The mechanical behaviour of type 304 austenitic stainless steel (ASS) welded joints were investigated in the post weld heat treated (PWHT) condition. 3mm thick as-received ASS was cut into cuboid pieces of 50mm x 20mm x 3mm and butt welded with the aid of shielded metal arc welding (SMAW) technique, stress relieved at 6000C which were later prepared into standard specifications of tests samples before heating them to 9100C. These heated samples were quenched into some selected vegetable (Jatropha and Neem) seed oils, and finally tempered to 3000C. The physiochemical characteristics and suitability of the vegetable oils as alternative quenchants to SAE 40 engine oil for industrial heat treatment were compared. Vickers hardness, izod impact, tensile tests and surface morphology examinations were carried out to characterize the mechanical properties of the welded treated and welded untreated (control) ASS samples. From the results obtained, it was observed that PWHT has slightly depreciated the mechanical properties of the substrates due to the presence of welding defects including microcracks and inclusions on the weldments and HAZ.