Study On The Effect Of Ni Content On The Welding And Corrosion Resistance Of Weathering Bridge Steels

In this paper we studied the variation of microstructure and mechanical properties of different Ni contents steels during the welding thermal cycle and corrosion behavior under simulated atmospheric environment and variation rules of rust layer during stabilization treatment of different Ni contents steels,by means of welding thermal simulation test,the dry-wet circulation accelerated corrosion test,outdoor rust layer stabilization process test,the mechanical performance test,electrochemical test,optical microscope,scanning electron microscope,X-ray diffraction and Raman spectrometer,the results showed that:Within the range of 0.21 wt.%-0.70 wt.%,the microstructure of the parent metal changed from quasi-polygonal ferrite and a small amount of granular bainite to granular bainite,and finally the microstructure was all granular bainite,with the increase of Ni content.with the increase of Ni content.The microstructure types of the four steels with different Ni contents were all granular bainite,at the heat input of 18 kJ/cm,The microstructure was significantly refined with the increase of Ni content,and the granular bainite and massive ferrite were transformed into granular bainite,and finally all of them were granular bainite,at the heat input of 35 kJ/cm.The low temperature impact energy decreases with the increase of heat input,at the same Ni content.The dry and wet cycle accelerated corrosion test showed that,with the increase of Ni content in simulated marine atmosphere and industrial atmosphere,the test steel rust layer gradually became denser,corrosion potential and capacitive reactance arc increased,and the proportion of stable phase increased,which significantly improved the corrosion resistance and decreased the corrosion rate.In the simulated Marine environment,when the Ni content was 0.21 wt.%,the elements of Ni and Cl were uniformly distributed in the rust layer.When the Ni content increased to 0.70 wt.%,the rust layer had a certain cationic selectivity that the element of Ni were aggregated in the inner rust and the element of Cl were aggregated outer rust layer respectively.In the simulated industrial environment,the elements in the rust were uniformly distributed and no aggregation was found.Outdoor rust layer stabilizing treatment studies have found that 0.35 wt.% Ni test steel in stabilizing 4-6 weeks tend to be dark brown,0.70 wt.% Ni test steel in stabilizing treatment 6-8 weeks tend to be dark brown.After 6 weeks,the surface of the two steel rust layers was mainly composed of the larger spherical deposits ?-FeOOH.With the time increase,the corrosion potential gradually increased and the rust layer gradually stabilized.