corrosion susceptibility
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CORROSION ◽  
10.5006/3936 ◽  
2021 ◽  
Author(s):  
Sara Filice ◽  
Joe McDermid ◽  
Joey Kish

The structure and composition of mill scale on linepipe steel formed with and without accelerated cooling conditions (ACC) was investigated and correlated to localized corrosion susceptibility. The mill scale structure/composition was investigated using scanning electron microscopy equipped with X-ray energy dispersive spectroscopy and electron back scatter diffraction, as well as X-ray diffraction. Localized dissolution of the mill scale was investigated using electrochemical techniques including open circuit potential measurements, electrochemical impedance spectroscopy, and electrochemical noise measurements in a corrosive phase solution. The various surface analytical and electrochemical techniques indicated that the mill scale formed without ACC consists of a relatively crack-free, thick inner wüstite layer with a thinner magnetite outer layer. However, the mill scale formed with ACC comprised a magnetite layer containing islands of retained wüstite, with some evidence of magnetite/iron eutectoid formation and which exhibited a relatively high density of through-scale cracks. These cracks can provide direct paths that connect the corrosive solution to the steel substrate, leading to more rapid breakdown of the mill scale. Additionally, the cracks can form a crevice between the mill scale and the steel surface, providing sites for pit initiation and growth. Coefficient of thermal expansion mismatch thermal stress calculations indicate that a magnetite-based scale is more susceptible to cracking/spalling than a wüstite-based scale, resulting in the ACC plate being more susceptible to localized corrosion.


2021 ◽  
Vol 904 ◽  
pp. 88-96
Author(s):  
Liang Chang ◽  
Xue Tao Zhang ◽  
Xiao Yuan Xie ◽  
Jing Miao Li ◽  
Qiang Dai ◽  
...  

In this paper, two kinds of heat affected zone (HAZ) simulation structures of 347H stainless steel, which are coarse grain zone (CGZ) and unmixed zone (UZ), were prepared by thermal simulator. The material properties of toughness, reheat crack susceptibility and intergranular corrosion susceptibility of the two kinds of HAZ simulation structures were studied by impact test, high temperature tensile test, electrochemical potentiodynamic reactivation (EPR) test and micro morphology test. The result shows that CGHAZ had better toughness. But after the stabilizing heat treatment, it was weakened while that of the UZ was enhanced. The reheat crack susceptibility of the CGZ and UZ both increases after stabilization heat treatment, and the tendency of the UZ are more obvious. Stabilizing heat treatment has a certain effect on the prevention of sensitization process, which can improve the intergranular corrosion resistance of the material. Stabilizing heat treatment is double-edged to 347H HAZ, and it needs combined with the specific situation to used.


CORROSION ◽  
10.5006/3917 ◽  
2021 ◽  
Author(s):  
Kang Wang ◽  
Charles Demarest ◽  
Mathew Asmussen ◽  
John Scully ◽  
Bi-Cheng Zhou

Rubidium (Rb) generated from the β-decay of Kr-85 has been theorized to be corrosive toward steel, specifically in the storage of Kr-85 nuclear waste streams. In the present study, the phase equilibria of RbxCryOz oxides with Rb in dry oxygen and water are investigated to understand a possible pathway to unusual deterioration of the corrosion resistance of canister steels in the presence of Rb. It was found that, in dry oxygen environments, the accumulation of Rb (more than 0.01 mol) can completely consume the Cr in 1 mol of AISI 4130 steel by forming -Rb2CrO4 and Rb3CrO4 and prevent the formation of protective Cr2O3 scale. In aqueous environments, RbxCryOz oxides are metastable species. In order to investigate their role, the probability of forming various oxides is invoked in order to avoid the all-or-nothing approach to oxide formation typical of E-pH diagram, which only predicts the most stable species dissolved, ionized or solid ionized. Thus, the probability of forming RbxCryOz was considered and reported herein. It was found RbxCryOz can possess a larger than 7% probability of forming over Cr2O3 in Rb rich case and 15% in Cr rich case, indicating that it is expected to find small amount of RbxCryOz in the thermodynamically formed reaction products. Even though Cr2O3 is more stable than RbxCryOz oxides, the protective Cr2O3 scale is likely to have some vulnerability to Rb, leading to one possible route for the decline in the corrosion resistance of steel canisters in aqueous environments. Therefore, from a thermodynamic perspective, the current study supports the hypothesis that Rb can thermodynamically react with Cr in steels and can lead to formation of RbxCryOz at certain potentials and pH levels, showing the Rb influence of steel corrosion cannot be discounted. The paper considers experimental mixed potential and pH levels observed and relationship to thermodynamic probability. From this relative corrosion resistance can be assessed in a preliminary way in aqueous environments.


2021 ◽  
Vol MA2021-02 (6) ◽  
pp. 541-541
Author(s):  
Manila Ozhukil Valappil ◽  
Farisa Forouzandeh ◽  
Marwa Atwa ◽  
Samantha Luong ◽  
Viola Ingrid Birss

Metals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1488
Author(s):  
Ulises Martin ◽  
Jacob Ress ◽  
David M. Bastidas

In this work, the influence of thermal (TT), mechanical, and thermomechanical (TMT) treatments using the ultrasonic nanocrystal surface modification (UNSM) on the corrosion protection properties of Inconel 718 was studied, correlating the changes in the electrochemical properties with the promoted microstructure. The UNSM treatment had a grain refinement effect on the top surface, reducing the grain size from 11.5 to 7.4 µm for the first 10 µm in depth. The high grain boundary density, due to the grain refinement, enabled a faster growth of the passive film. The impedance showed a decrease in the charge transfer resistance by three orders of magnitude, from 106 to 103 Ω cm2 for as-received to 1000 °C, as the TT temperature crossed the solvus of the γ′/γ″ and approached the solvus of the δ-phase. The UNSM treatment lowered the pitting corrosion susceptibility, increasing the charge transfer resistance and decreasing the effective capacitance of the double layer, leading to the thickest passive film with 6.8 nm.


2021 ◽  
Author(s):  
Joshua P. James

Abstract As more industries look toward additively manufactured (AM) components to combat lead times, re-design, cost of complexity, etc., those industries are faced with re-evaluating the performance of AM-based materials as compared to their well-documented wrought or machined counterparts. A particular alloy of interest to many industries including aerospace and energy/power generation is Inconel 718 due to its resistance to oxidation and high temperature degradation [1]. Additively manufactured Inconel 718 parts typically receive a series of post-build heat treatments prior to deployment. If not properly controlled, these post-build treatments may introduce secondary precipitates and other inhomogeneities that will affect the parts’ mechanical properties and susceptibility to corrosion. This is specifically true of susceptibility to localized corrosion mechanisms that may lead to crack initiation, accelerated crack growth and ultimately premature failure. By utilizing electrochemical parameter testing to analyze for localized breakdown potentials, this work investigates the variation in tolerance to localized corrosion that results from common post-build heat treatment steps and the secondary phase precipitation that can ensue in Inconel 718 AM parts.


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