Ti-Ni-B 형상기억합금의 상변태 및 열피로 특성

이오연,홍성원,임병희 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.8

The purpose of this study is to investigate the effect of heat treatment on the martensitic transformation behavior and thermal fatigue characteristics in Ti-:Vi-B alloys with various boron concentration. Three types of heat treatment are given to the specimens ; i) solution treatment ii) aging iii) cold work and low temperature anneal. This research had been performed by electrical resistance measurement, x-ray diffraction and transmission electron microscopy. In solution treated specimens, the Ms has been decreased with the increasing of boron content. However, It has not been affected by aging, while that of 30% cold rolled and annealed specimens has been remarkably increased in the vicinity of recrystallization temperature. R-phase transition which is related to abnormal increase of electrical resistance prior to martensitic, transformation has been formed at a boron content of 0.2at%. The cold worked and annealed specimens have a good thermal fatigue characteristics independent of boron concentration, because a high density of dislocations rearranged by the low temperature annealing after cold work has suppressed the introduction of dislocations during the thermal fatigue cycling.

析出硬化型 窒化鋼에 關한 硏究

李五演,南泰運,金文哲 전북대학교 공업기술연구소 1982 工學硏究 Vol.12 No.-

In this report, the nature of the surface layer of electrolytic iron, carbon steels, SKD-11 and stainless steels nitrided with ammonia gas under various conditions was investigated by microvickers hardeness test, X-ray diffraction and optiocal microscope. The results obtained are summarized as follows: (1) When the NH₃gas flow is increased to the critical rate of 200㎖/min, the 녁face hardness of the specimen increases sharply, but allowing the gas flow velocity to exceed to this value yields a lower hardeness. (2) In gas nitriding of electrolytic iron, increasing the nitriding temparature and time lead to an increase the thickness of the nitriding layer. (3) The decrease of the surface hardness in the nitrided electrolytic iron is due to the relief of stress by the formation of pores and pore channels in the zone of ε-phase richer in nitrogen. (4) The surface hardness of nitrided carbon steels increases with carbon content, since the partial pressure of nitrogen is low. (5) In SKD-11 and stainless steels, the depth of the nitrided layer depends upon the Cr, Ni content as alloying elements, and also the phases of the matrix at treating temperature. (6) In nitriding of stainless steels at 600℃ for 20hrs., martensitic structure of AISI 4021 shows the highest hardness, Hv 980 and the depth of the nitrided layer reaches 250㎛. (7) ε-Fe₂-₃N,γ'-Fe ₄N,α-Fe, CrN and Cr₂N phases are detected from the nitride surface in SKD-11 and stainless steel by X-ray diffraction analysis. These nitrides is caused to the surface hardening.

鋼의 이온 窒化法

李五演 大田工業專門大學 1979 論文集 Vol.25 No.-

The purpose of the present paper is to studv the time for case depth formation as a function of time for commercially important four different grades of steels by ion-nitriding, and to compare some of the results with conventional gaseous nitriding. These sample were ion-nitrided at different temperatures with cycle times ranging from 1 hour to 36 hours in a gaseous mixture of nitrogen and hydrogen under a total pressure of 7 Torr. The result summalized is as follow : 1. The rate of ion-nitriding is significantly faster than conventional gaseous nitriding. 2. The case depth as a function of treatment time at a given temperature follows the parabolic law for all four grades of steels. 3. Finally results of ion-nitriding at a temperature of 400℃ hare been presented to show the versatility of this process.

Ti-Ni 形狀記億合金의 마르텐사이트 變態에 미치는 Nb의 影響

李五演 全北大學校 1991 論文集 Vol.33 No.-

The transformation behavior of Ti-Ni alloys considerably affected by alloying elements and heat treatment conditions. In order to study the effect of Nb addition on the martensitic transformation behavior of Ti-Ni-Nb alloys, this study has been performed by electrical resistance measurement and X-ray diffraction. In case of 0.2at%Nb addition, Ms temperature has been increased about 20℃ rather than that of an equiatomic Ti-Ni alloy, but it has been found to be decreased with the increase of Nb content, while Ms temperature has been increased by the addition of 3.0at%Nb, The Ms temperature of Ti-Ni-Nb alloys has not been affected by aging, while that of 30% cold rolled and annealed specimens has been found to be remarkably increased in the vicinity of recrystallization temperature. However, it has been found to be almost constant above 600℃. R-Phase transition has been occurred in Ti_50Ni_50-x Nb_x(X=0.2∼3.0at%) alloys which were cold rolled and low temperature annealing, but this phenomenon has not been appeared in Ti_50Ni_48Nb_2 alloy.

高Cr鑄鐵의 耐磨耗性과 衝擊靭性 向上에 關한 硏究

李五演,金錫元,禹基道 전북대학교 공업기술연구소 1984 工學硏究 Vol.15 No.-

High chromium cast irons have been well-known for their abrasive wear resistance. Its principal mechanical properties are high hardness and good impact toughness,. Generally, abrasion resistance increases with an increase of material hardness. The mechanical properties of Cr cast iron is influ-enced by microstructual factors such as the volume of carbide, carbide morphology and structure of matrix. From this point of view, therfore, the purpose of this study was investigated in connection with the microstructual fators and the mechanical properties of Cr cast iron by destablized isothermal heat-treatment. Conclusions resulting from this study are as follows ; 1. In case of destabilized isothermal heat-treatment at 400℃ and 1000℃, hardness was remakably increased since carbide area percentage was increased in matrix with rapid-cooling rate. 2. since eutectic carbide(M_7C_3) was grown toward colony boundary while matrix was strengthened by solution hardening of Cr and Si, good impact toughness was obtained by destablized heat-treatment at 800℃ .3. In fractographs of these specimens, small amount of dimple patterns was presented. but almost of them was observed typical qussi-cleavage fracture mode to be seen in brittle materials. 4. In the using of this high Cr cast iron (2.45% C, 16.51% Cr) for pulverizing mills, the suitable mechanical properties such as toughness, hardness and wear resistance were obtained by destablized isothermal heat-treatment at 800℃

Ti-Ni-Al 형상기억합금의 상변능 및 변형거동

이오연,천병선,이순난 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.7

The effect of heat treatments and cold reduction on the martensitic transformation and pseudoelasticity behavior in Ti-Ni-Al alloys has been investigated by means of electrical resistance measurement, tensile test, optical and transmission electron micros copy. The transformation temperatures have linearly decreased with the increase of Al content and R-phases have been formed along the grain boundary. The thermal hysteresis of R-phase transition has been hardly affected by cold reduction, but that of martensitic transformation has been remarkably increased. The critical stress for the first stags in Ti_(50)Ni_(49)Al_(1.0) alloy is almost costant (40∼50 Mpa) irrespective of cold reduction, but that of stress induced martensite is considerably increased.

7XXX계 단조재의 피로 및 파괴인성에 미치는 제조공정의 영향

이오연,임재규,송기홍,손영일,은일상,신돈수 ( O . H . Lee,J . K . Lim,K . H . Song,Y . I . Son,I . S . Eun,D . S . Shin ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.3

The purpose of this study is to investigate the effect of impurity level and fabrication processes on the strength, fracture toughness and fatigue resistance of 7075, 7050 and 7175 high strength aluminum forgings. It has been verified that plane strain fracture toughness and fatigue characteristics of a specially processed 7175S-T74 alloy is superior to a conventionally processed 7075-T6/T73, 7050-T74 and 7175-T74 alloys. These beneficial effects primarily arise from two view points, i.e., the effect of reducing the impurity level of iron and silicon has significantly diminished the size and volume fraction of second phase particles such as Al_7Cu₂Fe and Mg₂Si. Futher reduction of the amount of nonequilibrium second phase particles has been observed by applying a special fabrication process.

Ti-Ni-B 형상기억합금의 마르텐사이트변태 및 인장변형거동에 미치는 열처리의 영향

이오연,박영구,안행근 ( O . Y . Lee,Y . K . Park,H . K . Ahn ) 한국열처리공학회 1995 熱處理工學會誌 Vol.8 No.1

The purpose of this study is to investigate the effect of heat treatments on the martensitc transformation and tensile deformation behavior in Ti-Ni-B alloys with various boron concentration. Three types of heat treatment are given to the specimens; i) solution treatment ii) aging iii) thereto-mechanical treatment. In solution treated specimens, R-phase transition which is related to abnormal increase of electrical resistance prior to martensitic transformation has been formed at a boron content of 0.2at% and the M, temperature has been decreased with the increasing of boron content. However, It has not been affected by aging, while that of thereto-mechanically treated specimens has been remarkably increased in the vicinity of recrystallization temperature. The thereto-mechanically treated specimen has showed a good thermal fatigue characteristics, shape memory effect and superelasticity in comparison with the solution treated specimen.

Ti-Ni-Cu 형상기억합금의 상변태 및 초탄성에 미치는 가공열처리의 영향

이오연,박영구,쳔병선 ( O . Y . Lee,Y . K . Park,B . S . Chun ) 한국열처리공학회 1994 熱處理工學會誌 Vol.7 No.4

Transformation behavior and superelastic behavior of Ti-Ni-Cu alloys with various Cu content has been investigated by means of electrical resistivity measurement, X-ray diffraction, tensile test and transmission electron microscopy. Two types of heat treatment are given to the specimens : i) Solutions treatment. ii) thermo-mechanical treatment. The transformation sequence in solution treated Ti-Ni-Cu Alloys substituted by Cu for Ni up to 5at.% occurs to B2◎B19` and it proceeds in two stages by addition of 10at.%Cu, i. e, B2◎B19◎B19`. Also, it has been found that Ti-30Ni-20Cu alloy transformed in one stage : B2◎B19. The thermo-mechanically treated Ti-47Ni-3Cu alloy transformed in two stages : B2◎rhomboheral phase◎B19`, while transformation sequence in Ti-45Ni-5Cu and Ti-40Ni-l0Cu alloy transformed as same as solution treated specimens. The critical stress for inducing slip deformation in solution treated and thermo-mechanically treated Ti-40Ni-l0Cu alloy is about 90㎫ and 320㎫ respectively.

0.14C-6.5Mn TRIP강의 기계적 성질에 미치는 제조공정의 영향

이오연,류성일,Lee, O-Yeon,Ryu, Seong-Il 한국재료학회 2001 한국재료학회지 Vol.11 No.5

본 연구는 제조공정을 달리한 0.14C-6.5Mn강을 2상영역에서 역변태처리 하였을 때 다량의 잔류오스테나이트를 생성시키기 위한 열처리 조건을 제시하고 잔류오스테나이트의 생성과 관련하여 미세조직 관찰, C, Mn의 분배거동 및 기계적성질을 조사하였다. 잔류오스테나이트는 역변태처리시 오스테나이트내에 C, Mn의 확산으로 농축되어 안정화되며 연성향상에 크게 기여한다. 30%이상의 잔류오스테나이트를 확보하기 위해서는 6457에서 역변태처리하는 것이 효과적이지만, 잔류오스테나이트의 부피 분율과 기계적안정성을 고려하면 $620^{\circ}C$에서 열처리하는 것이 바람직하다. 냉연재의 강도.연성조합값은 3강종 모두 $620^{\circ}C$에서 1시간 역변태처리한 경우 4000kg/$\textrm{mm}^2$정도로 매우 우수하지만 고온에서는 연성감소로 인하여 그 값이 현저하게 저하하였다. 0.14C-6.5Mn계 TRIP강에서 잔류오스테나이트 생성과 기계적성질에 미치는 1.1%Si 첨가효과는 매우 미약하였다. This research was examined the effect of intercritical heat treatment on the mechanical Properties and retained austenite formation in 0.1C-6.5Mn steels for the development of a high strength high ductility steel. using of transformation induced plasticity due to retained austenite. The stability of retained austenite is very important for the good ductility and it depend on diffusion of carbon and manganese during reverse transformation. It is effective to heat treat at$ 645^{\circ}C$ in order to obtain over 30 vol.% of retained austenite. However, it is more desirable to heat treat at $620^{\circ}C$, considering the volume fraction and mechanical stability of retained austenite. The strength-elongation combination in cold rolled steel sheets after reverse transformed at $620^{\circ}C$ for 1hr was about 4000k9/mm7, but it decreased rapidly with increasing holding time at high temperature due to the decrease of ductility. The addition of 1.1%Si in 0.14C-6.5Mn TRIP steel does not improve the mechanical properties and retained austenite formation.