We investigate the austenite stability in nanocrystalline Fe-7%Mn-X%Mo (X = 0, 1, and 2) alloys fabricated by spark plasma sintering. Mo is known as a ferrite stabilizing element, whereas Mn is an austenite stabilizing element, and many studies have focused on the effect of Mn addition on austenite stability. Herein, the volume fraction of austenite in nanocrystalline Fe-7%Mn alloys with different Mo contents is measured using X-ray diffraction. Using a disk compressive test, austenite in Fe–Mn–Mo alloys is confirmed to transform into strain-induced martensite during plastic deformation by a disk d. The variation in austenite stability in response to the addition of Mo is quantitatively evaluated by comparing the k-parameters of the kinetic equation for the strain-induced martensite transformation.

The impact properties of two austenitic Fe-23Mn-0.4C steels with different Al contents for cryogenic applications are investigated in this study. The 4Al steel consists mostly of austenite single-phase microstructure, while the 5Al steel exhibits a two-phase microstructure of austenite and delta-ferrite with coarse and elongated grains. Charpy impact test results reveal that the 5Al steel with duplex phases of austenite and delta-ferrite exhibits a ductile-to-brittle transition behavior, while the 4Al steel with only single-phase austenite has higher absorbed energy over 100 J at -196 oC. The SEM fractographs of Charpy impact specimens show that the 4Al steel has a ductile dimple fracture regardless of test temperature, whereas the 5Al steel fractured at -100 oC and -196 oC exhibits a mixed fracture mode of both ductile and brittle fractures. Additionally, quasi-cleavage fracture caused by crack propagation of delta-ferrite phase is found in some regions of the brittle fracture surface of the 5Al steel. Based on these results, the delta-ferrite phase hardly has a significant effect on absorbed energy at room-temperature, but it significantly deteriorates low-temperature toughness by acting as the main site of the propagation of brittle cracks at cryogenic-temperatures.

In the present study, we investigate the effects of milling time and the addition of a process control agent (PCA) on the austenite stability of a nanocrystalline Fe-7%Mn alloy by XRD analysis and micrograph observation. Nanocrystalline Fe-7%Mn alloys samples are successfully fabricated by spark plasma sintering. The crystallite size of ball-milled powder and the volume fraction of austenite in the sintered sample are calculated using XRD analysis. Changes in the shape and structure of alloyed powder according to milling conditions are observed through FE-SEM. It is found that the crystallite size is reduced with increasing milling time and amount of PCA addition due to the variation in the balance between the cold-welding and fracturing processes. As a result, the austenite stability increased, resulting in an exceptionally high volume fraction of austenite retained at room temperature.

The connecting rod is one of the most important parts in automotive engines, transforming the reciprocalmotion of a piston generated by internal combustion into the rotational motion of a crankshaft. Recent advances in highperformance automobile engines demand corresponding technological breakthroughs in the materials for engine parts. Inthe present research, the powder metallurgy (P/M) process was used to replace conventional quenching and/or temperingprocesses for mass production and ultimately for more cost-efficient manufacturing of high strength connecting rods.The development of P/M alloy powder was undertaken not only to achieve the improvement in mechanical properties,but also to enhance the machinability of the P/M processed connecting rods. Specifically MoS2 powders were added aslubricants to non-normalizing Fe-Cr-Mn-V-C alloy powder to improve the post-sintering machinability. The effects ofMoS2 addition on the microstructure, mechanical properties, and machining characteristics were investigated.

In the present study, we systematically investigated the effect of Mn addition on nitrogenation behavior and magnetic properties of Sm-Fe powders produced by reduction-diffusion process. Alloy powders with only single phase were successfully produced by the reduction-diffusion process. The coercivity of powder rapidly increased during nitrogenation and reached the maximum of 637 Oe after 16 hours. After further nitrogenation, it decreased. In contrast, the coercivity of powder gradually increased during nitrogenation for 24 hours. The coercivity of powder was higher than that of powder at the same condition of nitrogenation. It was considered that the Mn addition facilitates the nitrogenation of powder and enhances the coercivity.

The spinel Fe3O4 powders were synthesized using 0.2 M-FeSO4·7H2O and 0.5 M-NaOH by oxidation in air and the spinel LiMn2O4 powders were synthesized at 480 ℃ for 12 h in air by a sol-gel method using manganese acetate and lithium hydroxide as starting materials. The synthesized LiMn2O4 powders were mixed at portion of 5, 10, 15 and 20 wt% of Fe3O4 powders using a ball-mill. The mixed catalysts were dried at room temperature for 24 hrs. The mixed catalysts were reduced by hydrogen gas at 350 ℃ for 2 h. The carbon dioxide decomposition rates of the mixed catalysts were 90% in all the mixed catalysts but the decomposition rate of carbon dioxide was increased with adding LiMn2O4 powders to Fe3O4 powders.

The spinel LiMn2O4 powders were synthesized at 480℃ for 12 h in air by a sol-gel method using manganese acetate and lithium hydroxide as starting material and the Fe3O4 powders were synthesized by the precipitation method using 0.2M-FeSO4·H2O and 0.5M-NaOH. The synthesized Fe3O4 powders were mixed at portion of 5, 10, 15 and 20 wt% about LiMn2O4 powders through ball-milling followed by drying at room temperature for 48 h in air. The mixed catalysts were reduced at 350℃ for 3 h by hydrogen and the decomposition rate of carbon dioxide was measured at 350℃ using the reduced catalysts. As the results of CO2 decomposition experiments, the decomposition rates of carbon dioxide were 85% in all catalysts but the initial decomposition rates of CO2 were slightly high in the case of the 5%-Fe3O4 added catalyst.

This study was carried out to investigate the possibility whether Metal Injection Molding (MIM) process could be applied to 95wt.%W-3.5wt.%Ni-1.5wt.%Fe heavy alloy in order to obtain an intricate shape. Methylcellulose was used in the injection molding for binder. was added in solvent substituting Fe powder and was doped on W-Ni premixed powder. When was added in solvent, the binder separation occurred for injection molding so that the matrix content was changed. Such problem was solved when was doped. In this study. the debinding process did not affect residual carbon content. The sintered microsouctures as addition methods of Fe element and the sintering temperature from to , which are around the temperature of liquid phase formation, were observed.

AISI 4600계 철 분말에 Fe2P 분말을 사용하여 인(P)을 0~1.0% 그리고 흑연 분말을 사용하여 탄소를 0~0.8% 첨가하여 회전혼합기를 사용하여 혼합하였다. 흔합분말을 양단압금형에서 800MPa로 가압하여 성형체를 만들었다. 성형체는 진공 또는 수소와 질소 혼합가스 분위기에서 1150˚C에서 30분간 소결하였다. 소결체를 연마하고 2% 질산용액으로 에칭하였다. 소결체 조직을 Image Analyzer와 금속현미경으로 관찰하였다. 밀도는 ASTM B3l2로, 경도는 미세 비커스경도기로 측정하였다. 얻어진 결과는 다음과 같다. (1) Fe2P 첨가량이 증가하면, 소결체 조직은 치밀화되고 입자 크기는 더 커졌다. (2) Fe2P량과 함께 기공의 형상은 둥글고, 그 숫자는 감소하였으나 평균크기는 더 커졌다. (3) 입자의 크기는 Fe2P와 흑연분말을 동시에 첨가한 경우가 각각 단독으로 첨가한 경우보다 커졌다. (4) 미세조직에 미치는 소결분위기의 영향은 거의 없었다. (5) 경도는 인과 탄소량이 증가하면 상승하였다.