Stabilization Treatment of a Surface Rust Layer and Corrosion Resistance Mechanism of Q420NH Weathering Steel

Abstract Various solution systems have been used to stabilize Q420NH WS, and stability treatments have been evaluated through cyclic corrosion tests, X-ray diffraction, scanning electron microscopy, and electrochemical analysis. The microstructure and corrosion resistance of the rust layer on weathering steel, both untreated and treated with different stabilizers, were compared. The corrosion rate of the stabilized samples initially increased, but it subsequently decreased, resulting in fewer defects, such as cracks and pores, and increased density. The rust layer composition in both the untreated and stabilized samples consisted mainly of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> </mml:math> -FeOOH, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>γ</mml:mi> </mml:mrow> </mml:math> -FeOOH, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>β</mml:mi> </mml:mrow> </mml:math> -FeOOH, and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>Fe</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">/</mml:mo> <mml:mi>γ</mml:mi> <mml:mtext>-</mml:mtext> <mml:msub> <mml:mrow> <mml:mi>Fe</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> phases. Poststabilization, the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> </mml:math> -FeOOH content increased, peaking at 57% in the Group C sample. For the Group C sample, the open circuit potential of the rust layer was <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mo form="prefix">−</mml:mo> <mml:mn>308</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>mV</mml:mi> </mml:mrow> </mml:math> , with a resistance of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mn>220</mml:mn> <mml:mtext> </mml:mtext> <mml:mi mathvariant="normal">Ω</mml:mi> <mml:mo>·</mml:mo> <mml:msup> <mml:mi>cm</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> and a thickness of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mn>740</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>μm</mml:mi> </mml:mrow> </mml:math> . These values represented increases of 26.6, 103, 57.1, and 48%, respectively, compared with those of the untreated sample, enhancing corrosion resistance. The rare earth element Ce was primarily present as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>CeFeO</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> , significantly assisting in filling cracks and voids caused by rapid corrosion, thus promoting rust layer densification. Stabilizers can shorten the rust layer stabilization period, with Group C being the most effective.