Study On Microstructure And Properties Of SMAW Welded Joint Of 254SMo Super Austenitic Stainless Steel

254SMo super austenitic stainless steel has good mechanical properties,pitting corrosion, intergranular corrosion, crevice corrosion and stress corrosion resistance, especially in chloride beared media because of the high content of Cr,Ni,Mo and little amount of carbon.So it is widely used in severely corrosive environment, such as chemical, petroleum, natural gas, pulp and paper industry and desalination industry. But metal second phase such as sigma phase,chi phase and LAVES phase would precipitated when the steel used at high temperature for long or during welding process, which would make great damage on the mechanical properties and corrosion resistance. So this paper use OM,SEM,EDS and other techniques to mainly focused on aging treatment of solutioned254 SMo steel,and the influence of second phase precipitated in different aging temperature and time on mechanical properties and corrosion resistance was studied. Then, the influence of welding heat input on the microstructure and mechanical properties of welded joint was studied by using SMAW welding method.254SMo steel was solutioned at 1200? and aged at different temperature respectively keep 0.5 h, 1 h, 2 h. The results showed that the matrix of 254 SMo steel after solution treatment was full austenite organization, inside part of the grain were twin grain.With the increase of aging temperature, strip precipitates gradually increased along grain boundaries, precipitates inside grain reduced andtwin grains were found. At 1000? precipitates along grain boundary began to decrease, precipitates inside grain disappeared and twin grain increased. At1100?, precipitates were not found along grain boundary but little twin grains;Hardness value increased first and then decreased with the increase of aging temperature which reached maximum at 950?.Aging at 850? for 2 h,precipitates mainly were chi phase, which have little effect on the corrosion resistance of 254 SMo steel.Aging at 950?precipitation was sigma phase and increased with the increase of aging time, which has little effect on corrosion resistance when aging time was less than 1h and corrosion resistance became the worst for 2 h.So the actual production was avoided staying at this temperature for long.Microstructure and mechanical performance of 254 SMo steel welded joint were investigated in different welding heat input aby SMAW welding method.The results showed that the weld were dendrite and columnar crystal austenite, which composed of solidification subgrain boundaries, migration grain boundaries and grain boundaries. Between weld and heat affected zone were unmixed zone;When welding heat input is 1.25KJ/mm, there are a lot of dendrite and a little cellular crystal in the weld, the HAZ has a lot of fine precipitates, the hardness of the weld and HAZ is small, and the impact energy of HAZ is minimum. with the increase of heat input, seam in the dendrite decreased first and then increased, cellular crystal increased first and then decreased; The precipitated and crystal twin grain of 254 SMo steel weredecreased first and then increased. When heat input at 1.46 KJ/mm, weld and HAZ hardness reached the maximum, the precipitation is less, and the impact energy achieved the maximum value, which showed that the impact toughness was the best. Therefore,heat input at 1.46 KJ/mm was recommended in actual SMAW welding.