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유효선,윤재형,이덕연,정세희 전북대학교 공업기술연구소 1998 工學硏究 Vol.29 No.-
It has been well recognized that a long term service at elevated temperature of 350~550℃ induces temper embrittlement due to carbide precipitation and/or P, Sb and/or Sn segregation at grain boundaries and thereby deteriorates the grain boundary strength of heat resisting components in the energy-related plants. Therefore, it is very important to assess quantitatively the extent of temper embrittlement of heat resisting components to secure the reliable and efficient service condition and to prevent brittle failure in service. However, because fracture tests are limitted in size and number of specirmen obtained from the structural components, nondestructive tests are required. In this study, the optimum electrochemical estimation parameters related to test conditions were investigated and discussed by means of electrochemical polarization test methods(ECPTM) in special corrosive envrionment. The destructive small punch(SP) test was performed in order to establish a reliable and sensitive temper embrittlement evaluation tchnique.
회전굽힘 피로시험에 의한 변동응력하의 피로균열성장 거동
윤재영,유효선,정세희 전북대학교 공업기술연구소 1998 工學硏究 Vol.29 No.-
In this paper, to clarify the effect of variable amplitude stressing, under-stressing fatigue tests were carried out on small notched specimens of SCM440 under rotary bending fatigue testing by constant stress and two step stress fatigue tests. It is found that the relationship between surface fatigue crack length and internal crack length shows linear relation. As under-stress ratio(USR) became smaller and stress changing times became faster, fatigue crack growth was retarded and the number of delayed cycles by the under-stressing became longer. A case of fatigue crack length to the basis stress was 0.3mm, creak was observed at USR=0.764 and a case of a_1=0.5~1.1㎜, it was observed at USR=0.673