SHOT PEENING, LASER SURFACE MELTING AND THE CAVITATION EROSION OF AN AUSTENITIC GRAY IRON

An austenitic flake graphite grey iron in the as-cast condition (AC) was laser surface melted (LSM), and the AC and LSM irons were shot peened (ACp and LSMp). The irons were eroded in distilled water and 0.02% and 3.0% NaCl waters at 50-degrees-C using a 20 kHz, 15-mu-m peak-to-peak amplitude, ultrasonic device capable of electrochemical measurements. Laser surface melting eliminated the graphite flakes and formed a crack-free uniform layer of predominantly fine austenite and some martensite. The hardnesses of the AC, ACP, LSM, and LSMp irons were 200, 350, 700, and 750 HV, respectively. In distilled water, the erosion rate of the AC iron was reduced by factors of 0.80, 0.05, and 0.04, for the ACp, LSM, and LSMp materials, respectively. In salt water the corrosion rate was increased, and the corrosion-enhanced erosion rates of the AC, ACp, LSM, and LSMp materials were fractions 0.26, 0.16, 0.75, and 0.75, respectively, of the total erosion rate. Corrosion was highest in the irons containing graphite, but the effect of corrosion on the erosion rate was highest in the irons that did not contain graphite. Results of detailed metallographic examination are presented, and the mechanism of cavitation erosion damage is discussed.