The Influence of the Changing of Cyclic Frequency on the Corrosion Fatigue Fracture Behavior of the Dual Phase Steel in 3% NaCl Solution

J. Ocean Eng. Technol. 1995;9(2):141-148.

O Se-Uk,Sin Gyu-Dong,Kim Ung-Jip

3% NaCl 수용액중에서 복합조직강의 부식피로 파괴거동에 미치는 주파수변화의 영향

오세욱,신규동,김웅집

동아대학교 공과대학 기계공학과,부산전문대학 기계설계과,동아공업고등학교 기계과

Keywords: Dual Phase Steel, Fatigue Strength, Initial Fatigue Crack, Corrosion Pit, Interference, Fatigue Fracture Behavior

핵심용어: 복합조직강, 피로강도, 초기피로크랙, 부식피트, 간섭, 피로파괴거동

Abstract

Fatigue tests were carried out by a rotary bending testing machine of cantilever type. M.E.F.(ferrite encapsulated islands of martensite) materials were made by a series of heat treatment from a low carbon steel(SM 20 C). The fatigue tests were conducted at stress levels of 302 MPa and with frequencies of 25Hz, 2.5 Hz and 0.5 Hz in 3% NaCl solution. The fatigue strength increased with frequency got higher. The microcracks and corrosion pits were generated at the boundary between the matrix and the 2nd phase. The cracks generated by the corrosion pits were coalesced with the pits around the notch and became the initial crack. The $N_i/N_f$ ratio increased as the frequency and stress level decreased. The interference phenomenon increased with stress level and frequency gots higher. The crack propagation rate was delayed as the stress level lowers and the frequency gets higher, however, the range of the stress intensity factor depended only on a stress level.