Papers by Keyword: Alloying Element

Abstract: The addition effect of Mn alloying element on the oxide growth behavior of 800H nickel-based alloy has been study in this paper. The alloy was experienced a cyclic oxidation at 900 °C. The cyclic oxidation test was carried out at oxidizing temperature for one hour followed by cooling at about 200 °C for 20 minutes for each cycle. The test samples were exposed to the cyclic condition up to 150 cycles. The oxidized samples of selected cycles were characterized in term of oxidation kinetic, phase analysis using x-ray diffraction (XRD) spectrometer and oxide scale morphology in plan and cross-sectional view by using scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) spectrometer. As a results, the oxidation kinetic exhibited a weight gain pattern as the exposure cycle increase. Several protective oxide phases which are Cr₂O₃ and MnCr₂O₄ oxides were formed. In addition, continuous oxides scale was formed on the sample surface with evidence of Cr-Mn and Cr-rich oxide as detected by EDX analysis.

Abstract: The study on solution treated Fe-40Ni-24Cr Ni-based alloy on the isothermal oxidation has been investigated. The solution treatment process has been done at two temperatures, which are 1100°C and 1200°C. The alloys were soaking for 3 hours, followed by rapid cooling using water cooled. The solution treated Fe-40Ni-24Cr Ni-based alloy were experienced an isothermal oxidation test at 700°C for 500 hours exposure time. The effect of Nb alloying element on the oxide growth behavior has been characterized in termed of plan and cross sectional view using scanning electron microscope with energy dispersive x-ray spectrometer. As a results, good protective oxide scale has formed on the fine grain solution treated sample with homogeneous and dense oxide structure. On the other hand, coarse grain solution treated sample demonstrated an oxide exfoliation after 500 hours exposure around the overgrown Nb-rich oxide precipitate area, hence indicating poor oxidation protection.

Abstract: In this research, a 800H Ni-based alloy was experienced a solution treatment procedure at two different temperatures. The solution-treated alloys were undergo a high-temperature oxidation under isothermal conditions at 500°C for 500 hours in laboratory air. The alloy was characterized using OES, XRD, SEM and FESEM equipped with an EDX spectrometer. It was found that the solution-treated alloy at 950°C produced a small grain size, and alloy treated at 1100°C produced a large grain size. The XRD results show that various oxides phases were detected. The oxidation kinetics followed the parabolic rate law indicating the oxide was formed based on diffusion-controlled oxide growth rate. The alloys with small grain sizes exhibited a lower oxidation rate, hence have excellent oxidation resistance. This is due to the accessibility of the high ion diffusion route through the grain boundaries of small-grained alloy and thus permits the speedy establishment of the initial oxide layer. Uniform oxide scale formed on a small-grained oxidized sample with visible overgrow discrete oxide particle comprised of Ti-rich oxide. The large-grained oxidized sample indicates evidence of oxide exfoliation indicating poor oxidation protection.

Abstract: During low-temperature annealing, the segregation of the alloying element leads to a strong enrichment of the surface layer, causing a rearrangement of the surface electron structure. This change in the electron structure is manifested in the characteristic energy loss spectra. Annealing of single crystals at 400–500 K leads to an increase in the density of surface electron states. As shown by the calculations of the surface potential using experimental data on the temperature dependence of the surface concentration, dopant segregation causes a linear increase in the surface potential.

Abstract: This chapter primarily reviews the nature of water vapour when it presents in bulk gas. The change in a ratio between water vapour and corresponding dissociated hydrogen, which determine the thermodynamic stability of the oxide formation, is analysed when the oxidation kinetics are linear and parabolic. When water vapour reaches the solid/gas interface, chromium species volatilisation and oxidation controlled by surface reaction can occur. The adsorbed water vapour can be further incorporated into the oxide possibly in the form of hydrogen defects. The role of these defects on altering the defect structure of the oxide is discussed. Finally, characteristics of the oxide scale on stainless steels formed in the atmosphere containing water vapour are reviewed.

Abstract: This chapter introduces stainless steels and their classification for the high temperature applications. The enabling theories for the high temperature corrosion i.e. thermodynamics and kinetics are further addressed. The basic concept of thermodynamics is given and the stability of the formation of thermal oxide on stainless steel is exemplified. Types of defect in the oxide and Fick’s first law for the diffusion of defect though the oxide are introduced. Oxidation kinetics is explained with the emphasis on the derivation of the parabolic rate law.

Abstract: 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.

Abstract: Heat-resistance (scale resistance) is the steel corrosion fastness in dry gas at high temperatures. At the temperatures over 570 °С, the ferrous alloys oxidize, as ferric oxide (wustite) with simple cubic lattice appears on the metal surface. Such oxide lacks oxygen atoms (omission solid solution) and does not interfere with the diffusion between metal and oxygen. As a result of this process the brittle oxide-scale develops and the loss of metal increases. In order to increase the heat-resistance of steel, different alloying elements are included into its composition, forming oxides with the tight structure of crystal lattice. In this paper we’ve investigated the heat-resistance of some structural steels and analyzed their corrosion resistance in the high temperature aggressive environments of chemical productions.

Abstract: The present study was undertaken to investigate the effect of alloying additions and aging parameters (time and temperature) on the hardness and machinability of Al-Si alloys. Hardness, drilling force and moment and number of holes drilled/tool measurements were carried out on specimens prepared from grain refined, Sr modified and heat treated Al-Si alloys. Aging treatments were carried out for the as solution treated (SHT) specimens (after quenching in warm water). The specimens were aged at different conditions; artificial aging was carried out at 180˚C, 200 ˚C and 220˚C for 2 and 5 h. Hardness, drilling force and moment and number of holes drilled/tool as a function of different metallurgical parameters (i.e. %Si content, %Mg content, heat treatment parameters (time and temperature), Cu-intermetallics surface fraction and Fe-intermetallic surface fractions) are analyzed to acquire an understanding of the effects of these variables and their interactions on the hardness and machinability of heat treated Al-Si alloys.

Abstract: In modern society, due to the improvement of industrialized and development of marine economy, pollutants in the atmosphere and water aggravation corrosion of steel structure, annual worldwide economic losses due to corrosion is astronomical figures. Hence, atmospheric corrosion resistance of weathering steel has a broad market prospect. In addition, it also has excellent mechanics, welding and other properties. This paper mainly discusses the structure, production process, performance organization and the effect of various alloying elements on weathering steel.