Researches On Microstructures And Properties Of 2205 DSS Welding Joints

Welding thermal cycle has a great influence on the microstructures of DSS welding joints.The austenite and ferrite two-phase equilibrium can be easily damaged and large numbers of secondary austenite may precipitate in DSS welding joints.The precipitation of different types of secondary austenite can affect the mechanical properties and corrosion resistance of welding joints seriously,which restricts the application of DSS.Therefore,it's of great theoretical importance and practical value to study the phase transformation and its influence on the properties of 2205 DSS welding joints acquired by different welding methods.In this paper,submerged arc welding and deep penetration laser welding are applied to 6 mm and 2 mm thick 2205 DSS plates,respectively.The main purpose of this paper is to study the influence of welding parameters on the microstructures and properties of 2205 DSS submerged arc welding joints and analyze the cause of the formation of porosity in deep penetration laser welding joints.The main results are as follows:1 The width of heat affected zone gets large,the proportion of austenite increases,and the microstructure grows up when the heat input of submerged arc welding increases from 12.36 to 18.13 kJ/cm.2.For submerged arc welding,there are large numbers of fine widmanstatten austenite lath in welding metal and quadrangular austenites have a tendency of growing up in a single direction.With the increasing of heat input,the number of widmanstatten austenite lath decreases but the width of the lath increases remarkably.And the quadrangular austenites coarsen in all directions gradually growing into equiaxed austenite.The welding joints show the best mechanical properties when the volume fraction of austenite is mostly close to 50%.3.There is significant segregation of Cr,Mo and Ni in submerged arc weld metal.Secondary austenites are poor of Cr.Pitting corrosion occurs preferentially at ferrite/austenite phase interface.Secondary austenite is also a favorable position where pitting corrosion takes place.The corrosion resistance of the welding joints is the best when the phase ratio of austenite to ferrite is mostly close to 1:1.4.For deep penetration laser welding,the heat input decreases gradually with the increasing of welding speed,which leads to the reduction of the width of heat affected zone.The microstructures become finer and the austenite proportion decreases when the heat input is low.Both the austenites precipitating at ferrite/austenite phase interface and within ferrite grains reduce when heat input decreases.5.For deep penetration laser welding,the tendency of the formation of porosity decreases with the increasing of welding speed when using the same welding power.The tendency of the formation of porosity shows no relationship with welding power when the welding speed remains unchanged.Accordingly,using lower welding power and greater welding speed can inhibit the formation of porosity effectively.6.When welding heat input is large,the deep penetration laser welding 2205 DSS joints show features of brittle fracture due to the small amount of austenite content and the existence of porosity.However,when the welding heat input is small,even though the amount of austenite is less,the microstructures of welding joints are much finer.The finer microstructures can improve the strength of laser welding joints without reducing its ductility.