This study examines the effect of delayed quenching (DQ) temperature on the microstructure and mechanical properties of API X70 linepipe steels. Three types of steels were fabricated by varying the DQ conditions: Base (without DQ), LDQ (low-temperature delayed quenching at 700 °C), and HDQ (high-temperature delayed quenching at 740 °C). The microstructures were characterized using optical microscopy, scanning electron microscope (SEM), and electron back-scattered diffraction (EBSD), and their mechanical properties were evaluated through tensile and Charpy impact tests. The Base specimen exhibited the finest effective grain size and the highest bainite fraction, resulting in superior yield strength and impact toughness. In contrast, the LDQ specimen showed increased pearlite content and coarser grains, leading to the highest tensile strength due to work hardening, but reduced impact properties due to crack initiation at the pearlite regions. The HDQ specimen, with the highest ferrite fraction, showed the best ductility and acceptable strength, as well as improved lowtemperature toughness owing to increased resistance to cleavage propagation. EBSD analysis confirmed that finer grains and higher fractions of high-angle grain boundaries play a crucial role in enhancing impact energy and lowering the ductile-to-brittle transition temperature (DBTT). These findings highlight the importance of optimizing DQ parameters to achieve a balanced combination of strength–toughness in high-strength linepipe steels.

Conventionally, metal materials are produced by subtractive manufacturing followed by melting. However, there has been an increasing interest in additive manufacturing, especially metal 3D printing technology, which is relatively inexpensive because of the absence of complicated processing steps. In this study, we focus on the effect of varying powder size on the synthesis quality, and suggest optimum process conditions for the preparation of AlCrFeNi high-entropy alloy powder. The SEM image of the as-fabricated specimens show countless, fine, as-synthesized powders. Furthermore, we have examined the phase and microstructure before and after 3D printing, and found that there are no noticeable changes in the phase or microstructure. However, it was determined that the larger the powder size, the better the Vickers hardness of the material. This study sheds light on the optimization of process conditions in the metal 3D printing field.

국내에 도입된 오차드그래스 27 품종과 국내 합성 품종인 Hapsung 2호의 종자로부터의 캘러스 형성율, 형성된 캘러스의 크기, 캘러스로부터의 재분화율 및 재분화 효율을 4주령 및 6주령의 캘러스에 대하여 얻은 결과는 아래와 같았다. 1. 4주령의 캘러스에 대한 종자로부터 캘러스의 형성율은 치상 종자의 50% 이상이 캘러스를 형성한 형성율 상위 품종들은 93M > Sparta > Pizza> Condor > Lidaglo > Glorus >Hapsun

환경 스트레스에 의해 야기되는 활성 산소종에 의한 피해에 내성을 가지는 목초의 개발을 위하여 오차드그래스의 배반 조직 유래의 캘러스에 배추유래의 cytosolic glutathione reductase 유전자(BcGRl)를 Agrobucterium tumefaciens EHA101을 매개로 형질전환시켰다. Hygromcin으로 선발된 캘러스로부터 재분화된 식물체는 야생형과 비교하여 형태적으로 차이를 나타내지 않았다. PCR 및 Southern blot