Steels for bearings BHADESHIA, H. K. D. H
Progress in materials science,
02/2012, Letnik:
57, Številka:
2
Journal Article
Recenzirano
A casual metallurgist might be forgiven in believing that there are but a few basic types of steels used in the manufacture of some of the most technologically important engineering components, the ...rolling bearings. First the famous 1C-1.5Cr steel from which the majority of bearings are made. Its structure is apparently well-understood and the focus is on purity in order to avoid inclusions which initiate fatigue during rolling contact. Then there is the M50 steel and its variants, from which bearings which serve at slightly higher temperatures in aeroengines are manufactured, based on secondary-hardened martensite. The casual metallurgist would be wrong; there is a richness in the subject which inspires deep study. There are phenomena which are little understood, apparently incommensurate observations, some significant developments and other areas where convincing conclusions are difficult to reach. The subject seemed ready for a critical assessment; hence, this review. The structure and properties of bearing steels prior to the point of service are first assessed and described in the context of steelmaking, manufacturing and engineering requirements. This is followed by a thorough critique of the damage mechanisms that operate during service and in accelerated tests.
This paper presents an overview of the various methodologies used in the recovery of gold from secondary sources. Gold recovery is interesting due to its vast industrial applications, high market ...prices and extensively used precious metal, the sanctuary value attributed to gold during international political and economical crises, and the limited resource of this metal may explain the recent increasing gold share value. The state of art in recovery of gold from spent sources by pyrometallurgy; hydrometallurgy; bio-hydrometallurgy techniques is highlighted in this paper. This article also provides an overview of past achievements and present scenario of recovery studies carried out on the use of some promising methods which could serve as an economical means for recovering gold. The present review also highlights the used varieties of leaching, cementing, reducing agents, peeling, coagulants, adsorbents, agglomeration solvents, ion exchange resins and bio-sorbents in real situations and hopes to provide insights into recovery of gold from spent sources. Evaluation of lucrative and environmentally friendly technologies to recover gold from primary and secondary spent sources was made in this study.
► This paper has reviewed the most promising techniques for recovery of gold from spent materials, is an important subject not only from the point of monetary and high demand but also from waste treatment management. ► Although considerable research has been undertaken at a laboratory scale, most, if not all, of the technologies have proven to have limitation that hinder their widespread adoption in the gold recovery from secondary sources. ► Evaluation of productive and environmentally friendly technologies to recover gold from primary and secondary spent sources was made in this study.
Vanadium, as one of the important rare elements, is used mainly to produce certain alloys. Stone coal is an important vanadium-bearing resource in China and the gross reserves of vanadium in stone ...coal accounts for more than 87% of the domestic reserves of vanadium. Hence, much attention has been paid to research on extracting vanadium from stone coal. The traditional high salt roasting-water leaching (HSRWL) technique is the earliest technique applied in vanadium extraction from stone coal. This technique was widely adopted by small-scale factories for extracting vanadium from stone coal, but much caustic gasses and ultra-high salinity wastewater are generated and the total vanadium recovery is low in production, which makes this technique obsolete. Although the blank roasting-acid leaching (BRAL) technique, the blank roasting-alkali leaching (BRALL) technique, the calcified roasting-carbonate leaching (CRCL) technique and the direct acid leaching (DAL) technique are all more environmentally friendly in the roasting step compared to high salt roasting, each technique has its limitations and has not been applied in large scale production until now. The lately developed technique, the low salt roasting-cyclic oxidation (LSRCO) technique, is characterized by high vanadium recovery, low pollution and strong adaptability to raw ore and has good prospect of applications. Overall, the industry of vanadium extraction from stone coal is still underdeveloped in China now and much intensive research work is needed for the economic exploitation of stone coal at large scale.
► The nature of stone coal and the occurrence state of vanadium in stone coal were determined. ► The technical details of the representative techniques of vanadium extraction from stone coal were summarized. ► The newly developed technique, the low salt roasting-cyclic oxidation (LSRCO) technique, was elucidated in details. ► The development of the technology of vanadium extraction from stone coal in future were oriented and forecasted.
Various titanium metallurgical processes have been reviewed and compared for titanium dioxide and titanium metal, mainly focusing on the future development of hydrometallurgical processes. It is ...recognised that ilmenite is becoming increasingly important due to the rapid depletion of natural rutile. Many processes are commercially used or proposed to upgrade ilmenite to synthetic rutile. Most of these processes involve a combination of pyrometallurgy and hydrometallurgy and are generally expensive.
The commercialised thermo-chemical chloride processes such as Kroll and Hunter processes are batch operations and need higher grade natural rutile or upgraded synthetic rutile and slag as the feed and the involvement of cost sensitive chlorination and thermo steps. Many improvements for the thermo-chemical processes have been made, but they hold little potential for significant cost reductions beyond current technology. The development of the electro-chemical processes for direct reduction of TiO
2 and electro-slag as feed material and
in-situ electrolysis has achieved some success. However, some challenging issues such as redox cycling, feeding, kinetics, control heat balance have to be resolved before scaling-up to commercial applications.
Direct hydrometallurgical leach processes are advantageous in processing abundant ilmenite ores, low energy consumption and produce sufficiently high quality of pigment grade TiO
2 products for a wide range of applications and major demand. Novel BHP Billiton sulphate processes have been developed to improve leaching strategies, separation of metals by solvent extraction, reduced wastes and recycling acids, and very promising for commercial applications in future. Direct chloride leaching processes have been investigated intensively, featuring purification by solvent extraction and reclaiming HCl by hydrolysis or pyrohydrolysis. Caustic leach with high selectivity and titanium dioxide nano-technology has also been developed. Further development of direct leaching ilmenite coupled with solvent extraction for titanium pigment and metal production, is recommended.
► Various titanium metallurgical processes for the production of titanium dioxide and titanium metal have been reviewed and compared including: ► Processes to upgrade ilmenite to synthetic rutile. ► Thermo-chemical Kroll and Hunter processes. ► Electro-chemical processes for direct reduction of TiO
2 and electro-slag and
in-situ electrolysis. ► Direct hydrometallurgical leach processes.
Iron and steel manufacturing is among the most energy-intensive industries. Ironmaking accounts for the major share of total energy use in steel production in integrated steel mills that use blast ...furnaces and basic oxygen furnace. Although studies from around the world have identified a wide range of energy-efficiency technologies applicable to the ironmaking process that have already been commercialized, information is limited and/or scattered regarding alternative emerging or advanced energy-efficiency and low-carbon technologies that are not yet fully commercialized. This paper consolidates available information on 12 alternative emerging ironmaking technologies, with the intent of providing a well-structured database of information on these technologies for engineers, researchers, investors, steel companies, policy makers, and other interested parties. For each technology included, we provide information on energy savings and environmental and other benefits, costs, and commercialization status. All the alternative emerging ironmaking technologies eliminate energy-intensive coke production. COREX® Process, FINEX® Process, and Coal-Based HYL Process are very promising alternative emerging ironmaking technologies because they are already commercialized, but they have very low adoption rate in the steel industry worldwide.
A hydrometallurgical process is developed to recover valuable metals of the lithium nickel cobalt aluminum oxide (NCA) cathodes from spent lithium-ion batteries (LIBs). Effect of parameters such as ...type of acid (H2SO4, HNO3 and HCl), acid concentration (1-4 mol L-1), leaching time (3-18 h) and leaching temperature (25-90 degree C) with a solid to liquid ratio fixed at 5% (w/v) are investigated to determine the most efficient conditions of dissolution. The preliminary results indicate that HCl provides higher leaching efficiency. In optimum conditions, a complete dissolution is performed for Li, Ni, Co and Al. In the nickel and cobalt recovery process, at first the Co(II) in the leaching liquor is selectively oxidized in Co(III) with NaClO reagent to recover Co2O3, 3H2O by a selective precipitation at pH = 3. Then, the nickel hydroxide is precipitated by a base addition at pH = 11. The recovery efficiency of cobalt and nickel are respectively 100% and 99.99%.
In this paper, four different steel compositions, centered on Mn as the main alloying element, are designated as candidates for Third Generation AHSS grades. The design of these steels is based on ...controlling the deformation behavior of the retained austenite. Thus, heat treatment process parameters are determined in order to obtain different amounts and morphologies of retained austenite. The evolution of the microstructure, during processing as well as deformation, is characterized by using optical, electron microscopy techniques and mechanical tests. The effect of alloy composition and processing parameters on the deformation mechanisms of these steels is discussed.
Recovery of precious metals like gold, silver, palladium platinum etc. is interesting due to its high market prices along with various industrial applications. Conventional technologies viz. ion ...exchange, chemical binding, surface precipitation etc. which been have been developed for the recovery of such metals are not economically attractive. Biosorption represents a biotechnological innovation as well as a cost effective excellent tool for recovery of precious metals from aqueous solutions. A variety of biomaterials are known to bind the precious metals including algae, fungi, bacteria actinomycetes, yeast etc. along with some biopolymers and biowaste materials.The metal binding mechanism , as well as the parameters influencing the uptake of precious metals and isotherm modeling are presented. This article provides an overview of past achievements and present scenario of biosorption studies carried out on the use of some promising biosorbents which could serve as an economical means for recovering precious metals. The present review also highlights the use of biosorbents in real situations and hopes to provide insights into this research frontier.
Highly Anisotropic Steel Processed by Selective Laser Melting Niendorf, Thomas; Leuders, Stefan; Riemer, Andre ...
Metallurgical and materials transactions. B, Process metallurgy and materials processing science,
08/2013, Letnik:
44, Številka:
4
Journal Article
Recenzirano
Odprti dostop
For additive manufacturing of metals, selective laser melting can be employed. The microstructure evolution is directly influenced by processing parameters. Employing a high energy laser system, ...samples made from austenitic stainless steel were manufactured. The microstructure obtained is characterized by an extremely high degree of anisotropy featuring coarse elongated grains and a 〈001〉 texture alongside the build direction during processing. Eventually, the anisotropy of the microstructure drastically affects the monotonic properties of the current material.
Worldwide bauxite residue disposal areas contain an estimated 2.7
billion
tonnes of residue, increasing by approximately 120
million
tonnes
per
annum. The question of what to do with bauxite residue ...arose with the development of the Bayer process for alumina refining and the recognition that it generated a large amount of waste material. In the subsequent 120
years, residues have been primarily disposed into long-term storage, with a wide range of industry practice depending on local circumstances. Ideally this residue would be utilized as an industrial by-product for other applications, leading to a zero waste situation. Despite over 50
years of research and hundreds of publications and patents on the subject, little evidence exists of any significant utilization of bauxite residue. In this review of public domain information the reasons are examined, future opportunities are identified, and a way forward is proposed. All avenues of residue “re-use” (or more appropriately “use”) are considered, but emphasis is on the few highest volume uses of lowest risk. Utilization is defined as taking the residue in some non-hazardous form (as a by-product) from the alumina refinery site and then using it as feedstock for another distinct application. Although residues from different bauxites have generic similarities, their specific make-up and residue location can influence their suitability for a given type of use. There are four primary reasons for inaction on residue use: volume, performance, cost and risk, with the last two probably being paramount. In terms of cost there are better options for raw material input from virgin sources (lower cost for better grades) that do not come with the same perceived risks as bauxite residue. The risks are composition based (technical and community perception) and relate to: soda, alkalinity, heavy metals and low levels of naturally occurring radioactive material (NORM). Amongst the outcomes of this review are priority research recommendations to address the knowledge gaps identified that, amongst other factors, are impeding the implementation of residue use. This is the second in a series of four related reviews examining bauxite residue issues in detail.
►Review of options for utilization of bauxite residue. ►Over 50
years of research, hundreds of patents, no significant utilization. ►Four primary reasons for inaction on residue use: volume, performance, cost and risk. ►Zero waste out-come from value recovery very unlikely. ►Series of priority research recommendations made.
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