SYNERGISTIC EFFECT OF CORROSION AND CAVITATION EROSION OF HIGH NITROGEN STAINLESS STEEL

The cavitation erosion (CE) is a serious problem in engineering components in contact with a liquid in which the pressure fluctuates. The CE resistance of material is related to the microstructure, hardness, work hardening ability, superelasticity and superplasticity, or strain or stress induced phase transformation of material. The high nitrogen stainless steel (HNSS) is attractive for its low cost in application where a combination of good strength and toughness, high work hardening capacity, and corrosion resistance is required. These attractive properties cause the nitrogen alloyed stainless steels to be the good candidates with relatively high CE resistance. In this work, the CE behavior of HNSS in distilled water, 0.5 mol/L NaCl and 0.5 mol/L HCl solutions was investigated on the base of mass loss and polarization curve. The micrographs of damaged surface were observed by using SEM. The results showed that the cumulative mass loss of HNSS after subject to CE for 8 h was the highest in 0.5 mol/L HCl solution and lowest in distilled water. There existed an incubation period in mass loss rate curve and the incubation period shorted with the increase of the corrosive of tested solution. The plastic fracture was the dominant damage mode of HNSS subject to CE condition. The plastic deformation and dislocation motion of HNSS were facilitated by diffusion of hydrogen in HCl solution, therefore the initiation and propagation of crack were accelerated and removal of materials was accelerated by propagation and connection of cracks.