Study On The Structure And Properties On The Joint Of 22Cr Duplex Stainless Steel

Owing to two phases in duplex stainless steel(DSS),the inappropriate heat treatment and welding procedure in process of production may lead to the precipitation of harmful phases.During the welding process,the DSS base metal is subjected to a series of thermal cycles,which causes the occurring of complex microstructural transformations,affecting theδ/γphase balance in the steel and decreasing properties of the welding joint.A heat treatment subsequent to the welding operation restores the equilibrium between austenite and ferrite,and reduces segregation of alloying elements such as Cr and Mo which may have occurred during solidification of the weld metal. However,the role of heat treatment for the welding joint will be nothing if the temperature and cooling rate are not well defined.Therefore,the research in microstructures and properties of the welding joint postweld heat treated had some guiding significance for practical production.In this paper,22Cr DSS was produced in vacuum inductance furnace,and the manual electric arc process was used in the welding for the rolled steel.Then the solution treatment and aging treatment for welded splice was performed.The microstructural evolutions and properties of the welding joint were examined by OM, SEM,XRD,EDS,micro-hardness measurement,tensile test,impact test and pitting corrosion.Through the microstructure analysis of welding joint solution heat treated from 1050℃to 1200℃,it is indicated that a suitable heat treatment process can improve effectively the structure and properties of the welding joint.The increase of the solution temperature may leads to the increase of the ferrite content and grain coarsening. Considering theδ/γphase balance and microstructure characteristic of the welding joint after various heat treatment,a range of 1050-1100℃for solution treatment can be optimizing.The aging treatment of welding joint of 22Cr DSS was performed at 850? for various holding time.The results show that a huge of a phase precipitate atγ/αorα/αinterfaces in the joint metal including weld zone,heat affected zone and base metal. With increasing the aging time,a phase grow into the adjacent ferrite grains and its content increases.Its formation mechanism is a eutectoid reaction ofα→γ2+σ. Microstructural transformations in the weld zone is the most sensitive to the aging treatment.σphase precipitation can be availably restrained through increasing postweld solution temperature.Theσphase formed in the weld joint causes an increase of hardness and ultimate strength,but decreases severely the ductibility and impact toughness.The fracture converts from compound fracture to cleavage fracture due to theσphase-brittle phase precipitated between grain boundaries.Meanwhile,the corrosion resistance of the welding joint is directly influenced by the abundant sigma phases.