Research Article
Boriding kinetics of C35 steel: estimation of boron activation energy and the mass gain
- B. Bouarour, M. Keddam, O. Allaoui, O. Azouani
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- Published online by Cambridge University Press:
- 23 April 2014, pp. 67-73
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The present work is concerned with the determination of boron activation energy in the C35 steel and an estimation of the mass gain generated by the boriding treatment. The boride layers are produced by the pack-boriding method on the C35 steel in the temperature range of 800−1000 °C for a treatment time ranging from 0.5 to 8 h. The presence of both FeB and Fe2B phases was confirmed by the X-ray diffraction technique and by a microscopic examination of the cross-sections of borided samples. The boron activation energy was evaluated as 153.1 kJ mol-1 in the temperature range of 800−1000 °C. This value of energy is in agreement with the literature data. The mass gain was measured by weighing the samples before and after the boriding treatment by the weighing technique. The evolution of mass gain as a function of temperature and time can be described by a parabolic law. Finally, an iso-thickness diagram was established to be used as a tool to optimize the boride layers thicknesses according to the industrial application.
Measurements of heat loss and its distribution for the COREX-3000 ironmaking process
- W. Shen, S.-L. Wu, K.-P. Du, M.-Y. Kou, Y. Sun
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- Published online by Cambridge University Press:
- 23 April 2014, pp. 75-84
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The accuracy of the parameters is of great importance in the calculation and simulation of the COREX process. Therefore, it is necessary to measure some parameters, especially the heat loss and its distribution, which have not been reported before. Based on the characteristics of the two sets of the Baosteel COREX-3000 process, a method and standard are established for the heat loss and its distribution. Then the heat loss and distribution are calculated based on the measured parameters. The results show that the total heat loss of the two COREX processes is 495.4 MJ/tHM and 413.7 MJ/tHM. The heat loss caused by cooling water accounts for more than 93% of the total heat loss while the heat loss of furnace shells is less than 7%. The main heat loss caused by cooling water takes place at the tap hole zone, which is also the part of the COREX system with the most heat loss Its heat loss is about 30% of the heat loss caused by cooling water and 28% of the total heat loss of the COREX system. The main heat loss of furnace shells takes place at the dome of the melter-gasifier and the reducing gas entrance position of the shaft furnace, where the heat loss accounts for nearly 90% of the heat loss of furnace shells. It is also found that the energy utilization efficiency of the 1# COREX system is much lower than that of the 2# COREX system after comparison.
Tribological properties of Brass-graphite composite
- Zohair Sarajan
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- Published online by Cambridge University Press:
- 02 May 2014, pp. 85-93
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Brass-graphite composites were fabricated by adding graphite/Cu/Zn compact powder usingthe stir-casting technique and their tribological behavior against a brass disk was studied under simulated actual conditions, in comparison with the common graphite/brass composite The tribological properties of the brass-graphite composite were compared with different percentages of graphite in the structure using the pin-on-disk method. The experimental results showed that the 7−9 wt.% graphite creates a better wear resistance in high-pressure applications. Continuous Zn layers successfully covered the surface of the graphite particles, which could contribute to the improvement of interfacial wettability between graphite and brass. In this study, brass-graphite composites containing 8.4 ~ 15 wt.% of Ni-coated graphite were fabricated. The friction coefficient of composites decreased with increasing graphite content. The wear resistance was improved by the addition of Ni-coated graphite but degraded at high graphite content. The results indicated this composite showed much better mechanical properties and tribological properties in comparison with brass. The composite with 11.7 wt.% nickel-coated graphite showed the best tribological properties.
The behavior of arsenic trioxide in non-ferrous extractive metallurgical processing
- M. Sadegh Safarzadeh, J.D. Miller, H.H. Huang
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- Published online by Cambridge University Press:
- 14 May 2014, pp. 95-105
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Study of the acid bake-leach process has shown potential advantages for the treatment of enargite (Cu3AsS4) concentrates. Among the most important advantages of the process is the transformation of enargite to water-soluble copper sulfate and highly soluble arsenic trioxide (arsenolite). Because arsenic is retained in the condensed phase during the baking, the vapor pressure of arsenic trioxide should be estimated at typical baking temperatures (e.g. 473 K). To that end, the vapor pressure of As4O6 (g) was estimated under the baking conditions based on published thermodynamic values. The vapor pressure of arsenolite at 473 K was found to be approximately 9.03 × 10-4 atm. Based on the linear regression analysis of the published vapor pressure values for arsenolite in the temperature range 366−579 K, the equation for the best fit line was found to be as follows, with a correlation coefficient of 0.9973:
logPArsenolite (atm) = (-5780.7)/(T (K))+9.16.
Available information on arsenic trioxide does not allow a definite conclusion regarding the arsenolite/claudetite transformation temperature and their exact melting points. However, the transition temperature has been reported to be in the wide range of 240−506 K in different references. Furthermore, the thermodynamic information concerning arsenolite/claudetite is sparse and at times not consistent. An effort has been made in this paper to compile the most reliable thermodynamic information for arsenic trioxide (arsenolite and claudetite).
Influence de la vitesse de refroidissement sur la microstructure et la trempabilité des boulets de broyage
- A. Sadeddine, S. Aissat, M.A. Bradai, A. Benabbas
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- Published online by Cambridge University Press:
- 16 May 2014, pp. 107-117
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Les boulets de broyage ou de concassage sont des éléments de broyeurs utilisés dans les cimenteries; ils exigent une résistance à l’usure élevée sous l’action de produits abrasifs lors de la transformation de la roche en fines particules de taille inférieure au millimètre. Les traitements thermiques constituent une étape essentielle pour l’élaboration du boulet. Ils permettent d’obtenir des duretés et une résistance à l’usure convenables. Les analyses structurales et microstructurales par diffraction X et microscopie électronique à balayage permettent de comprendre leurs corrélations. Dans cet objectif, nous avons étudié l’influence de quelques facteurs déterminants dans ces traitements. Les facteurs considérés dans le présent travail sont : la température d’austénitisation (950 °C et 1050 °C), la sévérité du milieu de trempe (refroidissement à l’air ventilé et à l’huile) et le diamètre des boulets (boulets de diamètre 50 et 70 mm). Les résultats obtenus ont révélé la présence de carbures de type Cr7C3 répartis dans une matrice martensitique ou ferritique et que le taux de l’austénite présent dans les boulets trempés à l’air ventilé est inférieur à celui des boulets trempés à l’huile. La température d’austénitisation et la taille des boulets influent sur la trempabilité. En effet, l’écart de dureté entre la surface et le cœur des boulets de diamètre 50 et 70 mm chauffés à 1050 °C, refroidis à l’air ventilé et à l’huile, est plus important que celui des boulets correspondants chauffés à 950 °C. Une augmentation de la taille des boulets conduit à la diminution de la trempabilité notamment les boulets de diamètre 70 mm chauffés à 1050 °C.
Selection of vacuum pump system for steel degassing
- W. Burgmann, T. Gustafson, J. Davené
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- Published online by Cambridge University Press:
- 03 June 2014, pp. 119-128
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Steam ejector vacuum pumps (SVPs) are mainly used on larger melt sizes up to 350 t in integrated steel plants because of the availability of steam. The use of dry operating mechanical vacuum pumps (MVPs) for steel degassing has made a tremendous step forward in the past 10 years but is still confined to melts below 150 t while its progress towards larger melt sizes is not completed. Besides the consideration of investment and operating costs there is no restriction in using any type of modern vacuum pump system for all vacuum processes and plant designs. Both systems fulfil all metallurgical requirements. Considering the significant savings in operating cost offered by MVP systems it is worth reconsidering the efforts for reducing air leaks, the use of protective gases and pressure losses between the pump set and the metallurgical reaction vessel. Both systems have made progress in energy optimising but the MVPs have a striking energy advantage. Only the overall costs should be considered, including those necessary to meet emission constraints and safety standards, and only the pressure prevailing at the reaction vessel is to be considered when comparing vacuum pump systems. Also, the means and use of dust abatement systems should be reconsidered since they offer cost savings by reducing the frequency of cleaning, less wear, little sludge handling and the significantly lower design suction capacity of SVP systems. The SVP mass flow need is to be corrected by a special coefficient before being applied to the volume conveying MVPs. Depending on the operational pressure required for the pump design, MVP systems can reach the same performance at the reaction vessel with much less mass flow capacity than that needed by a SVP system.