Abstract: As an addition agent to the silver-copper brazing alloy,manganese penetrates with precedence through the oxide film on 1Cr18Ni9Ti stainless steel,and acts as a flux to make steel oxide permeable to the molten filler metal.When melting does occur, the Mn/Cu rich liquid precedes the bulk of molten filler metal and flows along the oxide/steel interface.The dissolving of base metal in Mn/Cu rich liquid makes the oxide film to be easily stripped and broken down,and paves the way for spreading of molten bulk filler metal on a large scale.As a result of manganese oxidations the residual partial pressures of the oxidizing gases in vacuum,mainly oxygen and aqueous vapour,are reduced obviously.