초록 ▼

A seamless double-walled tube having high corrosion resistance and relative flexibility prepared by a process for brazing non-ferritic steel surfaces such as nickel chromium or stainless steel to which a suitable brazing alloy such as copper has been mechanically attache which includes the steps of

A seamless double-walled tube having high corrosion resistance and relative flexibility prepared by a process for brazing non-ferritic steel surfaces such as nickel chromium or stainless steel to which a suitable brazing alloy such as copper has been mechanically attache which includes the steps of instantaneously elevating the surface of the stainless steel to a brazing temperature while maintaining the material in a humidified gaseous atmosphere consisting essentially of a non-reactive carrier gas and a reactive gas present in sufficient concentrations to achieve fluxing; maintaining the surface temperature of the steel for an interval sufficient to permit fusion between the selected metal and the non-ferritic steel surface; after metal fusion has been achieved, allowing the resulting fused metal material to cool to a first lowered temperature in a controlled non-oxidative atmosphere at a rate which retards the formation of fine-grained steel crystals in the metal; and after reaching a metallurgical transformation point, rapidly cooling the fused metal in a controlled atmosphere to a temperature below which the brazing metal is not reactive with oxygen.

대표청구항 ▼

A brazed double-wall non-ferritic stainless steel tube prepared by a process comprising the steps of: milling a sheet of non-ferritic steel having a selected brazeable metal component overlying at least one surface of said non-ferritic metal sheet and attached thereto, said selected metal capable of

A brazed double-wall non-ferritic stainless steel tube prepared by a process comprising the steps of: milling a sheet of non-ferritic steel having a selected brazeable metal component overlying at least one surface of said non-ferritic metal sheet and attached thereto, said selected metal capable of forming a metallurgical bond with said non-ferritic metal surface under controlled conditions, said milling step forming an unbrazed, unsealed continuous double-wall tube; removing lubricating material employed during said milling step from surfaces of said continuous tube; rapidly raising the temperature of said continuous tube to an elevated temperature sufficient to trigger fusion between said non-ferritic steel and said selected metal component layered thereon, said temperature elevation occurring in a humidified gaseous atmosphere consisting essentially of at least one inert carrier gas and sufficient hydrogen to achieve fluxing; after fusion has occurred, allowing said fused continuous metal tube to cool to a first lowered temperature lower than said fusion temperature and higher than the temperature at which initial metallurgical transformation of the non-ferritic stainless steel from an austenitic phase to and intermediate phase occurs, said cooling step occurring in a humidified gaseous atmosphere said cooling occurring at a rate which maximizes the temperature at which the non-ferritic steel is transformed from said austenitic phase to said intermediate phase; after reaching said first lowered temperature, rapidly cooling said fused continuous metal tube to a second lowered temperature, said second lowered temperature being lower than the temperature at which metallurgical transformation of said fused metal from said intermediate phase to a pearlite phase occurs; and, then slowly cooling said fused continuous metal tube in a non-oxidative atmosphere to a third lowered temperature below which the selected metal is not reactive with oxygen.