Atomspheric Corrosion Behavior Of Low Carbon Steel Containing Al-Si-Ni

Weathering steel is a kind of low alloy and high strength steel which possesses high resistance of atmospheric corrosion and is widely used in automobile, bridge and container. Every year one sixth of steel product yield is damaged by atmospheric corrosion which is one of the main causes that damage steel constructs. Researching and developing steel with excellent corrosion resistance is of great significance for prolonging the service life of constructs, lessening repairing times and costs and also for saving alloy resource. Now, it is widely concerned that Al, Si, and other elements are added to improve the corrosion resistance of steel.Based on the design principle of weathering steel, Al, Si, Cu, P, Cr or Ni alloy elements were added into the industrial iron. After smelting, forging and rolling, four designed steels containing Al-Si and Al-Si-Ni were obtained in order to decrease Ni content or replace it totally by Al and Si. Then the mechanical properties and atomspheric corrosion behaviors of the designed steels and the comparsion steel Q235 were tested. The surface and sectional morphologies of corrosion products were observed by OM and EPMA; XRD was used to determine the substantial phase composition of the corrosion products; the electrochemical behaviors of the rust layer which formed after the immersion wet-dry-cyclic corrosion tests were studied on the polarization curves and EIS. Meanwhile, the effect of alloys such as Al,Si,Ni,Cu,Cr on rust were researched and the further research of corrosion resistant mechanism was carried.The main conclusions are as following:(1) The mechanical properties of the designed steels are better than Q235. In Al-Si designed steel, the tensile strength of 2# steel reaches 505 MPa and is 1.35 times than that of Q235. The yield strength of 2# reaches 373.33 MPa and is 1.16 times than that of Q235. In Al-Si-Ni designed steel, the tensile strength and yield strength of 3# are 1.18 times and 1.48 times than that of Q235.(2) The results from immersion wet-dry-cyclic corrosion tests indicate that the annual corrosion rates are increase at early stage and then reduce gradually during the corrosion tests for the designed steels and Q235. After 120h corrosion test, compared with the annual rate of 3# Al-Si-Ni designed steel, the annual rate of 2# Al-Si designed steel is lower 0.145 mm/a than that of 3# Al-Si-Ni designed steel. The annual corrosion rate of Q235 is 1.96 times than that of 2# steel and is 1.78 times than that of 3# steel.(3) The X-ray diffraction test results thows that the corrosion products contain the oxides of Fe, such as FeOOH,γ-FeOOH,α-FeOOH,γ-Fe2O3, Fe3O4 after accelerated corrosion for 120h. The rust layer of 2# steel mainly contains Fe3O4 andα-FeOOH while FeOOH andγ-FeOOH are found in 1# steel. Fe3O4andα-FeOOH are mainly present in 3# steel while the rust layer of 4# steel mainly includes Fe3O4 andγ-FeOOH. The rust layer of Q235 mainly contains Fe3O4 andγ-FeOOH. Theα-FeOOH which possesses good stabilization mainly exits in 1#,2# steel and 3# steel and can improved corrosion resistance.(4) The rust layer contain the enrichment of Cu,Cr and the enrichment of Si,Al, but no obvious enrichment of P by micro-analysis of Electron probe. A small amount of the enrichment of Ni is found in the rust layer of Al-Si-Ni designed steel. These alloying elements are concentrated in rust layer close to the matrix, the rust layer is dense, strong attachment with protection. No alloying element enrichment is found in the rust layer of Q235.(5) The measurement results of electrochemistry polarization curves for the rust layer of the tested steels after corrosion tests for Oh,24h,72h,120h show that the corrosion current of the four designed steels are lower than that of Q235, the corrosion potentials are higher than that of Q235 after Tafel fitting. The corrosion current of 1# steel is lower than 2# steel in Al-Si designed steel, while the corrosion current of 4# steel is lower than that of 3# steel in Al-Si-Ni designed steel. EIS spectra results show that the rust layer impendences of the designed steels are higher than that of Q235. The impendence value of 2# is higher than that of 1# steel. Before accelerated corrosion and after accelerated corrosion for 24h, the impendence value of 3# is higher than that of 4# steel, but the value of 4# steel is higher than that of 3# steel after accelerated corrosion for 72h.