Fatigue fracture mechanism of 304 stainless steel manufactured by laser metal deposition

Laser metal deposition is a widely used laser additive manufacturing technology. The fatigue tests of 304 austenitic stainless steel manufactured by laser metal deposition are carried out and the fatigue fracture mechanism is studied. According to the experimental results, the S-N curve of 304 austenitic stainless steel manufactured by laser metal deposition is drawn. The results show that the stress amplitude has an important effect on the fatigue fracture morphology. The larger the stress amplitude is, the coarser the fatigue fracture is. Under the higher stress amplitude, there are randomly distributed holes and cracks on the surface of the fracture specimen. Material defects such as oxide inclusions and pores are the main causes of fatigue crack initiation, and large local plastic deformation under the large stress amplitude (such as 275 MPa) is also one of the causes of fatigue crack initiation. With the increase of stress amplitude, the fatigue bands become clearer. Under the higher stress amplitude, the intersection of multiple slip systems leads to the expansion of fatigue bands in different plane, and the tire indentation appears in the crack propagation zone. With the increase of stress amplitude, the number of secondary cracks increases due to the increase of plastic deformation in the fatigue crack propagation zone.