Abstract
M.Ing. (Mechanical Engineering)
This research study called for investigation on a filler metal, which would yield improved benefits, when welding 3CR12 stainless steel. The compared filler metals included AISI 308L, 309L and 316L. The study was performed by welding 2mm thick 3CR12 test plates – using the TIG welding process by testing of welded material’s behaviour by tensile testing, microstructural analysis, and hardness testing. The experimental set-up and procedure were based on the findings from previous studies and recommendations.
Defect-free welds were achieved on all the welded samples. The parent metal showed ferrite and pearlite microstructure; while the Heat Affected Zone (HAZ) contained coarse grains, as compared with Base Material (BM) and the fusion zone, it had more ferrite and less pearlite microstructure. The coarse grains were due to the higher heat input in this region. The fusion zone consisted of austenite, ferrite and martensite laths; this was probably due to the dissimilar weld joints of the austenitic filler metal and the ferritic base metal. The fracture of the tensile specimens was consistently located in the parent-metal zone, suggesting that the strength of the welded joint is greater than that of the parent metal.
The ultimate tensile strength of all the samples is above the minimum (450MPa) ultimate tensile strength of the 3CR12. Owing to their fine grains at the weld joint, the welded joints displayed a higher tensile strength than that of the parent metal.
The microstructural analysis indicated that the 309L sample has larger grains on the HAZ than on the PM and fusion zone; this implies that the 309L is more susceptible to heat in the HAZ when compared with the 308L and 316L samples. The maximum hardness was found to be in the fusion zone in all the welded samples; as a result of the fine solidification structure. The hardness values for 309L samples are lower than those of 308L and 316L samples. The root of the weld was weaker than the weld cap for all the filler metals tested. Filler metal 308L was found to be the optimum welding material for 3CR12; and it can be recommended for producing welds with high quality and strong integrity.