Oxidation Behavior Of Steel Research Articles

(Digital Presentation) Initial High-Temperature Oxidation Behavior of Iron Binary Alloys in Air

High-temperature corrosion is playing a critical role now in many modern industries such as aerospace, gas turbines manufacturing, and steelmaking. For instance, during hot rolling of the steel sheets -as one of the later steps in steel production- before coiling, high-temperature corrosion occurs in the form of oxidation. Such reaction in air is fast and causes the formation of an oxide scale at the surface. This can change the substrate metal in terms of composition and mechanical properties. Therefore, it is essential to study the initial oxidation behavior of steels at high temperatures when exposed to air. There are different mechanisms that can control the oxidation growth rate which lead to either linear or parabolic growth regimes.The goal of this work is to study the initial high-temperature oxidation behavior of binaries with different alloying element contents (<5 wt%). The kinetics, affecting parameters, and oxidation mechanism at different stages of the process were studied. The experiments were conducted in a Thermogravimetric Analyzer (TGA) to obtain continuous mass-gain data while controlling the atmosphere and the temperature. Fe-Mn and Fe-Si samples with different compositions were chosen for isothermal experiments at a range of temperatures (between 950 °C and 1150 °C). The chamber contained gas mixtures, including oxygen, nitrogen, and water vapor, applied with different flow rates. Depending on the alloying element content of the samples or the oxidizing condition such as gas mixture, it is expected to see different oxide phases, oxidation behavior, and growth regimes. Therefore, to find the phases present in the oxide layer and the elemental composition of the oxide layer as well as the metal substrate, X-Ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) measurements were conducted. Since the oxide phases present at room temperature after cooling the oxidized sample can be different with the ones forming at the oxidation temperature, in-situ XRD experiments were conducted. Moreover, both the surface and cross-section of the oxidized samples were characterized via SEM to observe the roughness and thickness of the oxide layer.Linear growth of the oxide layer was observed in the beginning of oxidation for all the samples at different oxidizing conditions, and parabolic growth of the oxide layer was seen only at higher oxygen partial pressures (> 25 kPa). Furthermore, the oxidation mechanism was observed to be gas-phase diffusion within the linear regime, where the linear rate constants agreed with the values calculated via an existing analytical model. The temperature and alloying element content had a negligible effect on the growth rate of the oxide layer. On the other hand, within the parabolic regime, those parameters were much more influential on the kinetics, where the diffusion of species through the oxide layer was the rate-limiting step in oxidation. The result of this work helps in better understanding the initial oxidation behavior of more complex steels at high oxygen partial pressures and determining the surface composition of the steels.

Comparative high temperature oxidation studies of HVOF IN 625 coating on T22 boiler steel at 900 °C and 700 °C

Abstract IN 625 coating was deposited on T22 boiler tube steel by high velocity oxy fuel (HVOF) process to increase high-temperature corrosion resistance. High-temperature oxidation behavior of steel with and without coating has been examined at 700 °C and 900 °C under cyclic conditions. Each cycle consisted 1 h of heating in the silicon carbide tube furnace followed by 20 min of cooling in air. The cyclic oxidation conditions have been chosen as these conditions resembles actual industrial environment conditions where occurrence of shutdown is very frequent. Cyclic studies give the more severe conditions for testing and may be similar to the actual industrial environment of frequent breakdown/shutdown occurrence. Thermo gravimetric technique was implemented to study the kinetics of corrosion by observing weight change after each cycle. The bare steel experienced higher weight gain, which may be credited to the development of un-protective Fe2O3 dominated oxide scales. Evaluation of corrosive products was done using X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDAX) and X-ray mapping techniques. It was observed that the uncoated steel suffered corrosion in the form of spalling and peeling up of its oxide scale. On the converse, the IN 625 coating provided significant resistance to the corrosion. The IN 625 coating was found to be more protective at 700 °C than at 900 °C. The better air oxidation resistance in the coatings may be attributed to the phases discovered in the oxide scale of the coated specimens which mainly consisted of oxides and spinals of nickel and chromium. The information gathering from the investigation will be useful to explore the possibility of the use of the HVOF spray coatings on the boiler tubes working in the range of 700–900 °C.

STUDY OF INTERFACE BETWEEN GLASS AND STEEL FOR CORROSION RESISTANCE APPLICATION

A protective glass- based coating of N-15 and N-25 glass was deposited on the Crofer steel by slurry method and its effect on 7500C-8500C has been studied. Oxidation behavior of steel at high temperature of 12500C was also investigated. Interface study of N-25 glass &amp;Crofer steel and N-15 glass &amp;Crofer steel has been done and found that coating of N-15 glass on the steel is more smooth and effective to prevent the surface of steel from corrosion.Structural study of different type of glass has also been done. Bare steel sample as well as coated steel sample was taken for the study of their isothermal oxidation which shows that the glass coating could prevent the corrosion and improve the quality of steel surface for practical application.This corrosion resistant effect takes place because a thin layer of molten glass is formed on the surface of steel at high temperature. This layer then acts as a diffusion barrier. This coating of glass and steel is cost effective, hence have wide application in many infrastructural construction where corrosion is a big challenge. It is also very useful in marine conditions where steel is most likely to be corroded be sea water.

Oxidation Behaviour of Steel During hot Rolling by Using TiO2-Containing Water-Based Nanolubricant

The formation and performance of oxide scale on a low-alloy steel were investigated during hot rolling at 850 and 950 °C under various lubrication conditions, including benchmarks (dry condition and water) and water-based nanolubricants containing various concentrations of nano-TiO2 from 1.0 to 8.0 wt%. The results showed that the addition of nano-TiO2 particles in the lubricant significantly reduced the thickness of oxide scale and surface oxide roughness. The reduction reached the maximum when the concentration of TiO2 was 4.0 wt%. Detailed oxide phase characterisation and oxide component fraction determination revealed that hot rolling destroyed the conventional multi-layer oxide scale and promoted magnetite and haematite formation because of easy access of oxygen from the deformed structure. The effect of TiO2 was explained by the decrease in the rolling force, which led to a higher fraction of dense retaining wustite and therefore reduced the extent of further oxidation. Increasing temperature did not change the trend of lubrication effect but raised the rate of steel oxidation in general.

Some Manifestations of Antioxidation Coating for Hot Precision Forging Gears

A high temperature protective coating was prepared onto the surface of 20CrMnTi steel by brushing technique, and the heated billet was subjected to hot forging. Compared with an uncoated sample, the effect of coating on high-temperature oxidation behavior of steel was investigated by scanning electron microscopy-energy dispersive spectroscopy and X-ray diffraction. Before hot forging, an oxide layer of 153 μm was formed on the surface of the uncoated sample; however, no oxide layer was formed on the surface of the coated sample. After hot forging, the thickness of scale on the surface of uncoated gear forging is 89 μm while the thickness of coating on the surface of coated gear forging is 39 μm. It is concluded that such a coating material not only enhances the dimensional accuracy but also improves the surface quality of the gear.

Oxidation behaviour of steels in advanced gas cooled reactors

EDF Energy operates 14 advanced gas cooled reactors (AGRs) in the UK to generate electricity. CO2 gas is used as the primary coolant in the AGRs, and a range of steels are used as for the structural components: e.g. 9Cr-1Mo ferritic steels and stainless steels. These steels are susceptible to both oxidation and carburisation in CO2 dominated primary coolant gas under high pressure between 300 and 650 °C. Material degradation is a key concern for lifetime extension of the power stations, and EDF Energy and its predecessors have carried out a series of research programmes to better understand steel oxidation behaviour in AGRs and to develop more realistic lifetime prediction methodologies. These are used to secure safe and reliable operation of the AGRs. In this paper, an overview of oxidation behaviour of steels used in AGRs and some examples from the above programmes are described.

Oxidation Behavior of Steel With Cr Content and Water Flow Rate

AbstractFast water flow facilitates ferrous ion transport leading to flow accelerated corrosion (FAC) of carbon steel and the possibility of a large accident through a failure of a secondary pipe in a nuclear power plant. Ion transport is directly linked to oxide properties such as the thickness, chemical composition and porosity. This work deals with a precise observation of the cross section of the corroded specimen focusing on an oxide passivity and its thickness using SEM (scanning electron microscope) and TEM (transmission electron microscope) as well as an apparent weight loss and a surface observation for the specimens corroded using a rotating cylindrical electrode autoclave system in pure water of pH 7 at 150°C having dissolved oxygen below 1 ppb within a flow rate range of 0 to 10 m/s. The Cr content in steel was changed from 0.02 to 2.4 wt%. Increasing the Cr content in the alloy, the FAC rate and oxide thickness decreased. The oxide porosity tends to decrease with the Cr content and immersion time owing to the development of Cr containing oxide. The oxidation behavior is not changed with the immersion time.

Influences of Alloying Elements on Oxidation Behavior of Steels and Microstructure of Oxide Scales

AbstractIn order to figure out the oxidation behavior of steels during heating, five micro-alloyed steels were subjected to continuous and isothermal oxidation using the thermo gravimetric analyzer and the Gleeble-3500 thermo-mechanical simulator. The microstructure of oxide scales, especially the thickness fractions of Fe2O3, Fe3O4 and FeO layers, was analyzed using the scanning electron microscope (SEM), electron probe microanalyzer (EPMA) and electron backscattered diffraction (EBSD) techniques. The micro-alloyed steels containing alloying elements (Si, Cr, Ni and Cu) show a higher oxidation resistance compared with the low carbon steel. It is found that alloying elements accumulated at scale/substrate interface during high temperature oxidation. Alloying elements function in two ways in the oxidation of steels: one is enhancing the scale/substrate interface and consequently suppressing the blister of scales; and the other is impeding the outward diffusion of iron cations from substrate to scales, resulting in the decrease of oxidation rate. As the diffusion of iron cations is impeded, the thickness fractions of Fe2O3 and Fe3O4 of micro-alloyed steels are more than those of low carbon steels.

Improvement in oxidation behaviour of steel by B4C–TiB2–TiC–Ni coating

In this study, B4C–TiB2–TiC–Ni coating was thermally sprayed on the surface of 4130 steel substrate by high velocity oxyfuel (HVOF) torch. Before the HVOF process, the B4C–TiB2–TiC–Ni powder was prepared by mechanical alloying (MA). In order to study the oxidation behaviour of the coating and 4130 steel, thermogravimetric analysis (TGA) was done. The structural evolution of the samples was investigated by X-ray diffractometry (XRD). The microstructure and elemental analysis of the samples were studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The coating showed higher oxidation resistance in comparison with the 4130 steel at high temperatures. It was also found that the dissolution of oxygen in the coating was the rate determining process of the coating oxidation, creating the quasi-cubic kinetic rate.

High Temperature Oxidation of 22wt.% Cr Austenitic Alloys upon Exposure to Hot Corrosion Environment with Na2so4

High temperature corrosion studies in today’s austenitic steels are of great interest to develop novel corrosion- and creep-resistant austenitic steels for advanced zero-emission power generation plants. These efficient power plants can offer advantageous considerations for the global need for energy and mitigation of climate change. However the aggressive environmental conditions poised challenges to current austenitic steels for long-term applications. To date, long-term application of austenitic steels has been restricted to service temperatures lower than 635 °C while future boilers are targeting temperatures of 700 – 750 °C. Therefore, extensive microstructural evolution studies of Fe-Cr-Ni steels exposed to high temperature conditions will contribute useful information to help retard degradation or enhance corrosion resistance properties while in search of novel compositions in austenitic steels.Protective Cr-rich oxide films formed on austenitic stainless steels play an effective role to lower high temperature corrosion. These oxide scales of low porosity, good adherence, low growth rate, and high mechanical and thermodynamic stability can provide good corrosion resistance properties. Hence, in the formation of a protective Cr-rich oxide scale as a barrier to further corrosion, diffusional transport of Cr within the alloy to the oxide scale is critical.The conditions of the exposure environments of the austenitic steels highly affect the growth and stability of these protective Cr-rich oxide scales. For example, the formation of volatile Cr species can lead to a depletion of Cr in the oxide scales and form Fe-rich oxide films, which inadequately function as a barrier to corrosion. Since the rate of diffusional transport of Cr in the oxide scale is compensated, accelerated localized attacks within the grains occur. In addition, the presence of H2O and CO2 in the exposure environment results in the formation of Fe-rich oxide scales and accelerated oxidation rates of most technical steels.Sulphurous corrosive components (SO2 and sulphate-based salt components) in commercial high temperature applications, for e.g. combustion, accelerate the corrosion rate, resulting in adverse modification of degradation properties in Fe-Cr-Ni steels. This deposit-induced intensified oxidation process is known as hot corrosion. In addition, Na and S exist as fuel impurities in power plants and lead to deposits of Na2SO4. These molten deposits can cause sulphate-deposit induced accelerated oxidation processes, which destroys the reaction-product oxide scales. Propagation modes of hot corrosion determined by these mechanisms are also dependent on the exposure temperatures and durations, and compositions of exposure gas, oxides and deposits. Hence, the influence of different exposure temperatures and durations on the mechanisms of the oxidation behavior of Fe-Cr-Ni steels studied in this work will help predict the behavior of austenitic steels in hot corrosion environments.In this work, the isothermal high temperature oxidation behaviors of a 22 wt.% Cr austenitic stainless steels, Sanicro25 (42Fe22Cr25NiWCuNbN), subjected to various exposure temperatures have been investigated. The exposure environment consists of O2+H2O+CO2+SO2+Na2SO4. The alloys were subjected to respective exposure temperatures of 600, 700 and 750 °C with different exposure durations of 300 h and 1000 h. They were also compared to results observed in Sanicro25 alloys which were subjected to similar environmental conditions at 700 °C but for a shorter exposure duration time of 168 h [1].Detailed microstructural investigations within the individual grains of the formed oxide, the oxide-metal interface and in the vicinity of the oxide-steel interface using XRD, SEM, FIB/SEM, TEM and EDX have been performed. These results yield insights to the microscopic mechanisms governing the oxidation behavior of steels with deposits of Na2SO4when subjected to aggressive high temperature environments related to oxy-fuel combustion.

Oxidation Behavior of Steel and Pure Copper at 500-700°C

The oxidation behavior of steel and pure copper has been investigated in the temperature range of 500-700°C at various oxygen pressures. The rate of oxidation was measured using thermal gravimetric apparatus (TGA). The morphology, composition and structure of the oxide scale were determined by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Influence of ceramic coating of MgO on oxidation behavior and descaling ability of low alloy steel

A high temperature MgO protective coating used onto 20Cr2Ni4A low Alloy steel was prepared by a slurry-spraying technique. The effects of coatings on high temperature oxidation behavior of the steel and the descaling ability of scale were invested. Metallurgical microscopy was used to characterize the surface topography of the samples. SEM and EDX were used to study the structure and element distribution of the oxide scale. The experimental results show the coating could enhance oxidation resistance of the steel effectively at 1100–1250°C. The metal losses of coated samples are diminished by about 65% when compared with the uncoated samples. The Mg-Fe spinel layer, formed at the outer layer of the scale, can decrease the cation diffusion velocity throughout the scale during oxidation. Si-rich layer, which is existed at the interface of scale and substrate, strongly adhered to the steel, resulted in bad descaling ability, is also reduced by the coating. Cr-rich layer formed between Si-rich layer and the outer scale of the coated sample is thicker than that of uncoated sample. The proposed mechanism of oxidation resistant MgO coating is discussed.

Influence of H2O and CO2 on the Oxidation Behaviour of Steels between 400-600°

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Oxidation Behavior of Stainless Steel with Electroless Ni-Fe-P Coatings

Ni-Fe-P coatings were deposited on ferritic stainless steel by means of electroless method. The oxidation behavior of the steel with these coatings were investigated at 800°C in air. The mass gain of the steel with Ni-Fe-P coatings deposited from solutions with different mass ratios of FeSO4 to NiSO4 decreased with increasing mass ratio. For the steel with Ni-Fe-P coating deposited in the solution with 0.25 of the mass ratio, the mass gain increased with the increase in oxidation time. While the mass gain of the steel with coatings deposited in solution with 0.5 and 0.75 of the mass ratio, respectively, became stable after 10-h oxidation. Compared with Ni-P, The Ni-Fe-P coatings improved the spallation resistance of the surface oxide scale. The oxide scale formed the bare steel consisted of Cr2O3 with TiO2 and (Mn,Cr)3O4 spinel. However, the oxide scale thermally grown on the steel with Ni-Fe-P coatings was composed of NiO, (Ni,Fe)3O4 spinel and Cr2O3.

The Influence of the Rare Earth Element Ce on the High-Temperature Oxidation Kinetics of Low-Cr Steels

The oxidation behavior of steels containing low-Cr concentrations (0.5-2.25 wt.%) has been studied in laboratory air in the temperature range of 400-550 °C. The oxidation rate of the steels was lower than that of pure iron, but higher than that of pure iron when a small amount of rare earth element cerium (0.03 wt.%) is added to the 2.25Cr1Mo steel. The mass change follows a nearly parabolic law for the case of pure iron and the steel without Ce addition, while linear behavior describes the oxygen uptake for the case of the 2.25Cr1Mo+0.03Ce steel. SEM cross-section observations and thermodynamic calculations confirm that there is no wustite (FeO) formation during oxidation of pure iron and low-Cr steels at 550 °C, whereas FeO might be formed in the oxide scale of 2.25Cr1Mo+0.03Ce at the same oxidation conditions (temperature, atmosphere, and exposure time). By investigating the temperature for FeO stability, this study reveals that the temperature for FeO formation on pure iron is 568 °C, for the 2.25Cr1Mo steel 589 °C, and 471 °C for the 2.25Cr1Mo+0.03Ce. This low value for the FeO stability temperature found for the steel 2.25Cr1Mo+0.03Ce steel explains why this steel oxidizes very fast at 550 °C.

Development of an Experimental Device to Study High Temperature Oxidation

An experimental device was designed and constructed to study the oxidation behaviour of steel. The device consists in a special chamber mounted within the frame of a servo-hydraulic testing machine holding the sample being studied. The atmosphere within the chamber can be controlled to be either inert or oxidation by flowing either nitrogen or dry air: a flow of 14 Nl/min was used for replacing either atmosphere in less than 0.1 s. The sample of steel was heated up to the testing temperature by induction. The testing procedure was designed to be flexible enough for heating up and cooling down the sample without oxidation. The device allowed for scales that ranged from a few micrometers to close to 300 μm. The growth kinetics recorded in this work was found to agree with previous published data. It can be concluded that the present device allows for studying the behaviour of thin crusts of steel oxide, which are classified as tertiary and can damage the surface of the steel during rolling.

Effect of Chromium Content on the Oxidation Behaviour of High-Speed Steels under Dry and Moist Air Environments

Development and use of high-speed steels for manufacturing the roll outer shell of hot strip mills represented a major recent technological advancement in the hot rolling field. However, it was observed that the oxidation behavior of these steels was different from that of conventional rolls. The high-speed steel oxidation rate is about four times higher than the alloys previously used. Furthermore, the rolling conditions are quite aggressive. Contact of the roll with the hot strip, air and water of the cooling system is expected to increase the oxidation of the roll surface in this wet atmosphere. Therefore, it is necessary to study their oxidation behavior in order to achieve the full potential of high-speed steel rolls for hot strip mills. In the present work, the oxidation behavior of three high-speed steels with differences in chromium content was studied. Corrosion tests were carried out in a thermobalance under dry and moist (12.5 % H2O) atmospheres at 765oC for 240 minutes. The corroded samples were examined by X-ray diffraction, scanning electron microscopy and energy dispersive micro-analysis. It was found that the variation of chromium content of the high-speed steels studied was sufficient to influence the oxidation behaviour. Samples with high chromium contents presented smallest final mass gain. The presence of humidity had a significant effect on the oxidation behavior.

The Effect of Grain-Boundary Diffusion on the Oxidation of Low-Chromium Steels

Even though the oxidation behavior of steels is generally considered as to be widely understood, a closer look reveals some open questions, e.g. regarding the influence of the substrate grain size on the overall oxidation kinetics. At temperatures below 570°C the main constituent of the oxide scale formed on top of low alloy steels is magnetite. As shown by gold marker experiments it grows outward and inward at the same time, the latter exhibiting a gradual transition to the more stable spinel compound FeCr2O4. As indicated by intergranular-oxidation attack below the superficial scale, inward oxide growth seems to be driven by oxygen transport along the grain boundaries serving as fast diffusion paths. This is supported by thermogravimetric oxidation tests in air on low-Cr steels with varying grain size: The smaller the grains the higher the oxidation rate. Recently, a numerical model for the diffusive transport processes based on the finite-difference approach has been developed, which distinguishes between fast grain-boundary diffusion and bulk diffusion. Qualitatively, it is capable to predict the relationship between substrate grain size and inward oxide growth kinetics. Together with the thermodynamic tool ChemApp and in combination with a data set for the Fe-Cr-O system the mechanism-based simulation of the overall oxidation process of low-Cr steels is possible.

The influence of cerium, yttrium and lanthanum ion implantation on the oxidation behaviour of a 20Cr25NiNb stainless steel in carbon dioxide at 900–1050°C

The influence of the implantation of 10 17 Ce + cm −2, 10 17 La + cm −2 and 10 −2 on the oxidation behaviour of 20Cr25NiNb stainless steel (where the composition is in weight per cent) in carbon dioxide has been examined at temperatures between 900 and 1050°C. The oxidation kinetics during isothermal exposures of about 250 h duration were followed using a controlled-atmosphere microbalance, and spallation during subsequent cooling to room temperature was assessed. The composition and microstructure of the multicomponent scales formed were examined by a range of surface-analytical techniques, with the location of the implanted atoms being established by dynamic secondary ion mass spectrometry. The oxidation of the 20Cr25NiNb stainless steel over this temperature range is characterized by the transition from protective- to non-protective-type behaviour with scale breakdown due to the occurrence of cracking during isothermal oxidation and due to spallation on thermal cycling. By incorporation within the oxide scale, and in particular by segregation to the oxide grain boundaries, the implanted reactive elements extended the temperature range of protective-type behaviour to 1000°C or less, depending on the element, by modifying the initial scale growth mechanism and also the resultant scale microstructure and mechanical properties. Implantation had no significant beneficial influence on the oxidation behaviour of the steel at 1050°C.

ChemInform Abstract: THE EFFECT OF CARBON, ZIRCONIUM, NIOBIUM, AND TITANIUM ON THE OXIDATION RESISTANCE OF CHROMIUM STAINLESS STEEL

AbstractKohlenstoff wirkt schädlich auf die Oxidationsbeständigkeit von Stahl mit 17% Cr.