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By Michael DiMatteo, Michael D. Gardner, Eric F. Perry, John K. Felbinger, Robert S. Evans

A hydrologically isolated surface coal mine was reclaimed using acid material handling, alkaline addition and ground-water management techniques. Eight pit floor drains were installed during reclamation to intercept ground-water flow in the mine backfill and minimize water table buildup. All drains began flowing within six months of installation. Water quality and ground-water discharge have been monitored for four years after mine closure. A thin water table aquifer about five to seven feet thick has developed in minespoil about 20 to 40 feet thick. Ground-water flow direction is largely controlled by geologic structure and the drains. Median ground- water discharge is about 0.43 gallons per acre per minute, and varies an order of magnitude between wet and dry seasons. About 19 % of precipitation enters the aquifer as recharge. Seven of the eight drains typically discharge net alkaline water. Alkalinity is produced continuously and concentrations are highest during dry periods. Conversely, sulfate and acidity concentrations increase during wet periods as slugs of accumulated acid products are leached. Overall water quality is controlled principally by minespoil geochemistry and added alkaline material. The drains have successfully directed ground-water to a planned discharge area. Without the drains, a ground-water mound was expected to form against a buried highwall and discharge over a large area.

Jan 1, 2000

By D. W. Wu, M. T. Haque

A novel impedance probe has been commissioned specifically for capturing fast dynamic information about filtration processes. It provides an attractive alternative to more complex measurement techniques in situations where the slurry system is primarily one-dimensional. The probe can monitor mud-line, slurry densification and drainage. Dynamic variations in cake permeability are obtained by combining dynamic mud-line information obtained with the probe and filtrate rate data derived from a leaf test apparatus. The measurements are re-viewed in relation to micro structural measurements obtained on iron ore filter cakes. The practical significance of these measurements for optimization of the filtration process is discussed.

Jan 1, 2000

By Clyde S. Brooks

This paper undertakes to assess what opportunities exist for the economical recovery of non-ferrous metals from spent catalysts. The most promising recovery appears to lie with metals such as Co, Mo, Ni, W, heterogeneous catalysts used on a large scale in petroleum processing. Nickel is a metal with diverse applications on a large scale notably in hydrocarbon steam reforming and in vegetable oil hydrogenation. In addition, several of the precious metals, notably Pt, Pd, and Rh, find extensive use in fossil fuel processing and in automotive and power plant flue gas control. The hydrometallurgical and pyrometallurgical alternatives for processing are identified and discussed, especially with citations to illustrate reduction to commercial practice. Promising directions for adaptation of appropriate, economic separation technologies for recovery of non-ferrous catalytic metals generated in significant amounts for the secondary metal markets are identified. Recycling

Jan 1, 2000

By Hani Henein, J. Barry Wiskel

"The easy accessibility and power of the PC, as well as the education of our engineering students in the use of these tools, are compelling reasons for developing computer aided instructional (CAI) tools. There are a wide range of areas in the engineering curriculum where students must learn the steps and the process of applying judgement in problem solving. In the typical course instruction, · an instructor introduces theory to students; the application of the theory to solving problems is often demonstrated in the abstract. Students therefore spend a significant amount of time learning how to apply the theory to problem solving. Additional time and effort must then be spent to get students to the point of learning concepts and integrating this knowledge. A number of computer aided packages have therefore been developed for use in several courses in the materials science and engineering curriculum that encompass both calculational and instructional capabilities. This paper presents an overview of some of these packages which include the solution of a non-linear equation, the instruction of binary diffusion couples, an introduction of crystallography, an introduction to heat transfer and the solution of thermodynamic stability diagrams. The context in which these CAI Tutorials were developed and are being used will be discussed. The pitfalls in the development of these packages will also be discussed. The use of the tutorials has important implications on the expectations from an engineering education of both instructor and student.IntroductionTraditionally, it is quite routine to teach engineering students how to use a computer (the PC today for undergraduates) as a tool in performing engineering calculations or in simulating a process or a unit operation. This often takes the form of one course in computer programming, whether it is Fortran, Visual basic or a spreadsheet, and another course in numerical computation. However, the materials and electronic revolution have brought about considerable advances in computer power and speed, and accessibility. Today, the manipulation of digital images, movies, and speech are commonplace on a desktop PC.' Many mathematical models that were executed only on workstations can now be readily handled on a PC. Concurrently, more of our students own a PC even if their curriculum does not require them to purchase one. Today, virtually every university student has been introduced to the PC in either their elementary or high school education. Hence, the increased capabilities and accessibility of the PC and the familiarity of students with this tool make it compelling to explore its use as an educational tool for our engineering students. This is not a traditional role of a computer in our engineering curriculum."

Jan 1, 2000

Stawell Gold Mines Pty Ltd operates two underground decline mines within the township of Stawell. An active exploration program and commitment by owners to improving the ore reserves has led to an improved mine life and reduced operating costs since the purchase of the operation by Mining Project Investors and Pittston Mineral Ventures in late-1992. Over the past six years of operation a cumulative 1 150 000 ounces of gold have been added to the mineral inventory. An improved geological understanding of the orebody has evolved over time increasing the ore reserves and allowing the development of long-term plans for the mines future. This has enabled important capital decisions to be made providing the impetus for improved productivity and thereby reduced operating costs. Co-operative mine planning and mine geology utilising best practice geological systems have enabled the effective extraction of a structurally complex and mineralogically varied deposit within a rural Victorian township. Detailed metallurgical research has improved the function of an aged and poorly designed circuit to boost the mill capacity whilst also improving the metallurgical recovery. The combination of metallurgical expertise and an understanding of the geological setting enable an effective control of metallurgical recovery.

Jan 1, 2000

By K. R. Robilliard

The Peru based tin mining company, Minsur S.A., commissioned Ausmelt Limited to design, supervise construction and commission a tin smelter and refinery for production of refined tin metal. The plant is located 240km south of Lima, near Pisco, Peru and is operated by Funsur S.A., the wholly owned subsidiary of Minsur S.A.. Selection of the Ausmelt Technology followed a series of crucible scale test work and pilot plant trials conducted at Ausmelt's facility in Dandenong, Australia and two feasibility studies undertaken by Ausmelt in 1991 and 1993. Ausrnelt began the plant design in 1994 with the construction phase following in 1995. Commissioning of the plant commenced early in 1996 with a target throughput of 30,000 tonnes per annum of concentrates. In mid 1998 oxygen enrichment of the Ausmelt lance air was introduced to expand the capacity to the throughput of 40,000 tonnes per annum of concentrates. The process route involves the use of an Ausmelt furnace for primary concentrate smelting, followed by a conventional tin pyro-refining circuit to produce high grade tin suitable for sale. Further work continues between Ausmelt and Funsur to investigate the use of an alternative, more economical, fuel source and the installation of a second Ausmelt furnace. The paper reviews the project to date with details of ongoing operations and developments at the Minsur Tin Smelter.

Jan 1, 2000

By E. A. Werner, A. Pichler, A. Spalek, G. Reisner, P. Stiaszny

"Interstitial free (IF) sheet steels are used for complex shaped parts because of their excellent formability. If a deep drawn part is subjected· to a impact deformation at low temperature brittle fracture of the part may occur. This phenomenon\ is called secondary work embrittlement (SWE). One possibility to characterize this material/structural behavior is the drop-weight test. The result of .this .test is a temperature at and below which a crack can initiated in a deep drawn part under the investigated set of parameters. This paper addresses the influence of the preforming process on the sus- . . ceptibili.ty of IF steels to SWE.IntroductionInterstiiial:free (IF-) steels are frequently used in the automotive industry for complex· shaped p·arts because of their excellent deep drawability. The microstructure of the steel consists of a highly ductile ferritic matrix with embedded precipitates of nitrides and/or carbides. Brittle fracture can occur in deep drawn parts, if they are subjected to a high speed deformation at lo""w temperature. This phenomenon is called ~econdary Work gmbrittlement (SWE) [1-11]. Up to now there are no standardized testing procedures available to quantify the sensibility of IF-sheet steel to SWE. Neveitheless, a reasonable testing procedure which allows to quantify the tendency of a predeformed part to SWE is necessary for further material development. A commonly used test method is the drop-weight test performed at low temperatures. In such ·tests a cone-like drop weight expands a deep drawn cylindrical cup [l-3, 6, 8, 9, 11]. From this expansion experiment the temperature is determined at and below which a brittle crack can be initiated in the deep drawn cup under the investigated impact test parameters. The highest measured temperature at which a deep drawn cup fails by brittle fracture is called frack appearances !emperature (CAPT). The lower the value of the CAPT the lower is the sensibility of a deep drawn part of IF-sheet steel to SWE. This paper aims to clarify the role of the preforming process on the impact behavior of an IF steel. For this purpose a numerical analysis of the deep drawing process and cup expansion tests are conducted."

Jan 1, 2000

By R Crookes

Mine to Mill optimisation is not a recently developed concept. It is one which is finally gaining greater acceptance in the Australian Mining Industry, possibly as a consequence of the downturn in markets and certainly made possible by the development of tools and techniques to measure and predict performance of mining equipment and milling plants. Fragment size after blasting has a major bearing on the performance of all aspects of mining and a major influence on the economics of the mine and mill. The process to optimise fragmentation consists of identifying the key factors, measuring their sensitivity through a modelling and trialing program and conducting economic evaluations on the changes on both the mine and mill. Management of the Ernest Henry copper-gold mine in NorthernQueensland, Australia, has espoused the Mine-to-Mill concept and isactively pursuing excellence in blasting to drive down the total cost of mining. Ernest Henry has extremely hard, wet and heavily jointed geological conditions, and had high powder factors and a large percentage of oversize material reporting to the crusher or ROMstockpile. A blasting improvement program was undertaken betweenErnest Henry Mining, Thiess Contractors and Orica Explosives tooptimise the ore size distribution, particularly the oversize component, as a step to reducing production costs. Measures of success included bringing the rock breaker back from double shifts to part-time operation and increasing direct dumping into the crusher from 70 per cent to 92 per cent. Tools and technologies to predict and measure the performance ofindividual blasts are needed before it is possible to optimisefragmentation or the downstream processes. These include suchspecialised Orica Explosives tools as SABREX, POWERSIEVE, andPOWERLINE and commercially available drill monitors. As importantare the more common still and video camera, borehole loggers,measuring tapes, surveying equipment such as face profilers, and ahigh-speed camera if possible. There are many tools which can be applied however it is rarely necessary or possible to use all of them due to time constraints and a point of diminishing returns. The critical point is knowing what the true parameters of the blast were compared to design - only then can the predictive tools be effectively utilised. Stage one of the program has seen gradual improvement as theunderstanding grew and practices have been implemented resulting inreduced bridging in the crusher, geological mapping with respective blast designs and the oversize component under control. This paper is about a process approach which links tools and technology to understand the fragmentation drivers and then to optimising the size distribution.The continuous improvement program continues...

Jan 1, 2000

By K. Yamaguchi, Y. Takeda

"Partial pressure - temperature - composition correlation diagrams of the Ga-As, In-As, Ga-P and In-P systems were contracted based on the obtained experimental data of the phase diagram and thermodynamic properties for the III-V systems. The total vapor pressures of arsenic or phosphorus at melting point of GaAs, InAs, GaP and InP were determined as 101, 10.1, 1510 and 253 kPa, respectively, at the corresponding melting points of 1509, 1211, 1739 and. 1336K , These diagrams are applied to the analysis of the horizontal Bridgman method and the liquid phase epitaxial growth technique. On the other hand, the analysis of the equilibrium state of the. chloride-CVD process was carried out using the data of the Gibbs energy of the compounds obtained by· authors.IntroductionThe group III-V compound semiconductors ate important materials used in optoelectronic liquid high speed electronic device. The crystal growth of the III-V compounds can involve processes that require contact between the solid, liquid and vapour phases at near equilibrium condition. Examples of processes that involve contact between the solid, liquid and vapour phases include bulk crystal growth such as the horizontal Bridgman and the liquid encapsulated Czochralski method and liquid epitaxy, and between the solid and vapor include chemical vapour deposition and molecular beam epitaxy. Therefore, the knowledge of the phase diagram and thermodynamic properties for the III-V binary alloys is essential for the analyses of crystal growth techniques of III-V compounds.For these reasons, a series of different · types calorimetric measurements had been carried out: (1) The heat contents of alloys for the Ga-As, In-As, Ga-P and In-P systems by a drop calorimeter [1;2,3]; (2) the heats of formation of the GaAs, InAs, GaP and InP compounds by a twin solution calorimeter [4]; and (3) the standard entropy of these compounds by an adiabatic calorimeter [5]. Based on the third law method, the Gibbs energies of these compounds were derived from the heat capacity, standard heat of formation and standard entropy data obtained by authors. Integral molar thermodynamic quantities of the liquid III-V .alloys were also determined from combining the heat contents of alloys with standard heat of formation and standard entropy data of the compounds· by applying the thermodynamic analysis method developed by Oelsen [6]. In the present study, the thermodynamic calculations for the crystal growth processes of the III-V compound were carried out using newly experimental data of the phase diagram and thermodynamic .properties measured by authors"

Jan 1, 2000

By R J. In, C Moore, P J. Moffitt, T Hansen

Telfer Gold Mine combines a world-class gold and copper resource and longevity of operation as a major gold and copper producer. Telfer Gold Mine has undergone a series of transformations since mining commenced as a high-grade narrow-vein oxide open pit operation in 1977. In 1986, the open pit operation converted from a narrow-vein, high-grade operation, to a low-grade high-volume oxide mining operation utilising dump leach processing technology. Mechanised underground mining of the high-grade narrow-veins commenced in 1990. Total recovered gold production between 1977 to 1999 has totalled 5.7 million ounces. The Telfer Extension Project consists of two pre-feasibility studies, the Surface Extension Project (SEP) and the I-Series Project (ISP). The combined studies represent one of the more significant resource evaluations undertaken in the gold industry in recent times. Geological activities for the SEP pre-feasibility study have included the drill definition of a large low-grade resource within an area of 25 km2 . The surface drilling program has completed 15 000 metres of HQ3 diamond drilling and over 30 000 metres of RC between last quarter of 1998 and late-1999. The ISP pre-feasibility study is currently evaluating the resource potential of both a high-grade low-volume and a lower grade bulk mining scenario, 800 m to 1200 m below the surface of Main Dome. 15 000 metres of underground diamond drilling have been completed between last quarter of 1998 and August 1999 as part of this study. Systems and cultures have been developed to maximise safety, monitor the quality assurance/quality control (QA/QC) on all aspects of the operation, and minimise impact on the environment. All data are stored in database systems, specifically designed for Telfer operations. 3D geostatistical resource estimation using ordinary kriging has been carried out for over 220 geological domains within the 25 km3 of mineralised system. Non-linear geostatistical techniques are being investigated as part of the pre-feasibility study.

Jan 1, 2000

By V. F. Swanson

A mathematical model for free and hindered settling of minerals was developed. This paper describes how to apply the model in designing systems, such as fluidized bed, elutriation, mixing pumping systems, involving solids and fluids.

Jan 1, 2000

By L. A. Cramer

Platinum metal was first utilized by the Inca civilization in South America where it was found in alluvial deposits along the San Juan and Atrato rivers that lie between the Andean mountain range in Colombia and the Pacific Ocean. The nuggets found in these rivers average between 77% and 86%platinum, 7%?8% iron and small amounts of copper, gold and other Platinum Group Metals (PGMs). The Incas often alloyed platinum with copper to increase its workability and fabricated various ornaments from it. With the arrival of the Spanish in the early 1700s, platinum was labelled a nuisance for the Spanish in their quest for alluvial gold because it concentrated with the gold and had to be removed by either extended amalgamation or by hand sorting. It was at this time that platinum received the root of its current name for the Spanish referred to it as platina del Pinto, platina being the somewhat derogatory diminutive of plata (silver). Pinto was a river in Colombia where the Spanish first distinguished it. The English eventually adopted ?platina? and it is only in recent times that the Latin name platinum has been accepted as the metal?s common English name. From its first introduction to European scientists in 1740, platinum was unappreciated because of its brittle nature and difficulty of working and as a result had little commercial value. Its ability to be dissolved in gold did lead to some counterfeiting of gold bullion and even to the debasement of gold currency.

Jan 1, 2000

By Jerry W. Danni, R. Craig Ford, Kermit C. Benke, Jim B. Finley, Donald D. Runnells

Steady-state water balance models have historically been used in the management of acid drainage at mine sites. Such systems could be more realistically described by non-steady-state conditions. In addition, the evaluation of alternatives for closure and management of acid drainage must consider non-steady-state conditions. Dynamic systems modeling is a method for simulating water management systems, offering flexibility in: (1) simulating either steady-state or non-steady-state conditions, (2) allowing "what-if' scenario testing. and (3) optimization of operation and closure alternatives. A case study is given for acidic drainage management during closure at a heap leach facility that demonstrates the utility of dynamic systems models.

Jan 1, 2000

By Robert C. Fouchard, Gordon Chalmers, David E. G. Jones, Ivana Alilovic, Phillip D. Lightfoot

There have been numerous international instances over the last several years in which pumping emulsion explosives has resulted in accidents, apparently as a result of increased thermal sensitivity under these conditions. The key questions for the explosive industry are (1) what are the parameters that influence the sensitivity of emulsion explosives and, (2) how do these various parameters interact. To address the sensitivity of emulsion explosives to various parameters, a study was undertaken using an accelerating rate calorimeter (ARC) and a heat flux calorimeter (HFC). The effects ofthe addition of ammonium nitrate (AN) prills and different grades of aluminum (Al) on the thermal behaviour of emulsion explosives were determined. Additionally, changes in pressure, atmosphere (inert or oxidizing) and sample vessel material were assessed for their impact on thermal sensitivity. Addition of AN prills, fine granular Al or atomized Al did not affect the onset temperature for exothermic decomposition, so that the maximum “safe” temperatures for emulsions containing these additives will be similar. There were differences in the rates of self heating, however: AN prills decreased the rate of self heating, whereas atomized Al increased it. The emulsion formulations containing atomized Al produced small holes in titanium vessels. This phenomenon did not occur in Hastelloy C vessels, providing a reminder that materials of construction need to be carefully considered for equipment used to manufacture or handle emulsion explosives.. Both ARC and HFC experiments gave lower onset temperatures in air than in argon. We attribute this to oxidation of the oil phase by air. This result is significant for dry-running pumping conditions, where emulsion is heated in the presence of excess air.

Jan 1, 2000

As economic, technological, regulatory and other forces continue to present the global mining industry with new opportunities and challenges, agile mining equipment manufacturers are stepping up their efforts to anticipate and meet the evolving needs of surface and underground mining operations. Operational excellence û the pursuit of efficient, lowest-possible-cost production û is a prime objective for all mines. As mineral commodity markets experience cyclical price highs and lows, mine operators, increasingly, look to their equipment suppliers for equipment and support that can help reduce multiple tangible and intangible operating costs. This paper explores how two mining equipment manufacturers û P&H Mining Equipment, a supplier of surface mining equipment and Joy Mining Machinery, a supplier of machinery for underground mining û are responding to the mining industryÆs aggressive pursuit of obtaining reduced operating cost with innovative products and support programs.

Jan 1, 2000

By V. V. Satya Prasad, A. Sambasiva Rao

Electroslag melting technologies have recently been developed for recycling light scrap of valuable metals and alloys such as superalloys and oxygen free high conductivity (OFHC) copper at Defence Metallurgical Research Laboratory (DMRL), Hyderabad. Conventionally, electroslag melting processes use consumable electrodes. Because of the difficulty in compaction of scrap into a consumable electrode of satisfactory quality, non-consumable electrodes such as graphite and water-cooled copper have been designed. Electroslag remelting using a water-cooled non-consumable electrode was developed to melt scrap of a nickel base superalloy. Sound ingots with smooth surface finish and properties comparable to vacuum melted superalloys could. be obtained from scrap using this process. A modified electroslag crucible melting process using graphite crucible and graphite electrode was developed for recycling OFHC copper scrap. Copper ingots with less than 10 ppm oxygen and electrical conductivity"" 100% IACS could be produced. The same process was also utilized to produce copper-based alloys such as copper-chromium and copper-titanium starting from copper scrap.

Jan 1, 2000

By M Gao

Six new IsaMills were installed for the George Fisher flowsheet in the Lead/Zinc Concentrator of Mount Isa Mines to produce a product P80 as fine as seven microns. The objective was better liberation of galena and sphalerite. The IsaMill commissioning was completed by the end of 1999. The six new IsaMills were running to the metallurgical specifications almost immediately after start-up. This paper reports the performance of the George Fisher IsaMills in the zinc circuits and some of the latest development in the IsaMill designs and maintenance during George Fisher commissioning.

Jan 1, 2000

By D. H. Horswill

Red Dog, the world’s largest zinc mine, is located ninety miles north of the Arctic Circle in northwest Alaska on lands owned by the Inupiat Eskimo organization called NANA. NANA received a subsurface title over this resource as part of their settlement lands under the Alaska Native Claims Settlement Act and subsequently entered into a Lease Agreement with Cominco in 1982. Cominco, an international mining company focused on zinc, built and operated the mine. NANA’s principle objective in the development of the mine was to have it contribute to the development of sustainable communities within their traditional region. This meant creating job opportunities in a modern economy while preserving the traditional subsistence lifestyles. Preservation of their culture, language, and traditions are as important to the NANA people today as they were through ages past. The principles of sustainable development – matching economic, environmental, and social goals through continuous communications and high commitment to efficient and effective operations – have been core values for the Red Dog Mine from the beginning. This paper will describe how a large mining operation in a remote corner of the world has been able to contribute toward sustainable development in that region.

Jan 1, 2000

By M Scamardella

The CSA Mine is located at Cobar, New South Wales, where it was in continuous operation from 1966 to the time it went into receivership on 29 January 1998. When it closed it was under the ownership of Golden Shamrock. Glencore International, in conjunction with Mt Lyell Mining, undertook a due diligence study to determine the feasibility to re-open the mine. This envisaged operating CSA Mine as a low-cost, copper concentrate producer under the direction of Cobar Management Pty Ltd (CMPL). The new workforce would consist of contractor trades people in operating functions under the co-ordination of CMPL staff, both on the surface and underground. This was the key to establishing the new culture in the workforce. The orebodies at CSA Mine are steeply dipping with copper-lead-zinc mineralisation in zones of strong alterations in a fine-grained siltstone host sequence. The predominant economic minerals are chalcopyrite, sphalerite and galena. The major gauge minerals are pyrrhotite, pyrite, chlorite, sericite and quartz. Ore for the project is being developed and mined from two high grade copper lenses within the QTS North system. Chalcopyrite occurs in two forms. The first consists of coarse chalcopyrite grains in association with pyrrhotite or pyrite. The second form consists of chalcopyrite grains intergrown with pyrrhotite grains. This form of chalcopyrite is quite rare. It allows electrochemical interactions between grains, resulting in rapid oxidation of the chalcopyrite surface. Physically this ore looks like, and has been mistaken for æpeacock oreÆ, ie bornite, but is infact oxidised chalcopyrite.

Jan 1, 2000

By Raghavan Srinivasan, Y. V. R. K. Prasad, William G. Frazier, Steve C. Medeiros

"Aerospace gas turbine disks operate in an environment of relatively high stresses caused by centrifugal forces and elevated temperatures. These severe conditions necessitate the need for materials with good high temperature strength and low cycle fatigue resistance. One class of alloys used for this task is the nickel base superalloys, out of which, lN 718 is the most widely used in the aerospace industry [I]. The properties of IN 718 are attributed to the combined effects of the chemistry, heat treatment, and microstructure. The chemistry is tailored not only for solid solution strengthening but also for precipitation hardening developed during heat treatment, which combined with a fine grained microstructure lead to excellent mechanical properties such as low cycle fatigue resistance and elevated temperature strength. The properties of a gas turbine disk are sensitive to the microstructure, in particular the grain size, which is dependent on the processing history. The ability to precisely control the microstructural development during forging is dependent on controlling the process so that the workpiece is deformed within a ""safe"" region where no microstructural damage or flow instabilities occur. The microstructural mechanisms during deformation may themselves vary within the ""safe"" region and it is desirable to determine them within the range of parameters that are commonly used in industrial processing. The objective of this work is to establish a relationship between the grain size and the process control parameters i.e., temperature and strain rate, in the hot working of IN 178.BackgroundIN 718 belongs to a class of nickel-iron base superalloys with a face-centered cubic (FCC) austenitic matrix strengthened by precipitation of ordered intermetallic or carbide precipitates and is a nickel-rich alloy strengthened by ordered body centered tetragonal (BCT) precipitates, Y"". The alloying of nickel and iron results in the formation of the austenitic matrix, y, while the addition of chromium and molybdenum cause solid solution strengthening. Also, alloying with niobium causes precipitation of the metastable hardening constituent Y"" (Ni3(Nb,Ti)). Extended aging treatments in the temperature range 650 °C - 980 °C allow the more stable orthorhombic 8 phase (Ni3Nb) to form. Trace amounts of boron are also added to serve as grain boundary strengtheners for high temperature creep resistance. Hot deformation of IN 718 is performed between the Y"" and 8 solvus temperatures to facilitate recrystallization and to control grain growth. While deformation below the Y"" solvus (""""962°C) produces no change in grain size, deformation above the Y"" solvus but below the 8 solvus will lead to a dynamically recrystallized microstructure. The presence of the 8 precipitates will pin the grain boundaries after recrystallization and restrict grain growth so that a fine grain microstructure is obtained. Deformation above the 8 solvus ("""" 1038°C) will lead to a microstructure which has undergone grain growth during deformation."

Jan 1, 2000