Band 34, Heft 2 -

This investigation is primarily aimed to study the high temperature corrosion behavior of different cold deformed low alloy ferritic 2.25 Cr-1 Mo steel in SO 2  + O 2 environment. The isothermal corrosion study is carried out in different cold deformed specimen in SO 2  + O 2 (ratio 2:1) at 923 K for 24 hours. The scale growth and reaction kinetics are studied and the morphology of the post corroded scales are characterized in SEM, EDS and XRD. The results indicate that all the specimens (undeformed and deformed) show parabolic growth rate. Further corrosion rate increases with the increase of percentage of deformation up to 50.45%. The specimen above 50.45% deformations reveals decrease in corrosion rate with increase percentage of deformation. Finally, corrosion mechanism for the different percentage cold deformed specimens are discussed in details in this paper.

The influence of small amounts of yttrium, electrochemically deposited on the surface of four steels utilized in the production of valves in car engines, on the protective properties of the oxide scale and its adherence to the surface of the oxidized materials has been studied under isothermal and thermal cycle conditions. Oxidation measurements have been carried out at 1173 K. It has been found that yttrium addition improves considerably the scale adherence to the substrate surface, increasing thereby corrosion resistance of the studied materials.

In age-hardenable Cu–Ti alloys, cold work before aging enhances their mechanical properties and shortens the aging time for obtaining the maximum hardness. In order to discuss hardening behaviors, microstructural evolutions such as dislocation rearrangements, progress of spinodal decomposition, and subsequent precipitation from the spinodal region during aging need to be analyzed precisely. Therefore, we employed a probing method combining the small- and the wide-angle X-ray scattering methods to characterize the precipitate size and the progress of spinodal decomposition, respectively. Sideband peaks appearing adjacent to Bragg reflection peaks in the X-ray diffraction patterns of a copper matrix were analyzed to estimate the development of compositional modulations of titanium accompanied by spinodal decomposition. The results of these analytical procedures revealed that the growth rates of the spinodal region and nanometer-scales precipitates in Cu–Ti alloys are less susceptible to dislocations introduced during cold working before aging, and that dislocations introduced during prior cold working annihilate in the initial aging stage. Consequently, overaging, which is mainly induced by dislocation annihilation, in a cold-worked Cu–Ti alloy occurs after a shorter aging time than in an unworked alloy.

In this study, the effects of SiC reinforcement volume fractions on hardness, porosity and abrasive wear behaviour were examined in Al 2014-SiC (<92.3 μm) reinforced metal matrix composites (MMCs) of 3%, 6% and 12% reinforcement–volume (R-V) ratios produced by melt-stirring. Abrasive wear tests were carried out by 320 mesh Al 2 O 3 abrasive paper and a pin-on-disc wear test apparatus, under 10N, 20N and 30N load, and at 0.2 ms −1 sliding speed. The same specimens were tested by 150, 240 and 320 mesh abrasive paper at 0.2 ms −1 sliding speed, under 10N, 20N and 30N load. After the tests, the microstructures of the worn surfaces were examined with scanning electron microscope (SEM) studies and EDS analyses. Besides, the amount of hardness and porosity of the specimens were identified. It was recorded that the amounts of hardness and porosity increases as the SiC reinforcement in the composite increases. The highest amount of abrasive wear was recorded in the specimens with 3% reinforcements. It was identified that the amount of abrasive wear decreases while the SiC reinforcement in the composite structure increases by volume, and that the amount of porosity and reinforcement volume (R-V) ratio are important parameters in abrasive wear.

The failure of the boiler tubes occur due to various reasons like creep, fatigue, corrosion and erosion. This paper highlights a case study of typical premature failure of a final superheater tube of 210 MW thermal power plant boiler. Visual examination, dimensional measurement, chemical analysis, oxide scale thickness measurement, microstructural examination are conducted as part of the investigations. Apart from these investigations, sulfur print, Energy Dispersive spectroscopy (EDS) and X ray diffraction analysis (XRD) are also conducted to ascertain the probable cause of failure of final super heater tube. Finally it has been concluded that the premature failure of the super heater tube can be attributed to the combination of localized high tube metal temperature and loss of metal from the outer surface due to high temperature corrosion. The corrective actions have also been suggested to avoid this type of failure in near future.

Removal of chlorine (Cl) from the CuCl residue in the process of zinc hydrometallurgy is of great importance to improve the process economics. The current processing methods result in generation of large quantities of polluted discharge necessitating waste treatment systems. The present work attempts to de-chlorinate the CuCl residue through thermal treatment with application of microwave, towards which the effect of the major experimental factors such as roasting temperature, heating duration and particle size of samples on the process has been investigated. And the changes of Gibbs free energy (ΔG) of the dechlorination reactions are calculated which show that: 1) CuCl can react with H 2 O and air to produce CuO and HCl(g); 2) CuCl can be oxidized by air into CuO and Cl 2 would be released. The tail gas chromatography, XRD and SEM-EDS analysis results of samples before and after microwave roasting verified the thermodynamics study results. Thus, the process of dechlorination by microwave roasting technology is feasible, and the tail gas can be mainly HCl(g) and air which can be absorbed with water and produce hydrochloride easily.

Hot deformation behavior of AISI 420 stainless steel was studied under hot compression tests in the temperature range of 950 to 1150 °C and strain rates of 0.01 s −1 and 0.1 s −1 . The study indicates that higher deformation temperature makes the peak stress pronounced and the occurrence of DRX is detected by inflection point in the work hardening rate vs. flow stress ( θ - σ ) plot, irrespective of the shape of flow stress curve. Local misorientation ( M L ) was calculated to reveal the local change in the crystal orientation. The distribution of M L suggested that the process of DRX reduces the local misorientation during hot deformation. The critical stress for initiation of DRX under different deformation conditions was determined by setting the derivative of the third order polynomial to θ - σ plot. A good linear relationship between critical stress ( σ c ) & critical strain ( ε c ) and Zener-Hollomon parameter was established.

Lately, materials research has shifted to composite materials from monolithic, adjusting to the global need for light weight, low cost, quality, and high performance in structural materials. Every effort aims to develop a material which can be appropriate for various industry and machinery purpose. In the present study, a modest attempt has been made to develop cast aluminum based silicon carbide (SiC) particulate metal matrix composite (MMC) and worked upon to raise the wettability factor between the matrix and dispersion phase. Magnesium (Mg) is used as wetting agent. It works by scavenging the oxygen from dispersoids surface and thinning the gas layer around dispersoids and this is done by forming MgO or MgAl 2 O 4 or both according to concentration of Magnesium added. Mg 2 Si is the compound responsible for strengthening. The combination of aluminum and magnesium seems to have synergetic effect on wetting and give appropriate strength. All mechanical properties obtained are well correlated with microstructure obtained by Scanning electron micrograph. Differential thermal analysis (DTA) and thermo gravimetric analysis (TGA) also justified the results obtained in present investigations.

This paper highlights a case study of typical premature failure of a radiant platen superheater tube of 210 MW thermal power plant boiler. Visual examination, dimensional measurement and chemical analysis, are conducted as part of the investigations. Apart from these, metallographic analysis and fractography are also conducted to ascertain the probable cause of failure. Finally it has been concluded that the premature failure of the super heater tube can be attributed to localized creep at high temperature. The corrective actions has also been suggested to avoid this type of failure in near future.

In this study, microwave was used to treat stainless steelmaking dust containing zinc oxide. The effects of heating time, carbon content and zinc oxide content on the removal efficiency of zinc oxide and the reduction efficiency of iron oxide were investigated. Experimental results show that, for the sample with 16% (mass percent, the same below) graphite heated for 10 minutes by 10 kW power microwave, the removal efficiency of zinc oxide is between 80% and 90% and the metallization ratio of iron oxide is between 40% and 60%; Initial zinc oxide content has a slight effect on the removal efficiency of zinc oxide. The results indicate microwave treatment is one of the feasible ways to process metallurgical solid waste containing the metal with low boiling point.

Self-propagating high temperature synthesis (SHS) is a very important technique for the synthesis of high technology ceramics, metals and alloys. SHS parameters of TiB 2 were carried out in this study. Mg stoichiometry as reductant, process atmosphere and addition of NaCl and MgSO 4 ·7H 2 O additives were investigated. HCl leaching was applied to SHS products to purify their TiB 2 contents. Stoichiometrically 100% Mg addition ratio and Ar atmosphere were determined as the optimum parameters. NaCl addition was also positively affected the specific surface area values. 11.78 m 2 /g specific surface area value was measured for 5.0% NaCl addition ratio.

Thermodynamic software (Thermo-Calc) is utilized to Q345E applicable to cryogenic flange. The aim is to study the equilibrium precipitation phases between 400 and 1600 °C, and the solubility of Nb and V in austenite. The effects of alloying elements, such as C, N, Nb and V, on these equilibrium precipitation phases are also discussed. Besides theoretical calculation, transmission electron microscopy (TEM) is used to observe these precipitation phases. The results show that main equilibrium precipitation phases are M7C3, MX#1 (Nb-rich), MX#2 (V-rich) and AlN. Among them, the MX#1 phase is composed of major elements (Nb, C, and N) and minor elements (V and Cr). For MX#2 phase, its major elements are V, C, Nb, and N, and minor element is Cr. The precipitation amount and temperature of MX#1 phase were controlled by Nb content, and little affected by the contents of C, N and V. TEM results reveal that the size of precipitation phases varied from several nanometers to more than 100 nm. Large precipitation particles belong to MX#1 phase (Nb-rich), and their morphology tends to be cubic. On the other side, the small precipitation particles are attributed to MX#2 phase (V-rich), and their morphology is spherical or elliptical. These results are consistent with the thermodynamic calculation results about phase composition and precipitation temperature of MX#1 and MX#2.

The present paper deals with the sliding wear behaviour of prealloyed chromium sintered steel (Fe-1.5Cr-0.2Mo) with graphite powder added in the amount of 0.7%. The wear characteristics, such as profilograms, wear tracks morphology and wear curves of the as sintered specimens and TiCN coating were investigated through pin-on-disk tests. The specimens were sintered in pusher furnace at the temperature of 1453 K for 2400 s in a nitrogen-hydrogem atmosphere. Dominant bainitic microstructures with evident features of plastic deformation at the worn surface were detected. The coating of the investigated prealloyed steels increases the wear resistance in comparison with the as-sintered state according to the wear curves. Microstructural and EDX analyses confirmed that delamination and oxidation wear are the main wear mechanism in wear tests.