• Korean Journal of Materials Research
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• v.14 no.6
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• pp.379-388
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• 2004

To investigate the effect of D-ferrite on the hot workability and surface defect of STS 304 billets containing 3 wt. % Cu, microstructure observations and high temperature mechanical properties test were carried out for the specimens extracted mainly from raw or oxidized billets. It was found that the total $\delta$-ferrite content has little influence on the hot workability, even though the fracture cracks due to high temperature tension or compression test were initiated and propagated mostly along $\delta$/${\gamma}$ boundary in the specimens. On the other hand, it was supposed that the direct causes of surface defects in the wire rolled from the as-continuously cast billet were the grain boundary embrittlement arose from the deep diffusion of oxygen into the grain boundary, and the oxidation of $\delta$-ferrite connected by a grain boundary to the surface during the billet reheating process as well.

• Journal of the Korean Dietetic Association
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• v.7 no.1
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• pp.28-37
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• 2001

The purpose of this study was to evaluate the status of sanitary management based on HACCP. The surveys which were on various aspects of general characteristics, food handling practice, personal sanitation, equipment sanitation, and equipment possession were carried out using questionnaires for 146 business and industry foodservice operations in Taegu and Kyungpook areas. The results of this study were summarized as follows. Forty-nine percent of surveyed foodservice operations was in Taegu, 51% in Kyungpook and 69.2% in direct foodservice operations and 28.1% in contracted foodservice operations. Seventy-eight percent of foodservice operations replied that they have done only basic sanitary management, while 13% surveyed stated that they were implementing HACCP. Food handling practice and personal sanitation were significantly better in Kyungpook area than in Taegu. Significantly high levels in food handling practice, personal sanitation, equipment sanitation, and equipment possession were seen in foodservice operations which had more than 1,000 meal served than those which had less than 1,000 meals served. According to the results of food handling practice, in items of food-temperature measurement during receiving, cooking, holding after cooking, and reheating, foodservice operations showed very low scores below the average. All foodservice operations presented good scores in the parts of personal and equipment sanitation. In equipment possession, sterilizing systems were generally not enough, dishwasher and sterilizing facilities of contracted foodservice operation showed significantly high scores. Therefore, the business and industry foodservice operations will have to pay special attention to temperature management in the foodservice production process as the first step to implement of HACCP.

• Korean Journal of Materials Research
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• v.21 no.4
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• pp.187-191
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• 2011

Prior austenite grain size plays an important role in the production of high strength hot-rolled steel. This study investigated the effect of Ti and C contents on the precipitates and prior austenite grain size. Steel with no Ti solutes had prior austenite grain size of about 620 ${\mu}m$. The addition of Ti ~ 0.03 wt.% and 0.11 wt.% reduced the prior austenite grain size to 180 ${\mu}m$ and 120 ${\mu}m$, respectively. The amount of Ti required to significantly decrease the prior austenite grain size was in the range of 0.03 wt.%. However, the amount of carbon required to significantly decrease the prior austenite grain size was not present from 0.04 wt.% to 0.12 wt.%. Oxides of Ti ($Ti_2O_3$) were observed as the Ti content increased to 0.03 wt.%. The specimen containing 0.11 wt.% of Ti exhibited the complex carbides of (Ti, Nb) C. The formation of Ti precipitates was critical to reduce the prior austenite grain size. Furthermore, the consistency of prior austenite grain size increased as the carbon and Ti contents increased. During the reheating process of hot-rolled steel, the most critical factor for controlling the prior austenite grain size seems to be the presence of Ti precipitates.

• Journal of Welding and Joining
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• v.28 no.5
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• pp.51-57
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• 2010

Brittle microstructure created in a heat affected zone (HAZ) during the welding of low alloy steel can be eliminated by post-weld heat treatment (PWHT). If the PWHT is not possible during a repair welding, the controlled bead depositions of multi-pass welding should be applied to obtain tempering effect on the HAZ without PWHT. In order to anticipate and control the tempering effect during the temper bead welding, the definition of temperature curve obtained from the analytical solution was suggested in this research. Because the analytical solution for heat flow is expressed as a mathematical equation of weld parameters, it may be effective in anticipating the effect of each weld parameter on the tempering in HAZ during the successive bead depositions. The reheating effect by the successive bead layer on the brittle coarse grained HAZ formed by earlier bead deposition was estimated by comparing the overlapped distance between the temperature curves in the HAZ. Three layered weld specimens of SA508 base metal with A52 filler were prepared by controlling heat input ratio between layers. The tempering effect anticipated by using the overlapped distance between the temperature curves was verified by measuring the micro-hardness distribution in the HAZ of prepared specimens. The temperature curve obtained from analytical solution was expected as a good tool to find optimal temper bead welding conditions.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.3
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• pp.483-494
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• 2023

Recently, gas turbine generators are widely used for frequency control of power systems. Although the inlet temperature of a gas turbine is a key factor related to the performance and lifespan of the device, the inlet temperature is not measured directly for reasons such as the turbine structure and operating environment. In particular, the inlet temperature of the reheating gas turbine is very important for stable operation management, but field workers are experiencing a lot of difficulties because the manufacturer does not provide information on the calculation formula. Therefore, in this study, we propose a method for estimating the inlet temperature of a gas turbine using a machine learning-based linear regression analysis method based on a polytropic process equation. In addition, by proposing an inlet temperature calculation algorithm through the usefulness analysis and verification of the inlet temperature calculation model obtained through linear regression analysis, it is intended to help to improve the level of reheat gas turbine combustion tuning technology.

• Journal of the Korean Society for Heat Treatment
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• v.37 no.4
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• pp.155-162
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• 2024

SCr420H steel which is commonly utilized for automotive components requires the carburizing heat treatment process. Abnormal grain growth during this treatment significantly affects the mechanical properties of the steel parts. Consequently, a process designed to prevent abnormal grain growth at certain elevated temperatures is essential. For enhanced grain refinement, we considered the addition of Nb in SCr420H steel. The experimental condition of the carburizing heat treatment involved reheating the steel sample to temperatures between 940℃ and 1080℃. Using scanning electron microscopy, we examined the microstructure of specimens treated with the secondary solution, revealing an organization of bainite and ferrite. Transmission electron microscopy was utilized to determine the type, shape, and size of the carbonitrides, showing a high fraction of AlN at the secondary solution treatment temperature of approximately 1050℃ and of (Nb,Ti)(C,N) around 1200℃. AlN particles measured about 100 nm and (Nb,Ti)(C,N) about 50 nm. Optical microscopy was utilized to assess grain size variations at different secondary solution treatment temperatures. It is noted that the temperature at which abnormal grain coarsening occurred rose with increasing secondary solution treatment temperatures, indicating a greater influence of (Nb,Ti)(C,N) with higher heat treatment temperatures. This research provides reference data for preventing abnormal grain growth in Nb-added low alloy steels undergoing carburizing heat treatment.

• Journal of the Korean Chemical Society
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• v.4 no.1
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• pp.18-26
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• 1957

There are two problems to be solved by our efforts in the enamel frit. One is how we can cover the enamel frit thin with complete milk white as possible, and the other is how it can be, made resistant for chemicals than before one. The frit which can solved the two problems just mentioned above is titanium enamel frit. This frit has been developed in America after War Ⅱ, and now the research for concerning antimony frit into titanium frit is under development entirely. In order to develope the enamel industry in Korea, it is urgent problem to convert antimony frit into titanium frit. By the way the titanium frit is emulsified titanium oxide crystal which made through reheating the supersaturated solution of titanium oxide in the basis of glass. Unfortunately, there are many obscure points in active fact or which influence on its composition and characteristics yet. However, this task was tried for the first in Korea. As first step, the test was carried on the reference books, and we can be possible convert antimony frit into titanium frit as a result of this experiment. As a conclusion, for the purpose of developing the enamel industry in Korea, we studied that the research for converting antimony enamel frit which has been used popularly into titanium enamel frit which is more economic and resistant for chemicals. As a result of experiments, the following points concerning with titanium frit have become clearly. 1. It is better when the composition of titanium enamel frit has as following table.Man Duck San Silica 24 An Yang Feldspar 20 Borax 28 Sodium Nitrate 4 Cryolite 7 Calcium Carbonate 3.6∼1 Titanium Oxide 10 Calcium phosphate 0 ∼3.2 Calcium Fluoride 0∼1.8 Antimony Oxide 0∼0.5 2. The amount of $TiO_2$, to be added is $10%\;to\;12{%,\;CaF_2\;is\;under\;1.8%,\;P_2O_5\;is\;under\;1.6%,\;Sb_2O_3\;is\;under\;0.5%$. 3. In the titanium frit, the limit of iron oxide amount to be included is under 0. 5%. 4. Comparing the titanium enamel frit with antimony enamel frit not only the titanium frit can be savely 20.6% in the price of raw materials, but one time of glazing and heating process is omitted in each case, and it is known the titanium frit is more resistant for chemicals than antimony frit.