• Journal of the Korean institute of surface engineering
• /
• v.53 no.2
• /
• pp.72-79
• /
• 2020

Two Fe-Cr steels of T22 steel and STS430 steel were corroded at 650 and 750℃ for 100hr in sewage sludge-(0.3% SO₂-6% O₂-10% H₂O-balance CO₂) mixed gas environment. T22 steel corroded faster than STS430, indicating that the Cr content significantly influence the corrosion rates. T22 formed thick and non-protective Fe₂O₃ as the major oxide and Fe₃O₄ as the minor one. With an increase in corrosion temperature, their corrosion rates increased, being accompanied with formation of pores and cracks in the thickened oxide scales that were non-adherent. STS430 steel formed Fe₂O₃, Fe₃O₄ as the outer scale and (Fe, Cr)-O as the inner layer by which its corrosion rate is greatly reduced. Both the T22 and STS430 steel samples formed multi-layered scales by outward diffusion of Fe ions and inward diffusion of oxygen and sulfur ions at high-temperature more than 650℃.

• Nuclear Engineering and Technology
• /
• v.29 no.5
• /
• pp.361-367
• /
• 1997

The phase separation in ferrite phase of duplex stainless steel is the primary cause of thermal aging embrittlement of the LWR primary pressure boundary components. In this study the phase separation of simulated duplex stainless steel was detected by Mossbauer spectroscopy and magnetic property analysis by VSM(Vibrating Specimen Magnetometer). The simulated duplex stainless steels, Fe-Cr binary, Fe-Cr-Ni ternary, and Fe-Cr-Ni-Si quarternary allots, were aged at 370 and 40$0^{\circ}C$ up to 5,340 hours. It was observed from Mossbauer spectra analysis that internal magnetic field increases with aging time and from VSM that the specific saturation magnetization and Curie temperature increase with aging time. These result are indicative that phase separation into Fe-rich region and Cr-rich region is caused by thermal aging in the temperature range of 370~40$0^{\circ}C$ In cases of specimens containing Ni, the increase of specific saturation magnetization is much higher. This implies that Ni seems to promote Fe-Cr interdiffusion, which accelerates the phase separation into Fe-rich $\alpha$ phase and Cr-rich $\alpha$' phase.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.05a
• /
• pp.385-388
• /
• 2009

Dry-sliding-wear behavior of Fe-18Cr-l0Mn steel with various carbon and nitrogen contents was characterized, and the effect of carbon and nitrogen contents on the wear was investigated. Dry sliding wear tests of the steel were carried out at room temperature against an AISI 52100 bearing steel ball using a pin-on-disk wear tester. Applied wear loads were varied from 10 N to 100 N, and the sliding distance was fixed as 720 m. Worn surfaces and the wear debris of the steel were examined using an SEM to find out the wear mechanism. It was found that the Fe-18Cr-10Mn with both carbon and nitrogen exhibited superior wear resistance to the steel with only nitrogen. The wear resistance of the Fe-18Cr-10Mn-xC-yN alloy increased with the increase of the carbon content. The excellent wear resistance of the Fe-18Cr-10Mn-xC-yN alloy was explained by the increased strain-hardening capability with the interstitial atoms.

• Corrosion Science and Technology
• /
• v.13 no.1
• /
• pp.1-5
• /
• 2014

A low carbon steel, Fe-2.25%Cr steel (ASTM T22), and Fe-2.25%Cr-1.6%W steel (ASTM T23) were aluminized by hot dipping into molten Al baths. After hot-dipping, a thin Al-rich topcoat and a thick alloy layer formed on the surface. The topcoat consisted primarily of a thin Al layer that contained a small amount of Fe, whereas the alloy layer consisted of Al-Fe intermetallics such as $Al_5Fe_2$ and AlFe. Cr, Mo, and W in T22 and T23 steels reduced the thickness of the topcoat and the alloy layer, and flattened the reaction front of the aluminized layer, when compared to the low carbon steel.

• Korean Journal of Materials Research
• /
• v.14 no.1
• /
• pp.52-58
• /
• 2004

The surface property and formation behavior of a boride layer formed on Ni-Cr-Mo steel in a plasma paste boronizing treatment were investigated. The plasma paste boronizing treatment was carried out at 973～1273 K for 1-7 hrs under the gas ratio of Ar:H$_2$ (2:1). The thickness of the boride layer increased with increasing temperature and time in the boronizing treatment. The cross-section of the boride layer was a tooth structure and the hardness was Hv 2000～2500. XRD analysis revealed that the compound was identified as FeB, $Fe_2$B, and mixed phase of FeB/$Fe_2$B in the boride layer formed at 973～1073 K, 1173K, and 1273K, respectively. The Ni-Cr-Mo alloy boronized at 1173-1273 K showed the best excellent wear resistance against the sand. As a results of corrosion test in 1 M $H_2$$SO_4$ solution, $Fe_2$B formed on the matrix alloy exhibited higher corrosion resistance than FeB.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2006.05a
• /
• pp.421-424
• /
• 2006

High nitrogen steels (HNS) exhibit both high strength and ductility during tensile deformation. In the present study the Fe-18Cr-14Mn-4Ni-0.9N high nitrogen steel was heat treated at $1000^{\circ}C$ and $1100^{\circ}C$ to produce $Cr_2N$ precipitates in austenite matrix and full austenite microstructures, respectively. Tensile tests of the heat treated specimens were performed at two different strain rates of 0.05/sec and 0.00005/sec. Each tensile curve of the specimens could be well characterized by the the modified Ludwik equation. Plastic deformation of the steel was adequately represented by the four parameters of the modified Ludwik equation. At 0.05/s strain rate, the specimen with the $Cr_2N$ precipitate exhibited higher strength than the full austenite specimen, while the full austenite specimen showed better mechanical properties at 0.00005/s strain rate. It was found that the $Cr_2N$ precipitates influences deformation behavior of the high nitrogen steel significantly.

• Corrosion Science and Technology
• /
• v.7 no.4
• /
• pp.201-207
• /
• 2008

$CO_2$ corrosion product scales formed on 13 Cr tubing steel in autoclave and in the simulated corrosion environment of oil field are investigated in the paper. The surface and cross-section profiles of the scales were observed by scanning electron microscopy (SEM), the chemical compositions of the scales were analyzed using energy dispersion analyzer of X-ray (EDAX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) to confirm the corrosion mechanism of the 13 Cr steel in the simulated $CO_2$ corrosion environment. The results show that the corrosion scales are formed by the way of fashion corrosion, consist mainly of four elements, i.e. Fe, Cr, C and O, and with a double-layer structure, in which the surface layer is constituted of bulky and incompact crystals of $FeCO_3$, and the inner layer is composed of compact fine $FeCO_3$ crystals and amorphous $Cr(OH)_3$. Because of the characteristics of compactness and ionic permeating selectivity of the inner layer of the corrosion product scales, 13 Cr steel is more resistant in $CO_2$ corrosion environment.

• Corrosion Science and Technology
• /
• v.14 no.3
• /
• pp.127-131
• /
• 2015

Model alloys Fe-9Cr, Fe-20Cr and Fe-20Cr-20Ni (wt. %) with 0.1 and 0.2 % Si were exposed to $Ar-20CO_2-20H_2O$ gas at $818^{\circ}C$. The undoped alloys formed a thick iron-rich oxide scale. The additions of Si reduced scaling rates of Fe-9Cr to some extent but significantly suppressed the formation of iron oxide scales on Fe-20Cr and Fe-20Cr-20Ni. Carburisation also occurred in all undoped alloys, but not in Si-containing Fe-20Cr and Fe-20Cr-20Ni. Protection against carburisation was a result of the formation of an inner scale layer of silica.

• Journal of Welding and Joining
• /
• v.23 no.2
• /
• pp.75-80
• /
• 2005

The effect of chemical constituents of $(Cr,\;Fe)_7C_3$ carbide phase on its hardness in the chromium-carbide type Cr white iron hardfacing weld deposits has been investigated. In order to examine $(Cr,\;Fe)_7C_3$ carbide phase, a series of filler metals with varying chromium contents was used. The alloys were deposited once or twice on a mild steel plate using the self?shielding flux cored arc welding process. The hardness of $(Cr,\;Fe)_7C_3$ carbide phase was measured by the micro-Vickers hardness test. It was shown that hardness of $(Cr,\;Fe)_7C_3$ carbide phase increased with increasing Cr content in $(Cr,\;Fe)_7C_3$ carbide phase. This behavior of the hardness of $(Cr,\;Fe)_7C_3$ carbide phase was explained by the types of chemical bonds that hold atoms together in $(Cr,\;Fe)_7C_3$ carbide phase.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2011.05a
• /
• pp.96-97
• /
• 2011

The T23 steel, whose composition was Fe-2.3%Cr-1.6%W, was arc-melted, and oxidized between $600^{\circ}C$ and $900^{\circ}C$ in air for up to 7 months. The amount of precipitates in the arc-melted microstructure was as large as 11.4 vol.%. The precipitates increased the oxidation rate of the arc-melted T23 steel. Owing to the low amount of Cr in the T23 steel, breakaway oxidation occurred after a few hours during oxidation above $700^{\circ}C$ in both arc-melted and as-received T23 steels. The scales that formed on arc-melted and as-received T23 steels were similar to each other. They consisted primarily of the outer $Fe_2O_3$ layer and the inner ($Fe_2O_3$, $FeCr_2O_4$)-mixed layer. The precipitates increased the microhardness and the oxidation rates.