• Transactions of Materials Processing
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• v.15 no.2 s.83
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• pp.112-117
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• 2006

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 IN-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 was investigated. Wear rates of the solution-treated steel specimen remained low until 5N load, 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. The transformed phase underneath a sliding track was investigated and analyzed using a TEM. Effects of the phase transformation during the wear and $Cr_{2}N$ precipitates formed during the isothermal aging on the wear of the austenitic steel were discussed.

• Journal of the Korean Ceramic Society
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• v.33 no.12
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• pp.1421-1425
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• 1996

Sintered Si3N4 and Inconel composed of Ni(58-63%) Cr(21-25%) Al(1-17%) Mn(<1%) fe(balance) were pressurelessly joined by using Ag-Cu-Ti brazing filler metal at 950℃ and 1200℃ under N2 gas atmosphere of 1atm and their interfacial structures were investigated. In case that the reaction temperature was low as 950℃ its interfacial structure was "Inconel metal/Ti-rich phase layer/brazing filler metal layer/Si3N4 " Ti used as reactive metal existed in between inconel steel and brazing metal and moved to the interface of between brazing filler metal nd Si3N4 according as reaction temperature increased up to 1200℃. The interfacial structure of inconel steel-Si3N4 reacted at 1200℃ was ' inconel metal/Ni-rich phase layer containing of Fe. Cr and Si/Cu-rich phase layer containing of Mn and Si/Si3N4 " Cr Mn, Ni and Fe diffused to the interface of between brazing filler metal and Si3N4 and reacted with Si3N4 The most reactive components of ingredients of inconel metal were Cr and Mn. On the other hand Ti added as reactive components to Ag-Cu eutectic segregated into Ni-rich phase layer,.

• Journal of the Korean institute of surface engineering
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• v.44 no.2
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• pp.55-59
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• 2011

In this study, the mechanical properties of boronized 316L austenitic stainless steel have been investigated. Boronizing was carried out in solid medium consisting of Ekabor powder at $900^{\circ}C$ and $1000^{\circ}C$ for 2, 4 and 8 hours, respectively. The properties of sample were analyzed by field emission scanning electron microscope, X-ray diffractometer, Glow discharge spectrometer, micro-hardness tester and ball-on-disk wear tester. Increasing the boronizing time and temperature, the hardness of boronized samples were shown over Hv 2000 and the thickness of boride layers were also increased linearly. XRD patterns of samples were revealed the presence of borides such as FeB, $Fe_2B$, CrB, $Cr_2B$ and $Ni_3B$. Friction coefficient of boronized STS 316L was shown the low value at $900^{\circ}C$ for 8 hours and $1000^{\circ}C$ for 4 hours, respectively.

• 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.

• 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.

• Transactions of Materials Processing
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• v.32 no.2
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• pp.53-60
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• 2023

A wide range of grain size was achieved in a Fe-Cr-Mn austenitic stainless steel (STS) by cold rolling and reversion annealing. The tensile characteristics of the STS were analyzed in terms of the dependence of strain induced martensitic (SIM) transformation on the grain size. In the ultrafine grain regime, the steel showed a high yield strength over 1 GPa, a discontinuous yielding, and a prolonged yield point elongation followed by considerable strain hardening. By increasing the grain size, the discontinuous yielding diminished and the yield point elongation decreased. The microstructural examination revealed that these tensile characteristics are closely related to the suppression of SIM transformation with decreasing the grain size. Especially, the prolonged yield point elongation of the ultrafine grained STS was found to be associated with development of unidirectional ε martensite bands. Based on the microstructural examination of the deformed microstructures, the rationalization of the grain size dependence of SIM transformation was suggested.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.6
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• pp.361-367
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• 2009

The two-step gas nitriding was adopted to increase the depth of surface hardening in 3%Cr-Mo-V steel. The two-step gas nitriding consisted of Step I; $520^{\circ}C{\times}20\;hrs$ and Step II; $550^{\circ}{\times}70\;hrs$. The layer of two-step gas nitriding showed better uniformity and deeper nitriding layer than one-step gas-nitriding layer. The maximum surface hardness showed the value of 850 Hv. The maximum depth of nitrogen permeation showed $750\;{\mu}m$ (350 Hv). X-ray diffraction analysis showed that compound layer was mainly consisted of CrN and $\varepsilon-Fe_3N$ phases. These phases were presumed contributing to surface hardening and wear resistance. However, the corrosion resistance of gas-nitrided Cr-Mo-V steel were not improved in the solution of 1 N HCl and NaOH. Therefore, it is necessary that the continuous study for improvement of corrosion resistance hereafter.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1993.11a
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• pp.48-48
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• 1993

• Korean Journal of Materials Research
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• v.13 no.1
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• pp.36-42
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• 2003

The oxidation behaviors of Y-Cr bilayer deposited on ferritic steel by magnetron-sputtering for application of the Fe-Cr alloys as interconnectors of planar-type solid oxide fuel cells (SOFCs) were studied. After oxidation at $800^{\circ}C$ for 40 hours, the major phase of $Y_2$$O_3$and the minor phase of $YCrO_3$, $Mn_{1.5}$ $Cr_{1.5}$ $O_4$and Cr$_2$SiO$_4$were formed in the Y/Cr bilayered samples, while the major phase of Cr$_2$O$_3$and the minor phase of $Y_2$$O_3$were formed as the major phase in the Cr/Y bilayered samples. The Log(ASR/T) that expresses electric resistance of the Y/Cr coated specimen with nonconducting $_Y2$$O_3$oxide showed high value of -2.80 Ω$\textrm{cm}^2$$K^{-1}$ / and that of the Cr/Y coated specimen with conducting $Cr_2$$O_3$oxide appeared to be -4.11 Ω$\textrm{cm}^2$$^{K}$ . The electric resistance of the Y/Cr coated specimen was largely increased due to the formation of high resistance oxide scales. However, the Cr/Y coated specimen did not show any increase in the electric resistance and had the long-term stability of oxidation because there was no formation of the secondary phases with low conductivity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.285-293
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• 2004

Oxidation behavior of 304 and 430 stainless steel were studied using thin film X-ray analysis and glow discharge spectrum analysis (here-after GDS). The oxidation layer of 304 stainless steel was composed of $Cr_2O_3\;and\;FeCrO_4$ and its thickness was about $1.5{\mu}m$ after $1\~5$ minutes of annealing at $1120^{\circ}C$ open air. However, the oxidation layer of 430 stainless steels was mainly composed of $Cr_2O_3$ and its typical thickness was 0.5um after $1\~5$ minutes of annealing at $1000^{\circ}C$ open air. Electro-chemical analysis revealed that the descaling of oxidation layer could be activated by Fe, Cr dissolution from the matrix behind the oxidation layer at the current density of $5\~10ASD$ and by Fe, Cr-oxide dissolution from the oxidation layer at the current density over than 10ASD. Electrolytic stripping of 430 and 304 revealed the intial incubation period of descaling by oxygen evolving at low current density range such as $5\~10ASD$. However the dissolution of oxide layer was occurred when applying the anodic current of $10\~20ASD$ on 430 and 304 stainless steels. It was suggested that the electrolytic pickling of high Cr bearing stainless steel such as 430 and 304 seemed to be the more effective in the high current density range such as $10\~20ASD$ than the low current density range such as $5\~10ASD$.