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Ti-Nb첨가 저합금강 용접열영향부에서의 열-응력 이력이 미세조직 및 기계적 성질에 미치는 영향에 관한 연구
문준오,이창희,Moon, Joonoh,Lee, Changhee 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.6
The influence of thermo-mechanical cycling on the microstructure and strength in the weld coarse-grained heat affected zone (CGHAZ) of Ti-Nb added low carbon HSLA steel was explored through Vickers hardness tests, nanoindentation experiments, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Undeformed and deformed CGHAZs were simulated using Gleeble simulator with different heat inputs of 30kJ/cm and 300kJ/cm. At high heat input of 300kJ/cm, the CGHAZ consisted of ferrite and pearlite and then their grain sizes were not affected by deformation. At low heat input of 30kJ/cm, the CGHAZ consisted of lath martensite and then the sizes of prior austenite grain, packet and lath width decreased with deformation. In addition, the fraction of particle increased with deformation and this is because the precipitation kinetics was accelerated by deformation. Meanwhile, the Vickers and nanoindentation hardness of deformed CGHAZ with 30kJ/cm heat input were higher than those of undeformed CGHAZ, which are due to the effect of grain refinement and precipitation strengthening.
핵융합로 구조용 저방사화강의 용접부 미세조직 및 기계적 성질
문준오(Joonoh Moon),이진종(Jinjong Lee),이창훈(Chang-Hoon Lee),이태호(Tae-Ho Lee),정승진(Seung-Jin Jung),정상훈(Sang-Hoon Jeong),홍현욱(Hyun-Uk Hong) 대한용접·접합학회 2018 대한용접·접합학회지 Vol.36 No.1
Microstructure evolution and mechanical properties in the welds of reduced-activation ferritic/martensitic steels were investigated. Three Fe-9Cr-1W-Ta-Ti alloys with different Ta and Ti contents were fabricated using a commercial vacuum-induction melting furnace. The welded samples were prepared by tungsten inert gas welding, and then the post-weld heat treatment (PWHT) was carried out. Mechanical properties in the welds before and after PWHT were evaluated by Vickers hardness tests and cross weld tensile tests, and then their results show that heat-affected zone adjacent to the base metal was the weakest region. This is because this region was the most experienced the tempering process repeatedly. In addition, tensile and yield strength decreased with an increase in Ti content and this is because the size of MX carbide increased with an increase in Ti content, resulted in a decrease of precipitation strengthening effect by MX carbide.
오스테나이트계 FeMnAlC 경량철강의 용접열영향부 미세조직 변화 및 인장특성에 관한 연구
문준오(Joonoh Moon),박성준(Seong-Jun Park) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.1
IMicrostructure evolution and tensile property in the weld heat-affected zone (HAZ) of austenitic Fe-30Mn-9Al-0.9C lightweight steels were investigated. Five alloys with different V and Nb content were prepared by vacuum induction melting and hot rolling process. The HAZ samples were simulated by a Gleeble simulator with welding condition of 300kJ/cm heat input and HAZ peak temperatures of 1150℃ and 1250℃. Microstructures of base steels and HAZ samples were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their mechanical properties were evaluated by tensile tests. The addition of V and Nb formed fine V and/or Nb-rich carbides, and these carbides increased tensile and yield strength of base steels by grain refinement and precipitation hardening. During thermal cycle for HAZ simulation, the grain growth occurred and the ordered carbide (κ-carbide) formed in the HAZs. The yield strength of HAZ samples (HAZ 1) simulated in 1150℃ peak temperature was higher as compared to the base steel due to the formation of κ-carbide, while the yield strength of the HAZ samples (HAZ 2) simulated in 1250℃ decreased as compared to HAZ 1 due to the excessive grain growth.
오스테나이트계 Fe-Mn-Al-C 경량철강의 용접열영향부 고온연성 거동 및 첨가 원소의 영향
문준오(Joonoh Moon) 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.6
Three austenitic Fe-Mn-Al-C alloys containing different Mo, Cr, and Si contents were prepared to evaluate the effects of alloying elements on the hot ductility behavior of the weld heat-affected zone (HAZ) of austenitic lightweight steels. HAZ simulations and hot tension tests were performed using a Gleeble simulator. The hot tension tests were conducted at 500 - 1220 ℃ during on-heating and on-cooling cycles. The results showed that the hot ductility significantly varied according to the behavior of κ-carbide precipitation with a decrease in temperature. The tensile ductility values of all the alloys were high at elevated temperatures above 1000 ℃ because of dynamic recrystallization. At intermediate temperatures of 700 - 900 ℃, significant ductility drops occurred in all alloys because κ-carbide precipitation, and the addition of Si resulted in more significant of ductility loss than in Cr or Mo added alloys. These different effects occurred because Mo and Cr suppressed κ-carbide precipitation, whersase Si promoted it. Ductility was recovered at low temperatures of approximately 500 ℃.