The microstructure near a diffusion interface was studied by means of scanning electron microscopy and electron probe microscopy, and the results indicated that the interface transition zone of Fe3Al/Q235 dissimilar materials was composed of a diffusion interface, a mixed transition region, and A/B transition regions at the sides of the interface. Microstructures of the interface and base materials were interlaced to form the microstructure of layer characteristic. With increased heating temperature and holding time, the width of the Fe3Al/Q235 interface transition zone increased and the microstructure gradually became coarse. The microhardness in the diffusion transition zone was decreased and there was a peak value at the diffusion interface. The distribution of Al, Fe, and Cr in the interface transition zone was increased or decreased monotonically with some local concentration fluctuation. There was nearly no change in the concentration of C element near the interface.

The characteristics of phase constitution near the interface of Fe3Al/Q235 diffusion bonding are researched by means of scanning electron microscope, X-ray diffraction and transmission electron microscope, etc. The test results indicated that an obvious diffusion transition zone forms near the Fe3Al/Q235 interface as a result of vacuum diffusion bonding (heating temperature 1050-1080℃, holding time 60min and pressure 9.8MPa). The maximum value of the Al content 13 in the transition zone was 16.6wt.% (about 28.5 at.%). The micro-hardness in the diffusion transition zone was HM 14 200-400. The transition zone consists of Fe3Al and a-Fe(Al) solid solution. There was no brittle phase of high hardness 15 near the diffusion interface. This is favorable to the enhancing of the toughness of Fe3Al/Q235 diffusion joint.

High strength steel; heat-affected zone; M-A constituent; fine structure.

Microstructure performance in the welding zone of T91 heat-resistan stell under the condition of TIG welding was researched by maean of metallography, X-ray diffraction and scanning electron microscope (SME). Experimental results indicated that microstructure of T91 weld metal was austenite+a little amount of 6 ferrite when using TGS-9cb filler wire. Substructure inside the austenite grain was crypto-crystal lath martensite, on which some Cr23C6 blocky carbides were distributed. The maximum hardness (HRC44) in the welding zone is near the fusion zone. There existed no obvioussoftening zone in the heat-affected zone (HAZ). For T91 Steel tube of 63mm

The brazing parameters and microstructure in the interface of WC-TiC-Co hard alloy and the brazing filler were investigated by means of inside-furnace brazing, scanning electron microscopy (SEM) and X-ray diffraction. Test results indicated that the brazing joint with which the interface combines excellently can be obtained by using Cu-Zn-Ni brazing filler alloy and controlling the heating temperature 940-960℃, the heat preservation time 10-15min and a suitable cooling. The crystal microstructure of the brazing filler alloy is α+β eutectic. The interface microstructure of the hard alloy and the brazing filler alloy distribute evenly. The interface zone consists of WC, TiC, CuZn (s-phase). There are no microcracks, inclusions, etc. nearby the interface. The interface zone is formed by mutual diffusion of the hard alloy and the brazing filler alloy under high temperature.