| Presently ultra-supercritical pressure thermal power units adopt some new type resisting steels, their alloying element contents are higher than those of steels used in boilers before, consequently the welding performances of the former decrease by comparison. It was an important problem to be faced with materials science that heat-resistant materials was researched and welding process was developed of heat-resistant materials among them.Heat-resistant steel is a kind commonly used for power plant boiler. Most factories use common argon-arc welding .It was the main question for heat-resistant materials bonded by argon-arc welding which workers was required higher technical skill, materials was required chamfering, cracks was easy produced at welding heat effecting area.Transient liquid phase (TLP) bonding is a material joining process that products a high quality bond at the interface of the parts to be joined.The TLP bond should consist of a primary solid solution with a composition similarly to that of the parent metal and free from precipitates.It is suitable to weld thermos power boiler pipes and power station steel pipes.In this dissertation, the recent research of transient liquid diffusion bonding is described.The systematical theory research on TLP diffusions bonding kinetics, bonding parameters and the bonding model is conducted,and according to the engineering application background, the experimental investigation of TLP diffusion bonding of T91, TP304H/12Cr1MoV, T91/12Cr2MoWVTiB using amorphous interlayer.In the experiments, samples were heated by intermediate-frequency induction and were carried out with the protection of argon in air atmosphere.The strengthening mechanisms of transient liquid phase diffusion bonding joint in the open environment were investigated. A novel heating process, double temperature model, has been proposed for transient liquid phase bonding to produce a homogenous joint with microstructure and properties that are similar to those of base metal. In contrast to conventional TLP bonding which maintains constant temperature during bonding, this novel heating process relies on a higher temperature for a short time (a few seconds) and a lower temperature for a long time (a few minutes). Owing to a fall of temperature, a super-cooling of composition is formed at the solid/liquid interface. Therefore, a seamless joint is produced rather than a planar interface in the conventional TLP bonding. The limit of the interface on bond strength is removed, and the joint properties are improved. It has been verified in experimental that a planar interface was observed in the conventional TLP bonding joint and no interface was found in the joint by double temperature model. The element distribution near the heat-resistance steel TLP diffusion bonding interface was calculated and measured by means of electron probe microanalysis. The phase components have been determined by X-ray EDS. Microscopic features of joints area have been analyzed by transmission electron microscopy (TEM).The effect of bonding process parameters and interlayer kinds on microstructure and property of transient liquid diffusion bonding joints of T91, TP304H/12Cr1MoV, T91/12Cr2MoWVTiB etc heat-resistance steel was investigated.It was observed that TLP diffusion bonding joints was significantly influenced by the interlayer matrix kinds, concentration and diffusibility of melting point depressant (MPD) atom.During the experiments, the selection of the interlayer, the design of the bonding process, the ascertainment of process parameters, as well as the atom diffusion model were systematically explored. Microstructure evolution during transient liquid phase bonding of heat-resistance steel has been investigated. The mechanical properties test was carried out at room temperature. The combination characteristics and bend fracture micro-morphology in the T91, TP304H/12Cr1MoV and T91/12Cr2MoWVTiB transient liquid phase bonding interface were analyzed by means of scanning electronic microscopy (SEM).The effect of transient liquid phase bonding technological parameters on combination characteristics and bend strength in heat-resistant steel transient liquid phase bonding interfaces was researched. The experimental results indicate that: T91 steel TLP bonding joint with the new process made at 1270℃for 30s and 1230℃for 3 min.Conventional process parameters is 1250℃for 3 min with FeNiCrSiBI interlay and 6 MPa pressure.TP304H/12Cr1MoV steel pipes were joined with new process made at 1260℃for 20s, 1230℃for 3min under 6 MPa pressure, with FeNiCrSiBII+BNi2 interlayer. 12Cr2MoWVTiB/T91 steel pipes were joined with new process made at 1260℃for 40s, 1230℃for 4 min under 6 MPa pressure, with FeNiCrSiBI.During the process of transient-liquid diffusion bonding for dissimilar steel tube pipes, diffusion of the main alloy elements is asymmetric.Microstructure and strengthen mechanism in the transient-liquid diffusion bonding interface of heat-resistance steel are first officially reported in this paper.The research also provided experimental basis and theoretical foundation for wide application of heat-resistance steel.The conclusions obtained from this paper have established an important foundation to study deeply the inner regularity of interface reaction during transient-liquid diffusion bonding of heat-resistance steel and other dissimilar materials.
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