The microstructure and grain-boundary misorientation of X80 high-strength pipeline steel are analyzed using the scanning electron microscope, the electron backscatter diffraction, and the transmission electron microscope, and the effect of grain-boundary orientation on slip dislocation is investigated by constructing a grain-boundary dislocation model. The results show that the anisotropy of the mechanical properties of X80 pipeline steel is related not only to grain size and microstructure type but also to grain-boundary orientation, which the obstruction effect of the high-angle grain boundary on slip dislocation is significantly greater than that of the low-angle grain boundary. The larger the orientation difference is, the more disorderly the arrangement of atoms on both sides of grain boundary is, and the more difficult it is for dislocations to slip across grain boundary, so the strengthening effect is more remarkable. Also, when the grain-boundary misorientation is greater than 15 , the strengthening effect tends to stabilize due to the influence of the interfacial superposition.
The microstructure of X80 pipeline steel in different directions were observed by SEM technique and its effective grain size and misorientation were statistically analyzed by EBSD system. Based on these results, the mechanical properties at 0°, 45° and 90° to the rolling direction of X80 pipeline steel were studied. The results show that, owing to finer grain size and less low-angle grain boundaries, strengths and impact toughness of X80 pipeline steel at 90° direction are optimal. While the pipeline steel possesses finer grain size, more high-angle grain boundaries and less low-angle grain boundaries, the crack propagation is effectively suppressed, then its impact toughness is improved.
In this paper, a fast prediction method for thermal fatigue life of PoP laminated BGA Product was proposed. Firstly, the stress and strain of the solder joints of each layer of the laminated device in thermal fatigue test was determined by finite element simulation method. According to the research idea of relative stress and strain, the solder joints were divided into sensitive solder joints and reliable solder joints. Secondly, sensitive solder joint were connected with PCB traces through the internal pads, bonding wires, TSVs and reliable solder joints to form a daisy chain. Through real-time dynamic monitoring of the resistance change of the daisy chain in thermal fatigue test to judge whether the solder joints fail, and record the occurrence time of the first failure solder joint. Finally, the thermal fatigue life of the product was estimated by the Norris-Landzberg formula.
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