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차체용 1.2GPa급 초고장력 TRIP강의 Weldbond 접합부의 기계적 거동
이종대,이소정,방정환,김동철,강문진,김목순,김준기,Lee, Jong-Dae,Lee, So-Jeong,Bang, Jung-Hwan,Kim, Dong-Cheol,Kang, Mun-Jin,Kim, Mok-Soon,Kim, Jun-Ki 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.5
The effect of weldbond hybrid joining process on the mechanical behavior of single lap and L-tensile joints was investigated for the newly developed 1.2GPa grade ultra high strength TRIP(transformation induced plasticity) steel. In the case of single lap shear behavior, the weldbond joint of 1.2GPa TRIP steel showed lower maximum tensile load and elongation than that of the adhesive bonding only. It was considered to be due to the reduction of real adhesion area, which was caused by the degradation of adhesive near the spot weld, and the brittle fracture behavior of the spot weld joint. In the case of L-tensile behavior, however, the maximum tensile load of the weldbond joint of 1.2GPa TRIP steel was dramatically increased and the fracture mode was change to the base metal fracture which is desirable for the spot weld joint. These synergic effect of the weldbond hybrid joining process in 1.2GPa TRIP steel was considered to be due to the stress dissipation around the spot weld joint by the presence of adhesive which resulted in the change of crack propagation path.
이종대,이소정,방정환,윤길상,김목순,김준기,Lee, Jong-Dae,Lee, So-Jeong,Bang, Jung-Hwan,Yoon, Gil-Sang,Kim, Mok-Soon,Kim, Jun-Ki 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.6
For the resistance spot welds of CR1180 and GA1180 TRIP steels, the weld quality evaluation method using the digitalized X-ray transmission imaging apparatus was investigated in comparison with the crosssectional examination method. In the case of the resistance spot welding of CR1180, three circular regions, such as WZ(white zone), GZ(grey zone) and DZ(dark zone), appeared on X-ray image and they corresponded to the diameters of indentation mark, nugget and corona bond, respectively. The variation of X-ray transmission thickness due to the thickness variation of the weld seemed to be mainly responsible for the formation of those contrasts. The X-ray image contrast formed from the variation of transmission thickness at the outer border line of DZ could also enable the inspections of the notch shape, nonuniformity of the welding pressure and spatter from its sharpness, concentricity and the normal straight line, respectively. The X-ray image of the resistance spot weld of galvannealed GA1180 TRIP steel was very similar to that of CR1180 TRIP steel except the crown shaped outer border line of DZ which was considered to be due to the melting behavior of zinc having the boiling temperature even lower than the melting temperature of steel.