• 한국주조공학회지
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• 제29권5호
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• pp.220-224
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• 2009

In order to investigate the microstructural morphology of the sulfide expected from the Fe-FeS phase diagram, a vacuum-sealed quartz tube where pure iron (99.9%) and sulfur (99.99%) powders were charged was heated upto $1000^{\circ}C$ in the electric resistance furnace, held for 96 hours and quenched in cold water and then, rod specimen was produced. Compositional difference of the sulfur between upper and lower parts of the rod was 7.5wt.% and segregation of the sulfur was gradually increased from the lower part to the upper one of the rod. The rod specimen was divided into three parts by the microstructural morphology of the sulfide. The upper part of the rod specimen revealed single phase FeS intermetallic. In the middle part of the specimen, hyper-eutectic microstructure where primary FeS was precipitated first and then, eutectic of $\alpha$-Fe and FeS was formed in the inter-dendritic region of the FeS. Especially, hypo-eutectic microstructure was appeared in the lower part of the specimen. After primary dendrite of $\alpha$-Fe solidified, FeS dendrite which included small amount of $\alpha$-Fe and FeS eutectic in the inter-dendritic region was formed.

• 한국표면공학회지
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• 제44권5호
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• pp.201-206
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• 2011

Fe-2%Mn-0.5%Si alloys were corroded at 600, 700 and $800^{\circ}C$ for up to 70 h in 1 atm of $N_2$ gas, or 1 atm of $N_2/H_2O$-mixed gases, or 1 atm of $N_2/H_2O/H_2S$-mixed gases. Oxidation prevailed in $N_2$ and $N_2/H_2O$ gases, whereas sulfidation dominated in $N_2/H_2O/H_2S$ gases. The oxidation/sulfidation rates increased in the order of $N_2$ gas, $N_2/H_2O$ gases, and, much more seriously, $N_2/H_2O/H_2S$ gases. The base element of Fe oxidized to $Fe_2O_3$ and $Fe_3O_4$ in $N_2$ and $N_2/H_2O$ gases, whereas it sulfidized to FeS in $N_2/H_2O/H_2S$ gases. The oxides or sulfides of Mn or Si were not detected from the XRD analyses, owing to their small amount or dissolution in FeS. Since FeS was present throughout the whole scale, the alloys were nonprotective in $N_2/H_2O/H_2S$ gases.

• Corrosion Science and Technology
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• 제13권2호
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• pp.41-47
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• 2014

The isothermal corrosion tests of several types of stainless steels, Ni-based alloys, and ferritic-martensitic steels (FMS) were carried out at the temperature of 550 and $650^{\circ}C$ in SFR S-$CO_2$ environment (200 bar) for 1000 h. The weight gain was greater in the order of FMSs, stainless steels, and Ni-based alloys. For the FMSs (Fe-based with low Cr content), a thick outer Fe oxide, a middle (Fe,Cr)-rich oxide, and an inner (Cr,Fe)-rich oxide were formed. They showed significant weight gains at both 550 and $650^{\circ}C$. In the case of austenitic stainless steels (Fe-based) such as SS 316H and 316LN (18 wt.% Cr), the corrosion resistance was dependent on test temperatures except SS 310S (25 wt.% Cr). After corrosion test at $650^{\circ}C$, a large increase in weight gain was observed with the formation of outer thick Fe oxide and inner (Cr,Fe)-rich oxide. However, at $550^{\circ}C$, a thin Cr-rich oxide was mainly developed along with partially distributed small and nodular shaped Fe oxides. Meanwhile, for the Ni-based alloys (16-28 wt.% Cr), a very thin Cr-rich oxide was developed at both test temperatures. The superior corrosion resistance of high Cr or Ni-based alloys in the high temperature S-$CO_2$ environment was attributed to the formation of thin Cr-rich oxide on the surface of the materials.

• 한국표면공학회지
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• 제22권1호
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• pp.10-16
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• 1989

The properties of carburization on Fe-Cr alloys at 900-96$0^{\circ}C$were investiged. The study on carbide layer which had developed during solid-carburizing was made by use of S.E.M, E.PM.A, and X-ray analyzer. The results obtained were summarized as follows, the composition of carbide and the value of activation energy for the growth of carbide layer on each Fe-Cr alloy were 1) Fe-1Cr : M3C and 52Kcal/mole 2) Fe-3Cr and Fe-5Cr : M7C3and 85-88Kcal/mole 3) Fe-7Cr and Fe-9Cr : (M7C3+M23C6)and 55-66Kcal/mole.

• 한국재료학회지
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• 제10권9호
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• pp.636-641
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• 2000

Zr-0.86Sn 합금이 $\beta{\rightarrow}\alpha$상변태 특성에 미치는 Fe와 V의 영향을 광학현미경과 투과전자현미경으로 연구하였다. 공냉의 경우에는 V의 첨가량이 증가함에 다라 $\beta{\rightarrow}\alpha+\beta$변태온도가 감소하여 미세한 $\alpha$-lath들의 폭을 더욱 감소시켰으나, Fe의 경우에는 첨가량이 증가함에 다라 오히려 $\alpha$-lath의 폭이 약간 증가하였다. 수냉의 경우에는 모든 합금에서 martensite 미세구조를 보였다. 수냉한 Zr-0.8Sn, Zr-0.8Sn-0.1Fe, Zr-0.8Sn-0.2Fe, Zr-0.8Sn-0.4Fe, Zr-0.8Sn-0.1V 그리고 Zr-0.8Sn-0.2V 합금에서는 주로 slipped martensite 미세구조가 형성된 반면에 수냉한 Zr-0.8Sn-0.4V 합금에서는 twinned martensite 미세구조가 관찰하였다. 수냉한 Zr-0.8Sn 합금에서 V의 첨가향이 증가함에 따라 slipped martensite에서 twinned martensite 미세구조로의 천이는 M(sub)s 온도의 감소에 기인한 것으로 생각된다.

• 한국분말재료학회지
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• 제6권1호
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• pp.96-102
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• 1999

The effect of Pb addition on microstructure and wear resistance was studied in rapidly solidified Al-20Si-5Fe-xPb(x=2, 4, 6 wt.%) alloys. The R/S Al-20Si-5Fe-xPb (x=2, 4, 6 wt.%) alloys showed a fine and homogeneous microstructure and an improved wear property compared with Al-20Si-5Fe alloy, while no significant change in UTS (Ultimate Tensile Strength) was shown. Contribution of the dispersoids on the wear property was discussed by showing the plastic deformation layers formed during wear track.

• Journal of Magnetics
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• 제4권4호
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• pp.131-135
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• 1999

The HDDR characteristics of the Nd-Fe-B-type isotropic and anisotropic HDDR alloys were investigated using three types of alloys: alloy A $(Nd_{12.6}Fe_{81.4}B_6), alloy B (Nd_{12.6}Fe_{81.3}B_6Zr_{0.1}), and alloy C (Nd_{12.6}Fe_{68.8}Co_{11.5}B_6Ga_{1.0}Zr_{0.1}$). The alloy A is featured with the isotropic HDDR character, while alloy B and C are featured with the anisotropic HDDR character. Hydrogenation and disproportionation characteristics of the alloys were examined using DTA under hydrogen gas. Recombination characteristics of the alloys were examined by observing the coercivity variation as a function of recombination time. The present study revealed that the alloy C exhibits slightly higher hydrogenation and disproportionation temperatures compared to the alloy A and B. Recombination of the anisotropic alloy B and C takes place more rapidly with respect to the isotropic alloy A. The intrinsic coercivities of the recombined materials rapidly increased with increasing the recombination time and then showed a peak, after which the coercivities decreased gradually. The degraded coercivity was, however, recovered significantly on prolonged recombination treatment. Compared with the isotropic HDDR alloy A the anisotropic HDDR alloy B and C are notable for their greater recovery of coercivity. The significant recovery of coercivity was accounted for the in terms of the development of well-defined smooth grain boundary between the recombined grains on prolonged recombination.

• 한국자기학회지
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• 제5권5호
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• pp.519-523
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• 1995

The Fe-TM-C-N nanocrystalline films (TM : Hf, Zr and Nb) are investigated to examine the relation between microstructure and soft magnetic properties. In these films, as the atomic radius of TM element increases, $P_{N2}$ which was added to get good soft magnetic properties was decreased and the maximum value of the permeability shifted to the high Fe range in the composition diagram. The best soft magnetic properties achieved in these films are : Hc of 0.15 Oe, $\mu_{eff}$ of 7800 (1MHz) and $4{\pi}M_{s}$ of 17.5 kG in Fe-Hf-C-N film ; Hc of 0.06 Oe, $\mu_{eff}$ of 2750 (1MHz) and $4{\pi}M_{s}$ of 16.8 kG in Fe-Zr-C-N film and Hc of 0.31 Oe; $\mu_{eff}$ of 2100 (1MHz) and $4{\pi}M_{s}$ of 15.5 kG in Fe-Nb-C-N film. It was considered that the stronger the bonding force between TM and C(N), the finer TM(C,N) phase is precipitated and therefore, the finer $\alpha$-Fe grains are formed. The effective permeability of the Fe-Zr-C-N films and Fe-Nb-C-N films remains nearly constant up to 10 MHz.

• 열처리공학회지
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• 제4권4호
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• pp.15-23
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• 1991

The damping capacities of the nonthermoelastic bcc type lath martensite and of the nonthermoelastic hcp type thin plate martensite in Fe-Mn alloys were studied. Fe-17%Mn alloy showing the hcp type thin plate martensite was superior to Fe-4%Mn alloy having the bcc type lath martensite in damping capacity. The damping capacity of the Fe-17%Mn alloy became greater with increasing the hcp martensite volume fraction. The damping mechanism of the Fe-4%Mn alloy was well explained by the dislocation model. However, the damping mechanism of the Fe-17%Mn alloy was explained on the basis of austenite/martensite interface moving model. The two alloys showed almost same levels of tensile strength. However, the elongation was greater in the Fe-17%Mn alloy than in the Fe-4%Mn alloy, showing lower yield strength in the former than in the latter. This result was considered to be attributed to formation of stress-induced martensite during tension test.

• 한국주조공학회지
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• 제29권6호
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• pp.270-276
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• 2009

After casting button-type small ingots of ternary Fe-Mn-S alloys which had three different Mn/S ratios (1, 5 and 70) in a vacuum arc furnace, the effect of the ratio on the sulfide formation was investigated. In case of the Mn/S ratio of 1, if alloy composition was located in an iron-rich corner on a Fe-Mn-S ternary phase diagram, only duplex MnS-FeS sulfide films were observed in the grain boundary. If the alloy composition was located in the miscibility gap area of the phase diagram, primary globular dendritic sulfides and dendritic sulfide slags were generated within the grain and tubular monotectic sulfides were also detected in the grain boundary. When the Mn/S ratio was 5, if the alloy composition was in the iron-rich corner, only bead-like sulfides were generated. On the other hand, if the composition was in the miscibility gap area, globular dendritic sulfides and dendritic sulfide slags were generated in the form of primary sulfide inclusions and rod-like eutectic sulfides were observed in the grain boundary. Especially, if the contents of Mn and S increased more in the miscibility gap area of the phase diagram, primary globular sulfides containing iron intrusions were observed. In case of Mn/S ratio of 70, if the contents of Mn and S was decreased in the Fe corner of the phase diagram, only bead-like sulfides were observed in the grain boundary. Despite the composition was outside the miscibility gap area of the phase diagram, if the contents of Mn and S increased, clusters of fine sulfide particles as well as fine spherical primary monophase sulfides were observed in the grain boundary.