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Mn-Mo-Ni 계 저합금강과 열재현 HAZ 의 파괴특성
김상호(Sang Ho Kim),이성학(Sung Hak Lee),임영록(Young Roc Im),이후철(Hu Chul Lee),김성준(Sung Joon Kim),홍준화(Jun Hwa Hong) 대한금속재료학회 ( 구 대한금속학회 ) 2002 대한금속·재료학회지 Vol.40 No.9
This study is concerned with the effect of alloying elements on mechanical and fracture properties of Mn-Mo-Ni low alloy steels and their heat affected zones (HAZ`s). Three kinds of steels whose composition were varied from the composition specification of SA 508 steel (Grade 3) were fabricated by vacuum-induction melting and heat-treatment, and their mechanical and fracture properties were examined. ASTM E1921 standard test method was employed to measure fracture toughness in the transition temperature region of the steels. As C content decreased and Mo and Ni contents increased, the amount of fine M2C carbides was greatly increased, while that of coarse cementites was decreased, thereby leading to the improvement of tensile and fracture properties. Brittle martensite-austenite constituents were also formed in these steels during cooling, but did not deteriorate fracture toughness because they were decomposed to ferrite and fine carbides after tempering. Their simulated heat affected zones also had sufficient impact toughness after post-weld heat-treatment. These findings suggested that the low-alloy steels with high strength and toughness could be designed by decreasing C and Mn contents and by increasing Mo and Ni contents.
초내열합금 Mar-M247LC 의 저주기 피로수명 평가
이후철,최병학 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.9
The low cycle fatigue (LCF) life prediction model for directionally solidified(DS) Mar-M247LC superalloy has been stuided as the variables of plastic strain and stress range. The plastic strain range is the general criterion for LCF life prediction model like Coffin-Manson equation. On the other hand the stress range is also important to the criterion for LCF life evaluation. The complex effect of plastic strain and stress range on LCF life could be considered as the calculation of hysteresis loop area in fatigue testing. The LCF life as a function of plastic strain and stress range has been measured at the variables of strain rate and DS direction.
이후철,이주완 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.4
The effects of Sn addition on the internal oxidation of Ag-Cd alloys were studied. Four types of Ag-15Cd alloys with p.3, 0.5, 0.8, snd 1.5 wt% Sn were prepared by induction melting in Ar atmosphere. Alloys were internally oxidized at 677, 735 and 782 C with 1.0-3.0×10^5 Pa oxygen partial pressure. Internal oxidation increased the hardness of all alloys by 65-100%. Alloys with higher Sn content showed higher hardness. Oxidation condition proved to have significant influence on the oxidation microstructure and wear resistance. The oxides observed after internal oxidation were identified as SnO₂, Cd₂SnO₄ and CdO. Cd₂SnO₄ particles were embedded within CdO particles. The mechanism of oxidation is considered as follows. First. Sn is oxidized to form SnO₂, then it transforms to Cd₂SnO₄ by furthier reaction with Cd and O. Finally CdO grows around the Cd₂SnO₄ particles. Because Cd₂SnO₄ particles act as nuclei far CdO precipitation, finer dispersion of oxides occurs in higher Sn content alloys resulting in higher hardness and improved wear resistance of the alloy.
구리 함유 극저탄소강의 집합조직발달에 미치는 코일링 온도의 영향
이후철,서동우,양영철 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.11
The effects of coiling temperature on the texture development and mechanical properties of a 1wt% copper containing extra low carbon steel were investigated. An experimental alloy was vacuum induction melted, forged and then hot rolled. Coiling process was simulated by annealing at 500℃ or 700℃ for 1 hour and was followed by furnace cooling. After the coiling simulation, specimens were cold rolled with reduction ratio of 80% or 90%. ε-Cu precipitates in ferrite matrix are rarely observed in specimens coiled at 500℃ and coiling does not affect the development of {111} recrystallization texture. However fine ε-Cu particles are precipitated in α-Fe matrix when coiled at 700℃ and the precipitates remarkably increase the intensities of α-fiber texture components during cold rolling, retard the recrystallization during annealing and suppress the development of {111} recrystallization texture. Coiling temperature does not affect the tensile properties of 1wt% copper containing steel but, in specimens coiled at 700℃, suppression of {111} recrystallization texture results in lower mean plastic strain ratio.