Modelling of heat input and obtaining the experimental data in welding of duplex stainless steels

Duplex stainless steels are widely used in defense industry, marine applications and storage tanks. Duplex stainless steels have equal amount of ferrite and austenite phases. Duplex stainless steels have general corrosion resistance, mechanical strength, ductility and pitting corrosion resistance with ferritic-asutenitic microstructure. Secondary phases (intermetallics) affecting the material properties negatively are comprised with ferrite-austenite transformation. Secondary phase comprising in duplex stainless steels depending the ferrite-austenite transformation are affecting material properties negatively, especially in welding. Higher heat input during the welding process and uncontrolled cooling after the welding process enhance the secondary phase formation. Avoding the secondary phase formation is very important with regard to cost reduction and prevention the negative effects of secondary phases on material properties. In this study, an approach for formation and identification the properties of secondary phases occur in heat affected zone of weldments is developed by using finite element method due to material and welding parameters. For this purpose, solution treatments, ageing and isothermal ageing with various temperature and time were applied to EN 1.4462 alloy. Heat treatment map of EN 1.4462 alloy was formed according to heat treatment experimental data. Especially, isothermal ageing conditions have notable effect on enhancing the secondary phase ratio and grain size. EN 1.4462 alloy was welded with flux cored wire and TIG by using filler materials in various thickness. Finite element modelling were performed due to material properties and welding parameters. Finite element modelling was performed by ANSYS software. The results of finite element modelling were evaluated with heat treatment experimental data and a prediction was developed for microstructural changes in EN 1.4462 alloy after the welding. Verification of prediction developed by finite element modelling results were done with microstructural characterization of weldments. Also, hardness test, tensile test and notch impact test were performed to determine the effects of microstructural changes on material properties in weldments. An approach for formation and identification the properties of secondary phases occur in heat affected zone of weldments is developed by verification of predictions with microstructural characterization of weldments.