low-Cr Steel Research Articles

Alloy design employing Ni and Mo low alloying for 3Cr steel with enhanced corrosion resistance in CO2 environments

In this work, low-Cr steels with enhanced corrosion resistance by employing Ni and Mo alloying were self-designed to provide an alternative option compared to a common 3Cr steel in CO2 environments, and the corresponding corrosion resistance mechanism was investigated by comprehensively evaluating corrosion behavior of three low-Cr steels exposed to CO2-saturated NaCl solutions over time periods of 6–168 h at 90 and 180 °C, involving electrochemical and immersion tests. The results indicate that a decrease of general corrosion rates only expresses at early stages of corrosion after an addition of Ni and Mo, whereas FeCO3 crystals instead of inner Cr-enrichment films play a decisive role in retarding long-term general corrosion rates. On the other hand, localized corrosion behavior of low-Cr steels is obviously retarded by employing Ni and Mo alloying, in which non-reactive nickel occupies a large amount of vacancies and restricts a diffusion of corrosive species. In addition, Mo accelerates an enrichment of Cr during early stages of immersion and followed by facilitating a rapid re-passivation capacity once films are broken, which reduces risks of perforation failure of pipelines.

11–23% Cr steels for solid oxide fuel cell interconnect applications at 800 °C – How the coating determines oxidation kinetics

The present work investigates the low-cost steels AISI 441, AISI 430, and AISI 444 against the tailor-made high Cr steel Crofer 22 APU (22.9 wt% Cr) at 800 °C in simulated solid oxide fuel cell (SOFC) cathode conditions. Furthermore, a low Cr steel, AISI 409 (11.4 wt% Cr) is included in the study. The oxidation, chromium evaporation, and area-specific resistance (ASR) of the uncoated and Ce/Co-coated steels are studied for up to 3000 h. Ce/Co-coated steels showed significant improvement in behaviour compared to their uncoated counterparts. The oxidation and chromium evaporation behaviour between the uncoated steels varied substantially while the Ce/Co coated steels exhibited highly similar behaviour. The area-specific resistance of the coated low-cost steels was on par with Crofer 22 APU. However, 430 formed a continuous silica layer, resulting in a higher ASR after 3000 h. Cross-sections of the uncoated and Ce/Co-coated steels were analysed using a scanning electron microscope and energy dispersive X-ray spectroscopy.

The role of Cr content on the corrosion resistance of carbon steel and low-Cr steels in the CO2-saturated brine

The selection of appropriate materials for the transportation pipelines is of vital importance to ensure the safety operation in Carbon Capture, Utilisation and Storage (CCUS). To clarify the effects of Cr content in steel on the resistance against general and localised corrosion, electrochemistry methods combined with pH measurements and various surface analysis techniques were implemented on X65, 1Cr, 3Cr and 5Cr steel samples in a CO2-saturated solution at 60 °C and pH 6.6 during 192 h of immersion. Additionally, thermodynamic and kinetic analyses of the formation of the corrosion products on carbon steel and low-Cr steels were performed. The results show that the general corrosion resistance increased with rising Cr content without the presence of significant corrosion products formation. However, with the formation and development of the corrosion products, the general corrosion resistance reduced with the increase in Cr content. The formation of the compact crystalline FeCO3 on X65 and 1Cr steel surfaces offered superior general corrosion protection, while cannot provide enough localised corrosion protection. By contrast, the double-structural corrosion product layers on 3Cr and 5Cr steels notably suppressed the localised corrosion, but providing poor protection against general corrosion over long immersion periods. This study reveals the contributions of Cr content on general and localised corrosion resistance at various periods, providing references for material selection and evaluation in CO2 environments relevant for CCUS.

Effects of silty sand and pH on the formation of corrosion film and corrosion behaviour of low-Cr steel in the CO2 environment

ABSTRACT The effects of silty sand and pH on the corrosion characteristics of 1Cr steel were investigated. The results revealed that silty sand changed the nucleation behaviour of FeCO3 crystal from homogeneous nucleation to heterogeneous nucleation through increasing the critical supersaturation of FeCO3. The compactness and protection of corrosion film were improved by silty sand. The amorphous FeCO3 content decreased as the pH increased in the CO2 environment with silty sand, while the Cr(OH)3 content increased. The critical pH for the good corrosion resistance of 1Cr steel was 4.5. The amorphous FeCO3 dominated the protective properties of corrosion film when the pH was lower than the critical pH, whereas the Cr(OH)3 was predominant when the pH was higher than the critical pH. Therefore, the corrosion resistance of 1Cr steel was reduced and then enhanced with increasing pH under silty sand condition.

The study on the influence of aluminum on the CO2 corrosion resistance of 3%Cr steel

PurposeThis study aims to report the CO2 corrosion performance of 3Cr steel and 3Cr2Al steel and reveal the role of aluminum in mitigating corrosion of low-Cr steel.Design/methodology/approachAluminum was added to 3Cr steel to prepare a new type of 3Cr2Al steel, and the effect of aluminum on the corrosion resistance of pipeline steel was studied using morphology observation and composition analysis, weight loss tests and electrochemical test.FindingsIn the CO2/O2 coexistence environment, the average corrosion rate of the 3Cr2Al steel was obviously lower than that of the 3Cr steel. The addition of aluminum expanded the range of prepassivation, and the dynamic potential polarization curve of 3Cr2Al steel showed duplex prepassivation phenomena. 3Cr steel underwent severe local corrosion, and 3Cr2Al steel underwent uniform corrosion. The addition of aluminum contributed to the formation of a dense corrosion product layer and greatly reduced the localized corrosion sensitivity.Originality/valueThe studies on CO2 corrosion of aluminum containing low-Cr steel are quite rare. This study clarifies the role of aluminum by comparing the corrosion behavior of 3Cr2Al and 3Cr steel. The effect of aluminum on the growth of corrosion product film was discussed, and the duplex prepassivation phenomena of Cr and Al were revealed.

High-Temperature Oxidation of Steels in Direct-Fired CO2 Power Cycle Environments

Future direct-fired supercritical CO2 power cycles require steels resistant to oxidation/corrosion in high-temperature CO2 environments containing various impurities. Herein we studied the oxidation behavior of 14 candidate steels in a simulated direct-fired CO2 power cycle environment consisting of 95% CO2, 4% H2O, 1% O2 with/without 0.1% SO2 at 1 atm and 550 °C, 600 °C, 650 °C for up to 2500 h. Steels with ≥ 11.5 wt% Cr exhibited at least partial coverage by Cr-rich oxide scales leading to a significant decrease in the oxidation rates in both gases. While SO2 had little effect on low-Cr steels that formed Fe-rich oxides, it generally worsened performance of high-Cr (> 11.5 wt%) steels by hindering the establishment of a protective Cr-rich oxide. This effect was most pronounced at the lowest temperature of 550 °C, which was attributed to strong preferential adsorption of sulfur-containing species within the oxide at relatively low temperatures.

Optimize Ni, Cu, Mo element of low Cr-steel rebars in tropical marine atmosphere environment through two years of corrosion monitoring

To optimize Ni, Cu, Mo element content of low Cr steel rebars in tropical marine atmosphere environment, five newly steel rebars were exposed in Dalat to carry out the outdoor exposure tests including weight loss method, surface characterization method and electrochemical test. The results show that when 0.15 wt% Mo is added in the steel rebar, the corrosion resistance is 31.8% higher than that of the steel rebar with 0.3 wt% Cu. The corrosion resistance of 0.3 wt% Cr added steel rebar is 63.4% higher than that of 0.2 wt% Ni added steel rebar. With the addition of 0.3 wt% Cu and 0.3 wt% Cr, the corrosion resistance is 46.3% higher than that of the steel rebar with 0.2 wt% Ni and 0.15 wt% Mo. Mo and Cr are the main elements to improve the protection of steel rebar rust layer. The corrosion products of the five steel rebars are composed of α-FeOOH, γ-FeOOH and Fe2O3 or Fe3O4. The higher the content of Cr is, the higher the ratio of α - FeOOH to γ-FeOOH (α/γ) in the rust layer becomes. The protective layer composed of CaMoO4 and Fe2(MoO4)3, formed by molybdate in alkaline environment hinders the further corrosion of steel rebars. Cr(OH)3 produced by hydrolysis of Cr in low alloy steel inhibits the growth of FeOOH in rust, resulting in the decrease of FeOOH particle size and the rust layer more compact. On the whole, the newly designed low alloy steel rebar with a little of 1.6Cr-0.15Mo elements can be well used in tropical marine atmospheric environment.

Electroless Ni–P coatings on low-Cr steels: A cost-efficient solution for solar thermal applications

The corrosion behavior of an electroless Ni–P coating on low-Cr X20CrMoV12-1 steel as a cost-efficient substrate-coating combination is investigated in molten NaNO 3 –KNO 3 nitrates at 600 °C. Results indicated that the as-deposited Ni–P coating was transformed to a thermally treated diffusion coating upon exposure to the molten salt without additional heat treatment prior to the exposure. Detailed evolution of the Ni–P coating and the oxidation behavior during the 1000-h immersion test is discussed. Results showed competitive corrosion resistance of the coating system compared to that of the sophisticated Ni alloy 230, with the advantage of an inherent barrier against Cr dissolution form the substrate. The significant corrosion resistance of the electroless plated Ni–P coating is attributed in part to the protective Ni--rich oxide scale and in other part to the in-situ formed Ni 3 P barrier at the oxide-substrate interphase boundary. - Electroless Ni–P coating was developed on a low-cost X20CrMoV12-1 substrate - Interdiffusion occurred during the immersion test at 600 °C - The as-coated substrate required no additional heat treatment prior to the molten salt exposure - An outer Ni–Cr rich oxide scale and an inner Ni 3 P layer formed during the immersion test - The Ni–Cr scale and Ni 3 P layer protected the substrate against molten salt corrosion and Cr-dissolution

Study on serration flow and dynamic strain aging of Cr–Ti–B low-carbon steel

Compression tests were carried out for hot-rolled Cr–Ti–B low-carbon steels with different Cr contents (low Cr and high Cr) at three strain rates (0.01, 0.1 and 1 s−1) and temperatures ranging from 250 to 650 °C. The serrated flow and dynamic strain aging (DSA) behaviors during deformation were systematically analyzed. The results showed that the effect of the strain rate on serration flow is more obvious than that of the deformation temperature, and the serration type changes from type C to type A with increasing strain rate. The occurrence temperature range of DSA in high Cr steel (350–450 °C) is higher than that in low Cr steel (300–400 °C) at a strain rate of 1 s−1. The activation energy for DSA close to that for the diffusion of carbon, which is considered to produce DSA. A Cr–C cluster is observed in high Cr steel, which clarified that the delaying mechanism throughout the DSA regime is attributed to the pinning of carbon diffusion by Cr atoms.

Effect of Co addition on microstructure and mechanical properties of new generation 3Cr-3W and 5Cr-3W steels

In this study, the effect of Cr and Co on microstructure and mechanical properties of low Cr-W steels was investigated. For this goal, 3% Cr-3%W and 5% Cr-3%W steels, this may be an alternative to new generation low Cr steels, containing 0%, 0.5%, 1.5%, 3%, 4.5% Co, produced by casting and hot rolling. The samples were annealed at 1100 °C for 1 h, followed by quenching in air and tempering for 2 h at 710 °C. Ferrite, bainite, and martensite phases were determined in various volume fractions according to the chemical composition. Carbides precipitated within the grain and grain boundaries during tempering. Co bearing caused an increase of A1, A3, and Curie temperatures. Co slightly increased hardness and strength in both 3 Cr and 5 Cr alloys. However, the hardness and strength of 5 Cr alloys with all Co ratios were almost same that of 3 Cr alloys. The Charpy-V impact energies of 5 Cr steel are lower than 3 Cr steel with the same Co amount. The addition of Co up to 1.5% in steels with 3 Cr did not make any major changes in the notch toughness. However, the addition of 3% Co to the alloy significantly reduced impact energy. In 5 Cr steel, notch toughness generally decreased with the increase of Co amount.

Comparisons of corrosion behaviour for X65 and low Cr steels in high pressure CO2-saturated brine

Appropriate materials for injection pipelines and tubing for carbon dioxide geologic storage is fundamental to ensure asset integrity and save cost. This paper evaluates the corrosion behaviour of X65, 1Cr, 3Cr and 5Cr, which have the potential to be injection pipeline/tubing materials. The influence of steel Cr content on the general and localised corrosion behaviour was investigated at time periods from 6 to 192 h at 60 ⁰C and 100 bar. The evolution, morphology and chemistry of corrosion products on the surface of each material were evaluated using a combination of scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction and related to their overall corrosion protection. Results indicate that prior to the formation of protective films on the steel surfaces, the resistance of the materials to corrosion increase with increasing Cr content (Corrosion resistance: X65 < 1Cr<3Cr<5Cr). However, as corrosion products evolve, the protection afforded to the different steels significantly varies and decreases with increasing Cr content. × 65 becomes the material with the lowest general corrosion rate by the end of the 192 h experiments and 5Cr exhibits the highest corrosion rate (ranking of corrosion resistance: X65 > 1Cr>3Cr>5Cr). In terms of the corrosion products on X65, both inner amorphous and outer crystalline corrosion layers consist of FeCO3. For the Cr-containing steels, the outer layer also comprises FeCO3, but the inner layer is enriched with Cr, and is predominantly amorphous Cr(OH)3. The extent of localised corrosion (determined using surface profilometry) is noticeably less for X65 compared to the Cr-containing steels. The paper raises questions about the benefits that low Cr steels offer towards extending component design life compared to carbon steel under the test conditions considered here.

High temperature oxidation of steels in CO2 containing impurities

Future power systems require steels that resist corrosion in high temperature CO2 containing combustion products/impurities. Here we evaluate the corrosion behavior of several commercial steels exposed to 95% CO2-4 % H2O-1 % O2, with/without 0.1 % SO2, at 550 °C and 1 atm. High-Cr steels formed thin Cr-rich oxides and low-Cr steels thick Fe-rich oxides during SO2-free exposures. Additions of SO2 had little effect on low-Cr steels but enhanced corrosion of high-Cr steels, where S within the chromia scale led to its failure and subsequent Fe-rich oxide nodule growth. The results are rationalized by considering the thermodynamic and kinetic factors controlling the reaction.

Cathodic reaction mechanisms in CO2 corrosion of low-Cr steels

The cathodic reaction mechanisms in CO2 corrosion of low-Cr steels were investigated by potentiodynamic polarization and galvanostatic measurements. Distinct but different dominant cathodic reactions were observed at different pH levels. At the higher pH level (pH > ~5), H2CO3 reduction was the dominant cathodic reaction. The reaction was under activation control. At the lower pH level (pH < ~3.5), H+ reduction became the dominant one and the reaction was under diffusion control. In the intermediate area, there was a transition region leading from one cathodic reaction to another. The measured electrochemical impedance spectrum corresponded to the proposed cathodic reaction mechanisms.

Impact of Solar Salt aging on corrosion of martensitic and austenitic steel for concentrating solar power plants

This work addresses the influence of molten nitrate salt chemistry on the corrosion behavior of a martensitic high temperature steel and an austenitic stainless steel. It is one of the first addressing controlled degradation of Solar Salt by controlling the gas atmosphere on top of the melt, thus driving the formation of corrosive ions, mainly oxide ions but also nitrite ions. The stainless steel and high temperature steel samples are subjected to the different operating conditions to demonstrate the variations in corrosivity as a function of gas atmosphere and additionally of artificially added chloride impurities. The results indicate that the atmosphere has a direct impact on the formation of corrosive oxide and nitrite ions. The low Cr-steel is found to be more sensitive to chloride impurities, while the stainless steel corrosion is enhanced by the presence of nitrites and oxide ions. All studies are supported by profound molten salt analysis throughout the experiments including the analysis of nitrate, nitrite, oxide and chromate ions as well as cation compositions. Steel samples are analyzed by scanning electron microscopy methods and corrosion rates are extrapolated from 1200 h experiments.

Corrosion Propagation Behavior of low-Cr steel Rebars in Simulated Concrete Environments

Corrosion Propagation Behavior of low-Cr steel Rebars in Simulated Concrete Environments

On the development of creep damage constitutive equations: a modified hyperbolic sine law for minimum creep strain rate and stress and creep fracture criteria based on cavity area fraction along grain boundaries

This paper reports (1) the latest development and application of a modified hyperbolic sine law for minimum creep strain rate and stress for both low Cr and high Cr steels, and (2) the development of a creep fracture criterion based on cavity area fraction along grain boundaries for high Cr steel. This work is part of the fundamental development of creep damage constitutive equations which were identified through a critical literature review. In the former the application of the new law results in an improved fitting; in the latter, a new creep fracture criterion based on cavity area fraction along grain boundaries was derived and quantitatively calibrated using the latest detailed cavity nucleation and growth kinetics models for high Cr steel. Furthermore, this paper revealed the trend of nucleation rate coefficient with stress, and the trend of creep life time coefficient with stress, which provide reliable and universal prediction capabilities. This paper contributes to the specific knowledge on the minimum creep strain rate and stress function, the development of a scientifically sound and novel creep rupture criterion based on the cavity area fraction along grain boundaries for high Cr steel, and the provision of creep damage/life prediction tools.

Corrosion behavior of low-Cr steel rebars in alkaline solutions with different pH in the presence of chlorides

Corrosion behaviors of HRB400 carbon steel and three low-Cr steel rebars in alkaline solution simulating concrete pore solution with various pH and chlorides values were studied using cyclic voltammetry, potentiodynamic polarization, electrochemical impedance spectroscopy, and Mott-Schottky combined with scanning electron microscope as well as X-ray Diffraction. Results show that pH and chloride play important roles in the formation of passive films on steel rebars. As pH value decreased, the pitting potential shifts negatively, the polarization resistance decreases while the density of current carrier in the passive film increases. In the absence of chloride, stable passive film cannot form on carbon steel in simulated concrete pore solution with pH9.6, Cr3+ cannot remain stable in the passive film on 3Cr and 5Cr steel, and passive film on low-Cr steels are more stable than that of carbon steel. While pitting corrosion is promoted by increasing chloride ions, Cr effectively reduces pitting propagation, resulting in the high passivation capability of steel rebar in carbonated concrete pore solution. The corrosion products of carbon and low-Cr steels have common characteristics, with Cr accelerating the formation of protective α-FeOOH and lowering the corrosion rate. Therefore, Cr-modified steel presents excellent passive behavior and pitting corrosion resistance in simulated carbonated concrete pore solution, which can be further enhanced by increasing the Cr content.

Effects of alloying elements and cooling rates on the high-strength pearlite steels

ABSTRACTThe effects of the alloying elements of Cr, Mn and the cooling rates after hot deformation on the microstructures and mechanical properties of pearlite steels were studied. Results show that increasing Cr and decreasing Mn significantly increase the eutectoid transformation temperature of steel. The grain sizes of prior austenite of the steels after hot deformation are ∼12 µm. However, the high-Cr–low-Mn steel exhibits a finer interlamellar spacing and some better mechanical properties than that of the high-Mn–low-Cr steel. A full pearlite microstructure with an interlamellar spacing of 97 nm was obtained on the former steel, which exhibits a hardness of HRC49, a tensile strength of 1700 MPa and an elongation of 19%.

Effect of Different Vanadate Salt Composition on Oil Ash Corrosion of Boilers

Corrosion in oil-fired boilers is accelerated in the presence of V, Cl and S which derive from low-grade fuels or the environment. 10CrMo9-10 steel is commonly used in such boilers. In order to evaluate the salts corrosion behavior of such low Cr steels, samples were immersed in several vanadate salt combinations of Cl, S, Na and Ca in air at 600 °C. Even during short-term exposure, different dominant corrosion mechanisms could be identified such as active oxidation, sulfidation and acidic or basic fluxing, depending on the exact salt composition. The aggressiveness of the different salt mixtures was ranked with regard to the metal loss. It is also demonstrated that corrosion can be reduced by the addition of a calcium-containing inhibitor.

Modeling of Intergranular Oxidation by the Cellular Automata Approach

Within this study, the application area of the cellular automata model for the prediction of internal corrosion during high-temperature applications has been extended to intergranular oxidation. Besides a significant mass transport by diffusion, chemical reactions and phase transformations have to be accounted for in a modeling framework for internal corrosion. In addition, grain boundaries play an important role as they are acting as fast diffusing paths where the transport of matter is by orders of magnitudes higher than inside the grain. Here, a numerical model is presented to describe intergranular oxidation attack. The model is applied to the nickel-based superalloy 80a and the low-Cr steel X60. It is shown that experimental and simulated results are in good agreement.