• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1555-1557
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• 1998

In order to investigate the core material for over-head transmission line with non-magnetic and high strength nitrogen steel, microstructure and several basic properties of Fe-Mn-Cr-Ni-N steel have been studied. It is necessary that core material have a $\gamma$ phase to have a non-magnetic characteristics. To acquire a $\gamma$ phase, Mn, Ni and C are added as a alloying element. It was found that Fe-25Mn-16Cr-1Ni-N alloy have a stable $\gamma$ phase. The precipitate from this alloy system was $(Cr, Fe)_7C_3$. High Mn and N steel satisfies Sievert's relation that solubility of nitrogen increases with the square root of partial pressure of gas in metal-gas system and the hardness have proportional relation with nitrogen concentration.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.105-108
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• 2005

Sliding wear mechanism of a high nitrogen austenitic 18Cr-18Mn-2Mo-0.9N steel has been investigated. Dry sliding wear tests of the steel were carried out at various loads of 1N-10N under a constant sliding speed condition of 0.15m/s against AISI 52100 bearing steel balls. Solution $(1050^{\circ}C)$ and isothermal aging $(900^{\circ}C)$ heat treatments were performed on the steel and the effect of the heat treatments on the wear were investigated. Wear rates of the solution-treated steel specimen remained low until 5N, and then increased abruptly at loads above 5N. The rates of isothermally aged specimens were low and increased gradually with the applied load. Worn surfaces, their cross sections, and wear debris of the steel specimens were examined with a scanning electron microscopy. Phases of the heat-treated specimen and the wear debris were identified using XRD. Phases transformed underneath the sliding track during the wear were investigated and analyzed using TEM. Effects of the phase transformation during the wear and $Cr_2N$ precipitates formed during the isothermal aging on the wear of the austenitic steel were discussed.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.2
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• pp.101-108
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• 1997

In high carbon steels, the cementite phase is more unstable thermally than graphite, and it can lead to a marked deterioration in the formability. Many studies have been carried out to evaluate the effect of the fundamental elements on the graphitization of cementite in high carbon steels. In this present work, the effect of Mn, Cr addition on graphitization in Fe-0.65%C-1.0%Si steel has been investigated by means of hardness testing, optical microscopy and EPMA. The nucleation of graphite may mostly depend on the dissolution rate of cementite into ferrite and the number of the nucleation sites of graphite. The graphitization was promoted by the addition of 0.1%Mn in high carbon steel, but retarded by more addition than 0.5% of Mn. By the more addition of Cr than 0.1%, the graphitization of high carbon steel was strongly retarded. Because Mn was moderate anti-graphitizer, but Cr was stroug anti-graphitizer.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1999.05a
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• pp.103-104
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• 1999

• Journal of the Korean institute of surface engineering
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• v.50 no.5
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• pp.386-391
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• 2017

Two kinds of steels whose compositions were Fe-34.4Cr-14.5Ni-2.5Mo-0.4W-0.4Mn-0.5Si-(0.009 or 0.35)S (wt.%) were centrifugally cast, and oxidized at $900^{\circ}C$ for 50-350 h in order to find the effect of sulfur on the high-temperature oxidation of Fe-34.4Cr-14.5Ni-2.5Mo-0.4W-0.4Mn-0.5Si-(0.009 or 0.35)S (wt.%) alloys. These alloys formed oxide scales that consisted primarily of $Cr_2O_3$ as the major oxide and $Cr_2MnO_4$ as the minor one through preferential oxidation of Cr and Mn. They additionally formed $SiO_2$ particles around the scale/alloy interface as well as inside the matrices. The high affinity of Mn with S led to the formation of scattered MnS inclusions particularly in the 0.35S-containing cast alloy. Sulfur was harmful to the oxidation resistance, because it deteriorated the scale/alloy adherence so as to accerelate the adherence and compactness of the formed scales.

• Journal of Welding and Joining
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• v.19 no.5
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• pp.534-539
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• 2001

The formation mechanism of microconstituents in brazed joints of duplex stainless steel and Cr-Cu alloy which is an essential process of rocket engine manufacturing was investigated using Cu base insert metal. $SUS329J_3L$ and C18200 were used for base metal and AMS 4764 was used for insert metal. The brazing was carried out under various conditions. There were various phases in the joints, because of reaction between liquid insert metal and base metals. Since liquid insert metal reacts with duplex stainless steel, liquid Cu from insert metal infiltrated into the $\alpha/\beta$ interface of duplex stainless steel. Through the process of Cu infiltration, isolated stainless steel pieces come into the liquid insert metal. Since liquid insert metal reacts with Cr-Cu alloy. Cr precipitates from C18200 come into the liquid insert metal. With increment of bonding temperature and holding time, amounts and sizes of phases increased. but Cr-Mn compounds decreased at 1303k for 1.2ks and Mn-rich phases disappeared Fe-Cr compounds formed.

• Journal of the Korean institute of surface engineering
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• v.49 no.6
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• pp.587-594
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• 2016

Various surface treatments and thin film coating processes on the surface of injection die steel have been developed to extend the life. Most of previous studies were mainly focused on investigating the wear and static bonding behavior of thin films. In this study complex surface treatments of DLC coating combined with ion nitriding were applied to increase fatigue life and wear resistance. Ion nitriding, DLC coating, and DLC coating following nitriding on the surface of Fe-3.0Ni-0.7Cr-1.4Mn-X steel were investigated to uncover the beneficial effect which is applicable to injection die. The effect of various surface treatments and coating conditions on high cycle fatigue resistance was studied. Surface morphology change during fatigue tests were observed with AFM. Fatigue life of the die steel increased by 10 to 1,000 times at the various level of stress amplitudes in the condition of DLC coating following the ion nitriding for 3 hrs comparing with the only DLC coated condition.

• Journal of Powder Materials
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• v.28 no.4
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• pp.336-341
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• 2021

In this study, a nanocrystalline FeNiCrMoMnSiC alloy was fabricated, and its austenite stability, microstructure, and mechanical properties were investigated. A sintered FeNiCrMoMnSiC alloy sample with nanosized crystal was obtained by high-energy ball milling and spark plasma sintering. The sintering behavior was investigated by measuring the displacement according to the temperature of the sintered body. Through microstructural analysis, it was confirmed that a compact sintered body with few pores was produced, and cementite was formed. The stability of the austenite phase in the sintered samples was evaluated by X-ray diffraction analysis and electron backscatter diffraction. Results revealed a measured value of 51.6% and that the alloy had seven times more austenite stability than AISI 4340 wrought steel. The hardness of the sintered alloy was 60.4 HRC, which was up to 2.4 times higher than that of wrought steel.

• Composites Research
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• v.35 no.4
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• pp.248-254
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• 2022

In this study, TiB₂-steel composite with high-fractional TiB₂ reinforcement was fabricated by gas pressure infiltration process and the microstructure analysis and compressive strength and hardness were evaluated. To elucidate the correlation between microstructure and mechanical properties for fabricated composite, after the compression test of TiB₂-steel composite, the fracture surface was analyzed and the fracture behavior on compression test was predicted. As a result of the compression fracture surface analysis, interfacial failure trace between the steel matrix and the reinforcement was observed, and the interface between the steel matrix and the reinforcement was analyzed using TEM. From the result of microstructure analysis on the fabricated composite, it was confirmed that, in addition to TiB₂ reinforcement and steel matrix, TiC phase and coarse (Fe,M)₂B (M=Cr,Mn) phase were formed. Throughout the thermodynamic calculation, it was confirmed that TiC and (Fe,M)₂B can be formed as a stable phase under the process condition. The fabricated TiB₂-steel composite had a significantly increased hardness, and the compressive strength and Young's modulus were improved by 3.07 times and 1.95 times, respectively, compared to steel matrix. It seems that the coarse (Fe,M)₂B (M=Cr,Mn) phase formed throughout the composite causes the deterioration of mechanical properties, and by controlling the formation of the (Fe,M)₂B (M=Cr,Mn) phase, it is judged that the mechanical properties of the TiB₂-steel composite can be further improved.

• Journal of Power System Engineering
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• v.16 no.5
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• pp.76-82
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• 2012

Duplex stainless steels have the dual microstructure of austenite and ferrite phases. This steel exhibits generally a high corrosion resistance and higher mechanical strength compared with austenitic stainless steels. The steels used in the investigation have the chemical composition of Fe-22Cr-xNi-yMn-0.2N in which the contents of Ni and Mn were varied with maintaining the equal [Ni/Cr] equivalent. The fraction of ferrite phase was increased with the increase of annealing temperature. The impact factor of Mn element on the [Ni] equivalent was amended on the basis of the results of the investigation. 4Mn-2Ni alloy showed the highest pitting corrosion resistance. The fraction ratio, grain size and misorientation angle between grains were measured, and the correlation with pitting potential was investigated.