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Ni기 삽입금속에 의해 진공 브레이징된 stainless steel의 특성평가
장세훈,홍지민,정창열,최세원,오익현,Chang, Se-Hun,Hong, Ji-Min,Jeong, Chang-Yeol,Choi, Se-Weon,Oh, Ik-Hyun 한국재료학회 2007 한국재료학회지 Vol.17 No.6
Microstructure and tensile strength of the vacuum brazed stainless steel were investigated in this study. For vacuum brazing of the stainless steel 303 and 304, the BNi-2, 3, 4 and 7 were used as filler metals. Among these filler metals, the BNi-2 showed excellent wettability at $1050^{\circ}C$. Indeed, the brazed stainless steel using the BNi-2 showed the highest tensile strength (483 MPa) among all brazed specimens. This is attributed to degree of interfacial reaction between the filler metal and stainless steel. Brazed stainless steel with BNi-2, 3 filler metals showed almost elastic deformation followed by plastic yielding and strain hardening up to a peak stress. On the other hand, it is likely that the fracture of the brazed specimens with BNi-4, 7 was occurred in elastic range without plastic yielding up to a peak stress.
고신율 금형주조용 Al-9wt%Si-Mg계 합금의 주조특성에 미치는 Fe, Mn함량의 영향
김헌주 ( Heon Joo Kim ),정창열 ( Chang Yeol Jeong ) 한국주조공학회 2013 한국주조공학회지 Vol.33 No.6
Effect of Fe and Mn contents on the castability of Al-9wt%Si-xMg-yFe-zMn alloy has been studied. The alloy was composed of α-Al phase, Al+eutectic Si phase, β-Al5FeSi compound and chinese script α-Al15(Mn,Fe)3Si2 compound. β-Al5FeSi and α-Al15(Mn,Fe)3Si2 compounds assumed to effect the fluidity and shrinkage behaviors of the alloy during solidification due to the crystallization of α-Al15(Fe,Mn)3Si2 and β-Al5FeSi compounds above eutectic temperature. As Fe and Mn contents of Al-9wt%Si- 0.3wt%Mg system alloy increased from 0.15wt% to 0.6wt% and from 0.3wt% to 0.7wt%, fluidity of the alloy decreased by 5.7% and 3.3%, respectively. And as Mg content of Al-9wt%Si-0.45wt%Fe-0.5wt%Mn system alloy increased from 0.3wt% to 0.4wt%, fluidity of the alloy decreased by 8.6%. When Fe content of the alloy increased from 0.15wt% to 0.6wt%, macro shrinkage ratio decreased from 6.1% to 4.1%, and micro shrinkage ratio increased from 0.04% to 0.24%. Similarly, Mn content of the alloy increased from 0.3wt% to 0.7wt%, macro shrinkage ratio decreased from 6.0% to 4.5% and micro shrinkage ratio increased from 0.12% to 0.18%. Judging from the castability of the alloy, Al-9wt%Si-0.3wt%Mg alloy with low content of Fe and Mn, 0.1wt% Feand 0.3wt% Mn, is recommendable.
승용디젤엔진 실린더 헤드용 Al-Si-Mg-(Cu) 합금의 저주기 피로 특성에 미치는 첨가원소 효과
진보라 ( Bo-ra Jin ),정창열 ( Chang-yeol Jeong ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.9
To improve automobile fuel efficiency and reduce emissions, there has been a growing demand for more durable alloys for engine components with improved high temperature fatigue resistance. This study examined the effect of alloying elements on the high temperature mechanical behavior of Al-Si-Mg-(Cu) casting alloys for diesel cylinder heads. Depending on the effect of the alloying elements on the strength of the matrix, hardness at high temperatures increased with increasing Cu and Ti content with a concomitant increase in tensile strength. The LCF (low cycle fatigue) lives decreased with increasing alloy content according to the Coffin-Manson relation, due to smaller elongation. On the other hand, an analysis of fatigue lives with hysteresis loop energy, which consists of both strength and elongation, showed that the fatigue lives were normalized with an alloy of the same strengthening mechanisms, regardless of the test temperature. In the case of the alloy without Cu, an obvious cyclic softening behavior was observed, whereas the cyclic softening decreased significantly and the peak stress was maintained at 250 ℃ for the alloy with Cu. Dynamic mechanical analysis results showed that the mechanical properties of the Al2Cu precipitate hardened alloy were maintained at temperatures over 250 ℃, whereas the degradation of mechanical properties of the Mg containing alloy occurred at 170 ℃ due to coarsening of the Mg2Si precipitation phase.(Received November 19, 2015; Accepted April 5, 2016)
1Cr-Mo-V 강에서 고온저주파 피로의 균열 전파속도에 관한 연구
남수우,정창열 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.3
Smooth cylindrical specimens of 1Cr-Mo-V steel were tested under HTLCF( high-temperature low-cycle fatigue) conditions to investigate the growth behavior of microcracks. HTLCF crack growth rate is analyzed based on the concept of J-integral by monitoring the hysteresis loop. A new approach that the crack growth rate is measured by the striation counting from the observation of SEM(scanning electron microscope) fractographs was shown to be successful in determining the LCF crack growth rate as well as the LCF life. It is shown that ΔJ is reasonable in characterizing the growth rate of fatigue microcracks at elevated temperatures but results in unacceptable deviations for the hold time cycling owing to the relative contribution of time dependent processes at the crack tip. Approach of C(t) correlated with ΔJ gives recommendable results for interpreting the crack growth rate with hold time.
1Cr-Mo-V 강의 피로 균열선단 변형의 온도 의존성에 관한 연구
남수우,이수찬,정창열 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.9
For the theoretical discussion of the crack advance phenomena, many models have been suggested. However, most of them could not suggest the exact processes of the crack-tip region in the low cycle fatigue conditions, but only rough approximations in terms of LEFM for the damage of crack-tip region. Recently, Oh and Nam suggested a new model of crack advance and life prediction based on the damage formation in fatigue process zone, where the concentrated degradation of the material occurred with crack advance. In the previous studies a parameter of α₁ which is the term of correcting plastic zone size was suggested to be constant by many researchers in a fixed temperature. But the experimental results for 1Cr-Mo-V steel showed that α₁ is a function of temperature, and the microhardness tests proved that the smaller the value of α₁ in high temperature, the smaller the size of cyclic plastic zone(n).