750℃에서 Alloy 800H 모재와 용접재의 저사이클 피로 거동

Abstract

One of the fourth generation reactors, Very High Temperature Reactor is used for a long time under high temperature of about 950 and high pressure of 4-7 MPa. Therefore, it is very important to select materials for stable use and to obtain data on high temperature properties of materials. Power transmission as well as starting and stopping of the reactor cause low cycle fatigue and creep-fatigue loads on the structure. Therefore, low cycle fatigue data at high temperature and sufficient understanding of Alloy 800H is important for the stable design of the reactor. However, most of the existing research has been done on the base material, and the actual structural members are joined by welding from a practical point of view. At present, many researchers are activel researching the weldments in consideration of this point, and it is important to understand the low cycle fatigue characteristics and the data of the weldments together with the base metal. The aim of this work is to investigate the low cycle fatigue behaviors of Alloy 800H Base metal and weldments at 750℃. Low cycle fatigue tests were carried out by a series of fully reversed strain-controls, four different strain amplitudes of 0.6%, 0.9%, 1.2% and 1.5%, under constant strain rate of 10-3/s. In all test conditions, the fatigue life of Alloy 800H Base metal and weldments were decreased with increasing the total strain range. The cyclic stress response behavior of the base metal showed the initial cyclic hardening phenomenon, whereas the weldments showed cyclic softening phenomenon. In the case of plastic strain amplitude, magnitude increased linearly as the total strain range increased. And also, under all testing conditions, crack initiation and propagation showed the failure mode of typical transgranular.