Oxidation Rate Of Steel Research Articles

Effect of TiN inclusions on oxidation behavior of austenitic stainless steels

The effects of TiN inclusions on the oxidation behavior of modified stainless steels have been investigated systematically in this study. It was found that the oxidation rate of steel with TiN stringers is almost seven times faster than the clean one during the homogenized treatment. In the oxidation layers, the TiN stringers induce the spall fracture and facilitate the air permeation. At the oxidation interface, the TiN inclusions act as the nucleation sites for the oxides and promote the internal oxidation. The air permeation and internal oxidation causes the severe oxidation of modified austenitic stainless steels.

Performance of stainless steel interconnects with (Mn,Co)3O4-Based coating for solid oxide electrolysis

Mixed transition-metal oxide coatings are commonly applied to stainless steel interconnects for solid oxide cell stacks. Such coatings reduce oxidation and Cr evaporation rates, leading to improved degradation rate and stack lifetime. Here, the ChromLok™ MCO-based composition (Mn,Co)3O4 is applied to Crofer 22 APU stainless steel and evaluated specifically for application in solid oxide electrolyzer stacks operating around 800 °C and utilizing oxygen-ion-conducting solid oxide cells. The MCO coating is found to decrease the stainless steel oxidation rate by about one order of magnitude, and decrease the Cr evaporation rate by fourfold. The coating also dramatically lowers the rate of area-specific resistance increase for stainless steel coupons oxidized for 500 h with constant current applied, from 33 mΩ∗cm2 kh−1 for an uncoated coupon to less than 4 mΩ∗cm2 kh−1 for coated coupons. The coating is demonstrated on full-scale interconnects for single-cells, where the coating dramatically reduces degradation rate, and for a stack, which displays stable operation for 700 h.

BEHAVIORS OF OXIDATION AND DECARBURIZATION ON SURFACE OF HIGH-CARBON STEEL WIRE RODS

The quality of high-carbon wire rods is subject to high requirements in terms of the size of the decarbonized layer, the amount and composition of the scale formed by the interaction of the oxidizing furnace atmosphere with the surface of steel. In this connection, studies of the kinetics of high-temperature oxidation of high-carbon steel are of great practical importance, both in the development of new and adjustment of existing modes of heat treatment of steel. The results of experimental studies of hightemperature oxidation and decarburization of the surface of high-carbon steel grade 80P on the synchronous thermal analysis device STA 449 F3 Jupiter presented. Temperature intervals of intensification of scale formation and decarburization of the surface in various media (weakly oxidizing and oxidizing) have been established. Phase transformations in high-carbon steel grade 80P have been studied by differential scanning calorimetry and the temperatures of the beginning and end of the formation of homogeneous austenite during heating have been established. It was noted that in the range of heating temperatures of steel 720‒950°C, along with phase transformations, the intensification of the processes of scale formation and depletion of the surface layers with carbon begins. The exponential dependence of steel loss on the heating temperature of the sample was obtained by thermogravimetric analysis. It was shown that the oxidation rate of the surface increases by 3 times with an increase in the temperature of the workpiece from 900 to 1000°C, and up to 1200°C ‒ by 8 times. It was noted that the temperature at which the oxidation rate of steel is minimal in the temperature range from 900 to 1000 °C is about 929 °C, in the range of 1100‒1250°C ‒ 1157°C. The obtained results can be used to select the main technological parameters of the heat treatment mode of wire rods made of 80P steel, which ensure the formation of a minimum amount of easily removed scale on the metal surface.

CHAPTER 4 High Temperature Oxidation of Stainless Steels

This chapter is dedicated to the description of high temperature oxidation of both chromia and alumina forming alloys. The defect structures of iron and chromium are firstly reviewed. The effects of elements on stainless steel oxidation behaviour are further addressed. For the chromia-forming stainless steel, the oxidation rate is reduced with the increased silicon content but not in a monotonic manner. Titanium and niobium can reduce breakaway oxidation of Fe–18Cr–10Ni austenitic stainless steel. Titanium can enhance the adhesion of scale to the Fe–18Cr by mechanical keying effect of TiO2 formed at the steel/scale interface. For the alumina-forming stainless steel, the formation of alumina and its transformation during oxidation are reviewed. Chromium can be added to reduce the critical aluminium content in the steels in order to form alumina at high temperatures. The addition of reactive elements with appropriate level can improve scale adhesion and reduce the steel oxidation rate. Refractory element like molybdenum can increase strength of material but also accelerate the oxidation rate of the steels containing reactive elements. The development of new alumina-forming austenitic alloy grades is finally described.

The influence of KCl on biomass ash melting behaviour and high-temperature corrosion of low-alloy steel

The main aim of this work was to determine the influence of KCl-rich ash deposits on 10CrMo9-10 steel oxidation rate. Two agricultural biomass samples: oat and rye straw, clean and doped with KCl were tested in this study. The addition of KCl does not decrease the melting temperature of the ash when KCl is not incorporated with mineral matter components.Corrosion experiments were performed at 550 °C and 600 °C, with corrosion coupons covered with real and synthetic biomass ash under oxidising conditions. The nonuniform distribution of KCl in ash affected the results and the effect of potassium concentration on oxidation rate was not observed in all cases. More severe influence of ash rich in KCl was observed at lower temperature, the reason is lower protective oxide scale formation rate and higher influence of ashes on steel material and scale.The temperature increase by 50 °C doubled the corrosion rate. At 550 °C KCl was most aggressive salt, but at 600 °C the influence of eutectic mixture KCl+K2SO4 was the highest. Even at lower temperature thermal decomposition of K2CO3 was observed affecting the results. It might be concluded that temperature and eutectic mixture formation are essential parameters in corrosion prediction.

Effect of oxygen partial pressure on oxidation behavior of ferritic stainless steel AISI 441 at high temperatures

In this investigation the oxidation behavior of AISI 441 stainless steel (SS) in the range from 850 °C to 950 °C was determined during 50 h in two different atmospheres: (a) synthetic air in a tubular oven; (b) argon with 1 ppm of O2 in a thermal balance. The oxidation kinetics was determined from the measured mass change as a function of oxidation time. Examination of the microstructure of the oxides and determination of their chemical composition were performed by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and glancing angle X-ray diffraction (GAXRD). Chemical analyses showed that films formed on the AISI 441 steel surface consisted mostly of chromium oxide but manganese, iron, titanium and silicon oxides were found in the oxidized layer. In synthetic air, the steel oxidation rate increased gradually as the temperature increased, but in the argon atmosphere with 1 ppm of oxygen, the highest oxidation rate was observed at 900 °C and the lowest at 950 °C.

Development of the technique for determination the rate of oxidation of structural steels in heavy liquid metal coolants

The article considers the main methods for studying the process of oxidation of structural steels and evaluating their corrosion resistance in heavy liquid metal coolants (HLMC) under static and dynamic conditions. It is shown that the main disadvantage of these methods is the impossibility of evaluating the results in real time. The authors propose a new method for the experimental determination of the oxidation rate of steels in molten HLMCs, which makes it possible to measure the reaction rate without depressurizing the plant, by periodically injecting air doses of a known volume and monitoring its response time. As additional data in the research methodology, the results of a chemical-spectral analysis of the coolant and slags were provided after the experimental campaign completion as well as a metallographic analysis of steel samples to determine the oxide coating thickness and its comparison with the calculated value for the integral oxygen assimilation by the system. To implement the methodology, a laboratory facility was proposed, equipped with an oxygen thermodynamic activity (TDA) sensor of the RF-IPPE design. The sensor is certified by Gosstandart of Russia (certificate RU. 31.002 A No. 15464), registered in the State Register of Measuring Instruments (No. 25282-03) and approved for use in the Russian Federation.

Acceleration of oxidation process of iron in supercritical water containing dissolved oxygen by the formation of H2O2

To improve fuel use and energy-conversion efficiency and reduce the emission of pollutants, oxygenation is now deemed an effective chemical treatment of water in supercritical and ultra-supercritical power plants. Supercritical water with dissolved oxygen significantly enhances the oxidation rate of steels in the main steam pipeline and super-heater header. However, at the atomic scale, the mechanism of metal oxidation in supercritical water containing dissolved oxygen is unknown and has not been investigated by simulation. In this work, the oxidation of iron in supercritical water containing dissolved oxygen is studied by ab initio molecular dynamics and first principles calculations. The results indicate that dissolved oxygen in supercritical water dramatically accelerates the oxidation of iron. With the help of oxygen, the decomposition of water occurs on the iron surface, thereby producing more iron oxides and iron hydroxides. Additionally, hydrogen peroxide (H2O2) forms as an intermediate product, instantaneously decomposing to form iron hydroxides, and this is another reason for the enhancement in the oxidation of steel by supercritical water containing dissolved oxygen. Based on the results from ab initio molecular dynamics, we develop herein typical models of water molecules and oxygen molecules reacting directly on the iron surface and then carry out first-principles calculations. The results show that water decomposes on the iron surface only with the assistance of adjacent oxygen molecules and in the absence of surrounding water molecules. This investigation deepens our understanding of the oxidation mechanism of metal in supercritical water containing dissolved oxygen. The ideas and methods implemented in this work can also be used to study other materials exposed to supercritical water involving oxygen.

Study of effectiveness of heavy metals ions as the inhibitors of steel corrosion

The effect of ions of d-metals on the processes of corrosion in a movable and immovable neutral aqueous environment has been investigated. It was shown that a number of ions, such as zinc, chromium, lead, under conditions of high aeration and temperature of 20 oС at concentrations of 2−5 mg/dm3, are effective inhibitors of steel corrosion. This is due to the formation of a passivation oxygen film on the surface of metal. The degree of corrosion protection is maintained at the level of 80−90 %. In the case of elevating the temperature to 50 oС, a significant (up to 40 %) decrease in the inhibitory properties of ions of d-metals is observed. This is due both to the destabilization of the oxygen passivation film and the growth of oxidation rate of steel with increasing temperature. It was demonstrated that phosphonic acids, such as oxyethyldidiphosphone acid, nitrilotrimethylphosphonium acid, due to the interaction of complexons with the surface of metals, stabilize the passivation oxygen film, providing a degree of protection against corrosion at 95−98 % at acid dose of 10 mg/dm3. However, when the temperature rises to 50 °C, a protective effect is reduced. It was established that the use of compositions based on OEDPhA/NTMPhA and Zn/Pb/Cr ions in the range of temperatures 20−50 oC provides a degree of protection of steel from corrosion at the level of 90 %. This is explained by the formation of three-dimensional complexes of phosphonic acids with metal ions and corroded iron

New insights into the effects of silicon content on the oxidation process in silicon-containing steels

Simultaneous thermal analysis (STA) was used to investigate the effects of silicon content on the oxidation kinetics of silicon- containing steels under an atmosphere and heating procedures similar to those used in industrial reheating furnaces for the production of hot-rolled strips. Our results show that when the heating temperature was greater than the melting point of Fe2SiO4, the oxidation rates of steels with different silicon contents were the same; the total mass gain decreased with increasing silicon content, whereas it increased with increasing oxygen content. The oxidation rates for steels with different silicon contents were constant with respect to time under isothermal conditions. In addition, the starting oxidation temperature, the intense oxidation temperature, and the finishing oxidation temperature increased with increasing silicon content; the intense oxidation temperature had no correlation with the melting of Fe2SiO4. Moreover, the silicon distributed in two forms: as Fe2SiO4 at the interface between the innermost layer of oxide scale and the iron matrix, and as particles containing silicon in grains and grain boundaries in the iron matrix.

Water Vapour Effects on Wustite Scale Growth at High Temperatures

High purity iron and a low carbon, low silicon steel were oxidised at temperatures of 800 to 1200oC, in atmospheres of N2-H2-H2O and N2-O2-H2O. Scales of wüstite grew at low oxygen potentials, and of FeO/Fe3O4/Fe2O3 at high potentials. In both cases, kinetics were parabolic after an initial transient period. The iron and steel behaved similarly in O2/H2O gases, but not in H2/H2O. Weight uptake kinetics for both metals were initially linear, changing to parabolic with time as diffusion slowed and became rate-controlling [1]. Iron generally reacted faster than steel, but eventually developed parabolic kinetics. The effect of p(O2) at fixed p(H2O) on kw for iron and steel is seen in Fig. 1 to be functionally similar. However, whereas the oxidation rate of steel is strongly dependent on p(H2O), that of iron is not [2,3]. The Arrhenius plot in Figure 2 shows that activation energies for the two materials are rather similar at 157 kJ mol-1 for temperatures of 800 to 1100oC, but iron oxidises almost three orders of magnitude faster than steel. However, at 1200oC, oxidation rates are closely similar.The predictions of the Wagner model of rate control by lattice diffusion of iron vacancies is shown to be quantitatively successful for reaction of pure iron in H2/H2O. The slower rates observed for steel are attributed to defect interactions with impurity species, perhaps including a hydrogen-bearing species. Gas composition effects on the parabolic rate constant, kw , for steel can be described by the expression: kw = A p(O2)1/4 + B p(H2O)1/2 (1)where p denotes partial pressure and A, B are constants. A model based on simultaneous diffusion of singly charged vacancies on cation sites and hydroxyl ions on anion sites is shown to account for this relationship. Scaling rates in O2/H2O also increased with water vapour level, a result attributed to gas phase transport within oxide pores which were present in the scales, but absent in wüstite grown in H2/H2O. Rates for iron and the steel were the same, in each case reflecting mainly the growth of a thick wüstite layer. The lack of impurity effects on the steel oxidation is attributed to the failure of hydrogen-bearing species to penetrate the outer layers of magnetite and hematite which form in these gases.

Aluminum-silicon coatings on austenitic stainless steel (AISI 304 and 317) deposited by chemical vapor deposition in a fluidized bed

Aluminum-silicon coatings were deposited onto stainless steels AISI 304 and AISI 317. The deposition was performed at 540°C with a ratio of active gases HCl/H2 of 1/15.3; argon was used as a carrier gas. The bed of the FBR-CVD process consisted of 2.5 g aluminum powder, 7.5 g silicon powder and 90 g alumina. After the coatings were deposited, each sample was given a heat treatment to improve its mechanical properties and oxidation behavior by diffusing the alloying elements. Thermodynamic simulation was performed with Thermo-Calc software to investigate the composition of the deposited material. The coated and uncoated specimens were exposed to temperatures of 750oC in an atmosphere where the vapor was transported to the samples using a flow of N2 of 40 ml/min and 100% water vapor (H2O). The coated specimens gained little weight during the thousand hours of exposure and will thus guard against a corrosive attack compared to the uncoated substrates. In addition, the coated stainless steels show an oxidation rate with a logarithmic trend while the uncoated steel oxidation rate showed a linear trend.

Substrate metal oxidation mechanisms for the appearance of defects in enamel coatings

The dependence of the oxidation rate of steel beneath an enamel film at its firing temperatures is studied. During the firing process foci of intense oxidation of metal with pronounced dark coloration appear in individual locations on the surface of steel samples, coated with a layer of enamel melt, in air. If the melt in such a focus is enriched with variable-valence oxides to acquisition of electronic conduction, then the oxidation process propagates with constant velocity in the fused enamel along the entire surface of the metal. The propagation velocity of the oxidation process depends on the viscosity and composition of the melt.

Valve steel oxidation rate in the exhaust gases of diesel engines fueled with 5% biocomponent diesel oil

Out of the many components of four-stroke diesel engines the exhaust valves are under significant constant thermal and mechanical loads. They operate in a highly corrosive environment of hot exhaust gases. The durability of these elements is determined by the creep resistance of steel i.e. simultaneous resistance to mechanical deformations under high temperatures and the resistance of the surface to corrosive hot exhaust gases. Long term cyclic heating and burning of the exhaust valves in the exhaust gases whose main components are oxygen, carbon dioxide and superheated steam results in a simultaneous rrosion of the steel surface and core diffusion of carbon and alloy elements in the thin layer of the steel surface. In extreme operating conditions this may lead to a deformation of the exhaust valves, a reduction of the air tightness of the combustion chamber or damage or destruction of the engine. The paper discuses the results of investigations of the influence of Cr, Ni, Mn and Si on the oxidation rate of high alloy austenitic valve steel in the diesel oil exhaust gases containing 5% of biocomponents. The corrosion tests were conducted in the temperate of 973 K and 1173 K under the conditions simulating the operation of the exhaust valves in diesel engines under heavy thermal loads. Based on the conducted research significant influence of the said alloy elements on the oxidation rate of the valve steel in the exhaust gases has been observed. The tests were conducted on the engine durability test stand in Automotive Research and Development Institute BOSMAL in Bielsko-Biała.

Effect of enamel layer thickness on defectiveness of enamel coatings

The dependence of the oxidation rate of steel under a film of enamel at the firing temperatures of the enamel is examined. The size of the critical gas bubble which breaks through the enamel film during annealing is calculated and determined experimentally.

Behaviour of Aluminide Diffusion Coatings on HCM12-A Steel by Al/Ce and Al/La CVD-FBR in Oxidation.

The steam oxidation behaviour at 800°C of aluminized HCM12A ferritic-martensitic steel has been studied. The aluminization process used was CVD in fluidized bed reactor (CVD-FBR), using a reactive bed modified with Ce or La particles. The obtained coatings were mainly composed of (Fe,Cr)2Al5 intermetallic phase. Long term oxidation (1000h) behaviour of the coated HCM12A was studied in 100%H2O atmosphere. By the application of the protective coating, the ferritic-martensitic steel oxidation rate is reduced considerably because of the alternately formation of Al2O3 and Cr2O3 + (Fe,Mn)3O4 protective scales on the substrate surface due to the diffusion processes that take place during the exposure at high temperatures in combination with the aggressive environment.

Current Understanding of Steam Oxidation - Power Plant and Laboratory Experience

This review discusses key papers presented at an EPRI sponsored Workshop on “Scale Growth and Exfoliation in Steam Plant” that was held at the National Physical Laboratory (NPL) in September 2003 [1]. Additionally, some more recent developments on modelling both scale growth and exfoliation are described. Scale exfoliation in the steam circuit of power plant boilers leads to tube blockages and, further downstream in the power plant, to erosion of the steam turbine blading; and this can have serious consequences for plant performance. Factors controlling this behaviour are reviewed. These include the thermochemistry of oxide formation as a function of operating conditions, scale microstructure and scale growth rates. It is well known that the oxidation rate of steels in steam is about an order of magnitude greater than that in air or oxygen, but the mechanism responsible for this increased rate is still unclear. Various hypotheses, which consider transport of volatile species through cracks and pores, diffusion of OH - or protons and direct access of steam to the metal oxide interface, are proposed to account for the increased rates of reaction in steam compared with air. Modelling exfoliation of thick oxide scales is considered in a number of ways. The basis of the original model by Armitt et al [2] has been extended and further developed. A popular approach is to assume that an oxide layer develops through-thickness cracks when a critical tensile stress (the oxide strength) or strain (the oxide strain to failure) is encountered. Another approach applies fracture mechanics principles to defects that are assumed to exist in the oxide layer, although there is great uncertainty regarding the relevant defect size distributions that control behaviour. A third lower bound (and conservative) approach is to consider the energetics of steady state through-thickness cracking that involves the fracture energy for through-thickness cracking and avoids the difficult issue of needing to know the defect size that initiates through-thickness cracking. Additionally, the need to incorporate kinetics of scale growth into the developing exfoliation models is briefly discussed.

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.

Effect of viscosity on lubricating and protective action of a glassy melt on hot rolling of 30X?CA steel

Variation of the viscosity of molten glasses xNa2O ⋅ yCaO ⋅ zB2O3 ⋅ nSiO2 in a temperature range of 1300–1700 K and the effect of the viscosity and Na2O content on the steel oxidation rate are considered.

Oxidation of Steel 30KhGSA in Borosilicate Melt Containing Iron Oxides

The kinetic specifics of the oxidation of alloyed steel under a protective layer containing iron oxide are considered. The dependence of the steel oxidation rate on the concentration of Fe2O3 in the melt is experimentally determined.