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슈퍼 듀플렉스 스테인리스강 UNS S32750의 FCA 다층 용접부의 용접 후 열처리 영향
장복수,문인준,임명진,김세철,김수성,이정원,박해웅,고진현,Jang, Bok-Su,Moon, In-June,Lim, Myung-Jin,Kim, Se-Cheol,Kim, Soo-Sung,Lee, Jung-Won,Park, Hai-Woong,Koh, Jin-Hyun 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.2
This study was carried out to investigate the effect of postweld heat treatment(PWHT, 930, 1080, $1230^{\circ}C$) on the microstructure, phase formation, pitting corrosion and mechanical properties such as hardness, tensile strength and impact values of super duplex stainless steel(UNS S32750) multipass welds. Based on the microstructural examination and X-ray diffraction analysis, it was found that the ${\sigma}$ phase was formed in the welds heat treated at $930^{\circ}C$ in which the ferrite content greatly decreased into 5~10% in the welds. The secondary austenite was formed in the reheated zone of welds and redissolved into ferrite with increasing heat treatment temperatures. The tensile strength and impact values of welds heat treated at $930^{\circ}C$ were the lowest and revealed the brittle fracture surface. The weight loss by pitting corrosion increased with test temperatures. It was confirmed that pitting corrosion occurred mainly in secondary austenite of reheated zones. The postweld heat treatment temperature is recommended to be in the range of $1050{\sim}1150^{\circ}C$.
슈퍼 듀플렉스 스테인리스강 UNS S32750의 FCA 용접 후 열처리가 공식에 미치는 영향
장복수,문인준,김세철,고진현,Jang, Bok-Su,Moon, In-June,Kim, Se-Cheol,Koh, Jin-Hyun 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.5
This study was carried out to investigate the influence of a sigma phase precipitation on the pitting corrosion resistance and microstructural change of super duplex stainless steels(UNS S32750). The welds made by FCAW (Flux Cored Arc Welding) were heat treated ($930^{\circ}C$, $1080^{\circ}C$, $1230^{\circ}C$) and quenched. Based on the microstructural examination, it was found that the ${\sigma}$ phase was formed in base metals and welds heat treated at $930^{\circ}C$ while there were little ${\sigma}$phases formed in base metals and weld metal experienced the relatively fast cooling from $1080^{\circ}C$ and $1230^{\circ}C$. On the other hand, the most weight loss due to pitting corrosion occurred in base and weld metals heat treated at $930^{\circ}C$. It was confirmed that the pitting corrosion occurred in the phase boundaries of ferrite/sigma and austenite/sigma. The pitting corrosion resistance decreased owing to an increase in Cr, Mo depleted areas adjacent to the intermetallic phases such as ${\sigma}$phases. The hardness was greatly increased due to the precipitation ${\sigma}$phases.
아연도금강관의 가스메탈아크용접에서 용접인자가 기공형성에 미치는 영향
임영민,장복수,고진현,Lim, Young-Min,Jang, Bok-Su,Koh, Jin-Hyun 대한용접접합학회 2012 대한용접·접합학회지 Vol.30 No.5
This study was carried out to investigate the effect of welding parameters such as shielding gas compositions welding voltage and welding current on the pore formation in the weld beads of galvanized steel pipes produced with gas metal arc welding. The porosity was evaluated and rated by metallography and radiographic test in terms of weight percentage, number and distribution of pores in weld beads. The porosity increased with increasing welding voltage and current, in which Ar gas produced the most porosity while $Ar+5%O_2$ generated the least porosity. It was found that the porosity could be reduced by selection of the proper gas mixture composition such as $Ar+5%O_2$ and $Ar+10%CO_2$ and by using current (130~150A) and voltage(16~20V).
슈퍼듀플렉스 스테인리스강 UNS S32750과 탄소강 A516-70의 이종금속 FCA 용접 특성에 대한 연구
문인준,장복수,김세철,고진현,Moon, In-June,Jang, Bok-Su,Kim, Se-Cheol,Koh, Jin-Hyun 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.4
The metallurgical and mechanical characteristics, toughness and corrosion resistance of dissimilar welds between super duplex stainless steel UNS S32750 and carbon steel ASTM A516Gr.70 have been evaluated. Three heat inputs of 21.12, 24.00, 26.88kJ/cm were employed to make joints of dissimilar metals with flux cored arc welding(FCAW). Based on microstructural examination, vermicular ferrite was formed in the first layer of weld at low heat input(21.12kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.61 while acicular ferrite was formed in last layer of weld at high heat input(26.88kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.72. Ferrite percentage in dissimilar welds was lowest in the first layer of weld regardless of heat inputs and it gradually increased in the second and third layers of weld. Heat affected zone showed higher hardness than the weld metal although reheated zone showed lower hardness than weld metal due to the formation of secondary austenite. Tensile strengths of dissimilar welds increased with heat input and there was 100MPa difference. The corrosion test by ferric chloride solution showed that carbon steel had poor corrosion resistance and pitting corrosion occurred in the first layer(root pass) of weld due to the presence of reheated zone where secondary austenite was formed. The salt spray test of carbon steel showed that the surface only corroded but the amount of weight loss was extremely low.
합금강(ASTM A387 Gr. 91) - 탄소강(ASTM A516 Gr.70) 이종금속의 FCA 다층 용접부 특성 평가
신태우(Tae Woo Shin),장복수(Bok Su Jang),고진현(Jin Hyun Koh) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.3
Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E91T1-B9C wire. Post-weld heat treatment was carried out at 750℃ for 2.5 h. Based on microstructural examination, tempered martensite and lower bainite were formed in first layer of weld metal. The amount of tempered martensite was decreased and the amount of lower bainite was increased with increasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered Martensite and lower Bainite. Tensile strengths of dissimilar welds decreased with increasing heat inputs. Dissimilar welds seemed to have a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals showed that the corrosion rate increased with increasing heat inputs due to the increase of the amount of lower Bainite.
HSB600강 가스메탈아크용접부에서 입열량과 용접후 열처리가 기계적 특성과 미세조직에 미치는 영향
주동휘(Ju, Dong-Hwi),장복수(Jang, Bok-Su),임영민(Lim, Young-Min),고진현(Koh, Jin-Hyun) 한국산학기술학회 2012 한국산학기술학회논문지 Vol.13 No.5
교량용 고성능 강재는 높은 인장강도, 항복강도, 고인성, 용접성등이 요구된다. 교량 구조용 강재인 TMCP HSB600강의 GMA용접부에서 입열량(1.4∼3.2kJ/mm)과 용접후 열처리가 기계적 특성과 미세조직에 미치는 영향을 조 사하였다. 용접된 상태에서는 입열량이 증가할수록 인장강도와 경도는 감소하였다. 입열량 1.4kJ/mm에서는 빠른 냉각 속도에 의해 베나이트적 페라이트와 탄화물 집합체 등의 경한 미세조직이 생성되었고 입열량 2.1kJ/mm에서는 침상형 페라이트가 다량 생성되었으며, 고입열량인 3.2kJ/mm에서는 입계페라이트 사이트 플레이트와 구형 페라이트가 많이 생성되었다. 용접 후 열처리를 통해 용접부의 잔류응력의 감소와 결정립 조대화로 인하여 인장강도와 경도는 감소하 였으나 충격흡수에너지에는 큰 차이가 없었다. High performance steel for bridges requires higher performance in tensile and yield strength, toughness, weldability, etc. The purpose of this study is to investigate the weldability of HSB 600 steel. The effects of heat input (1.4∼3.2kJ/mm) and postweld heat treatment (PWHT, 600℃, 40hr.) on the TMCP HSB600 steel weldments made by GMAW process were investigated. The tensile strength and hardness of as-welded specimens decreased with increasing heat input. Charpy V-notch impact energy did not show any significant difference by postweld heat treatment. The fine-grained acicular ferrite was mainly formed in the 2.1kJ/mm of heat input while polygonal and side plate ferrites were dominated in the high inputs. Meanwhile, tensile strength and hardness of PWHT weldments decreased due to the coarsening and globularization of ferrite microstructure and reduction of residual stresses with increasing heat inputs. However, there was no significant difference in the impact energy absorption.
HSB600강 GMA 용접부에서 입열량과 용접후 열처리가 미세조직과 기계적 특성에 미치는 영향
고진현(Koh, Jin-Hyun),김남훈(Kim, Nam-Hoon),장복수(Jang, Bok-Su),주동휘(Ju, Dong-Hwi),임영민(Lim, Young-Min) 한국산학기술학회 2011 한국산학기술학회논문지 Vol.12 No.12
본 연구에서는 교량용 구조용 강재인 HSB600 강의 용접부에서 입열량 (1.5∼3.6 kJ/mm)과 용접후 열처리 (PWHT, 600℃, 40hr.)가 미세조직과 기계적 특성에 미치는 영향에 관해 연구하였다. HSB600 강재를 GMA용접을 실 시하였다. 용접된 상태에서는 인장강도와 경도는 입열량이 증가할수록 저하되었으며 충격 흡수 에너지는 큰 차이를 보이지 않았다. 낮은 입열량인 1.5 kJ/mm에서 침상형 페라이트가 가장 많이 생성되었다. 용접후 열처리를 통해 경도 와 인장강도가 저하되었고, 용착금속의 충격흡수에너지가 증가되었다. The effects of heat input (1.5∼3.6 kJ/mm) and post weld heat treatment (PWHT, 600℃, 40hr.) on the TMCP HSB600 steel weldments made by GMAW process were investigated. The tensile strengths and hardness of as-welded specimens were decreased as heat input increased, but CVN (Charpy V-Notch) impact energy did not show any differences. The fine-grained acicular ferrite was mainly formed in the low heat input while polygonal and side plate ferrites were dominated in the high heat inputs. Meanwhile, tensile strength and hardness of PWHT weldments were decreased due to the coarsening and globular of microstructure as well as reduction of residual stresses.
스테인리스강 STS 316L과 탄소강 A516-70의 이종금속 GTA 용접부 특성에 대한 연구
김세철(Se Cheol Kim),신태우(Tae Woo Shin),문인준(In Joon Moon),장복수(Bok Su Jang),고진현(Jin Hyun Koh) 대한용접·접합학회 2015 대한용접·접합학회지 Vol.33 No.4
Characteristics of dissimilar metal welds between STS 316L and carbon steel ASTM A516 Gr.70 made with GTAW have been evaluated in terms of microstructure, ferrite content, chemical analysis, hardness and corrosion resistance. Three heat inputs of 9.00, 11.25, 13.00kJ/cm were employed to make joints of dissimilar metals with ER309 wire. Based on microstructural examination, the amount of vermicular type of δ-ferrite was increased with increasing heat input due to the increase of Creq /Nieq in the second layer of welds. Based on the EDX analysis of weld metals, Cr and Ni content in the 2nd layer increased while those content in the first layer of welds decreased with heat inputs. Cellular solidification mode in the 1st layer and dendritic solidification mode in the 2nd layer due to different cooling rates were prevailed, respectively. Heat affected zone which formed hard microstructure showed higher hardness than the weld metal. The salt spray test of dissimilar metals weld joints showed that the carbon steel surfaces only corroded. The weight loss rate due to corrosion increased up to 100hours but it decreased above 100 hours. There was little difference in the weight loss caused by corrosion regardless of heat inputs.
알루미늄 합금 AA6061-T6와 Silafont-36의 이종금속 레이저 용접부 특성에 관한 연구
현준혁(Jun-Hyeok Hyun),신태우(Tae-Woo Shin),장복수(Bok-Su Jang),김상호(Sang-Ho Kim),고건호(Gun-Ho Go),김태영(Tae-Young Kim),고진현(Jin-Hyun Koh) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.5
The characteristics of dissimilar weld metals between AA6061-T6 and Silafont-36 by laser welding were evaluated in terms of bead shape, microstructure, EDS analysis, hardness, and tensile strength. Laser power of 3.0, 3.5, 4.0kW and incident angle of 15, 20° were employed to make dissimilar weld metals. Bead shape of weld metal with 3.5kW, 15° was most stable. Microstructure of dissimilar weld metals consisted of columnar dendrite in area adjacent to fusion line and equiaxed dendrite in center of weld metal. Also, Mg2Si and α-AlFeMnSi were precipitated in weld metal. Microstructure in HAZ of Silafont-36 consisted of eutectic Al-Si, Mg2Si, and β-Al5FeSi. Si contents of weld metal made with 4.0kW, 15° were very high. And Mg contents of weld metals were relatively low because of vaporation of Mg. Hardness of weld metal made with 4.0kW, 15° was very high because Si contents of that were high. In tensile test, Specimens were fractured in Silafont-36 or weld metals. The fracture in base metals was due to low tensile strength of Silafont-36, and the fracture in weld metals was due to undercut or porosity.