Improvement of fatigue properties of 316L-2Cr13 multilayer steel compared with all martensite/austenitic multilayer steel

With the development of modern industry and the progress of science and technology, traditional single metal or alloy has been difficult to meet the requirements of modern industrial production and some specific working conditions for the comprehensive properties of materials. Composite materials emerge as the times require. As a typical composite material, multilayer steel has been widely used in practical industrial production and life applications in petrochemical industry, marine shipping, medical equipment, hardware tools and other fields due to its excellent performance. However, as an important index of material design, production and application, the fatigue performance is rarely studied. Therefore, there is an urgent need for fatigue properties of multilayer steel.

The composite plates were obtained by accumulative rolling, using solid solution austenitic stainless steel 316L and annealed martensitic stainless steel 2Cr13 as raw materials. The tensile test will be carried at the strain rate of 0.5mm/min. The tension tension fatigue test of 316L-2Cr13 multilayer steel, all 316L and all 2Cr13 multilayer steel with a stress ratio of R=0.1 was carried out by using the up-and-down method and group method. The frequency was 30HZ, and the S-N curve was obtained. In the process of S-N curve fitting, the least square method is used to fit the linear relationship of the obtained data. After the fatigue test, use SEM to analyze the fatigue fracture surface, analyze the fracture mode and fracture mechanism.

1. From the microstructure of multi-layer steel, 316L layer is mainly composed of austenite, and 2Cr13 layer is mainly composed of martensite and ferrite. 2. Summary from the subsequent tensile test results: Compared with the multi-layer steel composed of all austenitic stainless steel 316L or all martensitic stainless steel 2Cr13, the mechanical properties of the multi-layer stainless steel composite plate composed of 316L and 2Cr13 are more superior. It is concluded that the plasticity of brittle materials can be significantly improved after rolling. It can combine the advantages of the two materials. It has not only high strength, but also good plasticity (elongation). 3. The tensile fatigue test with a stress ratio of 0.1 has been carried out. The experimental results show that the fatigue data are relatively scattered due to the inhomogeneity of the rolled microstructure, and the fatigue performance of 316L-2Cr13 multi-layer stainless steel composite plate is obviously better than that of all 316L multi-layer steel and all 2Cr13 multi-layer steel. The fatigue limit of 316L-2Cr13 multi-layer steel can reach 286MPa, while the fatigue limit of all austenitic steel is similar to that of all martensitic steel, but there are great differences in different stress levels (the slope of the curve varies greatly). 4. After the fatigue test, the fracture surface is analyzed, and the macro morphology of the fatigue fracture surface of 316L-2Cr13 multi-layer steel can divide the fracture surface into three areas: crack initiation source area, crack propagation area, and transient fracture area. The austenite layer undergoes significant plastic deformation and a large number of fatigue striations, while the martensite layer is dominated by brittle transgranular fracture. At the later stage of crack growth, the austenite layer gradually presents dimples and the martensite layer presents a large number of cleavage surfaces. In 316L-2Cr13 multilayer steel, the two layers are connected by shear dimples in the transient fracture zone. 5. The fatigue fracture mechanism of 316L-2Cr13 multilayer steel is summarized. Compared with all martensite or all austenitic multilayer steel, the higher strength provided by the martensite layer makes the threshold value of crack growth higher, and the material is not easy to crack. When the crack nucleates under higher stress, the crack growth rate of the material is slowed down due to the excellent plasticity provided by 316L, which is reflected in the S-N curve, that is, the fatigue damage rate is small The threshold value of fatigue crack growth is high and the fatigue strength is superior.Conclusions: 316L-2Cr13 multilayer steel can combine the advantages of the constituent materials, not only has high strength, but also has excellent plasticity. The average tensile strength and elongation are 1147MPa and 23% respectively. 316L-2Cr13 multilayer steel is superior to all austenitic and all martensitic multilayer steel when the fatigue limit re stress ratio is 0.1, reaching 286MPa. In the process of cyclic loading, the higher strength provided by 2Cr13 layer makes the threshold value of crack propagation higher to prevent rapid cracking; The good plasticity provided by the 316L layer prevents fatigue crack growth. In combination, the fatigue performance of 316L-2Cr13 multilayer steel has been greatly improved compared with the other two materials. In the fatigue fracture surface, the austenite layer undergoes significant plastic deformation and a large number of fatigue striations, while the martensite layer mainly undergoes brittle transgranular fracture. In the later stage of crack growth, the austenite layer gradually presents dimples and the martensite layer presents a large number of cleavage surfaces.