Papers by Author: K.H. Kim

Abstract: In this study the fatigue properties due to cavitation damage of flame-quenched 8.8Al-bronze (8.8Al-4.5Ni-4.5Fe-Cu) as well as current nuclear pump materials (8.8Al-bronze, SUS316 and SR50A) have been investigated by using an ultrasonic vibratory cavitation test. For this the impact loads of cavitation bubbles generated by ultrasonic vibratory device quantitatively evaluated and simultaneously the cavitation erosion experiments have been carried out. The fatigue analysis on the cavitation damage of the materials has been made from the determined impact load distribution (e.g. impact load, bubble count) and erosion parameters (e.g. incubation period, MDPR). According to Miner’s law, the exponents b of the F-N relation (Fb
N = Constant) at the incubation stage (N: the number of fracture cycle) were 5.62, 4.16, 6.25 and 8.1 for the 8.8Al-bronze, flame-quenched sample, SUS316 and SR50A alloys, respectively. At steady-state, the exponents b of the F-N curve (N: the number of cycles required for a 1μm increment of MDP) were determined as 6.32, 5, 7.14 and 7.76 for the 8.8Al-bronze, flame-quenched sample, SUS316 and SR50A alloys, respectively.

Abstract: This paper reports on the formation of tensile stress induced cracks by the application of a flame hardening to 12Cr steels and the monitoring of the flame hardening process at the desirable residual stress state. During the flame hardening of the steels elastic residual tensile stresses were typically generated due to a phase transformation of austenite into martensite and they became greater by increasing both the process temperature and cooling rate. Eventually the cracks were nucleated and propagated across the prior austenite grain boundaries by a generation of large tensile stress, which was accompanied by a drastic decrease in the tensile stress due to a stress relaxation.