[en] In order to study the post weld heat treatment (PWHT) of the austenitic stainless steel 316LN, the effects on the microstructure and mechanical properties in TIG welded joints of 316LN austenitic stainless steel for nuclear fusion with the PWHT were investigated. The observation on the microstructure and mechanical properties change in weld were carried out by employing optical microscopy and scanning electron microscopy. The results show that the microstructure of the weld was fully austenite structure, and no precipitated phases were observed. The PWHT has a little effects on the tensile properties of the welded joint, the fracture of the tensile sample were all located at the base metal, while the elongation was enhanced notably after the PWHT. In the low temperature impact tests of the welded joints, the good resistance to this impact emerged, and the impact fracture mode of all samples were presenting ductile fracture according to the fracture analysis. (authors)