Jo Nov 3, 2026
Nowadays, rail failure in low temperature environments is a serious problem in many countries across the world. Generally, rails are often damaged due to the large amount of fluctuating stress and impact forces during operation. Rails tend to be damaged in winter when it is cold and the difference between low and high temperatures is great. In addition, the abnormal climate caused by global warming causes a rapid decline in winter temperature and the railroads in extreme regions cannot avoid rail failure at low temperatures, which is a serious problem. According to the research, 60-80% of the rails were damaged in winter from November to March, and 83-121 rails were damged between November and February with relatively low temperature conditions.
In general, different methods of heat treatment and alloying of various elements are widely used to enhance the microstructure and properties of steel. In the past, Ni and V were traditionally used to improve the low temperature properties of steel. Recently, the use of Ti and RE has also been being investigated. Therefore, research has been carried out to apply such alloying or heat treatment methods to rail steels. However, Ni, Ti, RE, etc. are resource-poor and cost-inefficient.
Jon Song Won, a researcher at the Faculty of Material Science and Technology, fabricated rails by adding barium to enhance the low temperature properties of rails and investigated the effect of barium on their microstructure and properties.
He carried out tensile, hardness and impact tests at low temperature to measure and analyze the mechanical properties of the rail steel with Ba addition. The test results showed that the tensile strength of rail steel with 0.03% Ba increased to 1 020MPa, the elongation to 8.0%, and the hardness to HB275 and impact value to 6.8J/cm2 at low temperature.
He investigated the low-temperature toughness mechanisms on the metallic structure of the samples by metal microscopy and scanning electron microscopy. At 0.025wt.% Ba, the average size of pearlite grains in the rail steel was 15μm, and grain refinement was observed in the microstructure. Changes in the size, distribution and shape of inclusions were also observed.
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Jo Nov 2, 2026
Archery is one of the excellent combat art speciality the Korean people practised and developed through generations.
The sport, which had widely been encouraged since the period of Tangun’s Korea, underwent remarkable development during the Koguryo Kingdom. The Koguryo people liked to do archery from their childhood, making it part and parcel of their everyday life. In order to promote archery and horse riding in the kingdom, a national hunting game used to be organized on Rangnang Hill on March 3 every year. In the Koguryo tomb murals still remaining to date, there are pictures portraying men on horseback chasing tigers to shoot arrows and those aiming their bows at roe deer or deer.
Later, too, the Koreans practised archery as a mass-based combat art for a long historical period. In the period of the Koryo Dynasty, South Phyongan Provincial people centring on Pyongyang became famous by shooting arrows particularly well, irrespective of social status.
During the feudal Joson dynasty, archery failed to make significant progress as compared to the previous eras, but it was continuously practised by soldiers and working people, with the result that many crack shots were produced.
Today, archery is encouraged as a sport and pastime as it helps people build up their physical strength and enrich their cultural and emotional life.
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Jo Oct 30, 2026
As twin-roll casting is a complex physical process, the structure and size of the metal feeding system, which supplies molten metal to the gap between two casting rolls, have a great influence on the quality of the products. In particular, the baffle is the key element for ensuring the uniformity of flow rate and temperature of molten metal at the outlet of the feeding system. The shape, size, number, and position of baffles have a significant impact on the flow characteristics of molten metal in the feeding system.
Therefore, optimizing the structure and design parameters of the feeding system is of great importance for ensuring good quality of products by adjusting the flow field of molten metal in the feeding system. In addition, the wider the strip in twin-roll casting is, the wider the feeding system gets. This increases the complexity of the flow characteristics of the molten metal, which leads to requirements for accurate structure and design parameters of the feeding system.
In order to improve the quality of strip edge in aluminum twin-roll casting, Kim Il Hyok, a student at the Faculty of Material Science and Technology, simulated the fluid flow behavior in different types of metal feeding systems (3C-type, 7C-type, and 2-split-type) by ANSYS Fluent.
Through simulations, he analyzed the effects of design parameters (shape, size, and position of baffles) of the feeding system on the distribution of fluid flow rate and temperature at the outlet of the feeding system. Based on the results, he concluded that the feeding system for the conformity of the flow rate and temperature of molten metal is of 2-split-type, and optimized its design parameters.
The optimized feeding system could ensure high quality of aluminum strips by eliminating the defects such as edge cracks.
If more information is needed, you can refer to his paper “Optimization of design parameters of metal feeding system for quality improvement of strip edge in aluminum twin-roll casting” in “The International Journal of Advanced Manufacturing Technology” (SCI).
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Jo Oct 29, 2026
Zirconium based alloys have been widely used in light water reactors due to their small neutron absorption cross sections, good corrosion resistance and excellent creep strength. Zircaloy-4 is a zirconium based Zr-Sn alloy, which is found in many applications in structural components such as fuel cladding tubes and pressure tubes.
Zircaloy-4 alloys are fabricated by several hot working methods such as hot rolling and hot extrusion, and numerical simulations are used to optimize and design the hot working process. So, predicting the hot flow stress evolution of Zircaloy-4 is of great importance for the numerical simulation of hot working processes.
Kim Hyok Song, a student at the Faculty of Material Science and Technology, constructed a modified Johnson-Cook model, a strain compensated Arrheniustype model, a modified Zerilli-Armstrong model and a microstructure-based model to predict the flow stress behavior of Zircaloy-4 in hot working. For this purpose, isothermal uniaxial compression tests had been conducted in the range of strain rates and deformation temperatures of 0.001-1s-1 and 750-1 000°C. Then, he compared the prediction accuracy of the proposed constitutive models in terms of correlation coefficient and average absolute relative error.
The results showed that the microstructure-based model is the most suitable for accurately predicting the hot deformation behavior of Zircaloy-4.
You can find the details in his paper “Constitutive Models for Predicting Flow Stress Behavior of Zircaloy-4 in Thermo-Mechanical Processing” in “Physics of Metals and Metallography” (SCI).
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Jo Oct 28, 2026
The main metallic metals used in medicine include titanium and its alloys, Co-based alloys and austenitic stainless steels. Titanium alloys are rarely used in friction contact due to their poor abrasion resistance. Austenitic stainless steels are used for short-term implants such as screws, plates and nails because austenitic stainless steels may cause allergic reactions in many patients due to their poor corrosion resistance. Meanwhile, Co-based alloys have been widely used as femoral elements because of their good corrosion and wear resistances and biocompatibility.
Chromium and molybdenum are important alloying elements of Co-based alloys. Chromium improves resistance against oxidation and corrosion at high temperature, while molybdenum of large atomic size increases the strength through solid solution strengthening.
The understanding of the hot flow stress behavior of materials is essential for the numerical simulation of thermo-mechanical processing routes such as forging, rolling, etc. So, it is quite important to develop a constitutive material model.
Ryang Chol Song, a student at the Faculty of Material Science and Technology, developed and compared several constitutive material models for accurately predicting the flow stress during hot working of Co-28Cr-6Mo alloys.
He constructed a modified Johnson-Cook (MJC) model, a strain compensated Arrhenius-type (SCAT) model and a microstructure-based constitutive (MBC) model in a wide range of temperatures (900-1 200℃) and strain rates (0.001-10s-1).
Then, he compared the average absolute relative error and correlation coefficient for the proposed models. The results are as follows. The correlation coefficient and AARE are 0.985 7 and 7.8% for the MJC model, 0.950 4 and 13.01% for the SCAT model, and 0.994 8 and 2.45% for the MBC model, respectively.
The results show that the proposed MBC model is best suited to predict the hot flow stress behavior of biomedical grade Co-28Cr-6Mo alloy.
For more information, please refer to his paper “Development of Several Constitutive Models to Predict Flow Stress of Biomedical Grade Co–28Cr–6Mo Alloy during Thermo-Mechanical Processing” in “Russian Journal of Non-Ferrous Metals” (SCI).
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Jo Oct 27, 2026
Austenitic stainless steels are widely used in a large number of fields such as energy, petroleum chemistry and biological engineering, due to their good plasticity, nonmagnetic property, biological interchangeability and anticorrosion. Now, austenitic stainless steels account for 70% of the production and application of stainless steels. The recent increase in demand for nickel chrome austenitic stainless steel is depleting nickel resources year by year.
Many researchers made efforts to use cheap elements instead of nickel. Addition of nitrogen element to austenitic stainless steels can raise the strength of austenitic stainless steels and stabilize the austenitic structure.
The Cr17Mn17Mo3NiN steel is a typical low nickel austenitic stainless steel where Mn, Mo and N are used instead of Ni. The Cr17Mn17Mo3NiN steel has improved strength, plasticity and local corrosion resistance.
Accurate prediction of the flow stress of Cr17Mn17Mo3NiN low nickel austenitic stainless steel in hot working processes is of primary importance in economizing the material for new austenitic stainless steel, designing rational hot working processes such as hot rolling and forging, and increasing the processing efficiency.
Jang Kun Song, a student at the Faculty of Material Science and Technology, proposed phenomenological and physical-based constitutive models for the Cr17Mn17Mo3NiN low nickel stainless steel, based on the true stress-strain curves acquired from isothermal uniaxial compression tests, and estimated and compared the prediction accuracy of the proposed constitutive models.
As a result, the flow stresses predicted by the newly modified Johnson-Cook model and the microstructural-based constitutive model were in good consistent with the experimental results. Especially, the prediction accuracy of the microstructural-based constitutive model was the highest.
For more information, you can refer to his paper “Comparison of phenomenological and physical-based constitutive material models for Cr17Mn17Mo3NiN low nickel stainless steel” in “Materials Research Express” (SCI).
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