Hardening phenomenon and effect of loading frequency on low-cycle fatigue property of 304 stainless steel manufactured by laser metal deposition

The hardening phenomenon and effect of loading frequency on low-cycle fatigue for 304 austenitic stainless steel (SS304) manufactured by laser metal deposition (LMD) are studied in the paper. The strain hardening exponent n of SS304 manufactured by LMD is obtained by fitting the static tensile data with the least square method, which is about 0.35. The SS304 manufactured by LMD has cyclic hardening under cyclic load with strain control. Under the different loading frequencies, SS304 manufactured by LMD has different cyclic hardening phenomenon. The fatigue life of SS304 manufactured by LMD decreases with the increase of loading frequency. As the increase of loading frequency, the average strain and strain amplitude increase. According to the observation of fatigue fracture morphology under the different loading frequencies, SS304 manufactured by LMD has the typical fatigue fracture characteristics under the lower loading frequencies (such as 5 Hz and 10 Hz), namely fatigue crack initiation zone, fatigue crack propagation zone and fatigue crack instantaneous fracture zone. However, because of the large plastic deformation at the initial stage, the typical fatigue fracture characteristics of SS304 manufactured by LMD cannot be observed under the higher loading frequency (such as 20 Hz).