| Interface diffusion behaviors of brass inner-clad carbon steel bimetallic tube have been investigated by means of optical microscope, scanning electron microscope (SEM) and alternating bending test. The influences of process parameters, such as surface preparation method, pressure, diffusion temperature and time, on interface bonding strength of copper-steel bimetal have been analyzed.Diffusion bonding results indicate that the interface situation is different merely by a cold drawing and then a diffusing process. The inter diffusion phenomenon near the interface of brass/steel was observed and the iron diffusion distance is much greater than that of copper and zinc was confirmed. The result in high temperature is better than in low temperature and the interdiffusion phenomenon near the interface of brass-steel was observed. The result of avulsion of brass /steel bimetallic tube approved reality that the interface of bimetallic tube is bonded.The good interface bonding was also realized through cold drawings of brass-steel duplex tube and diffusing processes. The interface bonding strength increases dramatically with increasing diffusion temperature in the drawing-diffusing process. There is an optimum diffusion time at the given temperature to bonding strength, which is enhanced rapidly in the beginning and finally will wave around certain value with the extending of diffusion time.If brass -steel duplex tube sealed by welding with solid in the cavity of it, high pressure caused by the solid gasification reacted greatly on the tube in the diffusing process. The results of inner-pressure diffusion of brass -steel duplex tube show that the solid selected for causing high pressure hasno harm to corrosion resistance of the inner brass layer but benefit to interface bonding by high pressure diffusion. Otherwise, metallurgical bonding has been made to brass -steel duplex tube without pressure with only a simple drawing-diffusing process by inner-pressure diffusion technique.
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