Development Of Novel Flux For Soldering304Stainless Steel

In recent years,304stainless steel (0Cr18Ni9) is applied more and more widely in the pipelinesystem. However, welded joint corrosion and leakage problems often occur as a result of theintergranular sensitization andCl-ion in304stainless steel welding and brazing at medium or hightemperatures. People around the world have developed304stainless steel soft solders in successionand intended to use the method of soldering in order to solve the above problems, failing for thereason that the flux activity could not meet the requirements. This study aims to develop the flux forsoldering304stainless steel at low temperature (below300℃) with soft solders for304stainless steelwith mechanism and reaction rule of the active ingredients researched.Three kinds of active substances, organic stannous salt, organic acid and amine, were selected asactivators. Contents of stannous methanesulfonate, hexanedioic acid and triethanolamine were22.0%,12.0%and7.0%respectively. Solvent system with content of24.0%containing monohydricalcohol, polyhydric alcohol and ether was optimized by mixture uniform design method. Ratios ofisopropanol, glycerine, ethylene glycol monobutyl ether were0.260,0.355and0.385.Film-forming agent was polyethylene glycol and its content was35.0%. Orthogonal experimentmethod was utilized to optimize the flux formula before adding emulsifier6500with content of0.5%into flux, which we called solid like processing to make flux be applied more conveniently.Mechanisms of response between oxide film on304stainless steel surfaces and flux and its removalwere discussed in detail in this paper. Mechanical properties of the soldered joints and the physicaland chemical properties of flux were tested and evaluated.Model of paste like flux for soldering304stainless steel developed in this study is FS213C.Properties of the flux were tested as follows. The spreading area of Sn-Cu-Ni solder on304stainlesssteel matching the flux was157.49mm2, increased by402.2%,387.7%compared with fluxes ofH3PO4-C2H5OH and ZnCl2-NH4Cl respectively. The mechanical properties of the soldered joints weresuperior to the existing literature data, which the tensile strength and shear strength of the jointsachieved to22.72MPa and33.93MPa respectively. The flux represented obvious purification andprotection effect while the fracture surfaces of the solders joints were clean without voidings orinclusions. Water pressure test value of the sodered seam was up to20MPa, far exceeding the designpressure value and actual working pressure value of stainless steel pipe. Performances of flux inappearance, corrosion, sealing and processing accorded with the demands of national standard. Development of the novel flux, which is mainly used for304stainless steel pipeline connectionin household or commercial water supply system, provides crucial technical support for the wideapplication of304stainless steel pipes in engineering.