• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.2
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• pp.349-356
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• 2002

For two kinds of 25Cr-20Ni stainless steels, STS310J1TB and STS310S with and without a small amount of Nb and N, creep behavior has been studied in a stress and temperature range from 147 to 392 MPa and from 923 to 773 K with a special reference to tertiary creep. The average creep life of STS310J1TB was about 100 times longer than that of the STS310S. The apparent activation energy for the initial creep rate was 330 kJ/mol in STS310J1TB, while that of the STS310S was 274kJ/mol in a power law creep region and 478 kJ/mol in a region of power law breakdown (PLB). The activation energy for STS310S below PLB is close to the for self-diffusion. When compensating for the temperature dependence of the Young's modulus and the omega value, it was found that the apparent activation energy for STS310J1TB was reduced to the activation energy for diffusion of chromium atom in gamma steel. The stress exponent of STS310S was about 12.3 above PLB and 5.1 in a power law creep region. Notwithstanding that the creep condition for STS310J1TB was in a power law creep region, its stress exponent was 7.9 larger than that of STS310S corresponding to the same creep conditions. This was ascribed to the presence of fine precipitates in STS310J1TB.

• Corrosion Science and Technology
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• v.14 no.4
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• pp.166-171
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• 2015

Knowledge of how metal releases from the stainless steels used in food processing applications and cooking utensils is essential within the framework of human health risk assessment. A new European standard test protocol for testing metal release in food contact materials made from metals and alloys has recently been published by the Council of Europe. The major difference from earlier test protocols is the use of citric acid as the worst-case food simulant. The objectives of this study were to assess the effect of citric acid at acidic, neutral, and alkaline solution pH on the extent of metal release for stainless steel grades AISI 304 and 316, commonly used as food contact materials. Both grades released lower amounts of metals than the specific release limits when they were tested according to test guidelines. The released amounts of metals were assessed by means of graphite furnace atomic absorption spectroscopy, and changes in the outermost surface composition were determined using X-ray photoelectron spectroscopy. The results demonstrate that both the pH and the complexation capacity of the solutions affected the extent of metal release from stainless steel and are discussed from a mechanistic perspective. The outermost surface oxide was significantly enriched in chromium upon exposure to citric acid, indicating rapid passivation by the acid. This study elucidates the effect of several possible mechanisms, including complex ion- and ligand-induced metal release, that govern the process of metal release from stainless steel under passive conditions in solutions that contain citric acid.

• Journal of the Korean Ceramic Society
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• v.48 no.1
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• pp.57-62
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• 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.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.117-122
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• 2001

For two kinds of 25Cr-20Ni stainless steels, SUS310J1TB TB and SUS310S with and without a small amount of Nb and N, creep behavior has been studied in a stress and temperature range from 147 to 392MPa and from 923 to 973K with a special reference to tertiary creep. The average creep life of SUS310J1TB was about 100 times longer than that of the SUS310S. The apparent activation energy for the initial creep rate was 330 kJ/mol in SUS310J1TB, while that of the SUS310S was 274 kJ/mol in a power law creep region and 478 kJ/mol in a region of power law breakdown (PLB). The activation energy for SUS310S below PLB is close to the that for self-diffusion. When compensating for the temperature dependence of the Young's modulus and the omega value, it was found that the apparent activation energy for SUS310J1TB was reduced to the activation energy for diffusion of chromium atom in a gamma steel. The stress exponent of SUS310S was about 12 above PLB and 5.1 in a power law creep region. Notwithstanding that the creep condition for SUS310J1TB was in a power law creep region, its stress exponent was 8.3 larger than that of SUS310S corresponding to the same creep conditions. This was ascribed to the presence of fine precipitates in SUS310J1TB.

• Corrosion Science and Technology
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• v.10 no.1
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• pp.24-29
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• 2011

The greatest purpose of chromate treatment is to improve anti-corrosion by stabilizing a metal surface. Because metal surface forms a compound by absorbing oxygen or water in the air by being generally unstable, it is necessary to improve anti-corrosion of the metal by forming the metal surface with a stable film. When considering the economical efficiency and requirements together because the film of the metal surface treated with chromate has good anti-corrosion and the stability also in the air by being compact and strong, Chromate treatment has been used most up to the electronics industry from the auto industry. However, these days, because hexavalent chromium is both a toxic agent to be able to cause cancers and deadly poisonous environmental pollutant, the strong legal controls on its use is being imposed all over the world. Because of this reason, a new anti-corrosion method is being required. Also, by users' various demands, the passivations that have recently been developed require various characteristics such as conductivity, chemical resistance, alkali cleaning resistance as well as anti-corrosion. We could confirm the results such as excellent anti-corrosion compared to chromate, conductivity, chemical resistance and detergent resistance as the result of analysis of various characteristics of the galvannealed sheet steels coated with Cr-Free solution developed in this research.

• 연구논문집
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• s.26
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• pp.121-132
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• 1996

The carburising surface modification treatment of the die steel has been used for improving wear resistance and heat cycle strength of the die and preventing a pitting on the surface because the carbides are forming in the matrix during carburising. Generally, the hot forging die was used after quenching-tempering treatment or nitriding after quenching-tempering treatment. The nitriding after carburising on the surface of a hot die steel and a wear resistance die steels was suggested by SOUCHARD, JACQUOT. and BUVRON. This surface modification treatment improved the adhesive and abrasive wear resistance and friction coefficient. The process was introduced to the forging die of stainless steel, titanium alloy steel, alloy and medium carbon steel and the physical properties of the die after the treatment were improved. The surface hardening treatment of the nitriding, the carburising, the boriding, and TD process were used to improved the life time of the forging die. Also, the coating process of PVD, CVD and PCVD were used and the hard chromium plating was occasionally used. Therefore, this study analyzed the effects of the carburising time and the conditions of nitriding on STD61 steel. The case depth, the surface hardness, the forming carbide size and shape during overcarburising process on the die steel were also examined.

• Journal of Power System Engineering
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• v.19 no.6
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• pp.12-18
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• 2015

Austenitic stainless steels generally experience the occurrence of chromium-depleted zones at the boundaries, known as sensitization, caused by the carbide precipitation that takes place due to a welding process or heat treatment. Normally, the depleted zones become the focus of the intense corrosion. In this study, the Cr-free organic/inorganic hybrid solution was developed, and the artificially degraded STS316S and STS347H with the solution-coating investigated the corrosion resistance by salt spray test. Both the OIBD-1 and OIBD-2 solutions improved the corrosion resistance of STS310S and STS347H. The corrosion resistance with the OIBD-1 solution was better than that of OIBD-2 solution. Additionally, Both solutions have been proven excellence in adhesion ability, boiling water resistance and flexibility. However, a problem of rubbing after the boiling was found out to be overcome.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.4
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• pp.426-431
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• 2008

The high-strength low-alloy(HSLA) steels have low carbon contents($0.05{\sim}0.25%$ C) in order to produce adequate formability and weldability, and they have manganese contents up to 1.7%. Small quantities of silicon, chromium, nickel, copper, aluminum, molybdenum are used in various combinations. The results contained in this paper can provide the valuable information on the development of $-40^{\circ}C$ low temperature HSLA. Furthermore, the present experimental data will provide important database for casting steel materials of the offshore structure.

• Korean Journal of Metals and Materials
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• v.48 no.5
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• pp.410-416
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• 2010

Studies were carried out to establish the technology for sodium-clad compatibility and to analyze the compatibility behavior of the Sodium-cooled Fast Reactor (SFR) cladding material under a flowing sodium environment. The natural circulation facility caused by the thermal convection of the liquid sodium was constructed and the 316-series stainless steels were exposed at $650{^{\circ}C}$ liquid sodium for 1458 hours. The weight change and related microstructural change were analyzed. The results showed that the quasi-dynamic facility represented by the natural convection exhibited similar results compared to the conventional dynamic facility. Selective leaching and local depletion of the chromium, re-distribution of the carbide, and the decarburization process took place in the 316-series stainless steel under a flowing sodium environment. This process decreased as the sodium flowed along the channel, which was caused by the change in the dissolved oxygen and carbon activity in the liquid sodium.

• Design & Manufacturing
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• v.16 no.1
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• pp.9-14
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• 2022

A lot of research is being done on metal materials to improve the lifespan of molded parts. As a result, excellent mold materials have been developed that withstand high hardness at high temperatures and frictional heat generated from high-speed cutting. In this study, the press mold life of powder high-speed tool steel and general high-speed tool steel was compared. Powdered high-speed steel is composed of alloying elements such as tungsten, maldividene, cobalt, chromium, and vanadium in steel, which improves wear resistance compared to high-hardness and high-speed tool steels. The mold parts of both steel types were manufactured in the same way from heat treatment to machining, and the powder high-speed tool steel was 66HRC and the high-speed tool steel was 61HRC. As a result of the experiment, it was observed that the number of punching of powder high-speed tool steel was improved by 40-50%, and powder high-speed tool steel had fewer impurities, uniform texture, and excellent surface structure. It has a microscopic structure.