Research On Welded Joints Of S31083 Duplex Stainless Steel

In the field of ocean engineering,materials are required to have multiple properties such as high strength,corrosion resistance,and fatigue resistance.As a material with excellent comprehensive properties,duplex stainless steel has been widely used in marine oil,marine energy and other fields.However,under harsh environments such as seawater corrosion and tides,the welded joints are prone to damage such as stress corrosion and intergranular corrosion,leading to structural failure.The performance of duplex stainless steel welded joints directly affects the reliability and safety of marine engineering structures.Therefore,it is of great significance to study the performance of duplex stainless steel welded joints.Welding is one of the important processes in the processing of duplex stainless steel and is also the main source of microstructural changes in duplex stainless steel.Different welding process parameters can lead to changes in the microstructure and performance of the welding joint,which directly affects the reliability and durability of the welding joint.Therefore,this thesis investigates the performance of duplex stainless steel welding joints under different welding heat inputs and cooling methods,analyzes the effects of different process conditions on the alloy element content,microstructure characteristics,and austenite/ferrite phase ratio of the welding joint,and explores the influence on the mechanical and corrosion resistance properties of the welding joint by combining metallographic analysis.This helps to reveal the rules of microstructure and performance changes in duplex stainless steel welding joints and provides a scientific basis for the design,manufacturing,and maintenance of marine engineering structuresThe alloy element analysis,macroscopic observation,metallographic observation,and determination and analysis of the proportion of austenite and ferrite phases were performed on the welding joints obtained under different welding process conditions.The research results showed that there were no welding defects such as porosity,lack of fusion,burn-through,and undercutting in the welding joint,which met the engineering acceptance standards.The determination of alloy element content showed that with the increase of welding heat input,the molybdenum element content in the weld zone was increased,and when the cooling method was water cooling,the nickel and nitrogen element content in the weld zone was increased,and the nickel element content in the base metal zone was increased.According to the determination and analysis results of the metallographic structure and phase proportion,the austenite content in the welding joint increased and the grain size became coarse block-like as the welding heat input increased.The austenite content in the water-cooled welding joint was higher than that in the room temperature-cooled welding joint,but the grain size was smaller.The welded joints obtained under different process conditions were subjected to tensile,bending,impact toughness,and microhardness tests and analyses.The research results showed that the mechanical properties of the welded joints obtained under different process conditions met the engineering acceptance criteria,but the properties varied slightly.As the welding heat input increased,the tensile strength of the welded joint decreased,the elongation increased,the impact toughness increased,and the microhardness value decreased slightly.When the cooling method was water cooling,the tensile strength of the welded joint increased,the elongation decreased,the impact toughness decreased,and the microhardness value increased.The welding joints obtained under different welding conditions were subjected to pitting corrosion,intergranular corrosion,stress corrosion,and electrochemical corrosion tests and analyses.The research results showed that the corrosion resistance of the welding joints obtained under different welding conditions had some differences,but all could meet the engineering acceptance standards.When the welding heat input increased,the resistance to pitting corrosion of the welding joint increased,but the intergranular corrosion and stress corrosion performance decreased.When the cooling method was water-cooling,the resistance to pitting corrosion,intergranular corrosion,and stress corrosion of the welding joint all increased.Combined with the results of the electrochemical corrosion test,it can be concluded that increasing the welding heat input and using water-cooling cooling method can improve the comprehensive corrosion resistance performance of the welding joint.