The Study Of Transient Liquid Phase Diffusion Bonding On X70 Pipeline Steel

Pipeline transport the blood of industry society:petroleum and natural gas. The pipeline construction rely on the level of welding. The traditional melt welding technology restricting the pipeline construction with heat, large residual stress, low efficiency. Transient liquid phase diffusion bonding (TLP) has been the attention of people of low residual stress and welding temperature, high automation, good forming effect. The application of the TLP technology in the construction of pipeline, can greatly improve the welding efficiency, reduce the cost of welding, which has a far-reaching significance in the welding of pipeline.This paper according to the characteristics of X70 pipeline steel, discussed the welding process of TLP, used the double temperature and pressure welding process by orthogonal test, bond with BNi2, FeCrNiB, Fe-Ni-B interlayer, temperature in 1160～1240℃, holding 120～480 s, under 1～5MPa, the major-minor order of test factors was welding temperature-interlayer-pressure-time, determined the optimal process parameters, at 1200℃ for 240 s under 3 MPa with FeCrNiB interlayer. Through the contrast test, determined the range of parameter at the best welding, at 1200～1240℃ for 240～480 s under 3-5 MPa with FeCrNiB and Fe-Ni-B interlayer. Through the microstructure observation we can find, the weld become narrow and the element diffusion capacity increases with the higer temperature, pressure and hold time. The weld mechanical properties were enhanced mainly because the formation of dendritic grain between the parent material and weld. Element analysis showed that B elements spread fast and uniform distribution of weld area; Si, Ni, Cr have an amount of residual because of low diffusion speed. The weld analysis by XRD, the residual Ni, Cr and Fe formed the three-phase grain. Analyze the temperature field and stress field of the heat preservation stage by ANSYS, the results show that the highly non-uniform welding temperature file caused large residual stress.The speed of X70 pipeline steel welding just need 4-8 min and no connected with pipe size. The weld width only about 10 to 20 microns lead to lower residual stress and deformation. The conclusion of X70 pipeline steel welding by TLP technology can be provide theoretical basis for actual production.