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複合組織鋼의 第2相 硬度變化가 腐蝕疲勞 크랙傳播에 미치는 影響
오세욱,김웅집 대한용접접합학회 1993 대한용접·접합학회지 Vol.11 No.2
The corrosion fatigue fracture behaviour of dual phase steel was investigated in 3% NaCl solution at 302MPa and 137MPa. Fatigue test was conducted by cantilever type of self-made rotary bending fatigue testing machine. The fatigue strength increased with increasing the hardness of 2nd phase. Corrosion pit originated at the boundary of the 2nd phase. The size and number of corrosion pits were influenced by the 2nd phase hardness, and pits remained constant in size just after they were transited into cracks. The life of crack initiation was effected by stress level. The shape of relation of .DELTA. K and da/dN has smaller scattering in it in 3% NaCl solution than that in air. The higher the 2nd phase hardness is, the greater the corrosion fatigue life becomes. Corrosion fatigue fracture behaviour was primarily effected by mechanical factor in case of high stress(302MPa), but by electro-chemical reaction in a lower stress(137MPa). As stress level got lower and hardness of the 2nd phase got higher, the roughness of fracture surface increased.
複合組織鋼의 回轉굽힘 疲勞크랙發生 및 傳播에 미치는 母相粒徑의 影響
吳世旭,金雄執 동아대학교 공과대학 부설 한국자원개발연구소 1984 硏究報告 Vol.8 No.1
The weight reduction and reliability of various steel used in industrial machinery have become a great importance as industry developes. For this reason a study on dual phase steel has been consisted different size of ferrite grain which has approximatly the constant plastic constraint effect and internal stress through heat treatments. They were prepared to able to apply the stress intensity factor equation K=σ√πℓ to the hollow shaft as assuming infinite plane without residual stress. Especially, it is possible to reduce the weight in hollow shaft and this hollow shaft is largely expected contribution in the machines operated with high speed or design manufacturing of aeronautical eguipments. Therefore, the fatigue crack behavior and fractography on the high-low stress level of M.E.F dual phase steel by rotary bending fatigue test were discussed. The results of the experiment are as follows. 1. The fatigue durability of the M.E.F dual phase steel is 1.6~1.8times greater than mild steel. 2. The initiation fatigue crack of the M.E.F dual phase steel and mild steel was created within 21~23%, 9% of fracture number of revolutions. 3. The smaller ferrite grain size is increased to m, decreased to C and located to high K range in M.E.F dual phase steel. 4. The fatigue and tensile fracture surface formed dimple facet and river pattern in M.E.F dual phase steel.
3% NaCl 水溶液中에서 複合組織鋼의 第2相 硬度 및 反復速度 變化가 腐蝕疲勞擧動에 미치는 影響
吳世旭,金雄執 東亞大學校 海洋資源硏究所 1992 硏究論文集 Vol.5 No.2
Only the 2nd phase hardness of martensite in dual phase steel which was composed of the martensite and ferrite was changed by heat treatment. The corrosion fatigeue fracture behaviors were conducted by cantilever by cantilever type of self-made roated bending fatigue testing machine at cyclic frequencies of 25Hz and 0.5Hz in 3% NaCl solution. The fatigue strength was increased as the hardness of the 2nd phase and cyclic frequency got higher. In case of 302 MPa and 25Hz , corrosion fatigue fracture behavior was effected by mechanics but in case of 137MPa and 0.5Hz. by electric-chemistry, Also it wsas effected by mechanics and corrosive dissolution of crack edge in cse more than crack length lmm at 137MPa, 0.5Hz. As cyclic frequency and stress level got lower , the relation of AK and da/dN decreased influence for changer of the 2nd phase hardness, A s stress level gor lower and hardness of the 2nd phase gor higher, the roughness of fracture surface was increased.
3% NaCl 水溶液中에서 複合組織鋼의 腐蝕疲勞擧動에 미치는 第2相 硬度變化의 影響
吳世旭(Sae-Wook Oh),金雄執(Woong-Jib Kim) 한국해양공학회 1992 韓國海洋工學會誌 Vol.6 No.2
The only hardness of 2nd phase of martensite in dual phase steel which was composed of the martensite and ferrite was changed. Fatigue test was conducted by cantilever type of self-made rotated bending fatigue testing machine. The corrosion fatigue fracture behaviors of dual phase steel were investigated in 3% NaCl solution at Nf=1.5×10<SUP>5</SUP> and Nf=1.0×10<SUP>6</SUP> cycles.<br/> The fatigue strength was increased with increasing the hardness of 2nd phase. The size and number of corrsion pits were influenced by the 2nd phase hardness and pits remain constant in size just after they were transited into cracks. The life of crack initiation was effected by stress level. The shape of relation of ΔK and da/dn has smaller scattering in it in 3% NaCl solution than that in air. The higher the 2nd phase hardness is, the higher the corrosion fatigue life becomes. Corrosion fatigue fracture behavior was effected by mechanics in case of Nf=1.5×10<SUP>5</SUP>cycles and by electric-chemistry in case of Nf=1.0×10<SUP>6</SUP> cycles.
吳世旭(Sae-Wook Oh),金雄執(Woong-Jib Kim) 한국해양공학회 1991 韓國海洋工學會誌 Vol.5 No.2
Not only difference of fatigue crack growth and propagation behavior resulted from the grain size, the hardness ratio and volume fraction in M. E. F. dual phase steel composed of martensite in hard phase and ferrite in soft phase, but also the effects of the plastic constraint were investigated by fracture mechanics and microstructural method.<br/> The main results obtained are as follows :<br/> 1) The fatigue endurance of M. E. F. steel increases with decreasing the grain size, increasing the ratio of hardness and volume fraction.<br/> 2) The initiation of slip and crack occures faster as the stress level goes higher. These phenomena result from the plastic constraint effect of the second phase.<br/> 3) The crack propagation rate in the constant stress level is faster as the grain size gets larger, the ratio of hardness lower and volume fraction smaller.
3% NaCl 수용액중에서 복합조직강의 부식피로 파괴거동에 미치는 주파수변화의 영향
오세욱(S.W. Oh),신규동(K.D. Shin),김웅집(W.J. Kim) 한국해양공학회 1995 韓國海洋工學會誌 Vol.9 No.2
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 137 MPa with frequencies of 25 ㎐, 2.5 ㎐ and 0.5 ㎐ in 3% NaCl solution.<br/> 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 Ni/Nf 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.
SM 30 C강의 중공 중실축 단면변화가 부식피로강도에 미치는 영향
신규동(Kyou-Dong Shin),장백선(Paik-Sun Chang),김웅집(Woong-Jib Kim) 한국해양공학회 1997 韓國海洋工學會誌 Vol.11 No.2
The corrosion fatigue test was conducted in air to investigate the corrosion fatigue strength of SM 30 C steel by which was corroded in the under sea and the sea surface in the conditions of 3.0% NaCl salt solution. The fatigue tests were carried out on a rotary bending testing machine of cantilever type. The corrosion effect of the sea surface condition was severed more than that of the under sea condition which was due to the periodic contact of air thus accelerated the corrosion. The difference of the fatigue strength between sea surface and under sea conditions decreased with increase of stress level and corroded period. In the case of the solid shaft and thickness 2㎜ of hollow shaft, the difference of corrosion fatigue strength decreased as stress level and corrosion periodic increasing. On the contrary in the case of thickness 1㎜ of hollow shaft, the difference of it increased as stress level, corrosion periodic increasing and also the condition of corrosion changed. The main factors affecting the degradation of fatigue strength due to corrosion were the reduction of sectional area and the increase of surface roughness. The interference phenomenon increased with stress level got higher.