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자동차 샤시부품용 고강도강재의 용접부 내구성능 향상기술 개발동향과 전망
배규열(Gyuyeol Bae),정홍철(Hongchul Jeong) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.6
In general, welds of advanced high strength steel (AHSS) do not exhibit appreciable increase in fatigue strength unlike the base metal case. Thus, weld fatigue strength is insensitive to the steel type and grade of current AHSS. The use of AHSS for light-weighting must be accomplished by improving the fatigue performance of the weld joint. This article review original work and important new developments in the field of weld fatigue behavior of AHSS in terms of mechanical and metallurgical factors. This review surveys the experimental literature, summarizes the current technological concepts, and identifies the outstanding issues with improving the weld fatigue performance. Suggestions for the directions of future research on AHSS weld fatigue are offered.
페라이트계 스테인리스강 재현 용접 열 영향부의 석출거동 및 열피로 특성에 미치는 구속응력의 영향
한규태(Kyutae Han),강용준(Yongjoon Kang),이상철(Sangchul Lee),홍승갑(Seunggab Hong),정홍철(Hongchul Jeong),이창희(Changhee Lee) 대한용접·접합학회 2015 대한용접·접합학회지 Vol.33 No.6
Thermal fatigue life of the automobile exhaust manifold is directly affected by the restraint force according to the structure of exhaust system and bead shape of the welded joints. In the present study, the microstructural changes and precipitation behavior during thermal fatigue cycle of the 18wt% Cr ferritic stainless steel weld heat affected zone (HAZ) considering restraint stress were investigated. The simulation of weld HAZ and thermal fatigue test were carried out using a metal thermal cycle simulator under complete constraint force in the static jig. The change of the restraint stress on the weld HAZ was simulated by changing the shape of notch in the specimen considering the stress concentration factor. Thermal fatigue properties of the weld HAZ were deteriorated during cyclic heating and cooling in the temperature range of 200℃ to 900℃ due to the decrease of Nb content in solid solution and coarsening of MX type precipitates, laves phase, M6C with coarsening of grain and softening of the matrix. As the restraint stress on the specimen increased, the thermal fatigue life was decreased by dynamic precipitation and rapid coarsening of the precipitates.
류강묵(Kang-Mook Ryu),김대우(Dae-Woo Kim),이진우(Jin-Woo Lee),방환철(Hwan-Cheol Bang),박철규(Chul-Gyu Park),정홍철(Hongchul Jeong) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.6
Tensile strength, 485~550MPa grade of Quenching & Tempering or Normalizing heat-treated SA-537/A537 steels has been widely used as a steel for storage tanks. Since these steels have high crack sensitivity due to the relative high carbon equivalent, low heat input welding processes such as SMAW, GMAW or FCAW are commonly used for fabrication of storage tank. In this study, we have developed thermo-mechanical control process-type SA-841/A841 steels guaranteeing 1-pass high heat input EGW to increase welding productivity as well as superior quality of welded joints to normal low heat input welding processes. Besides, alloy design in base metal and TMCP process have been also optimized to obtain proper impact toughens in HAZ. As a result, excellent impact toughness at low temperature has been obtained in coarse grain HAZ (CGHAZ) under 340kJ/cm of heat input condition in 40mm thickness plates. Besides, more than 100J of absorbed energy at -10℃ have been achieved by optimizing welding consumables for A841 with high input welding.