• Corrosion Science and Technology
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• v.15 no.5
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• pp.237-244
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• 2016

2205 duplex stainless steels have been used for the construction of the marine environment, because of their excellent corrosion resistance and high strength. However, the resistance to hydrogen embrittlement (HE) may be less than that of 316L austenitic stainless steel. The reason why 316L stainless steels have better resistance to HE is associated with crystal structure (FCC, face centered cubic) and the higher stacking faults energy than 2205 duplex stainless steels. Furthermore 2205 stainless steels with or without tungsten were also examined in terms of HE. 2205 stainless steels containing tungsten is less resistible to HE. It is because dislocation tangle was formed in 2205 duplex stainless steels. Slow strain-rate tensile test (SSRT) was conducted to measure the resistance to HE under the cathodic applied potential. Hydrogen embrittlement index (HEI) was used to evaluate HE resistance through the quantitative calculation.

• Journal of the Korean Society for Heat Treatment
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• v.15 no.2
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• pp.57-64
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• 2002

The 22%Cr-5%Ni-3%Mo duplex and 18%Cr-8%Ni austenitic stainless steels have been nitrogen permeated under the $1Kg/cm^2$ nitrogen gas atmosphere at the temperature range of $1050^{\circ}C{\sim}1150^{\circ}C$. The nitrogen-permeated duplex and austenitic stainless steels showed the gradual decrease in hardness with increasing depth below surface. The duplex stainless steel showed nitrogen pearlite at the outmost surface and austenite single phase in the center after nitrogen permeation treatment, while the obvious microstructural change was not observed for the nitrogen-permeated austenitic stainless steel. After solution annealing the nitrogen-permeated stainless steels(NPSA treatment) at $1200^{\circ}C$ for 10 hours, the hardness of the duplex and austenitic stainless steels was constant through the 2 mm thickness of the specimen, and the ${\alpha}+{\gamma}$ phase of duplex stainless steel changed to austenite single phase. Tensile strengths and elongations of the NPSA-treated duplex stainless steel remarkably increased compared to those of solution annealed (SA) duplex stainless steel due to the solution strengthening effect of nitrogen and the phase change from a mixture of ferrite and austenite to austenite single phase, while the NP-treated austenitic stainless steel displayed the lowest value in elongation due to inhomogeneous deformation by the hardness difference between surface and interior.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.123-123
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• 2015

0.087 wt.% Gd-lean duplex stainless steels were inert arc-melted and cast in a mold. The micro-hardnesses of the rolling, transverse, short transverse directions were 258.5, 292.3, 314.7 HV, respectively. The 33% cold rolled specimen had the crystallographic texture that mainly (100) pole was concentrated to normal direction and (110) pole was concentrated in the center of normal and rolling directions. The corrosion potential and corrosion rate in artificial sea water were in the range of $105.6-221.6mV_{SHE}$, $0.59-1.06mA/cm^2$, respectively. The friction coefficient and wear loss of the 0.087 wt.% Gd-lean duplex stainless steels in artificial sea water were about 67% and 65% lower than in air, whereas, the wear efficiency was 22% higher. The corrosion and wear behaviors of the 0.087 wt.% Gd-lean duplex stainless steels significantly depended on the gadolinium phases.

• Corrosion Science and Technology
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• v.5 no.6
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• pp.189-195
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• 2006

Effects of tungsten (W) on the precipitation kinetics of secondary phases and the associated resistance to pitting corrosion of 25%Cr duplex stainless steels were investigated through microstructural and electrochemical noise analyses. With the partial substitution of W for Mo in duplex stainless steel, the potential and current noises of the alloy were significantly decreased in chloride solution due to retardation of the ${\sigma}$ phase precipitation. The preferential precipitation of the $\chi$ phase in the W-containing alloy during the early period of aging contributed to retarding the precipitation of the $\sigma$ phase by depleting W and Mo along grain boundaries. In addition, the retardation of the nucleation and growth of the $\sigma$ phase in the W-containing alloy appears to be attributed to the inherently low diffusivity of W compared with that of Mo.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.507-508
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• 2006

In this communication the development of a new metal injection moulding (MIM) system for duplex stainless steels is presented. The metal powders were prepared by premixing 316L and 430L stainless steels gas atomised powders in a ratio of 50:50. The binder used to prepare the feedstock was composed by HDPE and paraffin wax. Torque measurements of the mixture indicated that the maximum amount of metal was 68 vol%. The polymeric part was driven off by thermal debinding and the sintering was performed in low vacuum. The final densities were close to the theoretical ones.

• Corrosion Science and Technology
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• v.9 no.5
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• pp.187-195
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• 2010

Hyper duplex stainless steels have been developed in Korea for the purpose of application to the seawater system of Korean nuclear power plants. This system supplies seawater to cooling water heat exchanger tubes, related pipes and chlorine injection system. In normal operation, seawater is supplied to heat exchanger through the exit of circulating water pump headers, and the heat exchanged sea water is extracted to the discharge pipes in circulating water system connected to the circulating water discharge lines. The high flow velocity of some part of seawater system in nuclear power plants accelerates damages of components. Therefore, high strength and high corrosion resistant steels need to be applied for this environment. Hyper duplex stainless steel (27Cr-7.0Ni-2.5Mo-3.2W-0.35N) has been newly developed in Korea and is being improved for applying to nuclear power plants. In this study, the physical & mechanical properties and corrosion resistance of newly developed materials are quantitatively evaluated in comparative to commercial stainless steels in other countries. The properties of weld & HAZ (heat affected zone) are analyzed and the best compositions are suggested. The optimum conditions in welding process are derived for ensuring the volume fraction of ferrite(${\alpha}$) and austenite(${\gamma}$) in HAZ and controlling weld cracks. For applying these materials to the seawater heat exchanger, CCT and CPT in weldments are measured. As a result of all experiments, it was found that the newly developed hyper duplex stainless steel WREMBA has higher corrosion resistance and mechanical properties than those of super austenitic stainless steels including welded area. It is expected to be a promising material for seawater systems of Korean nuclear power plants.

• Journal of Power System Engineering
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• v.17 no.6
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• pp.122-129
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• 2013

The microstructure and deformation behavior in 22Cr-0.2N micro-duplex stainless steels with various Ni and Mn contents were compared using by OM, TEM, and XRD. The 22Cr-0.2N duplex stainless steel plates were fabricated and hot rolled, followed by annealing treatment at the temperature range of $1,000-1,100^{\circ}C$. All the samples showed the common strain hardening behaviour during the tensile test at a room temperature. The steels tested at the temperatures of $-30^{\circ}C$ or $-50^{\circ}C$ showed a distinct inflection point in the stress-strain curves, which should be resulted from the formation of strain-induced martensite(SIM) of austenite phase. This was confirmed by TEM observations. The onset strain of a inflection point in a stress-strain curve should be depended up the value of $M_d30$. With the decrease of the tensile test temperature, the inflection point appeared earlier, and the strength and fracture strain were higher. The tensile behaviour was discussed from the point of austenite stability of the micro-duplex stainless steels with the different Ni and Mn content.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.136.2-136.2
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• 2005

• Transactions of Materials Processing
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• v.7 no.2
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• pp.107-113
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• 1998

The high temperature mechanical behaviour of duplex stainless steels was examined. The relation-ship between the dynamic recrystallization substructures and the flow behaviour was analyzed in detail, and the flow behaviour was analyzed in detail, and the mechanisms of dynamic recrystallization were also discussed. The formation of disloca-tion cells and subgrain structures is of great significance to the understanding of high temperature deformation.

• Composites Research
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• v.37 no.2
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• pp.94-100
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• 2024

In order to evade the premature failure of super duplex stainless steels (SDSSs) in some harsh environments, the increase of their mechanical properties is a promising approach. In this study, based on the laser powder bed fusion (LPBF) technique, SDSS matrix composites without post heat treatment were fabricated by using the powder mixture of SDSSs, super austenitic stainless steels (SASSs) and micron-sized TiC particles. Many in-situ TiC_xN_y nanoparticles were found to be formed by using micron-sized TiC particles in as-built composites, and both fine ferrite and austenite grains were generated. The as-built composites exhibited an excellent combination of high ultimate tensile strength (UTS) (~1066 MPa) and good uniform elongation (UE) (~15.6%), showing a better mechanical property compared with other reported LPBF-fabricated SDSSs, which was mainly attributed to the fine grain, Orowan and dislocation strengthening mechanisms. In particular, the successful fabrication of SDSS matrix composites can set the stage for producing high-performance metallic parts via LPBF technique.