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구상화 열처리된 고탄소강의 미끄럼 마멸 거동에 미치는 초기 미세조직의 영향 연구
허하리(H. L. Hur),권혁우(H. Gown),김명곤(M. G. Kim),김용석(Y.-S. Kim) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.10
This study was conducted to elucidate the effect of prior microstructure on sliding wear behavior of spheroidized high carbon (1 wt. % C) steel. The high carbon steel was primarily heat treated to obtain full pearlite and martensite microstructure before the spheroidization. Spheroidizing heat treatment was performed on the full pearlite steel and tempering was performed on the martensite steel to get spheroidized cementite in ferrite matrix. Sliding wear tests were carried out using pin-on-disk wear tester with th steel as a disk specimen. An alumina (Al₂O₃) ball was used as a pin counterpart. The sliding wear tests were carried out at room temperature in the air with humidity of 40±2%. Sliding distance and applied road were 300m and 100N, sliding speed and wear track radius were 0.1m/s and 9 mm, respectively. Worn surfaces and cross-sections of the worn surfaces were observed using SEM. Micro Vickers hardness of the wear-track subsurface was measured as a function of depth from the worn surface. After the spheroidizing heat treatment and the tempering, both pearlite and martensite exhibited similar microstructure of spheroidized cementite in ferrite matrix. Spheroidized pearlite specimens showed lower hardness than the tempered martensite, but wear resistance of the spheroidized pearlite was superior to that of the tempered martensite.
권혁우(H. Gwon),허하리(H. L. Hur),구본우(B. W. Gu),김종국(J. K. Kim),강용진(Y. J. Kang),김용석(Y. -S. Kim) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.10
Tribological characteristics of a-C:H coating and ta-C coating against AZ31 Mg alloy was investigated. The a-C:H coating was deposited on a STD-61 steel pin by the plasma-enhanced chemical-vapor deposition (PECVD) process. The hydrogen-free DLC (ta-C) was prepared by filtered vacuum arc deposition (FCVA). Dry sliding friction and galling characteristics of the two DLC coatings on the STD-61 steel against AZ31 Mg alloy disks were evaluated using a reciprocating sliding tribometer at room temperature and at 250 ℃. To represent a real sliding during the sheet metal forming process, single-stroke tests were adapted (10 mm of stroke length) rather than a reciprocating long sliding-distance test. Both a-C:H coating and ta-C coating suppressed the adhesion between the Mg alloy and the tool steel at room temperature, which kept the friction coefficient low. However, at 250 ℃, both DLC coatings exhibited severe adhesion to the Mg alloy, which increased the friction coefficient and the galling.
구상화 열처리된 고탄소강의 페라이트 기지 조직이 미끄럼 마멸 거동에 미치는 영향
허하리(H. L. Hur),권혁우(H. Gown),김명곤(M. G. Kim),김용석(Y. -S. Kim) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
This study was conducted to elucidate the effect of matrix ferrite microstructure on sliding wear behavior of spheroidized high carbon (1 wt. % C) steel. The high carbon steel was primarily heat treated to obtain full pearlite and martensite microstructure before the spheroidization. Spheroidizing heat treatment was performed on the full pearlite steel and tempering was performed on the martensite steel to get spheroidized cementite in ferrite matrix in both full pearlite and martensite microstructure. Sliding wear tests were carried out using pin-on-disk wear tester with the steel as a disk specimen. An alumina (Al2O3) ball was used as a pin counterpart. After the spheroidizing heat treatment and the tempering, both pearlite and martensite exhibited similar microstructure of shperoidized cementite in ferrite matrix. Spheroidized pearlite specimens showed lower hardness than the tempered martensite, but wear resistance of the spheroidized pearlite was superior to that of the tempered martensite.
탄소강의 초석페라이트와 시멘타이트의 형상이 미끄럼마멸 거동에 미치는 영향 분석
허하리(H. L. Hur),권혁우(H. Gwon),김명곤(M. G. Kim),김용석(Y. S. Kim) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.5
This study was conducted to elucidate the correlation between wear resistance and cementite morphology (degree of spheroidization) in carbon steel. For that purpose, we analyzed effect of the existence of pro-eutectoid ferrite and cementite morphology on the sliding wear of medium and high carbon steel. AISI 52100 bearing steel and S45C medium carbon steel were heat treated to obtain full pearlite and ferrite + pearlite microstructure. After the heat treatment, a spheroidizing heat treatment was performed on both steel to spheroidize the pearlite. Sliding wear tests were carried out using a pin-on-disk wear tester with the steel specimens as a disk. An alumina (Al₂O₃) ball was used as a pin counterpart. The sliding wear tests were carried out at room temperature in the air with humidity of 40±2 %. Adapted sliding distance and applied load was 300 m and 100 N, respectively. Sliding speed was 0.1 m/s and the wear-track radius was 9 mm. Worn surfaces and cross-sections of the wear track were examined using an SEM. Micro Vickers hardness of the wear-track subsurface was measured as a function of depth from the worn surface. It was found that sliding-wear resistance of both AISI 52100 bearing steel and S45C steel decreased as the cementite morphology become more spheroidized.
구상화 열처리된 고탄소강의 미끄럼 마멸 거동에 미치는 시멘타이트 형상과 페라이트 기지조직의 영향
허하리(H. L. Hur),권혁우(H. Gown),구본우(B. Gu),김용석(Y. -S. Kim) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.10
This study was conducted to elucidate the effect of cementite morphology and matrix ferrite microstructure on sliding wear behavior of spheroidized high carbon (1 wt. %C) steel. The high carbon steel was primarily heat treated to obtain full pearlite and martensite microstructure before the spheroidization. Spheroidizing heat treatment was performed on the full pearlite steel for 100 hours at 700 ℃ and tempering was performed on the martensite steel for 3 hours at 650 ℃ to get spheroidized cementite in ferrite matrix in both full pearlite and martensite microstructure. Sliding wear tests were carried out using pin-on-disk wear tester with the steel as a disk specimen. An alumina(Al₂O₃) ball was used as a pin counterpart. The sliding wear tests were carried out at room temperature in the air with humidity of 402%. Adapted sliding distance and applied load was 300 m and 100 N, respectively. Sliding speed was 0.1m/s and the wear-track radius was 9mm. Worn surfaces and cross-sections of wear track were examined using an SEM. Micro Vickers hardness of the wear track subsurface was measure as a function of depth from the worn surface. After the spheroidizing heat treatment and the tempering, both pearlite and martensite exhibited similar microstructure of spheroidized cementite in ferrite matrix. Spheroidized pearlite specimens showed lower hardness than the tempered martensite, but wear resistance of the spheroidized pearlite was superior to that of the tempered martensite.
마그네슘 합금의 판재 성형 시 금형-판재간 응착문제 해결을 위한 표면처리
권혁우(H. Gwon),김명곤(M.-G. Kim),허하리(H.-L. Hur),박영희(Y.-H. Park),김용석(Y.-S. Kim) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.5
In this study, surface of a AZ31B Mg alloy sheet was coated with Mg(OH)₂ film and its tribological characteristics were evaluated during hot forming. The coating was applied to the sheet with a hope of avoiding tribological problems during sheet forming the alloy sheet such as wear, stciking and galling of forming tools and sheets. Flat surface-on-disk reciprocating tests were carried out using the AZ31B Mg alloy sheet and STD-61 tool steel as the surface and the disk, respectively. The tests were performed at various applied loads under both dry and lubricated condition at room temperature and 250℃. Tool steel disks with PVD coatings were also evaluated. Galling of the AZ31B magnesium alloy sheet was examined by measuring friction coefficient, surface roughness and observing slid surfaces of both the Mg alloy sheet and coated tool surface by OM and SEM. The Mg(OH)₂ film reduced friction coefficient and effectively suppressed galling of the Mg alloy sheet.
Mg 합금 판재성형 중 발생하는 galling 현상과 마찰계수와의 상관관계
권혁우(H. Gwon),김명곤(M. G. Kim),허하리(H. L. Hur),김용석(Y.-S. Kim) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.10
Correlation between galling which occurs during Mg alloy sheet forming using a steel die and friction coefficient measured during the sheet forming was investigated. Sliding friction (and/or wear) characteristics of the sliding couples including AZ31B Mg alloy and STD61 tool steel were evaluated using a disk-on-flat friction tester at 250℃. Both a Mg alloy sheet without any pretreatment and the alloy sheet with Mg(OH)₂ film on a surface were tested. Tribological behavior of the Mg alloy sheets slid against bare and DLC coated STD61 tool steel were examined in this study. Galling, which related with a material-transferring, was found to be controlled by mechanisms of adhesive junction forming, shear deformation and fracture of the junctions. The mechanisms also control the degree of resistance against relative sliding between the couples, which was measured as a friction coefficient. The correlation between the galling and the friction coefficient was discussed.
마그네슘 합금에 대한 DLC 코팅의 온도에 따른 마찰기구 해석
권혁우(H. Gwon),김명곤(M.G. Kim),허하리(H.L. Hur),김용석(Y.-S. Kim) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
The sheet-forming of Mg alloys is carried out at elevated temperature (250 ℃) due to their low formability at room temperature. The high-temperature process results in a typical surface damage, the galling. In this investigation, tribologcial characteristics of DLC coating which had been widely used for low-friction processes against AZ31 Mg alloy were investigated. Dry sliding friction and galling characteristics of AZ31 Mg alloy disks which were slid against uncoated and DLC-coated STD-61 steel pin were evaluated using a reciprocating sliding tribometer at room temperature and 250 ℃. To represent a real sliding during the sheet metal forming process, single-stroke tests were adapted (10 mm of stroke length) rather than a reciprocating long sliding-distance test. The DLC coating suppressed adhesion between the alloy and the tool steel at room temperature, which kept the friction coefficient low. However, at 250 ℃, severe adhesion occurred between the two surfaces, which increased the friction coefficient and the galling.