Study on microstructure and properties of seawater corrosion-resistant steel bar 00Cr10MoV
With the depletion of land resources, human beings have accelerated the pace of going to the sea, and major projects such as cross-sea Bridges, undersea tunnels, and offshore oil platforms have been continuously built. However, the biggest challenge for these Marine engineering materials is corrosion in the Marine environment. As one of the most commonly used engineering building materials, steel bar's corrosion resistance to seawater directly affects the durability of concrete structures in Marine environment.
At present, the more widely used corrosion resistant steel bars are coated steel bars, stainless steel bars and alloy corrosion resistant steel bars. A steel company researchers developed a low-alloy corrosion-resistant steel bar 20MnSiCrV, its room temperature structure is ferrite and pearlite, yield strength of 450MPa, tensile strength of 650MPa, corrosion rate is lower than 70% of ordinary threaded steel bar. On this basis, the alloy composition is further optimized, and the high corrosion resistance alloy threaded steel bar 00Cr10MoV is developed. In this work, the microstructure, mechanical properties and corrosion resistance of 00Cr10MoV steel bar were systematically analyzed, and the comparison and discussion were made with the common thread steel bar 20MnSiV.
The chemical composition of the material was tested, smelted and moulded into 80kg ingot in 150kg vacuum induction furnace, and the ingot was welded to 140mm×140mm×12m square billet tail after forging, and finally hot-rolled into Φ25mm threaded bar in the production workshop. Three sections of steel bars were cut from three finished steel bars and processed into tensile specimens. The yield strength, tensile strength and elongation of the specimens were measured on 5585 electronic universal material testing machine. The microstructure of the cross section of the sample was observed, and the hardness of different tissues of the sample was tested by Tukon 2100B digital closed-loop control Vickers hardness tester. The distribution of alloying elements in the tissues was observed by Shimazu 1610 electron probe microanalyzer (EPMA). The corrosion resistance was further evaluated by means of salt spray, cyclic immersion corrosion test, electrochemical impedance spectroscopy and polarization curve.
The results show that:
(1) The microstructure of seawater corrosion-resistant 00Cr10MoV steel bar is mainly composed of ferrite and bainite, the yield strength reaches 450MPa or more, and the comprehensive mechanical properties are excellent;
(2) Under the conditions of accelerated corrosion test, the corrosion rate of 00Cr10MoV steel is less than 5% of the ordinary thread bar 20MnSiV; The corrosion products are mainly α-FeOOH, β-FeOOH and γ-FeOOH, and also contain a small amount of Fe3O4 and a small amount of chlorine-containing products Na3CrCl16, Fe+3O (OH, Cl).
(3) The addition of alloying elements Cr and Mo improves the self-corrosion potential and charge transfer resistance of 00Cr10MoV steel in 3.5%NaCl neutral aqueous solution, reduces its corrosion current density, and greatly improves its seawater corrosion resistance compared with 20MnSiV steel.
