http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Microstructural Evolution of HSLA ISO 3183 X80M (API 5L X80) Friction Stir Welded Joints
Tahiana F. C. Hermenegildo,Tiago F. A. Santos,Edwar A. Torres,Conrado R. M. Afonso,Antonio J. Ramirez 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.5
Evaluation was made of friction stir welded joints, identifying conditions that resulted in satisfactory welded joints free fromdefects and with microstructural characteristics that provided good mechanical properties. Microstructural characterizationand cooling curve analysis of the joints with lower and higher heat inputs evidenced deformation below and above the nonrecrystallizationtemperature (T nr ) and dynamic recrystallization during microstructural evolution. Microscopy analysesshowed acicular ferrite, bainitic ferrite, and coalesced bainite microstructures in the stir zone of the cold weld (lower heatinput), while the stir zone of the hot weld (higher heat input) contained bainitic ferrite, acicular ferrite, coalesced bainite,martensite, and dispersed carbides. Granular bainite and dispersed carbides were observed in all the heat aff ected zones. Analysis of the microstructural transformations, together with the thermal history of the joints, showed that the variable thathad the greatest infl uence on the morphology of the bainite (granular bainite/bainitic ferrite) was the deformation temperature.
극저탄소 냉연강판에서 합금원소 및 어닐링조건이 미세조직에 미치는 영향
정우창 ( Jeong U Chang ) 한국열처리공학회 2004 熱處理工學會誌 Vol.17 No.2
N/A Effect of annealing parameters on the formation of ferrites transformed at low temperatures were studied in cold-rolled ultra low carbon steels with niobium and/or chromium. Niobium and chromium were found to be effective in the formation of the low temperature transformation ferrites. The low temperature transformation ferrites more easily formed when both higher annealing temperature and longer annealing time, allowing substitutional alloying elements to distribute between phases, are in combination with faster cooling rate. It was found from EBSD study that the additions of niobium or chromium resulted in the increase in the numbers of high angle grain boundaries and the decrease in those of the low angle grain boundaries in the microstructures. Both granular bainitic ferrite and bainitic ferrite were characterized by the not clearly etched grain boundaries in light microscopy because of the low angle grain boundaries.
Yong Hwan Cho,Jaeeun Lee,Wung Yong Choo,Juseok Kang,Heung Nam Han 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.6
The effect of separation on the fracture surface of ferrite–bainite dual-phase pipeline steels during a drop weight tear test(DWTT) was investigated via microstructural analysis and fracture surface examination. Two specimens (ST1 and ST2) weredesigned to have a dual-phase microstructure, with different ferrite and bainite fractions, by controlling the reduction ratioand holding time in the ferrite–austenite two-phase region during the thermomechanical process. Notably, ST2, which had alonger holding time for the retained austenite to absorb carbon, exhibited a harder bainite but softer ferrite phase comparedto ST1. The greater hardness difference between those phases in ST2 induced the strain incompatibility frequently evidentat the phase boundaries, resulting in lower ductility during the tensile test. Owing to the strain incompatibility, ST2 alsogenerated more separation over a wider temperature range during DWTT. At low temperatures, where the brittle fracture wasprominent, it was observed that ST2 generated separations on its fracture surface, whereas ST1 did not. These separationsformed a local shear lip around themselves, thereby obstructing cleavage fracture propagation from the notch. Hence, it wasconfirmed that ST2 had a higher DWTT shear area than ST1 over a temperature range near the ductile–brittle transitiontemperature (DBTT). As a result, the DBTT of ferrite–bainite dual phase steel could be improved by increasing the amountof separation during DWTT.
SAVYASACHI NELLIKODE,SIVA PRASAD MURUGAN,백영곤,정승진,김인찬,이창훈,문준오,박영도 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11
The objective of the present study is to investigate and compare the impact of bainitic microstructure and M-A constituents formed at different inter-critical temperatures on the toughness of 355 MPa and 420 MPa HSLA steel for offshore structural applications. High strength low alloy steels of grade 355 MPa and 420 MPa steels for offshore applications are simulated using Gleeble thermo-mechanical simulator at different inter-critical temperatures between Ac1 and Ac3. In this study, the effects of microstructural features on ICCGHAZ on toughness and crack initiation and propagation were investigated. ICCGHAZ simulated at lower temperature region of Ac1 to Ac3 microstructure composed of bainitic ferrite (BF) and granular bainite (GB). MA constituents are distributed in the form of necklace at prior austenitic grain boundaries. ICCGHAZ simulated at higher temperature region of Ac1 to Ac3 microstructure composed of GB and BF with some acicular ferrite. MA constituents are distributed along the grain boundaries and lath boundaries. Secondary cracks are initiated at MA constituents that existed along prior austenitic grain boundaries and propagated linearly into GB/BF area in ICCGHAZ. BF & GB show straight cleavage cracks indicating brittleness. A significant percentage of cracks initiated through the necklace MA at the grain boundaries easily propagated through bainitic ferritic lath.
열연 590FB강의 일축인장 시 미소역학적 변형거동 및 파괴거동에 미치는 베이나이트의 강도계수의 영향
김은영 ( Eun-young Kim ),김성일 ( Sung Il Kim ),최시훈 ( Shi-hoon Choi ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.11
The effect of the strength coefficient (K<sub>B</sub>) of bainite on micromechanical deformation and failure behaviors of a hot-rolled 590MPa steel (590FB) during uniaxial tension was simulated using the elasto-plastic finite element method (FEM). The spatial distribution of the constituent phases was obtained using a phase identification technique based on optical microstructure. Empirical equations which depend on chemical composition were used to determine the stress-strain relationship of the constituent phases of the 590FB steel. The stress-strain partitioning and failure behavior were analyzed by increasing the K<sub>B</sub> of bainite. The elasto-plastic FEM results revealed that effective strain in the ferrite-bainite boundaries, and maximum principal stress in fibrous bainite, were enhanced as the increased. The elasto-plastic FEM results also demonstrated that the K<sub>B</sub> significantly affects the micromechanical deformation and failure behaviors of the hot-rolled 590FB steel during uniaxial tension. (Received February 2, 2016; Accepted May 19, 2016)
Ferrite-Bainite dual phase 강의 피로균열진전 특성 평가
김덕근(Deok-Geun Kim),조동필(Dong-Pil Cho),오동진(Dong-Jin Oh),김명현(Myung-Hyun Kim) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.1
With the recent increase in size of ships and offshore structures, there are more demand for thicker plates. As the thickness increases, it is known that fatigue life of the structures decrease. To improve the fatigue life, post weld treatments techniques, such as toe grinding, TIG dressing and hammer peening, are typically employed. However, these techniques require additional construction time and production cost. Therefore, it is of crucial interest steels with longer fatigue crack growth life compared to conventional steels. This study investigates fatigue crack growth rate (FCGR) behaviours of conventional EH36 steel and Ferrite- Bainite dual phase EH36 steel (F-B steel). F-B steel is known to have improved fatigue performance associated with the existence of two different phases. Ferrite-Bainite dual phase microstructures are obtained by special thermo mechanical control process (TMCP). FCGR behaviours are investigated by a series of constant stress-controlled FCGR tests. Considering all test conditions (ambient, low temperature, high stress ratio), it is shown that FCGR of F-B steel is slower than that of conventional EH36 steel. From the tensile tests and impact tests, F-B steel exhibits higher values of strength and impact energy leading to slower FCGR.
Microstructural control of hot rolled strips and their tensile strengths after hot stamping process
하원,이창훈,박철재 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.1
The influence of microstructure of hot rolled strips on tensile property after hot stamping was investigated using boron-bearing steel of1470 MPa grade for hot stamping. Hot rolled strips with two kinds of microstructures were produced by mill trial based on a timetemperaturetransformation (TTT) diagram that resulted from a dilatometric experiment. The first had a ferrite-pearlite banded microstructureand the other had a bainitic microstructure. The strip with bainite had a higher tensile strength after hot stamping compared withthe tensile strength of the strip with ferrite-pearlite banded microstructure after hot stamping. The former almost fully transformed tomartensite after hot stamping, while the latter transformed to partial martensite and ferrite that originated from the inhomogeneous hardenabilityof the ferrite-pearlite banded structure due to segregation of alloying elements such as carbon and manganese.
Jang, H.,Kim, J.H.,Jang, C.,Lee, J.G.,Kim, T.S. Elsevier Sequoia 2013 Materials science & engineering. properties, micro Vol.580 No.-
The low cycle fatigue (LCF) resistances of two heats of SA508 Gr.1a low alloy steel, heat FP with a ferrite-pearlite microstructure and heat BA with a bainite microstructure, were compared in 310<SUP>o</SUP>C air and deoxygenated water. The LCF life of heat FP was shorter than that of heat BA in 310<SUP>o</SUP>C deoxygenated water while the LCF life of both heats was comparable in 310<SUP>o</SUP>C air. Such behaviors were explained considering the dynamic strain aging (DSA) behaviors in both environments and their microstructures. Based on cyclic stress and tensile behaviors, it was found that heat BA showed higher degree of DSA than heat FP in 310<SUP>o</SUP>C air, but both showed similar degree of DSA in 310<SUP>o</SUP>C deoxygenated water because the degree of DSA was reduced by absorbed hydrogen. In case of microstructure, heat FP had a lower fatigue cracking resistance due to the stress concentration effect in ferrite-pearlite interface. As a result, in 310<SUP>o</SUP>C air, where the effect of DSA was large enough to override the microstructure effect, LCF life of heat BA was similar to that of heat FP. On the other hand, LCF life of heat BA was longer than that of heat FP in 310<SUP>o</SUP>C deoxygenated water, where the effect of DSA was not so significant.