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By Xiping Chen, Wangxing Li, Jiemi Zhou

"Desulfurization methods suitable for anode-grade petroleum coke (coke for short) used in primary aluminum industry are coke desulfurization during calcination, desulfurization in soakage and desulfurization in mediums. Coke desulfurization during calcination is discussed in this paper. Influences of calcination temperature, holding time and coke granularity on coke desulfurization were discussed. Experimental results show that calcination temperature has a remarkable influence on coke desulfurization. When the temperature is high enough desulfurization ratio of coke can reach 85% only by calcination. Holding time has a definite influence on coke desulfurization, but desulfurization ratio is low at the temperature of 900~1300°C. The influence of holding time is obvious when calcination temperature surpasses 1400°C. The influence of coke granularity is smaller compared with calcination temperature and holding time.IntroductionPetroleum coke is main raw material for carbon anode in primary aluminum industry, and its weight percentage in carbon anode is about seven percent. Green coke can not be directly used for anode production because of its immanent moisture and volatiles. Green coke must be calcined in order to meet the request of anode production. Calcination is a heat-treatment process during which green coke is heated to a given temperature to remove volatiles, moisture and some sulfur. Real density, strength, electrical conductivity and anti-oxidation ability of petroleum coke can be improved by calcination and calcined coke can be received [1, 3, 4]. Sulfur in calcined coke finally goes into carbon anode. During baking or aluminum smelting, the sulfur in anode ultimately changes into SO2 and emits from anode into the atmosphere. Excess SO2 easily leads to acid rain which brings heavy pollution to the environment [1, 2]. With the development of Chinese aluminum industry, consumption of anode-grade petroleum coke increases year by year, the total consumption in 2007 surpassed 4.5 million tones and the yearly emission of SO2 from aluminum smelters has exceeded 270 kilotones. From 2005 Chinese government began to limit the emission of SO2 from primary aluminum industry, so desulfurization of anode-grade petroleum coke becomes more and more urgent. Some relationship need to be found and used to guide desulfurization of petroleum coke."

Jan 1, 2008

By Liang Yu, Yuhua Li, Yuanchi Dong

"High alumina slag, with alumina normally more than 15 pct, is encountered with blast furnaces in China because of high alumina/silica ratio in iron ore as well as sinter and high ash content in coke for cost reason. High alumina slag with high viscosity and high liquidus temperature would lead to higher slag volume and thereby, furnace productivity. In the present work, liquidus temperature of high alumina slag, based on Meishan factory, Baosteel China, were investigated. A liquidus temperature model was introduced in the present work based on basic physical chemistry theory and focused on the chemical composition area used in Meishan factory(pct): Al2O3 from 14 to 17.5 and MgO from 8 to 12, so that the blast furnace slag could be designed for optimum blast furnace performance.IntroductionBlast furnace slag composition[1] has very important bearing on its physicochemical characteristics which affects smoothness of operation, slag handling, coke consumption, the degree of desulphurization, hot metal productivity and its quality etc. The slag properties which affect most are liquidus temperature, viscosity, sulphide capacity and alkali capacity. Variation of these slag characteristics with composition and temperature has been a field of active researches as these its great influence on the blast furnace operation. In the early years, most of these studies were carried out over low alumina blast furnace slags with alumina normally less than 15 pct. High alumina slag was first introduced in India because of its high alumina/silica ratio iron ore as well as sinter and high ash content in coke[2]. And then this problem becomes common as higher alumina/silica ratio iron ore imported and used [2-5]. The most important problem caused by high alumina content is liquidus temperature and then viscosity of the slag.Generally speaking those reported works [2-5] investigated a pretty wide range of chemical compositions and then obtained complex model, respectively. In fact, every factory has its own interest because of different resources. For example, the Al2O3 content from 20% to 30% pct was studied in Tata Steel India [2], but it is too high for Baosteel Meishan. A very lower percentage of alumina content, 14-18 % pct, was mainly used."

Jan 1, 2008

By R. T. Hernández, I. Hilerio, A. Altamirano, M. A. Barrón

"The principal objective for finishing surfaces is to protect and/or to decorate them. This can be achieved by adding or removing material from the work surface. The addition of aggregated material is called coating or recovering. In this work, mecano-chemical techniques are investigated for surface finishing. For these techniques, barreling or polishing by the friction method will be used. These are the cleaning or finishing processes most used for great volumes of small pieces. These methods improve the surface finishing by eliminating burrs, sharp pointed, tool marks and crusts of casting. They are used to clean metallic pieces, ceramics and polymeric materials. The process is based on rubbing or friction by abrasives. The pieces are arranged in the barrel with an abrasive and an additive (water or chemical additive). The machine produces a rotating movement on the pieces. When the abrasive passes against the surfaces of the pieces, it produces an action of rubbing and impact that cleans the surfaces. The rubbing action is developed when the upper layer of the charge slides to the lower extreme when the barrel rotates. The barrel can be hexagonal or octagonal to facilitate the sliding of the charge. The barrels can be between 15 to 120 cm in length and they can have almost any diameter and velocity of rotation. There are several types of barrel: individual, multiples, and multiple compartments. The barrels are rotated using a wheel spindle or rolling pins, that the can ride horizontally or be tilted to produce an additional movement of the charge.IntroductionShot penning is a cold method in which compressive effects are induced on an exposed surface of a metallic piece, by the impact of a rain of shots directly on the surface of the metal, at great speed under controlled conditions. This differs from cleaning with the help of air, because even when shot penning cleans the surface of the metal, this function is incidental. The main purpose of shot penning is to increase the resistance of the piece to fatigue. The process has other applications: raises the tensile strength and decrease corrosion fracture."

Jan 1, 2012

By Dmitri Goljandin, Jaan Kers, Xiangjun Zuo, Lifeng Zhang, Priidu Peetsalu

"In this paper, the mechanical milling of the electronic wastes was carried out. The metal parts and plastic parts were roughly separated. The final plastic powder size could be as small as ~100 µm. Then the pyrometallurgical recycling Printed Circuit Boards (PCB) was executed. The mechanisms of thermal degradation and combustion are investigated using TG/DTA and MS. Some chemical powders, such as Na2CO3, NaHCO3, NaOH and CaCO3 are used to control the exhausted toxic gas such as Br2. Introduction Waste electric and electronic equipment (WEEE), or electronic wastes (E-wastes), has been taken into consideration not only by the government but also by the public due to their hazardous material components [1-3]. From the point of material composition, electronic wastes can be defined as a mixture of various metals, particularly copper, aluminum, and steel, attached to, covered with, or mixed with various types of plastics and ceramics [4]. Precious metals have a wide application in the manufacture of electronic appliances, serving as contact materials due to their high chemical stability and their good conducting properties. Platinum group metals are used among other things in switching contacts (relays, switches) or as sensors to ascertain the electrical measurand as a function of the temperature [5]. Table 1 [6] gives examples of the metal composition of different electronic scraps from literatures. Additionally, non-ferrous metals and precious metals content have gradually decreased in concentration in scraps. The value distributions for different electronic scrap samples are shown in Table 2 [6], where the metal price data are from London Metal Exchange (LME) (Octoebr 2007). It can be seen that for cell phones, calculators, and printed circuit board scraps, the precious metals make up more than 70% of the value, for TV boards and the DVD player they still contribute to about 40%. This indicates that the major economic driver for recycling of electronic waste in industry is from the recovery of precious metals. Behind the precious metals come copper and zinc, while Al, Pb, and Fe are less value. Recycling of electronic waste is an important subject not only from the point of waste treatment but also from the recovery aspect of valuable materials."

Jan 1, 2008

By W. G. Davenport

The paper "Copper Smelting to the Year 2000" was presented at the CIM Conference of Metallurgists in Sudbury, August 1979. That paper predicted, in part, that high matte grade, high oxygen smelting - particularly in flash furnaces - would dominate copper smelting until the beginning of the next millennium. The present paper re-evaluates that prediction and examines the changes that have occurred and will occur in copper extraction in the 1990's. Of particular interest is the question as to whether major competitors are on the horizon for flash smelting and Peirce-Smith converting. Recent results with direct-to-blister smelting, lance smelting and submerged-tuyere smelting are reviewed and their roles in future copper smelting are predicted. Requirements for H2SO4 plants which handle the off-gases from modern smelting/converting processes are also examined.

Jan 1, 1993

By C. I. A. John

The slag dump at ZCCM's Nkana Division contains some 16 million tomes of slag, deposited since the mid-1930's. The average cobalt grade of the slag is 0.65% with some areas as high as 3%. Current arisings of slag from Nkana Smelter also contain significant tonnages of cobalt. Intensive investigations were conducted in the past into methods of recovering cobalt from these slags, although none of the processes was developed to a commercial scale. The company is now working to develop a long-term strategy for ensuring the continuing production of cobalt at optimum levels, and the resource represented by the Nkana slags will be a major component in such a strategy. The present paper reviews the various processes which have been considered for recovering cobalt, both from the dump slag and from the current slags.

Jan 1, 1993

By Shichao Zhao, Ke Xie, Qijie Zhai, Wenbin Xia, Yuanyi Guo, Changjiang Song

"This paper investigated the structure evolution and phase formation ofFe-(11,13,15wt.%)Mn alloy under near-rapid solidification conditions. It is found that the area ratio of equiaxed zone in the Fe-13Mn alloy is the largest. And the primary dendrite arm spacing of Fe-(11,13,15wt.%)Mn alloy increased clearly with increasing distance from the surface. The volume percentage of HCP phase increased with increasing manganese content in the range from 11 pct to 15pct.IntroductionThe developing trend of automobile is the energy conservation, enviromnent protection, light weight, and high security. So the material would be required to the higher strength, higher plasticity and more likely to processing of automotive steel. Fe-Mn based alloys is considered as a potential material to the third generation automobile steel for its high damping performance [1], good mechanical properties [2-3], and high young's modulus [4]. And it is important that metastable HCP phases of Fe-Mn based alloys, which attracts technological interest for theoretical and experimental research [5-6].Metastable materials have been extensively used in the area of iron steels. Among various fabrication methods for high performance materials, rapid solidification is one of most popular ways to produce advanced materials by obtaining metastable phases. The solidification of metals in metastable phases provides access to an extended range of materials properties with novel properties [7]. Thus, in this work, Fe-Mn alloy metastable materials prepared by near rapid solidification is studied."

Jan 1, 2013

By T. V. Jayaraman, Kranti Kumar, Paul Praveen J., Dibakar Das, A. R. James

"Lead free piezoelectric ceramics with high piezoelectric coefficients are in great demand for sensor and actuator applications. Synthesis and characterization study of one such lead free system, barium zirconate titanate - barium calcium titanate [xBZT-(1-x)BCT] (x = 0.5), via solgel method have been carried out. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the formation of single phase BZT-BCT nanoparticles (<50 nm). The as-synthesized powders were calcined at 1000°C and the powders were pressed into cylindrical pellets. Solid-state sintering of the green pellets at 1550°C for 2 hrs resulted in single phase perovskite structure. Hysteresis loops were obtained which indicates the ferroelectric nature ofBZT-BCT. The bulk ceramic samples with the highest sintered density (~93%) were subjected to electrical poling and the piezoelectric properties ( d33, kp, & i:,) were measured. The structure and piezoelectric properties were investigated and correlated for the given composition of the BZT-BCT system.IntroductionPiezoelectric ceramics are widely used in various sensors and actuators and most of the piezoelectric ceramics, which are presently used, are lead based, which contains at least 60% lead (Pb) by weight. The critical disadvantage of these lead based piezoelectric ceramics is their hazardous effect related to the toxicity of lead, which poses a serious environmental concern starting from their processing to the disposal stage[l]. It is well known that a material to be a good piezoelectric it requires a morphotropic phase boundary (MPB) i.e. the composition induced phase transition between any two ferroelectric phases."

Jan 1, 2013

By Susana Caballero, Lourdes Yurramendi

Air Pollution Control (APC) ashes from Municipal Solid Waste Incineration (MSWI) plants need to be treated prior to landfilling due mainly to their heavy metals content. This research evaluates the capacity of the APC residues to sequester carbon dioxide, while the ash becomes stabilized for storage. It has the benefit of using two wastes, with no addition of any raw material. APC samples from different MSWI plants were treated by gas/solid accelerated carbonation at different temperatures and carbon dioxide concentrations to evaluate the residue behaviour to the process. The extent of carbonation was evaluated by means of weight gain upon carbonation and by the measurement of the final carbonate content. The APC residues were analyzed before and after the treatment in order to know their composition and their leaching behaviour according to the criteria for the acceptance of wastes at landfills established by the European Council Decision 2003/33/EC.

Jan 1, 2008

By Keith E. Forrester

This paper presents results of bench scale laboratory evaluation of a processes developed by FESI and Brookhaven National Laboratories for the extraction and recovery of Pb and other heavy metals from incinerator ash which was subsequently modified by FESI for the extraction and recovery of Pb from soils excavated from a FESI client scrap yard and battery breaking operation facility. The specific waste matrix presented within the paper is a battery acid contaminated surficial soil at 0" to 12" depth. The extraction method was found to be highly successful on the bench scale in generating a final post-extracted soil matrix which passed TCLP Pb regulatory limits and retained minimal Pb after aggressive extraction application. The paper findings at this time are brief, as a majority of the research results are currently being compiled and additional efforts are underway based upon initial screening findings.

Jan 1, 1995

By Cam T. Nhan

The potential use of coal fly ash as a construction material has been recognized for many years,. In this work, an admixture of the ash residue is investigated for use as a landfill liner. In particular, its performance as a chemical barrier to the leachate from the municipal solid waste (MSW,) is determined. The test specimens are a water compacted admixture of class F fly ash, low in calcium content, which is blended with lime dust and calcium bentonite. MSW is passed through the compacted fly ash specimens under a gravitational head. The. diffusion of elements in the leachate through this material is monitored as a function of time. The distribution profiles of the retained elements in the compacted admixture provide prediction of the long term performance of the compacted admixture directly affect the leachate diffusion rate, hence, the mobilities of the retained elements.

Jan 1, 1992

By T. C. Tseng

Austenitization is a critical stage in heat treatment of steels. The available kinetic data in reference to various initial microstructures are very limited, particularly at high heating rates. In this study, integrated experimental and computational approaches have been conducted to quantify the progress of austenitization and the attained microstructure. In particular, the study is concentrated on cementite and carbide dissolution in two steel grades. Various computational methods are developed to facilitate the study: (l) an algorithm for direct determination of kinetics data as well as progress of transformation from high-rate dilatometer tests; and (2) a suite of mesoscale computational models for particle dissolution, elements diffusion, mechanics, thermodynamic and the resulting kinetics of transfonnation. Critical exprimentation is carried out using advanced techniques in microstructure characterization, chemical analysis, and Gleeble thermal-mechanical simulator on specimens of well-controlled initial microstructures. Keynotes: Cementite, Carbite, Dissolution, Steels, Austenitization

Jan 1, 2003

By J. Michael Canty

Over 25 years of US research in Mineral Recovery from Geothermal Solutions have lead to few commercial applications. With the World Bank program in Kamchatka, Russia in September 2005 a step was taken to vitalize and coordinate the many efforts to advance economic mineral recovery systems worldwide. The US Department of Energy is helping to spur on the interest and research needed to realize the many benefits of extracting minerals from geothermal solutions. The excitement of recovery of minerals from geothermal brines has many positive angles. The economics of certain geothermal site is improved if a revenue is arrived from a sellable commodity with the geothermal power. The use of cleaner geothermal brines also improves the capable use of the brine before reinjection. We will review the history of Geothermal in the USA and the opportunities for recovery of different minerals and the markets for them.

Jan 1, 2006

By Miguel Olivas-Martínez

A two-dimensional computational model for the hot filament chemical vapor deposition (HFCVD) process to produce diamond films is presented. The model incorporates the transport of momentum, energy, and mass inside the reaction chamber of a HFCVD reactor. The gas-phase homogeneous reactions were represented by a simplified reaction mechanism. The gas-phase transport equations were coupled to the kinetic expressions representing the catalytic dissociation of the molecular hydrogen at the filament surface and the deposition rate of the diamond film on the substrate. The computational model was solved numerically by means of a commercial software. The model predictions showed good agreement with the experimental data reported in the literature in terms of both temperature and methyl concentration profiles along the filament-substrate center distance. Examples of the potential applications of the present formulation for the design and further optimization of the HFCVD reactor are discussed.

Jan 1, 2006

By W. John Rankin

Professionals, technical and non-technical, working in the mineral and metal commodity industries need to understand the concept of sustainability and its implications for the industry. Undergraduate courses have not done this well in the past. Much has been written in this field, and there have been great advances in understanding. However, much of what has been published is superficial and sometimes misleading, and there is as yet no coherent, single account that can serve as an introduction or overview for mineral industry graduates. This paper presents an outline which can guide readers in developing an understanding of the topic and its relevance to their work. Key references are provided, particularly those accessible on the internet, which will serve to introduce the reader to the important principles and understandings. The guide should also be useful to academics preparing students to work in the minerals and metal production sectors.

Jan 1, 2010

By S. C. Flood, J. D. Hunt

"The columnar-equiaxed transition (CET) has been studied numerically under unsteady-state conditions using mathematical models that: (i) include a non-equilibrium undercooling at the columnar front;and(ii) describe the simultaneous evolution of the columnar and equiaxed zones.The results are discussed and compared with those produced by a steady-state analysis.IntroductionThe majority of the previous work on the columnar-equiaxed transition (CET) has concentrated on the production of equiaxed nuclei, regarding this as being the critical step in the formation of an equiaxed zone. Recently, the growth of equiaxed grains has been considered and this is not unreasonable because, for an equiaxed zone to be present, the grains must grow as well as nucleate. Since the growth rate of the grains will be determined by the thermal environment at and ahead of the columnar tips, it was decided to model the liberation and flow of heat during solidification to discover whether the various trends in the columnar range might be explained by their effect on the temperature profile throughout the casting. The models presented here for the solidification of a casting are the first to include the latent heat liberated ahead of the columnar front. Burden and Hunt (1) consider its effect only qualitatively, and although Lipton et al (2) adopt a criterion for the CET which is based on the thermal interaction of the columnar and equiaxed grains, they do not actually include the latent heat in their calculations.It can be argued that the latent heat liberated by the equiaxed grains in the bulk will retard the columnar dendrites in a casting: once the equiaxed grains are sufficiently well-established, the latent heat that they evolve could slow down the columnar growth to such an extent that the equi axed would dominate. Alternatively, the latent heat produced by the equiaxed grains might suppress further equiaxed solidification by raising the bulk temperature. The nature of the thermal interaction between columnar and equiaxed growth is not obvious, and because it is dependent on the material parameters and the dimensions of the system, it cannot be considered effectively in a qualitative way but has to be studied quantitatively: hence the need for the mathematical models discussed in the following pages. The results of the models are discussed in the light of a steady state analysis."

Jan 1, 1986

By Hai-Xing Fang, Chao Liu, Tao Zhang, Bing Xie, Hong-Yi Li, Cui Li

"Hongge Ore, a kind of vanadium-titanium magnetite ore containing high content of chromium, is valuable resource for extracting Fe, V and Cr in China. During present processing of the ore, vanadium and chromium were both concentrated in slag, leading to higher content of chromium in the vanadium slag than that of common one in Pan-Steel. Mineral phases and characteristics of spine! crystals, which influenced greatly subsequent roasting process, in the vanadium slag under different cooling conditions were investigated by using XRD and SEM/EDS. Results showed that vanadium slags containing various contents of chromium were composed of spine!, in which V and Cr were both concentrated, olivine and pyroxene. Growth rate of spine ls decreased sharply below 1350°C. The non-isothermal crystallization process could be described by modified Avrami equation and Ozawa equation. Avrami exponent and Ozawa index were calculated and growth mechanism of spine! crystals was discussed.IntroductionVanadium (V) as well as chromium (Cr) is important non-ferrous metal widely used in materials and chemical industries [1, 2]. Especially, both of them are important alloying elements for the production of high alloyed steels to achieve desired physical-chemical and mechanical properties. Vanadium-titanium magnetite ore in Panzhihua-Xichang area (China) is an important raw material for extracting vanadium. During the extracting process, vanadium is firstly reduced into hot metal and then concentrated in slag phase by blowing oxygen into the hot metal in converter [3]. This kind of slag containing 5~20 wt% V20 3 are usually roasted with sodium or calcium salts and then leached to obtain vanadium containing solution and final products. Current vanadium slag obtained from normal vanadium-titanium magnetite ore contains low content of Cr20 3 and chromium extraction is thus ignored. However, chromium content in the vanadium slag would be increased intensively when the Hongge Ore used, which is also important vanadium titanium magnetite in Panzhihua-Xichang area containing 0.2~0.8 wt% Cr203. Therefore, this kind of vanadium slag with high content of chromium would also be important sources for vanadium and chromium extraction. According to previous work [4], both vanadium and chromium could be extracted from vanadium slag with high content of chromium by salt roasting and leaching, which is illustrated in Fig.1."

Jan 1, 2013

By Tzu-Chien Lin, Jack Tsai, Ming-Yu Lin, Der-Ray Huang, Jiin-Sen Chen, Jing-Xuan Lin

"In this paper, some DVD-R discs have been selected for long time light exposure test and high temperature and humidity test. Generally, recordable media under long time light exposure maybe be defected seriously. If we use Jitter value 8% as a reference to determine the life time of DVD-R samples, some discs defect after 5 hours of light exposure while some discs can endure over 25 hours. Also if we use reflectivity 45% to determine the life time, some discs defect after 30 hours light exposure while some discs can endure over 40 hours. From our results, the good samples show good characteristics of PI error. The absorption spectrum of recordable media is a good reference to justify the quality of dye media. These results can be used to estimate the life time of recordable discs.IntroductionIn general, the life time of DVD-R with a layer of organic dye recording layer is required for preservation in decades. In addition to optical characteristics and thermal properties, we still need to consider the stability of the dye in recording media. The presentation of the color on organic dye is not only related to the material's property but also related to the light exposure. In this study, we focus on the absorption characteristics and reflectivity of organic dye in optical recording layer after light exposure. The optical properties of discs depend on the functional groups and molecular structure [1]. According to ""DVD Specifications for Recordable Disc (DVD- R)"", the reflectivity should higher than 40%. From measured reflectivity, we can confirm that the important issue is whether dye be affected by light exposure or not. Because each specific functional group absorbs the specific spectrum, we can check the characteristics of functional groups from their UV/Visible Spectra. We also use High-performance liquid chromatography (HPLC) to detect the different components of dye on the recording layer [2]. The jitter value test is to test the error cause by digital signal of recording media. If we use jitter value 8% as a reference to determine the life time of DVD-R samples, the purpose of this study is to investigate the jitter values of recording media after high light exposure and high temperature/humidity test. The results of these test will be helpful for the development of long-life optical storage media."

Jan 1, 2012

By Robert Fritzsch, Ragnhild E. Aune, Mark William Kennedy, Behzad Mirzaei

"The quantitative particle concentration can give important information about the cleanliness of melts for quality control in primary and secondary production of aluminum. Manual quantification of the particle concentration is normally a time consuming process and human control can bias the acquired images and particle count.The present paper explains the automated image-processing steps for the quantification of SiC-particles, with equivalent diameters from 2 to 25 µm, in solidified A356. A total of 700 micrographs, acquired with a standard white light microscope with 10 x magnification, were analyzed. The applied software (Image Pro-Plus 7.0 from MediaCybemetics®) allows for programming of macros which in tum provides the user with a higher degree of control. The automated results are compared with the results obtained by manually counting the particles in the same micrographs. The impact of the automated results on the estimated filtration efficiency was established to be only -3%.IntroductionInclusions are both indigenous and exogenous particulates that are present in commercial metals such as aluminum. If large individual or large numbers of inclusions are present, they can have a significant negative impact on the appearance, mechanical and chemical behavior of products produced from the metal. Aluminum is known to contain large numbers of inclusions: =50 µm in size, e.g. typically <l ppm by volume or <100,000 inclusions of>20 µm per kg of metal as detectable using a Liquid Metal Cleanliness Analyzer, LiMCA [1]. Depending on the final application of the aluminum, inclusions can render the metal 'not fit for purpose', and result in serious economic consequences to metal producers.It is not surprising that the aluminum industry has developed a number of treatment processes to improve metal cleanliness, given the large number of high value products whose quality can be adversely affected by inclusions. CFFs are the most commonly applied filtration process and have been used to filter >50% of the world production of aluminum since the 1990's [2].Inclusions in aluminum may be particles, bifilms [3] or clusters of: oxides (Al2O3 , SiO2), spinels (MgO· Al2O3), carbides (SiC, Al4C3), nitrides (AlN), borides (TiB2), sulfides, phosphides and intermetallics [ 4]."

Jan 1, 2013

By D. F. Liub, Z. Y. Liu, W. Y. Xue, Y. F. Shenb, Y. D. Wang

"The microstructure characteristics and deformation behavior of ultrafme grained (UFO) 304SS fabricated by accumulative rolling and armealing have been investigated by means of tensile tests, electron-backscatter-diffraction (EBSD) and transmission electron microscopy (TEM) techniques. The volume fraction of martensite phase decreases with increasing armealing temperature. In the grain sizes ranging from 300 nm to 10 µm, the strength held Hall-Petch relationship. The sample with an average grain size of 300 nm exhibited extra high yield strength of 1700 MPa and a tensile strength of 1780 MPa, while the elongation retains 12%. The limited uniform elongation in the UFO materials could be explained in terms of plastic instability. Very interestingly, for the bulk material with an average grain size of 1.200 µm, the high yield strength and uniform elongation were simultaneously achieved to be as 1000 MPa and 18%, respectively.IntroductionUltra-high strengths have been achieved in elemental metals by employing heavy plastic deformation, or by creating ultra-fine-grained (UFO) structure. Here UFO materials are defined as polycrystalline solids with property-controlling microstructural features below the 1 µm level. Typical processing routes include severe plastic deformation (SPD) [1, 2], which decomposes the grains through dislocation accumulation and reorganization (polygonization). Several different kinds of SPD process for bulk materials are typically as equal-charmel angular pressing (ECAP) [3], high-pressure torsion (HPT) [4] and accumulative roll-bonding (ARB) [5]. One of the main motivations for such a push for the very small grain sizes stems from the expectation of unprecedented mechanical strength, as predicted by the well-known Hall-Petch relationship that projects a continuous rise of strength with decreasing grain size [6]. However, these ultra-high strength metals no longer have the high ductility typical of their conventional coarse-grained counterparts, because the undesirable inhomogeneous deformation on the microstructure level can lead to the early onset of failure, severely limiting the useful ductility [2]. Recently, the interesting strategies have been performed to increasing simultaneously the ductility and strength ofUFG pure copper and nanostructured alloys by Zhao et al [7, 8]. In a pure copper, a high ductility has been achieved without sacrificing strength by introducing a high density of pre-existing twins and a large fraction of high-angle grain boundaries. Their encouraging results trigger our motivation to obtain high strength and ductility from the commercially bulk material."

Jan 1, 2013