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권혁우(H. W. Kwon),윤나래(N. Yoon),김종철(J. C. Kim),정영중(Y.-J. Jeong),김용석(Y.-S. Kim) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.10
During sheet metal forming of Mg alloys, significant tribological problems such as wear, friction and galling occur. "Galling is the gross damage include scratching, grooving and plastic deformation of surfaces of metal sheet (or tools), which is associated with adhesive or stiction. When two surfcaces contact each other, a real contact will occur as asperities, and the contact forms as adhesive particle. The formation of the adhesive particle is one of major causes of the galling occuring at surfaces of the metal sheet and tools. In the present study, the galling characteristics between AZ31B Mg alloy sheets and tool steels (STD-11, STD-16) were evaluated. Reciprocative sliding test. Wear volume of the AZ31B alloy sheet and tool steels were calculated. Worn surfaces of the AZ31B sheet and tool steels were observed by SEM and EDS, and the topography of the survaces was obtained by a surface profilometer. Severe damage due to adhesive particles was observed on the AZ31B Mg alloy specimens. It is conformed that a material pick-up (adhesion) occurs almost instantaneously when asperities of the Mg alloy sheet and the too steels contact, which produces adhesive particles.
0.25 wt.% C 탄소강의 미세조직 변화와 3 - body 연삭마멸 특성
정영중(Y.-J. Jeong),김종철(J. C. Kim),윤나래(N. R. Yoon),권혁우(H. W. Kwon),김용석(Y.-S. Kim) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.10
This investigation was performed to reveal the effect of microstructure on 3-body abrasive wear behavior of the 0.25wt.% C steel. The steel was heat treated under different conditions to obtain PF/P (Polygonal ferrite & Pearlite), AF(Acicular ferrite) and PF/TM (Polygonal ferrite & Tempered martensite) microstructures. Three-body abrasive wear tests were carried out using a ball-cratering tester. The ball was an AISI 52100 steel ball. The ball-surface was roughened by rotating on a specimen to feed slurries easily into the contact between the ball and the specimen. The roughening distance was 7.85 m. The slurry of Al2O3 particles(4μm) suspended in water with concentration of 0.75 g/ml was fed on top of the ball throughout the test at a rate approximately 1.445 g/min. All tests were performed with a normal load of 0.2N, sliding(ball rotation) speed of 0.05 m/s and sliding distance of 50 m. Microstructure of the heat treated specimens was observed by an optical micorscope, and worn surface were observed by a stereoscopic microscope and SEM (scanning electron microscop). Hardness of the stell was measured by a micro Vickers hardness tester. The PF/P microstructure showed the best 3-body-abrasive-wear resistance among the microstructures examined in the present study.
구본우(B. W. Gu),권혁우(H. W. Kwon),김용석(Y. S. Kim) 한국소성가공학회 2016 한국소성가공학회 학술대회 논문집 Vol.2016 No.4
During the sling wear of a ferrous metal, a subsurface layer is formed of which the microstructure, constituting phases and the mechanical property are different from those of the original wearing metal. Since the wear occurs at the layer, it is important to understand how the wear rate varies with different layers. The layers are composed of oxide layers, MMLs and deformation layers. Their formation mechanisms are known to vary depending on sliding-wear test conditions such as counterpart material and environmental conditions. In this research, two different counterparts, AISI 52100 steel and Al₂O₃ were utilized to see the effect of counterpart on the formation of the layers and subsequent wear behavior. Sliding wear tests of the pure iron were carried out to exclude other effects from the carbide and cementite phases in the air and in an Ar atmosphere. After the sliding wear test, worn surfaces, debris and cross sections were analyzed by SEM, TEM and EDS. Wear rates were analyzed by comparing constituting phases, mechanical properties and thickness of the layer, which changed with the two different counterparts and test environments.