Speaker
Description
Stainless steel is a very popular material for cryogenic temperature applications since it does not exhibit ductile to brittle transition at low temperatures. In most of the cryogenic temperature equipments, welded joints of stainless steel are extensively used. The strength of the welded area will be less than the original material since the gap is filled by melting the welding rods. This is due to lower packing density of atoms of the filler metal as compared with the main material. In this experimental study, the welded joints made out of SS304 are subjected to cryogenic treatment for thirty six hours at 80K in a specially designed and developed cryogenic treatment system which uses LN2 as the cooling medium. The cryotreatment unit is made of a double walled stainless steel with polyurethane foam (PUF) insulation filling up the annular space. Test specimens housed within this unit is gradually cooled to cryogenic temperature by the closed loop circulation of cold nitrogen gas by forced convection. Test specimens of SS304 were prepared following the guidelines of ASTM standard E8 and their mechanical strength properties (yield strength, ultimate tensile strength and percentage elongation) were determined with the help of Universal Testing Machine (UTM) following the test procedure specified by ASTM A370-2022. Same tests were conducted on welded test specimens to determine their strength properties. Later, many specimens were prepared with the welded joints at the critical area and divided into two batches. One batch was subjected to cryotreatment alone and the other batch was tempered at 440 Celsius for one hour after cryotreatment. Strength tests were conducted on specimens of both these batches. Experiments have rendered encouraging results which are analysed and discussed.
