Behavior Of Oxide Scales Research Articles

Growth behavior and microstructure of oxide scales grown on WSi 2 coating

Growth behavior and microstructure of oxide scales formed on WSi 2 coating by isothermal oxidation between 800 and 1300 °C were investigated. At and below 1000 °C, lamellar WO 3 embedded in the amorphous SiO 2 matrix was formed from the direct oxidation of WSi 2 by inward diffusion of oxygen through short-circuit paths. At the intermediate temperatures between 1100 and 1200 °C, fastest oxidation rate was observed. The oxide scale consisted of the spheroidal WO 3 particles embedded in the amorphous SiO 2 matrix. WSi 2 was initially oxidized to form W 5Si 3 and SiO 2 followed by the oxidation of W 5Si 3 to form WO 3 and SiO 2 phases. At 1300 °C, oxide scale consisted of continuous cristobalite SiO 2 and W 5Si 3 layer underneath, leading to the slowest isothermal oxidation behavior. It is concluded that the interplay of phase stability of WSi 2, defect formation process, and viscosity of SiO 2 gives rise to unique and complex oxidation behavior especially at intermediate temperatures.

Modelling of Oxide Scale Evolution in Hot Rolling and Descaling

Oxide scale behaviour in thermomechanical processing has been the subject of intensive research for several years that allowed developing a finite element (FE) based model to simulate a range of events of relevance to the process and the surface quality of the hot rolled product. A range of experimental techniques have also been developed, each providing a partial insight. An overview of this research is presented in the sequence of rolling and finishing with descaling. The model has been extended to provide the basis for detailed numerical investigations of the roll/stock interface behaviour during multi-pass hot rolling operations. The modelling techniques have been used for providing design criteria for AISI430 ferritic stainless steel scale failure during bending. Modelling of near surface deformation during rolling of aluminium alloys is under consideration.

Deformation and Fracture Behavior of Surface Oxide Scale on Fe-13Cr Alloy in Hot-Rolling Process

The behavior of the surface oxide scale on steel products during hot rolling process influences the surface properties of final products. To investigate the deformation and the fracture behavior of surface oxide scale of Fe-13Cr alloy, a hot rolling test was carried out. The oxide scale rolled out was observed in detail by using TEM. The specimen was hot-rolled after oxidation at 1100 for 90 minutes in air. The hot rolling tests with two conditions (. The hot rolling test of the outer scale {=whole layer scale} , . The hot rolling test of the inner scale that removed the outer scale) were carried out. The rolling reduction rate was 25, 44, 58, and 68%. The outer scale was composed of Fe2O3 and F3O4, and the inner scale was composed of Fe3O4, FeCr2O4, and a small amount of Fe2SiO4. Fe2SiO4 formed along the grain boundaries of the other oxides (Fe3O4, FeCr2O4) was observed by TEM. In the test , Fe2O3 of the outer scale was pulverized to fine particle that looks like red powder, and Fe3O4 of the outer scale was cracked by hot rolling. A ductility-like behavior was observed in the inner scale (Test ). That is, it was found by the SEM observation that porosity and micro cracks of the surface oxide disappeared gradually according to the increase in the rolling reduction. It was thought that the porosity and the micro cracks eased the compression stress caused by hot rolling. In the case of high reduction rate, FeSi2O4 ,which is a low melting point oxide, formed on grain boundary caused grain boundary slipping. When the rolling reduction is very high, plastic deformation by dislocation occurred in Fe3O4 and FeCr2O4. However, these oxides were broken, when their plasticity would not be able to accept considerably high rolling reduction.

Oxide scale behaviour on aluminium and steel under hot working conditions

Elevated temperature exposure to air of aluminium alloys and steel during thermomechanical processing inevitably results in oxide scales forming on the surface. With carbon and low alloy steels, the oxide scale is distinct and relatively easily removed from the surface in between hot rolling passes or when cooling down after rolling. The scale can behave in a brittle or ductile manner. The oxide scale that forms on aluminium alloys is much more tenacious. There is also strong evidence of the plastic deformation which results in intermixing of the surface metal and oxide scale, leading to a complex subsurface layer. This paper contrasts these two metals’ behaviour, based on laboratory measurements and computer-based simulations

Modelling the Behaviour of Oxide Scale in Hot Rolling

Oxide scale behaviour in thermomechanical processing has been the subject of intensive research for several years that allowed development of a finite element (FE) based model to simulate a range of events of relevance to the process and to the surface quality of the hot rolled product. Oxide scale failure is predicted taking into account the main physical phenomena such as stress-directed diffusion, fracture and adhesion of the oxide scale, strain, strain rate and temperature. The most critical parameters for scale failure are measured during modified hot tensile testing and depend on the morphology of the particular oxide scale, scale growth temperature, and are also very sensitive to the chemical composition of the underlying metal. The work integrates finite element analysis with a range of experiments each to provide partial insight into oxide fracture, friction, heat transfer, pick-up and descaling, amongst others. An overview of this research is presented, revealing a variety of phenomena of considerable technological importance.

Mechanical behaviour of iron oxide scale: Experimental and numerical study

The paper addresses the identification of constitutive parameters of thick, brittle layers on metal substrates. Application is to the iron oxide behaviour during hot rolling processes of steel, where oxide scale breaking and embedding is one of the major causes of surface defects. Contact management of a FEM software has been adapted in order to address the transitions corresponding to transverse oxide fracture, along with two other mechanisms, namely delamination and interfacial stick/slip. It is applied to the hot strip rolling process to show pre-bite cracking and its consequences (“micro-extrusion” of the metal). To approximate the stress state prevailing at roll bite entry, the Four-Point Hot Bending Test (4PHBT) has been selected for the measurement of oxide properties. Oxidation is made in situ in the test rig under conditions similar to a hot strip mill (HSM) environment. Comparison of load-deflection curves for oxidized and non-oxidized samples allows the mechanical properties of the oxide to be determined. Above a critical temperature T c – around 700 °C, but depending on strain rate – the oxide is ductile (with a very narrow plastic strain range, ɛ p < 10 −2) and elastic-viscoplastic (EVP) constitutive parameters are identified numerically. Below T c, brittleness is manifested by an array of transverse, through-thickness cracks. Acoustic emission (AE) has been used to help detect the onset of fracture, while numerical simulation gives the critical fracture stress at the corresponding point of the load-deflection curve. Results for four low carbon steel grades are compared.

Isothermal oxidation behavior of two-phase TiAl–Mn–Mo–C–Y alloys fabricated by different processes

The isothermal oxidation behavior of two-phase Ti–46.6Al–1.4Mn–2Mo–0.3C–0.3Y based alloys in synthetic air at 800 and 900 °C was investigated. The main emphasis was focused on the effect of microstructures obtained by different processes of extrusion, melting and hot rolling, i.e. fully lamellar, nearly lamellar and duplex. On the exposure for 350 h at 800 °C, the growth rate and the spallation behavior of oxide scales of the alloys depended strongly on the fabrication process. The extruded alloy with a fine fully lamellar microstructure showed an excellent oxidation resistance due to the lowest mass gain and strong adhesion of the scale to the substrate, and Y-addition was effective in improving oxidation resistance because of its oxygen-scavenging effect in EPM processing. However, the overall oxidation process was dominantly controlled by the beneficial effect of the Mo-addition in the melted alloy due to the doping effect and formation of Mo-rich Al-depletion layer close to the substrate. The rolled alloy with the duplex microstructure greatly accelerated the oxidation rate because of a high volume fraction of α 2-Ti 3Al. At 900 °C, the melted alloy showed an excellent oxidation resistance during 350 h exposure. The oxidation rate and the spallation resistance of oxide scales did not depend strongly on the microstructure for the extruded or the rolled alloy. The poor spallation resistance of the oxide scales in the extruded alloy was probably related to thicker Mn-containing scales. Neither Mo-rich layer nor Y-rich zone in the oxide scales in the rolled alloy was observed at two exposure temperatures as a result of fast oxidation rate of the scale.

Long-Term, Cyclic Oxidation Behaviour of Alumina- and Chromia-Forming Alloys

The oxidation resistance behaviour of a number of surface-treated FeCrAl commercial alloys and some model alloys of well-defined composition, incorporating a range of reactive elements in trace amounts, has been studied under thermal cyclic conditions in air with and without additions of water vapour. Additions of reactive elements such as Zr, La, Y, Hf modify the oxidation resistance behaviour of FeCrAl-alloys by improving the scale adherence and consequently may extend the lifetime of FeCrAl steels. The presence of the water vapour can affect oxidation in a number of different ways. Our results may indicate that high content of water vapour can cause the lives of such alloys to be decreased. This work forms part of a larger European-funded project to evaluate physical properties, microstructural features, oxidation/corrosion resistance and lifetime improvement. The correlation between alloy parameters and lifetime; as well as the modeling of oxide scale behaviour as function of cycling conditions is also studied.

Fracture behavior of steam-grown oxide scales formed on 2–12%Cr steels

Fracture behavior of steam-grown oxide scales formed on 2–12%Cr steels

Fracture behavior of steam-grown oxide scales formed on 2–12%Cr steels

A room temperature three point bent-beam test was conducted for preoxidized coupon specimens of ferritic 2%Cr (T22), 9%Cr (T91), and 12%Cr (T122) steels in order to examine the fracture/spalling behavior of steam-grown oxide scale. Test specimens were reacted with atmospheric 100% steam at 550–750°C for 1000-4800 h. Oxide scale thickness of the tested steels was 15–1150 μm for the 2Cr steel, 30–450 μm for the 9Cr steel, and 25–60 μm for the 12Cr steel. External tensile strain of up to 1.86% was loaded to each preoxidized specimen surface and the fracture/spalling behavior of steam-grown oxide scale was investigated visually and by microscopic observation. For the 2Cr steel, scale greater than 380 μm exfoliated without applying any external strain. For thin-scaled specimens of 15–20 μm thick, a tensile strain of 0.25% and more caused through-scale cracking perpendicular to the scale/metal interface. For these specimens, cracks along the scale/metal interface also resulted, and the oxide scale became separated from the base metal. For the 9Cr steel, scale exfoliation due to cooling was not prominent even for specimens with 450 μm thick scales. External tensile strain of 0.91% and 1.86% caused through-scale cracking to the oxide scale, but the scale/metal interface remained intact and scale exfoliation did not take place. This was the same for the 12Cr steel. Clearly, spalling resistance of the steam-grown oxide scale was significantly higher for the 9Cr and 12Cr steels than for the 2Cr steel.

Growth behavior and microstructure of oxide scale formed on MoSi2 coating at 773 K

Growth behavior and microstructure of oxide scale formed on MoSi2 coating by cyclic oxidation testing in air at 500 °C were investigated using field emission scanning electron microscopy, cross-sectional transmission electron microscopy, glancing angle x-ray diffraction, and x-ray photoelectron spectroscopy. MoSi2 coating was prepared by chemical vapor deposition of Si on a Mo substrate at 1100 °C for 5 h using SiCl4–H2 precursor gas mixtures. After the incubation period of about 454 cycles, accelerated oxidation behavior was observed in MoSi2 coating and the weight gain increased linearly with increasing oxidation cycles. Microstructural analyses revealed that pest oxide scale was formed in three sequential processes. Initially, nanometer-sized crystalline Mo4O11 particles were formed with an amorphous SiO2 matrix at MoSi2 interface region. Inward diffusing oxygen reacted with Mo4O11 to form Mo9O26 nano-sized particles. At final stage of oxidation, MoO3 was formed from Mo9O26 with oxygen and growth of MoO3 took place forming massive precipitates with irregular and wavy shapes. The internal stress caused by the growth of massive MoO3 precipitates and the volatilization of MoO3 was attributed to the formation of many lateral cracks into the matrix leading to pest oxidation of MoSi2 coating.

Effect of Hot Rolling Conditions on Deformation Behavior of Oxide Scale at High Temperatures

Effect of Hot Rolling Conditions on Deformation Behavior of Oxide Scale at High Temperatures

Hot-Rolling Experiments on Deformation Behaviour of Oxide Scale

A new test technique developed by the authors allows to investigate the brittle-ductile behaviour of oxide scale during the hot-rolling process. Sandwich specimens were pre-oxidised and then welded so as to be gas-tight. A micro-alloyed deep-drawing quality steel (interstitial free steel) and a fine-grained low-pearlite structural steel served as test material. The experiments were performed at temperatures up to 1050 °C. Optical metallography was used to describe the changes of the scale layers. The method is quite good to describe the results qualitatively whereas it is rather difficult to derive quantitative results.

Cracking behavior of oxide scale formed on Ti3SiC2-based ceramic

The cyclic oxidation and acoustic emission (AE) tests were carried out for studying cracking behavior of oxide scales formed on Ti3SiC2-based ceramic at 1100°C. A duplex oxide scale with an outer layer of pure TiO2 and an inner layer of a mixture of TiO2 and SiO2 was formed. The oxide scale did not spall from substrate during the cyclic oxidation at 1100°C for 360 times. However, a great number of micro-cracks penetrating whole inner oxide layer were detected. AE test showed that the oxide scale did not crack during the isothermal oxidation at 1100°C for 1 h, however, the scale cracked during the cooling stage. Comparing the growth rate and thickness between the oxide layers formed during the isothermal oxidation and cyclic oxidation, respectively, indicated that cracks in the inner oxide layer served as paths mainly for outward diffusion of titanium and for inward diffusion of oxygen, resulting in increased growth rate of the outer oxide layer. Because of entire and compact TiO2 consisted of outer oxide layer, and low thermal stress resulting from small mismatch of thermal expansion coefficients between the oxides and the substrate, Ti3SiC2 exhibited excellent cyclic oxidation resistance at 1100°C for 360 cycles.

High temperature tension tests and oxide scale failure

The mechanical failure of oxide scales in high temperature tensile tests has been investigated in the present work. The results of experimental tests and three-dimensional finite element modelling are presented. The cracking behaviour of oxide scales formed on mild steel has been studied using a high temperature tensile test technique at 800-870°C. Induction heating equipment has been used to construct a vertical cylindrical furnace. To imitate the surface conditions of the flat rolling process, a special geometry of specimens has been designed; the oxide scale forms on a gauge section with plane surfaces and a rectangular cross-section. A varying number of cracks have been detected, and the appropriate gauge geometry is defined for future investigations. A comparison between round and flat specimens is presented.

Nickel high temperature oxydation under creep loading using acoustic emission monitoring

We have studied the cracking behavior of oxide scales developed on high purity nickel single crystal during creep deformation under oxygen at 550°C. The oxide microstructure exhibits a network of parallel cracks with a constant spacing between cracks. The deterioration of the oxide scale is monitored by acoustic emission. The creep deformation mechanisms with oxide scale are investigated and compared to vacuum creep experiments. Differences in creep behavior between these two atmospheres are obvious. This study is followed by a stress relaxation analysis. The acoustic emission technique provides a large number of results for the understanding of damage of the oxide scales during creep deformation at 550°C.

RA602CA

Abstract RA602CA has a high creep rupture strength with alloying additions of titanium, zirconium, and high carbon. High chromium combined with aluminum and yttrium give the alloy a tight oxide scale and good cyclic oxidation behavior. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as creep. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, and joining. Filing Code: Ni-586. Producer or source: Rolled Alloys Inc.

Behaviour of surface oxide scale before roll bite in hot rolling of steel

Hot stalling rolling tests using mild steel slabs with thin and thick scale layers, and cold stalling rolling simulation tests using lead slabs coated with brittle lacquer layers, have been conducted to investigate the behaviour of the surface oxide scales before hot rolling. The effects of rolling reduction, temperature, scale thickness and structure, and slab geometry were examined. The experimental results indicate that the oxide scale can either adhere and deform with the parent steel, or delaminate from the parent steel, or suffer from cracking before hot rolling, depending on the hot strength of the scale and the stress status in the scale, which depend on rolling reduction and temperature, and scale thickness and structure. Therefore, the cracks observed in the oxide scales on the steel slab after hot rolling are generally the combined results of cracking before rolling and further cracking in the roll gap. On the basis of comparative analysis, the prerolling behaviour of the oxide scales in a laboratory scale rolling mill and in an industrial hot strip mill is discussed.

Modelling the boundary conditions for thermo-mechanicalprocessing - oxide scale behaviour and composition effects

It is known that better understanding of events at the tool-workpieceinterface will lead to better definition of the boundary conditions for theprocess models. The deformation of the oxide scale on the surface of steelbeing hot worked contributes to the interface complexity. This scale has acomplicated microstructure, and can deform or fracture. In hot rolling, thedeformation of the scale begins before the steel makes contact with theroll, under the influence of a tensile stress as the roll draws the metalinto the roll gap. Tension tests under controlled conditions have been usedto simulate this initial deformation and have revealed ductile and brittlebehaviour, according to the operating conditions. This behaviour is alsovery sensitive to small changes in the chemical composition of theunderlying steel. This is illustrated for two low-carbon steels. Thelaboratory observations are complemented by finite element modelling of thetensile deformation, which is capable of reproducing both ductile andbrittle behaviour of the oxide scale with the same model. The model isadjusted to mimic the effect of changing the chemical composition of thesteel.

Behavior of Oxide Scale on 9Cr–1Mo Steel Under Varying External Stresses

The effects of different external stresses on the oxidation behavior of9Cr–1Mo steel were investigated. Tensile specimens were subjected tostresses of 11, 20, 28, and 40 MPa and the oxidation behavior was studiedat a temperature of 973 K. The elongation of the specimen was determined byan extensometer. An acoustic-emission unit was employed to monitor theintegrity of the oxide scale. The oxide scale was found to undergo bucklingbefore spalling, in the case of unstressed specimens, and in the case ofthose specimens subjected to a stress up to 28 MPa. The specimen with 40 MPastress showed the development of cracks. The application of external stressup to 28 MPa (average strain rate for 28 MPa stress was1.2 x 10-7 s-1) had a beneficial effect with respectto the adherence of the oxide scale. The specimen with 40 MPa of stress(average strain rate of 5.2 x 10-77 s-1) showedsubstantial weight gain on oxidizing up to 140 hr. The unstressed specimenrevealed enhanced spallation when compared with the stressedones. Investigation by SEM revealed the spalling of the oxide scale when theduration of oxidation was higher than 70 hr at all stress levels employed inthe present investigation. Formation of cracks at 40 MPa exposed fresh areasto oxygen and caused accelerated oxidation. Analysis by energy-dispersiveX-ray spectrometry (EDS) revealed the segregation of chromium at the oxideridges. The segregation of silicon was also significant for the specimensubjected to a stress of 40 MPa. Analysis by XRD clearly revealed thepresence of oxides of chromium and iron (Cr2O3 andFe2O3) and spinel-type oxide (FeCr2O4).