Effect of two step heating process on joint microstructure and properties during transient liquid phase bonding

摘要

45MnMoB steel was joined by transient liquid phase (TLP) bonding using three two step heating processes. The joining area was first heated up to 1250°C and kept for 5 s, and then cooled down to 1210, 1220 and 1230°C named second holding temperature respectively and kept for 120 s. The interface morphology of the bond made using two step heating process was also compared with that of conventional TLP bond at a constant temperature. The results show that two step heating process can produce a cellular interface at the initial stage, which is different from the planar interfaces associated with conventional TLP bonding. No bond interface can be found in the final joint by two step heating process and the microstructure of joint is similar to that of base metal. With the increase in second holding temperature, oxide scale particles and porosities in the bond region are decreased noticeably both in size and amount, and the bond strength is increased. The bond fails at the base metal and no failure occurs when the joint is tensioned and bent to 180° at 1250 and 1230°C respectively. Therefore, two step heating process can produce a homogenous joint, free of bond interface and identical in composition and properties to that of the base metal.