Study On Vacuum Brazing Of Austenitic Stainless Steel And Copper

In order to sove a welding problem of a military production about304austeniticstainless steel and pure copper structure, the process of vacuum brazing for them wasinvestigated, with the homemade CuMnNi solder as well as commercially availableBAg72Cu solder. By metallographic microscope, shearing test, SEM, and EDS the effectsof different processing parameters on microstructures and properties of the joints wereanalyzed.With CuMnNi filler metal, the vacuum brazing process of304austenitic stainless steeland pure copper were carried out, we can get the following conclusions:（1）The degree of vacuum has a great effect on the wetting properties of the solder.Under middle vacuum condition(5.0×10^-1～1.0×100Pa), CuMnNi solder can not wetting304austenitic stainless steel; However, under high vacuum condition(3.0×10^-2～8.0×10^-3Pa), the brazing material have a good wettability on304austenitic stainless steel.With the brazing temperature growing, wetting angle decreased, the solder wettability on304austenitic stainless steel is getting better and better;（2）Brazing temperature had a significant effect on the shear strength of the brazedjoints and solder joints microstructure. Brazing temperature is too low, the joint strength islower. With the brazing temperature increases, the strength of the joint is improved.Continue to improve the brazing temperature after935℃, small changes in joint strength;（3）Holding time of brazing joint strength. Holding time is too short, solder and basemetal metallurgical interaction is weak, the lower strength of brazed joints; with holdingtime exceeds10minutes, holding time of the subject test, structure of the soldered seam arecompact, the strength of the joints are high and did not change large;（4）Under high vacuum condition at a brazing temperature of950℃, the brazeholding time15min, brazed joints tissue density, shear strength up to128MPa.With BAg72Cu solder, the vacuum brazing proceess of304austenitic stainless steeland pure copper were carried out, we can get the following results:（1）The shear strength of the brazed joint under high vacuum condition are allsignificantly higher than that of under middle vacuum condition’s brazed joints. This is dueto the vacuum conditions, brazing cracks;（2）The brazing temperature the brazed joints Organization and shear strength had asignificant effect. As brazing temperature rise, brazed joint strength first increased and thendecreased in the brazing temperature of865℃, the highest shear strength of the joint brazed joints we get;（3）The holding time of brazing has some effects on the brazed joints structure andshear strength. With too short holding time, the diffusion of elements between the liquidsolder and base metal are inadequate, metallurgy role is weak, the joint strength is lower;holding time over10minutes, full element diffusion between the liquid solder and basemetal brazing, structure of eutectic in the proportion has small changes. Brazed jointperformance stable in a relatively long period of time has great significance for theindustrialized production.（4）Uunder high vacuum condition, the brazing temperature is865℃, with brazeholding time10min, the dense structure of brazed joint will be got, the highest shearstrength of the joint is up to160MPa.