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STS 321 강의 소둔열처리 조건이 입계부식특성에 미치는 영향
안용식,이용득,원태연,박미남 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.1
In this study, the effect of annealing temperatures, especially without the additional stabilization treatment, on the intergranular corrosion in STS 321 stainless steel was investigated. Nitric acid immersion and Electrochemical Potentiokinetic Reactivation(EPR) tests were periormed to find out an optimum annealing temperature. Also the effect of annealing temperature in relation with the sensitization, i.e. precipitation behavior of the Ti-precipitates, was studied. According to the microscopic results, titanium nitrides formed by solidification and also sulfides were observed in the hot band. On the other hand, titanium carbides and carbosulfides were detected in the annealed hot strip. The optimum annealing temperature for improving intergranular corrosion resistance was found about 1020∼1040℃. This was related to the increase of titanium carbide precipitation during sensitization.
Incolloy 800H 합금의 크리프성질에 미치는 냉간가공의 영향
정원섭,안용식,정해용 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.1
The Influence of cold pre-deformation on the creep properties at 800℃ has been investigated on the Fe-based superalloy INCOLLOY 800H. The material was plastically deformed in tension or compression at room temperature. Then, creep specimens were machined with the axis either transverse or parallel to the direction of cold deformation. The predeformed specimens show significantly lower creep rate and lower creep strain than unpredeformed specimens. This effect was already found after 2% predeformation and became even more pronounced with increasing pre-deformation. At higher creep stresses, recovery is easier and the effect on the creep rate and ductility is reduced. All creep specimens after cold deformation failed by intergranular fracture, in contrast that the undeformed specimens show transgranular fracture mode for creep stresses higher than 70 MPa.
이일옥,정원섭,안용식,정원배 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.8
In order to examine the reduction behaviour of fine iron ores in gas conveyed systems, rise rate of particles temperature are examined and effect of temperature, grain size and feeding rate of iron ore on reduction rate were studied. Results can be summarrized as follows ; 1. After supply of fine ores in gas conveyed systems, their velocity became almost instantaneously equal to the gas velocity. Accordingly the reduction time is nearly equal to the length of reactor tube divided by gas velocity. 2. Calculation of rise rate of particles temperature with assumption of lumped -heat-capacity systems showed that particles temperature became equal to the surrounding temperature in 0.1∼0.3 sec for the grain size below 100㎛. Temperature rise was slow for the paticles with grain size above 100㎛. 3. The reduction rate increased with the increasing temperature and with the decreasing ratio of fine iron ore to gas volume. 4. The fine ores which can be difficultly treated in the fludized bed could be reduced in the gas conveyed systems.
역변태를 이용한 준안정 오스테나이트계 스테인리스강의 강화
정병호,김영환,김창규,안용식,정해용,강창용 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.11
Austenite phase in metastable Fe-Cr-Ni ternary stainless steels was fully transformed to martensite(α') phase by 90% cold rolling and this martensite single phase reverted to austenite again at temperature range from 773 to 1073K. The mixed phase structure consists of reversed ultra-fine austenite grains with the diameter of 0.5 ㎛ and remained α'. Their mechanical properties were investigated as a function of α' content and austenite stability. The main results may be summarized as follows : (1) The good combination of high yield strength over 800MPa and elongation near 20% was obtained from the mixed structure containing a higher content of α', as Ni and Cr contents are lowered. (2) In the mixed structure, elongation was greatly affected by the TRIP behavior in the initial stage of deformation. (3) The ultra-fine graining of austenite more stabilized the mixed structure. (4) The abrupt drop of elongation in the mixed structure occurred at a limited content of α' in according to the difference of austenite stability. This phenomenon was well explained by the criterion equation of the plastic stability.
초미세립의 역변태 오스테나이트와 잔류 마르텐사이트와의 2상혼합조직 스테인리스강의 기계적 성질
정병호,김영환,김창규,안용식,정해용,강창용 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.1
The mechanical properties in a series of low carbon Fe-(15.5∼18.5)%Cr-10%Ni ternary stainless steels with two phase structure of deformation-induced martensite(α′) and reversed austenite(γ) after annealing for 0.6ks in the temperature range of 750 to 1100K were investigated as a function of α′ content and γ stability with transformation-induced plasticity(TRIP). All the steels almost transform to lath α′ from γ by 90% cold rolling and show α′ structure below γ content of 10%. The increase of Cr contents increases γ stability and hence decreases γ′ content in the same reduction of area. The deformed α′ rapidly reversed to γ in the temperature range of 773 to 873K and then the reversion was completed at about 1073K. The reversed γ has a ultrafine grain diameter of 0.5㎛. As a result of ultrafine grain structure of γ, the (α′ + γ) mixed structure was more stabilized. The good combination of high strength and elongation was obtained from the mixed structure containing a higher amount of retained α′ with decreasing Cr content. For example, for 15.5%Cr-10%Ni steel the proof stress of 0.79GPa and ultimate true tensile stress of 1.06GPa were obtained with elongation of 30%. The elongation caused by TRIP in the mixed structure was greatly affected by transformation behavior to α′ from γ in the initial stage of deformation.