• Journal of Welding and Joining
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• v.14 no.4
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• pp.71-78
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• 1996

The effect of chemical composition on mechanical properry and corrosion resistance of austenitic stainless steel was investigated. The main results obtained were as follows : 1. There was a linear relationship between the tensile strength of stainless steel and the $Cr_{eq}/Ni_{eq}$. The larger the $Cr_{eq}/Ni_{eq}$ was the higher the tensile strength of stainless steel. 2. There was a good correlationship between $Cr_{eq}/Ni_{eq}$ and intergranular, gerneral corrsion rate. 3. Intergranular corrosion rate decreased linearly with increasing Cr content. 4. General corrosion rate decreased linearly with increasing Ni content. 5. Logarithm corrosion rate of intergranular and general corrosion has a linear relationship with all of the factor of $Cr_{eq}/Ni_{eq}$, Cr and Ni content.

• Journal of Korea Foundry Society
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• v.19 no.5
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• pp.410-418
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• 1999

To overcome the undesirable deformation, peeling off and geometrical restrictions which were mainly caused by differences in thermal expansion coefficients during the cladding of aluminum strip and stainless strip, new processing method based on vacuum die casting is designed and implemented in fabricating Fe-17wt%Cr steel (stainless steel). To increase cast-bonding ability, the surface of Fe-17wt%Cr steel is electrochemical etched to have optimum pit size (above 0.2 mm) and pit density (above 30%). The implementation of vacuum die casting by using surface treated stainless steel (Fe-17wt%Cr Steel) produces good trial products having acceptable cast-bonding ability. The enabling conditions for cast-bonding are pouring temperature $690^{\circ}C$, filling speed 30 m/sec and casting pressure $800\;kg/cm^2$. The microscopic observation of cast-bonded Al/Fe-17wt%Cr steel does not show any evidence of intermetallic compounds. The bonding strength of trial products is $150-400\;kg/cm^2$ and this is stronger than conventionally cladded metal having $30-70\;kg/cm^2$.

• Korean Journal of Metals and Materials
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• v.48 no.3
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• pp.194-202
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• 2010

Application of a stronger and more durable material for reactor pressure vessels (RPVs) might be an effective way to insure the integrity and increase the efficiency of nuclear power plants. A series of research projects to apply the SA508 Gr.4 steel in ASME code to RPVs are in progress because of its excellent strength and durability compared to commercial RPV steel (SA508 Gr.3 steel). In this study, the microstructural characteristics and mechanical properties of SA508 Gr.3 Mn-Mo-Ni low alloy steel and SA508 Gr.4N Ni-Mo-Cr low alloy steel were investigated. The differences in the stable phases between these two low alloy steels were evaluated by means of a thermodynamic calculation using ThermoCalc. They were then compared to microstructural features and correlated with mechanical properties. Mn-Mo-Ni low alloy steel shows the upper bainite structure that has coarse cementite in the lath boundaries. However, Ni-Mo-Cr low alloy steel shows the mixture of lower bainite and tempered martensite structure that homogeneously precipitates the small carbides such as $M_{23}C_6$ and $M_7C_3$ due to an increase of hardenability and Cr addition. In the mechanical properties, Ni-Mo-Cr low alloy steel has higher strength and toughness than Mn-Mo-Ni low alloy steel. Ni and Cr additions increase the strength by solid solution hardening. In addition, microstructural changes from upper bainite to tempered martensite improve the strength of the low alloy steel by grain refining effect, and the changes in the precipitation behavior by Cr addition improve the ductile-brittle transition behavior along with a toughening effect of Ni addition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.9 s.252
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• pp.1034-1040
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• 2006

Due to the need of increasing thermal efficiency, supercritical pressure and temperature have been utilized in power plants. It is well known that 9Cr1Mo steel is suitable fer use in power plants operating at supercritical conditions. Therefore, to ensure the safety and the soundness of the power plant, creep characterization of the steel is important. In this study, the creep characterization of the gCr1Mo steel using small punch creep(SP-Creep) test has been described. The applied load and the central displacement of the specimen in SP-Creep test have been converted to bearing stress and strain of uc, respectively. The converted SP-Creep curves clearly showed the typical three-stage behavior of creep. The steady-state creep rate and the rupture time of the steel logarithmically changed with the bearing stress and satisfied the Power law relationship. Furthermore, the Larson-Miller parameter of the SP-Creep test agreed with that of the tensile creep test. From the comparison with low Cr-Mo steels, the creep characteristics of 9Cr1Mo steel proved to be superior. Thus, it can be confirmed that the 9Cr1Mo steel is suitable for supercritical power plant.

• Korean Journal of Materials Research
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• v.11 no.4
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• pp.324-328
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• 2001

CrN films were deposited onto STD61 steel substrates using an arc-ion plating apparatus, with and without ion-nitriding pretreatment, and their oxidation was studied between 700 and $900^{\circ}C$ for 40hr in air. The oxidation behavior was examined by thermogravimetric analyses, X-ray diffraction. EDS and SEM. The deposited CrN films consisted of CrN and $Cr_2$N phases. The CrN films increased the oxidation resistance of the substrate by forming a protective $Cr_2$$O_3$ layer. The ion-nitriding pretreatment has not affected the oxidation resistance of the CrN film.

• Journal of the Korean institute of surface engineering
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• v.27 no.1
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• pp.19-28
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• 1994

A study on adhesion property of evaporated Al-Cr films was conducted on steel sheet by using two-source evaporator. Adhesion of Al-Cr coated steel was evaluated by tape test after $180^{\circ}$bending. Adhesion was decreased with increasing the Cr content in Al-Cr films. It was thought that the decrease in adhesion with increasing Cr content be related to insufficient wetting and diffusion of Cr atoms in the film. Best adhesion was achieved in the case of pure aluminum film..

• 연구논문집
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• s.23
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• pp.109-120
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• 1993

A study on corrosion and adhesion properties of evaporated Zn-Cr films were conducted on steel strip by two-source evaporater. Corrosion resistance of Zn-Cr coated steel was evaluated by salt spray test in 5% NaCl. Adhesion property of Zn-Cr films on steel substrate was evaluated by tape test after $180^\circC$ bending. Adhesion was improved with increasing the Cr content and reached the maximum at the Cr content of 6 to 8wt%. Corrosion resistance was enhanced with increasing the Cr content and improved by rolling Zn-Cr coated specimen, as a post-treatment.

• Laser Solutions
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• v.3 no.1
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• pp.29-37
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• 2000

For a development purpose of thick metal / metal Graded-Boundary Materials(GBM), a basic research on the fabrication of Ni-Cr/steel GBM was carried out by a laser beam and its mechanical properties and thermal characteristics were investigated. In order to produce a compositionally graded boundary region between substrate steel and added Ni-Cr alloy, a series of surface alloying treatments was performed with a high power CO$_2$ laser beam. Ni-Cr sheet was placed on a low carbon steel plate(0.18%C), and then a CO$_2$ laser beam was irradiated on the surface to produce a homogeneous alloyed layer. On this first surface-alloyed layer, another Ni-Cr sheet was placed and then the CO$_2$ laser beam was irradiated again to produce second surface-alloyed layer. Sequential repetitions of laser surface alloying treatment 4 times resulted in a graded-boundary region with the thickness of about 1.4mm. Simultaneous concentration profiles of different kinds of alloying elements(Ni and Cr) showed from 42%Ni, 45%Cr and 13%Fe on surface region to 0%Ni, 0%Cr and 99%Fe in substrate region. Also a thermal conductivity gradient resulted in graded-region and its value changed from 0.03㎈/cm s$\^{C}$ in surface region to 0.1㎈/cm s$\^{C}$ in substrate region. Microstructural observation showed that any visible root porosities and solidification shrinkage cracks were not formed in graded region between alloyed layer and substrate region during rapid cooling.

• Journal of Korea Foundry Society
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• v.5 no.4
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• pp.271-282
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• 1985

In order to investigate the mold reaction characteristics of Mn steel and Cr steel castings individually, the mold reaction products were examined by scanning electron microscopy, electron prove microanalyzer and X-ray diffractometer. From this experiment, the results were summarized as follows: 1) The mold reaction depth increased with increase of Mn content, while it decreased with increase of Cr content. 2) Mold reaction depth decreased with Mn content at $1200^{\circ}C$. 3) Mn, among the reaction products, forms a low fusion silicate, Mn $O.SiO_2$ while Cr forms a stable oxide, $CrO_3$ which hindering the reaction between FeO and $SiO_2$ thus the formation of $FeO.SiO_2$ was depressed.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.211-216
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• 2002

To investigate transition region in welded overlay relating to disbonding crack, the effect of vanadium addition on disbonding of Cr-Mo steels overlay welded with austenitic stainless steel was studied. V modified Cr-Mo steels have a higher resistance to disbonding than V free Cr-Mo steel. One reason is due to the fact that fine vanadium carbide precipated in base metal traps hydrogen and thus decreases the susceptibility to the disbonding. The second is related to the higher stability of the vanadium and stable carbides formed during PWHT, in which the carbon diffusion to the interface is lower than for V free Cr-Mo steel. Decreasing the carbon content at the interface of the weld overlay shows good resistance to the disbonding. Hence, it is important to control the carbon content at the interface of the weld overlay.