Atmospheric Corrosion of Weathering Steels for Assembly Steel Structure

Assembly steel structure buildings with characterization of energy saving, environmental protection and source recycling, are in line with the future development direction of Chinese buildings. But, steel corrosion protection have to be concerned in the steel structure design since ordinary steels are susceptible to corrosion. The high cost of rust cleaning and air and soil pollution caused by powders during rust cleaning, organic chemicals or deposited metals of corrosion protection coatings, restrict the development of steel structure buildings. Because of cost saving and reduction of environmental pollution, the research and development of new self corrosion protection steels without additional coatings is of great significance to the development of steel structure buildings. Therefore, Q390 weathering and anti-seismic hot-rolled H-section steel named Q390NHD, was developed with the addition of Ni, Cr and Cu alloy elements to meet the requirements of atmospheric corrosion resistance, and with vanadium micro-alloying, V (C, N) precipitation strengthening during cooling process after hot rolling, combined with the characteristics of section steel hot rolling process. The corrosion resistance was studied by periodic immersed comparison test, and corrosion problem during long term atmospheric exposure was analyzed, and the feasibility of the use of Q390NHD steel without coatings in the assembly steel structure buildings was demonstrated. The chemical contents of Q390NHD section steel are mainly composed of m(C) ≤ 0. 12,m(Si) ≤ 0. 50,m(Mn) ≤ 1. 50,0. 20≤ m(Ni) ≤0. 65,0. 30≤m(Cr) ≤1. 25,0. 20≤m(Cu) ≤0. 55,m(V) ≤0. 12 and so on. The mechanical properties of Q390NHD steel are as follow, lower yield strength R_eL is above 400 MPa, tensile strength R_m was botween 560-600 MPa, yield ratio was not more than 0. 80, elongation with short proportional specimens not less than 25%, and V-notch impact test energy at - 20 ℃ was not less than 34 J/cm², which meet the requirements of anti-seismic design of steel structure parts assigned in Chinese standard GB 50017—2017 Standard Design of Steel Structure. The corrosion rate of Q390NHD steel for the 72h period immersed test was 1. 665g/(m²·h), 47% of ordinary steel's, which meant the former corrosion resistance was more than 2 times of the latter, equivalent to that of 09CuPCrNiA steel. According to ISO 11844-1 ∶2006 standard, the 70 year total corrosion thickness of Q390NHD steel is not more than 0. 031 mm at inner corrosivity class IC3, less than 0. 3 mm at the more severe class IC4, and below 0. 7 mm at the most severe class IC5. So, the new developed steel, Q390NHD, can be used without coating in steel structure buildings for common offices and residences in most part of China.