API X80 라인파이프강의 미세조직과 기계적 특성에 미치는 냉각조건의 영향

한승엽 ( Seung Youb Han ),신상용 ( Sang Yong Shin ),이성학 ( Sung Hak Lee ),배진호 ( Jin Ho Bae ),김기수 ( Ki Soo Kim ) 대한금속·재료학회 2009 대한금속·재료학회지 Vol.47 No.9

In this study, four API X80 linepipe steel specimens were fabricated with varying cooling rates and finish cooling temperatures, and their microstructures and crystallographic orientations were analyzed to investigate the effects of cooling conditions on their tensile and Charpy impact properties. All the specimens consisted of acicular ferrite, granular bainite, and secondary phases such as martensite and martensiteaustenite constituent. The volume fraction of secondary phases increased with increasing cooling rate, and the higher finish cooling temperature resulted in the reduction in volume fraction and grain size of secondary phases. According to the crystallographic orientation analysis data, the effective grain size and unit crack path decreased as fine acicular ferrites having a large amount of high-angle grain boundaries were homogeneously formed, thereby leading to the improvement of Charpy impact properties. The specimen fabricated with the higher cooling rate and lower finish cooling temperature had the highest upper shelf energy and the lowest energy transition temperature because it contained a large amount of fine secondary phases homogeneously distributed inside fine acicular ferrites, while its tensile properties well maintained.

베이나이트계 후판강의 모재 및 열영향부의 미세조직과 기계적 특성에 미치는 화학 조성의 영향

조성규,주형건,신상용,Cho, Sung Kyu,Joo, Hyung Goun,Shin, Sang Yong 한국재료학회 2019 한국재료학회지 Vol.29 No.4

In this study, three kinds of bainitic steel plates are manufactured by varying the chemical compositions and their microstructures are analyzed. Tensile and Charpy impact tests are performed at room and low temperature to investigate the correlation between microstructure and mechanical properties. In addition, heat affected zone (HAZ) specimens are fabricated by a simulation of welding processes, and the HAZ microstructure is analyzed. The base steel that has the lowest carbon equivalent has the highest volume fraction of acicular ferrite and the lowest volume fraction of secondary phases, so the strength is the lowest and the elongation is the highest. The Mo steel has a higher volume fraction of granular bainite and more secondary phases than the base steel, so the strength is high and the elongation is low. The CrNi steel has the highest volume fraction of the secondary phases, so the strength is the highest and elongation is the lowest. The tensile properties of the steels, namely, strength and elongation, have a linear correlation with the volume fraction of secondary phases. The Mo steel has the lowest Charpy impact energy at $-80^{\circ}C$ because of coarse granular bainite. In the Base-HAZ and Mo-HAZ specimens, the hardness increases as the volume fraction of martensite-austenite constituents increases. In the CrNi-HAZ specimen, however, hardness increases as the volume fraction of martensite and bainitic ferrite increases.

해양플랜트용 후판강의 미세조직과 기계적 특성에 미치는 압연 조건의 영향

김종철,서용찬,황성두,신상용,Kim, Jongchul,Suh, Yonhchan,Hwang, Sungdoo,Shin, Sang Yong 한국재료학회 2018 한국재료학회지 Vol.28 No.8

In this study, three kinds of steels are manufactured by varying the rolling conditions, and their microstructures are analyzed. Tensile and Charpy impact tests are performed at room temperature to investigate the correlation between microstructure and mechanical properties. In addition, heat affected zone(HAZ) specimens are fabricated through the simulation of the welding process, and the HAZ microstructure is analyzed. The Charpy impact test of the HAZ specimens is performed at $-40^{\circ}C$ to investigate the low temperature HAZ toughness. The main microstructures of steels are quasi-polygonal ferrite and pearlite with fine grains. Because coarse granular bainite forms with an increasing finish rolling temperature, the strength decreases and elongation increases. In the steel with the lowest reduction ratio, coarse granular bainite forms. In the HAZ specimens, fine acicular ferrites are the main features of the microstructure. The volume fraction of coarse bainitic ferrite and granular bainite increases with an increasing finish rolling temperature. The Charpy impact energy at $-40^{\circ}C$ decreases with an increasing volume fraction of bainitic ferrite and granular bainite. In the HAZ specimen with the lowest reduction ratio, coarse bainitic ferrite and granular bainite forms and the Charpy impact energy at $-40^{\circ}C$ is the lowest.

HSLA 강의 CGHAZ 미세조직과 샤르피 충격 인성에 미치는 Mo과 Nb의 영향

김민구,조성규,신상용 대한용접·접합학회 2022 대한용접·접합학회지 Vol.40 No.1

In this study, the effects of Mo and Nb on the microstructure and Charpy impact properties of coarse-grain heat af- fected zone (CGHAZ) in high-strength low-alloy (HSLA) steels were investigated. The high-Mo steel had a lower volume fraction of acicular ferrite (AF) and higher volume fraction of granular bainite (GB) than those of the low Mo steel. The high-Mo CGHAZ specimen had a lower volume fraction of AF and higher volume fraction of GB compared to the low-Mo CGHAZ specimen. This is because, an increase in Mo lowers the bainite transformation temperature, induces the formation of GB and bainitic ferrite (BF), and reduces the diffusion velocity of carbon, thereby inhibiting the formation of ferrite. The Nb-added steel had a volume fraction similar to that of AF but small- er packet sizes of GB compared to the non-Nb steel. Compared to the non-Nb CGHAZ specimens, the Nb-added CGHAZ specimen had a lower volume fraction of AF, a higher volume fraction of GB, smaller packet sizes of GB and BF, and a smaller prior austenite grain size. This is because, Nb forms Nb(C,N) to inhibit the grain growth, thus inhibiting the formation of GB and BF. The Nb-added low-Mo CGHAZ specimen with the highest AF fraction and smallest average grain size had the highest Charpy-absorbed energy. However, articles in the Journal of Welding and Joining reported that the other CGHAZ specimens with high volume fractions of GB and BF with coarse packets showed low Charpy-absorbed energy.

Effects of acicular ferrite on charpy impact properties in heat affected zones of oxide-containing API X80 linepipe steels

Sung, H.K.,Shin, S.Y.,Cha, W.,Oh, K.,Lee, S.,Kim, N.J. Elsevier Sequoia 2011 Materials science & engineering. properties, micro Vol.528 No.9

This study was concerned with effects of acicular ferrite on Charpy impact properties in heat affected zones (HAZs) of two API X80 linepipe steels containing oxides. In the one steel, Mg and O<SUB>2</SUB> were additionally added to form a larger amount of oxides than the other steel, which was a conventional X80 steel containing a considerable amount of Al and Ti. Various HAZ microstructures were obtained by conducting HAZ simulation tests under different heat inputs of 35kJcm<SUP>-1</SUP> and 60kJcm<SUP>-1</SUP>. Oxides present in the API X80 linepipe steels were complex oxides whose average size was 1-2μm, and the number of oxides increased with increasing amount of Mg and O<SUB>2</SUB>. The volume fraction of acicular ferrite present in the steel HAZs increased with increasing number of oxides, and decreased with increasing heat input. When the volume fraction of acicular in the HAZ was higher than 20%, Charpy impact energy at -20<SUP>o</SUP>C was higher than 100J as the ductile fracture mode was dominant. Particularly in the steel HAZs having a larger amount of oxides, Charpy impact properties were excellent because oxides worked as nucleation sites of acicular ferrite during welding. Charpy impact properties of the HAZs could be well correlated with the volume fraction of acicular ferrite and number of oxides under different heat input conditions.

Effects of Mn and Al contents on cryogenic-temperature tensile and Charpy impact properties in four austenitic high-Mn steels

Sohn, S.S.,Hong, S.,Lee, J.,Suh, B.C.,Kim, S.K.,Lee, B.J.,Kim, N.J.,Lee, S. Elsevier Science 2015 Acta materialia Vol.100 No.-

Effects of Mn (19 and 22wt.%) and Al (0 and 2wt.%) contents on tensile and Charpy impact properties in four austenitic high-Mn steels were investigated at room and cryogenic temperatures. The cryogenic-temperature tensile test results indicated that the yield strength was higher in the Al-added steels than non-Al-added steels, which could be explained by a stress-induced martensitic transformation in the non-Al-added steels. The reduction in ductility was largest in the 19Mn steel, where the transformations to ε- and α'-martensites occurred and their fraction was highest. Charpy impact energies of the 19Mn and 22Mn steels rapidly dropped with decreasing temperature, whereas those of the 19Mn2Al and 22Mn2Al steels slowly decreased. According to the EBSD analysis data of the cryogenic-temperature Charpy impact specimen, the transformation to ε- and α'-martensites readily occurred in the 19Mn and 22Mn steels, which resulted in the large reduction in impact energy. In the 19Mn2Al steel composed of highly stable austenite, the time needed for sufficient deformation to trigger the martensitic transformation was very short under the impact testing condition. In the Al-added steels, any martensites were not found, while many deformation twins were formed, thereby leading to high Charpy impact energy.

Compression after Impact and Charpy Impact Characterizations of Glass Fiber/Epoxy/MWCNT Composites

Özgür Demircan,Kemal Kadıoğlu,Pınar Çolak,Erdinç Günaydın,Mustafa Doğu,Neslihan Topalömer,Volkan Eskizeybek 한국섬유공학회 2020 Fibers and polymers Vol.21 No.8

In this study, glass fiber/epoxy resin/multi-walled carbon nanotubes (MWCNTs) were used to fabricate hybridcomposites with biaxial warp-knitted fabrics. The biaxial warp-knitted fabrics were grafted with various amounts ofMWCNTs and the hybrid composites were fabricated using the resin transfer molding (RTM) method, subsequently. Thefabricated samples were subjected to compression after impact and Charpy impact tests. The hybrid composites exhibitedhigher compression after impact modulus and strength with 26 % and 17 % compared to the samples without nanotubes,respectively. Moreover, the MWCNTs integrated specimens showed 17 % improvement of Charpy impact strength againstspecimens without carbon nanotubes in 0odegree direction. Fracture surface analysis revealed lower number of cracks andshorter crack propagation lengths in the MWCNTs reinforced specimens. The improvement in mechanical properties of thehybrid composites can most likely be attributed to an increase in interfacial adhesion due to the presence of the carbonnanotubes.

A Study on the Impact Test Analysis of Specimens for Designing the Housing of Precision Guided Projectile

고준복(Jun bok Ko),이소담(So dam Yi),박은주(Eun joo Park),백기봉(Ki bong Baek),김명섭(Myeong seop Kim),서석훈(Suhk hoon Suh) Korean Society for Precision Engineering 2019 한국정밀공학회지 Vol.36 No.6

The precision-guided projectile is a weapon system for precision attacks, and the cannon-launched projectile is guided by a control device. The electrical actuator system is a subsystem of the control device, and the whole projectile undergoes high axial and lateral impact force for 1 to 10mseconds. In this study, a charpy, and a tensile impact analysis were conducted, using specimens made in the materials of SUS630 and Al7075-T6 to understand fracture mechanics and impact property, such as energy change rate. The impact analysis and gas-gun impact test were conducted, to validate the optimized housing model.

해양플랜트용 후판강의 FCAW HAZ 미세조직과 샤르피 충격 특성의 상관관계

이훈,이현욱,조성규,최동기,김형찬,권용재,이정구,신상용,Lee, Hun,Lee, Hyunwook,Cho, Sung Kyu,Choi, Dongki,Kim, Hyoung Chan,Kwon, Yongjai,Lee, Jung Gu,Shin, Sang Yong 한국재료학회 2019 한국재료학회지 Vol.29 No.8

In this study, the correlation between microstructure and Charpy impact properties of FCAW(Flux cored arc welding) HAZ(Heat affected zone) of thick steel plates for offshore platforms was investigated. The 1/4 thickness(1/4t) location HAZ specimen had a higher volume fraction of bainite and finer grain size of acicular ferrite than those of the 1/2 thickness (1/2t) location HAZ specimen because of the post heat effect during the continuous FCAW process. The Charpy impact energy at $-20^{\circ}C$ of the 1/4t location HAZ specimen was lower than that of the 1/2t location HAZ specimen because of the high volume fraction of coarse bainite. The Charpy impact energy at -40 and $-60^{\circ}C$ of the 1/2t location HAZ specimen were higher than those of the 1/2t location HAZ specimen because the ductile fracture occurred in the fine acicular ferrite and martensite regions. In the ductile fracture mode, the deformed regions were observed in fine acicular ferrite and martensite regions. In the brittle fracture mode, long crack propagation path was observed in bainite regions.

논문 : 단상영역에서 압연된 API X80 라인파이프강의 인장 및 샤르피 충격 특성에 미치는 Mo, Cr, V의 영향

한승엽 ( Seung Youb Han ),신상용 ( Sang Yong Shin ),서창효 ( Chang Hyo Seo ),이학철 ( Hak Cheol Lee ),배진호 ( Jin Ho Bae ),김기수 ( Ki Soo Kim ),이성학 ( Sung Hak Lee ),김낙준 ( Nack J. Kim ) 대한금속재료학회 ( 구 대한금속학회 ) 2008 대한금속·재료학회지 Vol.46 No.12

This study is concerned with the effects of Mo, Cr, and V addition on tensile and Charpy impact properties of API X80 linepipe steels. Four kinds of steels were processed by varying Mo, Cr, and V additions, and their microstructures and tensile and Charpy impact properties were investigated. Since the addition of Mo and V promoted to form fine acicular ferrite and granular bainite, while prohibiting the coarsening of granular bainite, it increased the strength and upper shelf energy, and decreased the energy transition temperature. The Cr addition promoted the formation of coarse granular bainite and secondary phases such as martensite-austenite constituents, thereby leading to the increased effective grain size, energy transition temperature, and strength and to the decreased upper shelf energy. The steel containing 0.3wt.% Mo and 0.06wt.% V without Cr had the highest upper shelf energy and the lowest energy transition temperature because its microstructure was composed of fine acicular ferrite and granular bainite, together with a small amount of hard secondary phases, while its tensile properties maintained excellent.