Study On Microstructure And Properties Of A-TIG Welded Joint Of 1Cr18Ni9Ti Austenitic Stainless Steel

1Cr18Ni9Ti austenitic stainless steel is a kind of stainless steel material with good mechanical properties,which is widely used in manufacturing industry.TIG is one of the common methods of welding stainless steel,but its penetration is shallow.When welding medium and heavy plates,it needs grooving,which has low production efficiency and poor economy.A-TIG is a new type of welding method to increase penetration by coating activator.It can penetrate medium and thick plates at one time without groove,so as to improve production efficiency.Therefore,SiO₂?TiO₂?A1₂O₃?CuO?NiO?MnO?Cr₂O₃?CaO?Fe₂O₃ and B₂O₃ are selected as the single-component activators in this paper.The composition of the existing activators is adjusted,and the adjusted activators are compared with those developed at home and abroad.The A-TIG process test of the adjusted activators is carried out to study the effect of the black slag on the structure and properties of the weld joint.The mechanism of increasing penetration in A-TIG welding was analyzed.It is found that the optimum welding parameters of 1Cr18Ni9Ti austenitic stainless steel A-TIG with self-made activator are:welding current 175A,welding voltage 14V and welding speed 80mm/min.The surface of the weld is smooth and uniform,with less black slag and good forming.Under this process,the equiaxed grain area of the weld is the largest and the structure is fine.By comparing the penetration and width of joints of A-TIG welding with conventional TIG welding,it is found that the maximum penetration of joints coated with C4 activator reaches 4.29mm under the same parameters,while that of conventional TIG welding is 1.38 mm.The penetration of joints coated with C4 activator is 3.11 times of that of TIG welding,and the penetration width also decreases.The weld without slag removal contains slag inclusion,but the quantity is small.The slag inclusion in the weld is less.The slag inclusion in the weld comes from the activator.The weld center of the slag-removed and non-slag-removed specimens is composed of equiaxed grains.The microstructure of the weld is austenite and ferrite.The grain size of the former is finer and the elements in the slag are evenly distributed except element C.Compared with the welded joints without slag removal,the tensile strength of the welded joints increased by 2.21%,while the hardness changed slightly.The application of activator promotes the shrinkage of arc anode and arc column,the shrinkage of anode spots,and the arc migrates to the side without activator.The arc morphology is stable during welding.The mechanism of the increase of penetration by activator is the joint effect of arc shrinkage?mainly plasma shrinkage?and the entry of activator elements into the weld.The microstructures of the welds without and with surfactants are austenite and ferrite.After adding surfactants,the chemical composition of the joints increases slightly and the grains are refined.Compared with TIG welding,the tensile strength of joints coated with C4 activator increased by 4.3%,and the weld hardness increased.