• Journal of Korean Society of Water and Wastewater
• /
• v.23 no.6
• /
• pp.843-853
• /
• 2009

The sediment samples were collected from Seonakdong River and were analyzed for sulfide species such Acid Volatile Sulfide(AVS) and Elemental Sulfur(ES) and Chromium Reducible Sulfide(CRS). Then characteristics of the formation of sulfide species were investigated for six selected samples. Finally the relationship between environmental factors and sulfate reducing rate(SRR) was investigated using two selected samples. Concentrations of AVS and CRS were relatively high, which suggests that organics input to the sediments has been continued until recently and that potential of heavy metals leaching from the sediments is low. SRR in the sediments was closely related to fraction of fine particles(silt+clay) and also to dissolved organic carbon content of the sediment(DOCsed). The dependences of environmental factors such as organic content, temperature, sulfate concentration on the SRR was relatively strong in the selected experiments conducted with the samples from Noksan gate and Daejeo gate samples. The environmental factor dependencies were stronger in the Noksan gate samples than in the Daejeo gate samples, which is probably due to higher surface area of the Noksan gate sediments.

• Journal of the Korean institute of surface engineering
• /
• v.48 no.2
• /
• pp.62-67
• /
• 2015

Nickel is a commercially important and versatile element in electroplating. The applications of nickel electroplating fall into three main categories: decorative, functional and electroforming. In decorative applications, electroplated nickel is most often applied in combination with electrodeposited chromium. Nickel is deposited on surfaces to improve corrosion and wear resistance or modify magnetic and other properties. Electroforming is electroplating applied to the fabrication of products of various kinds. Nickel is deposited onto a substrate and then removed from it to create a part made entirely of nickel. In this study, mechanical property of Ni electrodeposits in various manufacturing condition such as temperature, current density, pH and electrolyte content, was investigated to understand effect of electrolysis condition on mechanical property. Vickers hardness increased as the temperature and pH increased and current density and electrolyte content decreased and pH increased. The results were explained by cathode overvoltage and hydrogen evolution.

• Journal of the Korean Society for Heat Treatment
• /
• v.22 no.4
• /
• pp.210-216
• /
• 2009

Stainless steel EGR cooler of diesel engine is widely used to prevent the corrosion due to the content of sulfur in diesel fuel. The strength of brazed joint between stainless steel materials is very important. It is essential to observe the spreading ratio of the filler metals under the condition of deoxidation or vacuum during heating process. In this experiment, spreading ratio was tested to find the optimum brazing condition for stainless steel using brazing filler metals of FP-613, BNi-2 and BNi-5 on sus304 and sus410. Anti-corrosion tests were also performed on the above filler metals with solution of 5% $H_2SO_4$, 65% $HNO_3$ and 5% $NH_4OH$. Consequently FP-613 has good ability for anti-corrosion with 30% of chromium content compared with other filler metals. The optimum brazing conditions are occurred at $960^{\circ}C$ for 90 min. and at $1090^{\circ}C$ for 50 min. at the same degree of vacuum, $2{\sim}3{\times}10^{-3}$ Torr.

• Journal of the Korean Society of Industry Convergence
• /
• v.25 no.6_2
• /
• pp.987-992
• /
• 2022

STS 410, a representative martensitic stainless steel, contains 13 % chromium and is used for building materials, automobile parts, office equipment, kitchen utensils, and tableware. In general, the strength of STS 410 changes by the carbon content, and STS 410 of low carbon has excellent toughness and high carbon has excellent abrasion resistance. In this study, a fatigue test was performed on the STS 410 material to evaluate the exact fatigue limit and to evaluate the behavior of the material against fatigue. In addition, the effect on burnishing, a kind of plastic processing that creates a smooth surface by pressing a ball or roller on the inner and outer surfaces of the material was evaluated. The fatigue limit was 509 MPa for the STS 410 material, and the result was 54.5 % of the tensile strength. The fatigue limit was 542 MPa for the specimen of diamind burnished STS 410 material, and it was 58.5 % of the tensile strength.

• Journal of the Korea Organic Resources Recycling Association
• /
• v.6 no.1
• /
• pp.1-12
• /
• 1998

To examine the possibility of protein recycling of shaving scraps containing chromium generated from manufacturing process of leather, the optimum hydrolysis conditions and the withdrawal methods of low molecular weight protein for using the liquid fertilizer sources by investigation of solubilities of hydrolyzed protein, inorganic nutrients contents and molecular weight distributions of hydrolyzed protein from shaving scraps treated with mixed alkaline inducing agents and mixed alkaline proteolytic enzymes including MgO were investigated. In hydrolysis of shaving scraps treated with mixed alkaline inducing agents, the solubility of shaving scraps were clearly different with 65~85% according to the sorts of the inducing agents, and the degree of hydrolysis was high in the order of NaOH, $Ca(OH)_2$ and KOH. The average molecular weights of withdrawal hydrolyzed protein were 10, 40 and 80 KD treated with NaOH, $Ca(OH)_2$ and KOH, respectively. And the chromium contents was about 15 ppm. In hydrolysis of shaving scraps treated with mixed alkaline proteolytic enzymes, the bility of shaving scraps were high in the order of alcalase, esperase and savinase. In c of treating 0.5% alcalase, the low molecular weight of hydrolyzed protein could be withdrawn. The solubility of the hydrolyzed protein was about 85%, the average molecular weight of the protein was below 1 KD and chrome content of the protein was below 10 ppm.

• Proceedings of the KWS Conference
• /
• 2002.10a
• /
• pp.250-254
• /
• 2002

Intergranular corrosion of austenitic stainless steels is a conventional and momentous problem during welding and high temperature use. One of the major reasons for such intergranular corrosion is so-called sensitization, i.e., chromium depletion due to chromium carbide precipitation at grain boundaries. Conventional methods for preventing sensitization of austenitic stainless steels include reduction of carbon content in the material, stabilization of carbon atoms as non-chromium carbides by the addition of titanium, niobium or zirconium, local solution-heat-treatment by laser beam, etc. These methods, however, are not without drawbacks. Recent grain boundary structure studies have demonstrated that grain boundary phenomena strongly depend on the crystallographic nature and atomic structure of the grain boundary, and that grain boundaries with coincidence site lattices are immune to intergranular corrosion. The concept of "grain boundary design and control", which involves a desirable grain boundary character distribution, has been developed as grain boundary engineering. The feasibility of grain boundary engineering has been demonstrated mainly by thermomechanical treatments. In the present study, a thermomechanical treatment was tried to improve the resistance to the sensitization by grain boundary engineering. A type 304 austenitic stainless steel was pre-strained and heat-treated, and then sensitized, varying the parameters (pre-strain, temperature, time, etc.) during the thermomechanical treatment. The grain boundary character distribution was examined by orientation imaging microscopy. The intergranular corrosion resistance was evaluated by electrochemical potentiokinetic reactivation and ferric sulfate-sulfuric acid tests. The sensitivity to intergranular corrosion was reduced by the thermomechanical treatment and indicated a minimum at a small roll-reduction. The frequency of coincidence-site-lattice boundaries indicated a maximum at a small strain. The ferric sulfate-sulfuric acid test showed much smaller corrosion rate in the thermomechanically-treated specimen than in the base material. An excellent intergranular corrosion resistance was obtained by a small strain annealing at a relatively low temperature for long time. The optimum parameters created a uniform distribution of a high frequency of coincidence site lattice boundaries in the specimen where corrosive random boundaries were isolated. The results suggest that the thermomechanical treatment can introduce low energy segments in the grain boundary network by annealing twins and can arrest the percolation of intergranular corrosion from the surface.

• Nuclear Engineering and Technology
• /
• v.45 no.4
• /
• pp.513-522
• /
• 2013

The ODSCC detected in the TSP position of Ulchin 3&4 SGs are typical ODSCC of Alloy 600MA tubes. The causative chemical environment is formed by concentration of impurities inside the occluded region formed by the tube surface, egg crate strips, and sludge deposit there. Most cracks are detected at or near the line contacts between the tube surface and the egg crate strips. The region of dense crack population, as defined as between $4^{th}$ and $9^{th}$ TSPs, and near the center of hot leg hemisphere plane, coincided well with the region of preferential sludge deposition as defined by thermal hydraulics calculation using SGAP computer code. The cracks developed homogeneously in a wide range of SGs, so that the number of cracks detected each outage increased very rapidly since the first detection in the $8^{th}$ refueling outage. The root cause assessment focused on investigation of the difference in microstructure and manufacturing residual stress in order to reveal the cause of different susceptibilities to ODSCC among identical six units. The manufacturing residual stress as measured by XRD on OD surface and by split tube method indicated that the high residual stress of Alloy 600MA tube played a critical role in developing ODSCC. The level of residual stress showed substantial variations among the six units depending on details of straightening and OD grinding processes. Youngwang 3&4 tubes are less susceptible to ODSCC than U3 and U4 tubes because semi-continuous coarse chromium carbides are formed along the grain boundary of Y3&4 tubes, while there are finer less continuous chromium carbides in U3 and U4. The different carbide morphology is caused by the difference in cooling rate after mill anneal. There is a possibility that high chromium content in the Y3&4 tubes, still within the allowable range of Alloy 600, has made some contribution to the improved resistance to ODSCC. It is anticipated that ODSCC in Y5&6 SGs will be retarded more considerably than U3 SGs since the manufacturing residual stress in Y5&6 tubes is substantially lower than in U3 tubes, while the microstructure is similar with each other.

• Fibers and Polymers
• /
• v.2 no.1
• /
• pp.157-162
• /
• 2001

Dyebath used for metal complex dyeing of nylon microfiber was recycled to reduce the overall amounts of metal complex dyeing effluents. Instead of discharging the dyebath after each dyeing cycle, the residual dyebath was analyzed spectrophotometrically and reconstituted to the required concentration of dyes and auxiliaries. Dyebaths were reused eight times and the CIELAB coordinates of dyed samples were measured after each recycling. Color difference($\Delta$E*) between the sample dyed in the fresh bath and that from reused dyebath was maintained below 1.5. The levelness and fastness of dyed fabrics from recycled dyebath were not impaired either. Chromium content of each recycled dyebath was similar to that of the first residual dyebath.

• Journal of the Korean institute of surface engineering
• /
• v.50 no.4
• /
• pp.272-276
• /
• 2017

The response of AISI 310 type austenitic stainless steel to the novel low temperature plasma carburizing process has been investigated in this work. This grade of stainless steel shows better corrosion resistance and high temperature oxidation resistance due to its high chromium and nickel content. In this experiment, plasma carburizing was performed on AISI 310 stainless steel in a D.C. pulsed plasma ion nitriding system at different temperatures in $H_2-Ar-CH_4$ gas mixtures. The working pressure was 4 Torr (533Pa approx.) and the applied voltage was 600 V during the plasma carburizing treatment. The hardness of the samples was measured by using a Vickers micro hardness tester with the load of 100 g. The phase of carburized layer formed on the surface was confirmed by X-ray diffraction. The resultant carburized layer was found to be precipitation free and resulted in significantly improved hardness and corrosion resistance.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2012.11a
• /
• pp.175-177
• /
• 2012

A corrosion resistance and hard nitrocarburized layer was distinctly formed on 310 austenitic stainless steel substrate by DC plasma nitrocarburizing. Basically, 310L austenitic stainless steel has high chromium and nickel content which is applicable for high temperature applications. In this experiment, plasma nitrocarburizing was performed in a D.C. pulsed plasma ion nitriding system at different temperatures in $H_2-N_2-CH_4$ gas mixtures. After the experiment structural phases, micro-hardness and corrosion resistance were investigated by the optical microscopy, X-ray diffraction, scanning electron microscopy, micro-hardness testing and Potentiodynamic polarization tests. The hardness of the samples was measured by using a Vickers micro hardness tester with the load of 100 g. XRD indicated a single expanded austenite phase was formed at all treatment temperatures. Such a nitrogen and carbon supersaturated layer is precipitation free and possesses a high hardness and good corrosion resistance.