| In recent years, the stainless steel brazing process has been widely applied in industrialfields such as manufacturing plate-fin heat exchanger, but the research mainly focused onthe austenitic stainless steel products, meanwhile there is little study of15-5PH withexcellent performance. In this paper, based on univariate analysis, using SEM, EDS, XRD,depth of field microscope, hardness and tensile test, the influence of Vacuum Brazing andHeat Treatment（VBHT） and aging treatment parameters, such as brazing temperature,holding time, brazing joint clearance, aging temperature and so on, on microstructure andproperties of brazing joint and base metal has been systematically researched.The results showed that the brazing joint can be divided into four parts: reaction zoneon base metal, reaction zone in the brazing joint, diffusion zone and central zone of brazingjoint. Black compounds phase in central zone are mainly boride and small amounts ofsilicide.Brazing temperature keeping in the range of1000~1100℃, with brazing temperatureincreasing, black compounds phase in the central zone transferred from continuous mesh tothin strips, when the temperature reaching1100℃, only nickel-based solid solutionappeared in brazing joint. The brazing joint clearance firstly decreased and then increased,grain of base metal grew gradually conversely, the microhardness of central zone in brazingjoint decreased in line with the increase of temperature. The tensile strength of brazing jointfirstly increased and then decreased, when the temperature was1075℃reached maximumtensile strength of1063.37MPa.Brazing holding time in the range of10~30min, only nickel-based solid solutionexisted in brazing joint at20min, and martensite lath gradually became wider when thebrazing temperature was1075℃. With the increase of brazing holding time, themicrohardness of central zone decreased, in addition, the tensile strength of brazing jointfirstly increased and then decreased, which was related with the number of central brittlecompound, the solubility of solid solution in diffusion zone and the element and dissolutionin the reaction zone. At lower temperature of970℃with the holding time extending,compounds phase still existed in central zone, but the number of compounds had decreased.When maintaining brazing temperature of1075℃for15min then970℃for10minbefore quenching treatment, the process adopted single piece of brazing filler metalcontaining nickel-based solid solution. The brazing clearance were between58to75 microns when the process adopted three pieces of brazing filler metal, meanwhile, blackcompounds phase exited in central zone again. After aging at500℃for90min, the tensilestrength of joint can reach more than950MPa.Adopting the optimized VBHT process, aging treatment had no obvious influence onmain organization of brazing joint, and the hardness of diffusion zone was the lowest.Between200~650℃, with the increase of aging temperature, the number of black temperedmartensite in base metal increased gradually, and the hardness in base metal increased to thepeak point and then decreased. The reversed austenite formed in base metal when thetemperature reached650℃. In the process of No.4-6aging at450℃, the hardness of basemetal reached the peak of45.3HRC, at the same time, maximum tensile strength of1165.49MPa appeared at450℃.The optimized technological parameters of this paper were：holding temperature of1075℃for15min and970℃for10min before quenching, two pieces of brazing fillermetal about60microns, aging at450℃for about90min. |
PDF Full Text Request