Effect Of Nickel On Microstructures And Properties Of443Ferritic Stainless Steel Welded Joints

443ferritic stainless steel is a kind of ultra pure high chromium ferrite stainless steel. Because of its economic price and excellent properties, it is used as an potential replacement of304austenitic stainless steel. However, the heat affected zone grains of443ferrite stainless steel grow significantly in the process of welding, that leads to the embrittlement sharply of welded joint, which limits the use of443ferrite stainless steel. Therefore, it is important to improve the performance of welded joint.Because nickel can improve the strength and toughness of material, four groups of4mm thickness443ferritic stainless steel plates were welded in this subject, their nickel content was0.28%、0.55%、0.86%and0.96%respectively. In this topic we analyzed the microstructure of four kinds of welded joint, tested conventional mechanical properties and corrosion resistance, and finally explored the effect of trace nickel on microstructures and properties of welded joints.The microstructures showed that The HAZ grain size of0.96%Ni、0.86%Ni、0.55%Ni and0.28%Ni is72.52μm、77.83μm、88.49μm and101.33μm respectively, The HAZ grain size of0.96%Ni reduce by28.43%compared with0.28%Ni. Four kinds of weld seams are composed of acicular ferrite and austenite.Tensile test results show that four kinds of welded joint is shear fracture in the parent metal and the angle is45°along the drawing direction. The welded joint tensile strength of0.96%Ni.0.86%Ni、0.55%Ni and0.28%Ni is487.85MPa、452.50MPa、416.64MPa and378.78MPa, The welded joint tensile strength of0.96%Ni is28.80%higher than that of0.28%Ni. The welded joint elongation of0.96%Ni、0.86%Ni、0.55%Ni and0.28%Ni is32.29%、29.20%.27.75%and25.56%, The welded joint tensile elongation of0.96%Ni is26.33higher than that of0.28%Ni.Impact experimental results show that at room temperature the HAZ impact energy of0.96%Ni、0.86%Ni、0.55%Ni and0.28%Ni is9.4J、7.8J、6.8J and5.3J, the HAZ impact energy of0.96%Ni is77.36%higher than that of0.28%Ni. At-20℃the HAZ impact energy of0.96%Ni、0.86%Ni、0.55%Ni and0.28%Ni is6.2J、4.7J、4.2J and2.7J, the HAZ impact energy of0.96%Ni is129.63%higher than that of0.28%Ni. the impact fracture morphology SEM show that four kinds of are brittle fracture at room temperature and-20℃.Fatigue experiment results show that fracture path of four kinds welded joint is located at weld toe, all of the fatigue crack expanded along the heat affected zone. Under the5×106cycles the welded joint fatigue strength of0.96%Ni.0.86%Ni、0.55%Ni and0.28%Ni is243.78MPa.230.14MPa.196.79MPa and138.68MPa, the welded joint fatigue strength of0.96%Ni is75.79%higher than that of0.28%Ni.Intergranular corrosion experiment results show that four kinds of welded joint surfaces are no change after intergranular corrosion, and there are not cracks in surfaces of four kinds of welded joints after bending180°Perpendicular to the weld seam.Salt spray corrosion experiment results show that the corrosion resistance rank of0.96%Ni、0.86%Ni、0.55%Ni and0.28%Ni respectively level D、D、E and F. After672hours the corrosion rate of0.28%Ni、0.55%Ni、0.86%Ni and0.96%Ni respectively is0.63×10-8g·mm-2·h-1、0.53×10-8g·mm-2·h-1、0.38×10-8g·mm-2·h-1and0.23×10-8g·mm-2·h-1.In summary, the Ni combining with Ti and Nb formed intermetallic compound particles in443ferritic stainless steel, these particles which dispersed in the matrix could prevent grain growth of parent metal and HAZ. Therefore, trace nickel can obviously improve organization and performance of443ferrite stainless steel welded joint.