compared at room temperature and low temperature.It is found that the cyclic stress response and fatigue life are higher at-163 °C.The initial phase of the tests increases rapidly,so that the hardening phase is concentrated in the initial phase of the tests.(2)The effects of tensile pre-strain,torsional pre-strain,and hydraulic pre-strain on material properties at room temperature are compared.These methods can increase the yield strength and reduce the wall thickness,but the fatigue life after strain strengthening is reduced.In order to ensure the safety of the pressure vessel under fatigue load,it should be used with caution.(3)Based on the fast hardening speed of s at the initial stage of low temperature cycling,a strain strengthening method that pre-strain at room temperature and cycling 300 cycles at low temperature(PRT-C300LT)is proposed,and compare it with pre-strain at room temperature and pre-strain at low temperature.It is found that after PRT-C300 LT treatment,the stress response is highest because the martensite content was higher than the other two pre-strain methods.At the same time,the plastic strain amplitude is lower than the other two pre-strain methods,the cyclic plastic accumulation per cycle is small,and the fatigue life is the highest.Therefore,PRT-C300 LT not only greatly improves the stress response,but also guarantees the safety of the pressure vessel under fatigue load,which is of great significance to the improvement of strain strengthening technology.