The effect of Al and Nb contents, cooling rate and rolling condition on the microstructure and corrosion behaviour of HSLA steel
TL;DR: In this article, the effect of the addition of aluminium and niobium, and processing conditions, including cooling rate and rolling condition, on the corrosion behaviour of HSLA steel in 10 wt% sulfuric acid environment has been investigated.
Abstract: The effect of the addition of aluminium and niobium, and processing conditions, including cooling rate and rolling condition, on the corrosion behaviour of HSLA steel in 10 wt% sulfuric acid environment has been investigated The experimental procedures included electrochemical corrosion techniques using potentiodynamic and electrochemical impedance spectroscopy, as well as weight loss method The microstructure was examined using optical and scanning electron microscopes in order to investigate the effect of the microstructural features on the corrosion behaviour Surface films were evaluated by X-ray photoelectron spectroscopy (XPS) to identify the corrosion products formed on the surface The results showed that increasing the Al content enhanced the corrosion resistance through obstructing pitting attack on the surface by the refinement of grain boundary carbides and the formation of a protective passive layer rich in carbide and oxide compounds The combination of both Al and Nb promoted the corrosion resistance further, by enriching the passive layer with Nb and higher levels of carbide and oxide compounds, despite the presence of martensite and grain size refinement by niobium carbonitride (NbCN) Increasing the cooling rate reduced the corrosion resistance due to the refinement of grain size, giving a higher density of grain boundaries that act as active sites, besides increasing the level of carbide distribution in the microstructure Controlled rolling offered higher corrosion resistance than hot rolling, independent of the composition, because of the absence of martensite, the presence of low-angle boundary and the refinement of grain boundary carbides provided by controlled rolling
Figures (7)
Table 1. Composition (wt%), rolling condition and cooling rate of the HSLA steels chosen for examination. 
Figure 6. Electrochemical corrosion data for the hot rolled steel 0.16%Al-0.018%Nb steel at both cooling rates (17 and 33°C min-1): (a) Potentiodynamic polarisation curves, (b) Nyquist plots. 
Figure 5. Electrochemical corrosion data for the hot rolled steel at 33°C min-1 for 0.02%Al, 0.16%Al and 0.16%Al-0.018%Nb: (a) Potentiodynamic polarisation curves, (b) Nyquist plots. 
Table 4. Summarised XPS data for surface products of the examined hot rolled steels at 33°C min-1, (%). 
Figure 8. The corrosion rates based on the weight loss method of the examined steels 0.02%Al, 0.16%Al and 0.016-0.018%Nb, and 0.16-0.018%Nb at both cooling rates; 17 and 33°C min-1, and 0.16-0.018%Nb at both rolling conditions (hot and controlled rolling). 
Table 3 Corrosion current density (iCorr) and corrosion potential (ECorr) obtained from the potentiodynamic polarization curves for the examined HSLA steels. 
Figure 7. Electrochemical corrosion data for the hot rolled 0.16%Al-0.018%Nb steel at both rolling conditions (hot and controlled rolling): (a) Potentiodynamic polarisation curves, (b) Nyquist plots.
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TL;DR: In this article , the effects of Cr and Ni on the microstructure and corrosion resistance of high-strength low alloy steel (HSLAs) were investigated by optical microscopy, scanning electron microscopy and X-ray diffraction.
Abstract: The effects of Cr and Ni on the microstructure and corrosion resistance of high-strength low alloy steel (HSLAs) were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, electrochemical tests, X-ray photoelectron spectroscopy and Raman spectroscopy. The results showed that the grain size and microstructure of the steel were optimized due to the increase of crystallinity and Cr3C2 relative content by adding Cr and Ni. The tensile strength was enhanced because of the refined crystalline strengthening, phase transformation strengthening and solution strengthening. Electrochemical tests displayed that the self-corrosion current density of steel and the total anode current density as well as the number of total anodes of the WBE decreased significantly by adding Cr and Ni during immersion in 3.5 wt% NaCl solutions for 24 h. During the corrosion process, the composition and phase structure of the rust layers changed for the existence of Cr and Ni in the Cr–Ni steel, and the formation of NiFe2O4 and FeCr2O4 promoted the increase of the Fe2+/Fe3+ ratio and the relative content of α-FeOOH in the rust layers enhancing the compactness and protectiveness of the corrosion products. Besides, the microstructure of the steel containing Cr and Ni had significant effects on the mechanical strength and corrosion resistance.
4 citations
TL;DR: In this article, the effect of Mo content on the microstructure, thermal conductivity, and corrosion resistance of the die steels was investigated by optical microscopy, scanning electron microscopy and x-ray diffraction.
Abstract: In this work, effect of Mo content on the microstructure, thermal conductivity, and corrosion resistance of the die steels was investigated by optical microscopy, scanning electron microscopy, x-ray diffraction, laser thermal conductivity meter, electrochemical experiments, and pitting tests. The microstructure of the die steels is mainly composed of lath-shaped tempered martensite. At all the tested temperatures, the thermal conductivity of the die steels is decreased with the increase in Mo content from 1.2 to 5.0 wt.%. However, electrochemical experiments indicate that increase in Mo content in the die steels can reduce the corrosion current density and increase the charge transfer resistance in 0.5 mol·L−1 HCl solution. Furthermore, it was found that Mo in the die steels is beneficial to decrease weight loss and pitting corrosion rate, which improves the pitting corrosion resistance of the die steels.
3 citations
TL;DR: In this article , a series of AFA stainless steels with different Al and Nb contents were studied in supercritical CO 2 by SSRT, and the results showed that Nb element plays a precipitation strengthening on the mechanical properties, while it shows few effects on the corrosion properties.
Abstract: Abstract SCC of a series of AFA stainless steels with different Al and Nb contents were studied in supercritical CO 2 by SSRT. The results show that Nb element plays a precipitation strengthening on the mechanical properties, while it shows few effects on the corrosion properties. The surface oxide film of the Al-free material only consisted of amorphous Cr 2 O 3 and Cr-rich spinel. With the addition of Al, the Al 2 O 3 layers are formed and significantly decreases the element diffusion, thus inhibiting the initiation of SCC. Fe 3 O 4 fills the interior of cracks of both Al-free and Al-containing materials. The Al 2 O 3 layer is formed at the crack tip of Al-containing materials. Because the matrix grains are large, the protective Al 2 O 3 layer can only be formed at the crack tip, which cannot completely hinder the outward diffusion of ions on the crack walls and its protective effect on the crack propagation is limited.
2 citations
TL;DR: In this article, a comparison between three-and two-dimensional models and thermal and thermo-mechanical response of work-rolls with variable boundary conditions has been investigated.
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TL;DR: In this article, an overview on aluminum-based hydrogen production methods, their limitations and challenges for commercialization is given. And a newly developed concept for cogeneration of hydrogen and electrical energy is discussed.
Abstract: The hydrogen economy has been identified as an alternative to substitute the non-sustainable fossil fuel based economy. Ongoing research is underway to develop environmentally friendly and economical hydrogen production technologies that are essential for the hydrogen economy. One of the promising ways to produce hydrogen is to use aluminum or its alloys to reduce water or hydrocarbons to hydrogen. This paper gives an overview on these aluminum-based hydrogen production methods, their limitations and challenges for commercialization. Also, a newly developed concept for cogeneration of hydrogen and electrical energy is discussed.
434 citations
15 Mar 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, deformation dilatometry has been used to simulate controlled hot rolling followed by cooling of a Nb-V low carbon steel, looking for conditions corresponding to wide austenite grain size distributions prior to transformation.
Abstract: Deformation dilatometry has been used to simulate controlled hot rolling followed by cooling of a Nb–V low carbon steel, looking for conditions corresponding to wide austenite grain size distributions prior to transformation. Recrystallization and non-recrystallization deformation schedules were applied, followed by controlled cooling at rates from 0.1 °C/s to about 200 °C/s, and the corresponding continuous cooling transformation (CCT) diagrams were constructed. The resultant microstructures ranged from polygonal ferrite (PF) and pearlite (P) at slow cooling rates to bainitic ferrite (BF) accompanied by martensite (M) for fast cooling rates. Plastic deformation of the parent austenite accelerated both ferrite and bainite transformations, displacing the CCT curve to higher temperatures and shorter times. However, it was found that the accelerating effect of strain on bainite transformation weakened as the cooling rate diminished and the polygonal ferrite formation was enhanced. Moreover, it was found that plastic deformation had different effects on the refinement of the microstructure, depending on the cooling rate. An analysis of the microstructural heterogeneities that can impair toughness behavior has been done.
143 citations
25 Jul 2007-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the microstructure and the corrosion behavior of ultrafine-grained interstitial free (IF) ferritic steel processed by equal channel angular pressing (ECAP) at room temperature following route C were investigated.
Abstract: The microstructure and the corrosion behaviour of ultrafine-grained interstitial free (IF) ferritic steel processed by equal channel angular pressing (ECAP) at room temperature following route C were investigated. Already after the first pass of ECAP, the microstructure was refined by a factor of approximately 200. On further passes, ECAP was found to lead to continuous grain refinement, while elongated grain structure produced in the first pass was retained throughout all processing cycles. After 8 passes, the microstructure comprised bands of elongated grains of average length of 500–1000 nm and average width of 200–300 nm. Corrosion characteristics of a non-deformed coarse grained specimen and an ultrafine-grained specimen that had undergone 8 passes of ECAP were investigated using electrochemical potentiodynamic tests. ECAP induced grain refinement does not appear to influence the electrochemical characteristics in neutral NaCl solutions. This encouraging finding demonstrates that ECAP, while enhancing mechanical characteristics, does not compromise corrosion resistance of IF steel. A protective oxidic layer is formed in alkaline NaCl solution, which reduces the corrosion rate significantly.
132 citations
25 Jun 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the isothermal precipitation kinetics of carbides in both strain-free and strained austenite (γ) of a microalloyed steel were quantitatively investigated through the electrical resistivity and transmission electron microscopy.
Abstract: The isothermal precipitation kinetics of carbides in both strain-free and strained austenite (γ) of a microalloyed steel were quantitatively investigated through the electrical resistivity and transmission electron microscopy. The (Nb,Ti)C carbides at the interfaces of the undissolved (Ti,Nb)(C,N) carbonitrides were observed at all temperatures in strain-free γ. However, for strain-induced precipitation, above 950 °C, the precipitation of (Nb,Ti)C carbides near the undissolved (Ti,Nb)(C,N) carbonitrides was predominant due to the recrystallization of strained γ. Meanwhile, the fine (Nb,Ti,V)C carbides were homogeneously precipitated in non-recrystallized γ at 850 °C and 900 °C, as well as near the undissolved (Ti,Nb)(C,N) particles. The electrical resistivity method was successfully used to quantitatively measure the isothermal precipitation kinetics of carbides in both strain-free and strained γ. The precipitation-time–temperature diagrams of the carbide in strain-free and strained γ, with nose temperatures of 950 °C, were generated and the precipitation kinetics were greatly accelerated by the applied strain.
97 citations
TL;DR: In this paper, a nanocrystallized surface was fabricated on low-carbon steel by ultrasonic shot peening (USSP) technique, and the electrochemical corrosion behavior of the SNC low carbon steel with different grain sizes was studied by electrochemical methods.
Abstract: A nanocrystallized surface was fabricated on low-carbon steel by ultrasonic shot peening (USSP) technique. The grain size on the top latter of the surface narrocrystallized (SNC) low-carbon steel was about 20 nm. which increased with distance from the peening surface. The electrochemical corrosion behavior of the SNC low-carbon steel with different grain sizes was studied by electrochemical methods in 0.05 M sulfuric acid (H2SO4) + 0.05 M sodium sulfate (Na2SO4) aqueous solution. Grain sizes <35 am showed a strong effect on the electrochemical corrosion behavior. The corrosion rate of the SNC low-carbon steel increased with the decreasing of grain size. This was attributed to the increased number of the active sites caused by SNC low-carbon steel.
95 citations