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By Jimmy Thompson

The Santa Clara Valley Transportation Authority is designing the Silicon Valley Rapid Transit Project in San Jose, California. The project includes 6.9 km (4.3 miles) of twin-bored tunnels to be constructed through downtown San Jose using two earth pressure balance machines (EPBMs). This paper begins with a project description and update of the project status followed by a description of the relationship between anticipated ground conditions and EPBM requirements. Topics addressed include soil conditioning, abrasion resistance, annulus grouting, face pressure estimation, additional pressure control devices and control measures to limit over-excavation and settlement.

Jan 1, 2008

By M. Z. He

Attractive particle interactions which underpin the sliming of gangue mineral particles onto valuable mineral phases are encountered in a number of flotation circuits. Sliming leads to poor flotation recovery of the valuable minerals and high recovery of the gangue particles in the concentrate. To mitigate sliming, low molecular weight poly-electrolytes are commonly used as dispersants during pulp conditioning prior to flotation separation of the valuable and gangue mineral phases. In the present work, the sliming mechanism of sericite onto chalcocite and the influence of interfacial chemistry and two anionic copolymer dispersants (carboxylate substituted polyacrylamide, polymer Cyquest 3223 and sulfonate substituted polymaleic acid, polymer P80) on the sliming interactions were probed in the pH range 5~9. It was shown that the sliming occurred under solution conditions where both chalcocite and sericite particles were negatively charged, as evidenced by their apparent particle zeta potentials. The suspension pH had a profound effect on sliming process as the extent was markedly greater at lower than higher pH. The sliming was found to be due to the chalcocite dissolution, Cu (I) release and oxidation to Cu (II), followed by hydrolysis and specific adsorption, leading to sericite particle surface charge reversal and the formation of electropositive sites on chalcocite surface in the pH range 5~9. Addition of polymer Cyquest 3223 or P80 not only increased the magnitude of zeta potentials of both sericite and chalcocite particles but also reduced the formation of Cu (II) ions and complexes, which mitigated the sliming behaviour. The adsorption of polymer Cyquest 3223 or P80 at 3 g polymer / kg solid or more had a significant impact on the zeta potentials of both sericite and chalcocite particles. Sericite-chalcocite particulate adsorption studies showed that sliming was completely suppressed via an electro-steric repulsion mechanism resulting from anionic polymeric dispersant adsorption at dosages > 3 g polymer / kg solid.

Jan 1, 2014

By Allan D. Taylor, Robert S. Shoemaker

Adopting as a principle the phrase "the mill of yesterday should not be built with the high cost money of today," the authors have designed a hypothetical concentrator which could be built for a typical southwestern United States (or other similar area) copper ore. Many of the design features could also be used for other ores in other climates. Functional design, large equipment, and outdoor type of construction have been combined in a concentrator (which includes all ancilliary facilities such as truck and maintenance shops, offices, warehouse, nominal tailings disposal, and water supply) which could be built today for substantially less than the cost of comparable but conventional plants.

Jan 1, 1973

By K L. Avarmaa, M A. Rhamdhani, A D. P Putera, H T. B M Petrus, G A. Brooks

Multistage slag treatment was carried out to investigate boron removal from metallurgical grade silicon. Boron is known to be one of the most difficult elements to remove from silicon. Depending on boron initial concentration, boron can be removed from silicon into certain level; most previous studies have attained final 50–100 ppmw (parts per million weight) boron in the silicon using slag treatment. The term ‘multistage’ refers to a process where the resulting silicon from the initial slag treatment is further refined multiple times using a new slag. In this study, an initial slag composition of 45CaO-45SiO2-10Al2O3 (wt per cent) was utilised. Using this technique, boron level in the silicon was expected to be gradually lowered because the new slag will always have more capacity to reach the equilibrium distribution coefficient (LB = (ppmwB)slag/(ppmwB)Si). The current study was carried out through combined thermodynamic calculations (using FactSage™ ver 8.2, by Thermfact Ltd, thermochemical package) and high-temperature experimentation. The thermodynamic calculations were carried out for reactions at 1500, 1550, and 1600°C for three different scenarios: 1. Single stage refining with varied slag to Si ratio. 2. Multistage refining with slag to Si ratio of 1:1. 3. Multistage refining with slag to Si ratio of 2:1. The multistage experimental work was carried out at 1550°C under inert gas atmosphere each time for 2 hrs, with slag to Si ratio of 2:1. The simulation results indicate that the boron distribution coefficient stay essentially constant with varying slag to Si ratio and temperature, around 1.8 to 2, and the experimental results measured LB in the same range, between 1.5 and 2.5. By harnessing this feature, the simulation showed that boron can be removed by approximately 78 per cent in each stage. The experimental result confirmed that the boron concentration in the silicon was reduced by a total of 97.8 per cent from its initial value using four stages of slag treatment, from initial 270 ppmw down to 6 ppmw.

Aug 21, 2024

By V Morand, W R. H Ramsay

Structural, mineralogical, and textural data from the Tarnagulla Goldfield demonstrate that the area has undergone three significant phases of deformation. The first phase of deformation (D1) predates the intrusion of the Tarnagulla pluton, which has been dated using K/Ar as 391 ¦ 5MY. We regard this pre-granite deformational event as the major regional deformation. Gold-bearing quartz veins have been deposited in dilational sites on west-dipping reverse faults. These sites demonstrate a geometry related both to faulting associated with D1 and the plunge of the F1 fold axes. This evidence, together with chronology of unmineralised ? D2 and D3 faults, the absence of quartz veining associated with D3 events, and the deformation of carbonate-quartz-biotite-sulphide aggregates within Sl by later S2, lead us to conclude that the bulk of the mineralisation was essentially syn- or late D1 . d18O values for fluids in equilibrium with vein quartz from Central Victoria have indicated equivocal support for either a magmatic or metamorphic origin. Our evidence supports a pre-magmatic origin for mineralisation at Tarnagulla and hence tends to favour a metamorphic fluid source.

Jan 1, 1995

Improving the Sustainability of Primary Metal Production - The Need for a Life Cycle Approach

Sep 13, 2010

By A. Yazadni-Chamzini

Maintenance strategy selection plays a significant role in mining design. The nature of maintenance strategy selection is a complex multi-criteria decision making (MCDM) problem including both tangible and intangible parameters which are often in conflicting with each other. Moreover, when decision makers are uncertain in determining and defining the ratings and the weights of alternatives and criteria respectively, fuzzy theory provides an appropriate tool to handle the existing uncertainties. In this paper, a new fuzzy MCDM method based on the concepts of TOPSIS and AHP was proposed to evaluate the feasible maintenance strategy. The linguistic terms are employed to assess the ratings and weights. Fuzzy AHP is utilized to calculate the weights of the evaluation criteria; then, the rankings of alternatives are computed based on fuzzy sets theory and TOPSIS. A real world case study is presented to illustrate a potential application of the proposed model.

Jan 1, 2012

In Alaska?s southwest corner, in the Bristol Bay region, 476 holes have been drilled to help define the size of the Pebble Project. The results indicate that the deposit holds close to 32 Mt (72 billion lbs) of copper and 2.9 Gt (94 million oz) of gold. The Pebble Partnership, an Alaskan limited partnership of Anglo American and Northern Dynasty Minerals, owns the project that consists of two world-class mineral deposits. Currently in the prefeasibility and prepermitting stage of development, the Pebble Project is one of the largest and highest profile exploration projects in North America. History The Pebble West Project was originally discovered in 1988 by Cominco (now Teck Cominco). Drilling programs in 1997 defined a near-surface mineral deposit of 1 Gt (1.01 billion st). Minerals found included copper, gold and molybdenum. Northern Dynasty Minerals acquired the property in 2001 and, by 2005, it had confirmed a measured and indicated resource of 4.1 Gt (4.5 billion st) containing 1.2 kt (42.1 million oz) of gold, 11.2 Mt (24.7 billion lbs) of copper and 612 kt (1.35 billion lbs) of molybdenum and additional silver. By September 2005, Pebble East, a deeper, but richer deposit had been found. Drill data by the end of 2005 confirmed a 3.4-Gt (3.7-billion st) inferred resource containing 19 Mt (42.6 billion lbs) of copper, 1.2 Mt (39.6 million oz) of gold and 1.2 Mt (2.7 billion lbs) of molybdenum.

Jan 1, 2009

By C. E. Brechtel

A testing program was conducted to design a cemented backfill fur hydraulic placement in underhand cut and fill mining of a steeply dipping coal seam. The testing evaluated the use of three different backfill aggregates, locally available at the coal mine, with Portland cement and five different pozzolans, including a Class F fly ash, a Class C fly ash, a cement kiln dust and ground smelter slag. Both viscosity and uniaxial compressive strength of backfill mixtures with different pozzolan and Portland cement contents were used to evaluate their suitability. Based upon the results of preliminary testing, an optimum mixture of alluvial sand with six percent Portland cement and ten percent Class F pozzolan was chosen for further compression testing.

Jan 1, 1985

By Tatsuo Itou

Both sales volume of Aluminum Can and its recycling rate are remarkably increasing here in Japan. In 1993, recycled can volume was 11.78 billion cans ( 116,258 metric tons ) and its recycling rate 57.8 percent. We, MITSUBISHI MATERIALS CORPORATION. the leading manufacturer of aluminum can in Japan and our affiliated companies are very deeply involved in recycling used beverage cans ( U.B.C ) and recycling them back to can stock. In this paper. I would like to present the following; 1. Recent trend of beverage can consumption in Japan. 2. Trend of aluminum can and its recycling rate in Japan. 3. Future of aluminum can business in Japan.

Jan 1, 1995

By Mehmet Guney

During the last decade various modifications of room and pillar and sub-level methods have been tried in an effort to eliminate gob-fires, dangers from roof falls, surface subsidence and to increase efficiency of extraction in the Armutcuk Mine, Turkey. It was eventually decided that the most likely system to give maximum benefits in view of existing geological conditions and coal seam characteristics was a system of cut-and-fill stoping employing hydraulic stowing. This paper has attempted to examine the trends of working techniques of hydraulic stowing. In addition, the results achieved and technical problems involved are discussed.

Jan 1, 1968

By Dimas de Andrade Pacheco

O estudo do efeito da adição de nióbio em um ferro fundido branco alto cromo tratado termicamente com 25%Cr e 3%C foi estudado neste trabalho por microscopia ótica, microscopia eletrônica de varredura e difração de raios X. Partindo de uma liga hipereutética, a adição de 2% de nióbio foi definida considerando que todo Nb adicionado se encontraria na forma de carbonetos de nióbio, NbC, e com o objetivo de obter uma microestrutura próxima à eutética. A adição promoveu um refinamento da microestrutura, sendo que uma fração volumétrica de 27% de carbonetos M7C3 foi observada. Carbonetos grosseiros, inicialmente formados, não são facilmente observados. Uma microestrutura formada por NbC e eutético, M7C3 + matriz (austenita ou martensita), foi obtida. Os carbonetos de nióbio formados são encontrados principalmente na forma compacta. É esperado, portanto, que, a liga com adição de 2% de nióbio apresente melhor resistência ao desgaste abrasivo que a liga sem nióbio, em razão dos carbonetos primários, frágeis e grosseiros, terem sido praticamente suprimidos após a adição de Nb e uma microestrutura mais refinada tenha sido obtida.

Oct 30, 2017

By Arthur Aracely de Araujo Alves, Joelson Inacio Dantas Teixeira, Flanelson Maciel Monteiro, Carlos Vinicios Galdino de Melo, Pedro Henrique Medeiros Câmara, André Luiz Moura dos Santos, Kleison Barbosa Cândido da Silva

A argila é uma matéria prima com diversas finalidades na indústria. Entre as principais características desse material, destaca-se por ser terrosa, de granulometria fina, e suscetível à moldagem em função da consistência plástica que adquire em presença de certa quantidade de água. No caso do revestimento cerâmico, estes podem ser classificados de acordo com características do processo, propriedades tecnológicas e aplicações. A cor de queima do suporte é um fator de grande importância tecnológica e classifica os revestimentos em produtos de cor vermelha e produtos de cor branca. Contudo, este trabalho tem como objetivo o estudo das propriedades tecnológicas de uma argila de coloração branca, oriunda da cidade de Vera Cruz/RN que é localizada na microrregião do agreste potiguar, a fim de analisar suas propriedades tecnológicas e indicar sua viabilidade econômica. Para tanto, os corpos de prova foram confeccionados por pressão uniaxial, usando uma prensa hidráulica com uma pressão de 21 MPa. As amostras foram sinterizadas em um forno tipo mufla nas temperaturas de 900°C, 1000°C e 1100°C, com taxa de aquecimento de 10 °C/min e isoterma de 60 minutos. As propriedades tecnológicas das amostras foram analisas usando os ensaios de retração linear (RL%), massa específica aparente (MEA), absorção de água (AA%), perda ao fogo (PF%) e porosidade aparente (PA%). A composição química da argila foi analisada através da fluorescência de raios-X (FRX). Ao final do processo observou-se que a argila pode ser usada para compor massas cerâmicas, especialmente pela sua coloração clara, todavia os valores dos ensaios de AA% e PA% foram elevados o que demostra que o material necessita de outros componentes mineralógicos para ser usado industrial, especialmente na indústria de revestimentos.

Mar 1, 2019

By Rafael Fernandes Reis

A solidificação do aço no molde é determinante para a qualidade superficial da placa, considerando que os principais defeitos tendem a se formar nos primeiros estágios de formação da pele. Assim, diversos parâmetros do processo que afetam a solidificação no molde devem ser considerados e um deles é a oscilação do molde. A partir de amostras da face estreita de placas obtidas no processo industrial, duas técnicas para avaliar o efeito da oscilação foram desenvolvidas com base em perfilometria a laser e metalografia. Em relação à perfilometria a laser, desenvolveuse um método de análise da profundidade das marcas de oscilação. Foi comprovada a correlação da profundidade média dessas marcas com o tempo de estripamento negativo. A segunda técnica refere-se ao ataque metalográfico à base de ácido pícrico, que se mostrou eficiente para visualização, via microscopia ótica, do gancho na base da marca de oscilação. Bolhas de argônio e partículas de pó fluxante podem ser aprisionadas na região do gancho de oscilação, e eventualmente ocasionar defeitos nos produtos laminados. O uso das técnicas apresentadas nesse estudo forneceu subsídios à tomada de ações visando a diminuição da profundidade do gancho e da marca de oscilação, resultando em melhoria da qualidade superficial das placas produzidas.

Aug 16, 2017

By D. D. Pollock, D. I. Finch

PREVIOUS work' on a four-component system (Cu-Mn-Ni-Fe) resulted in the development of consistent relationships between the chemical composition and the electrical properties of these manganin-type alloys. The present study was undertaken to develop alloys with temperature coefficients of resistivity and thermoelectric properties more desirable than those of the manganin type, and to determine whether the relationships which had been found for the Cu-Mn-Ni-Fe alloys could be extended to five-and six-component alloy systems. PREPARATION OF ALLOYS The five- and six-component alloys were made from OFHC copper rod, ARMCO iron, electrolytic nickel, manganese cathode chip, and special high-purity aluminum and indium. A Cu-Mg master was used for deoxidation. The compositions of these materials are given in Table I. The alloys were melted and cast as indicated previously,' except that no cover was used and the melts were teemed. EXPERIMENTAL PROCEDURE The finished wire size of 0.0808 in. diam was again selected for the reason that the test specimens would be self-supporting, thus eliminating any extraneous effects which might have been introduced by winding smaller diameter wire on spools or forms. The following tests were performed on the finished wires: A) Chemical Analyses—All of the components of these alloys were determined by premium gravimetric methods. The principle residual impurity contained in these alloys is 0.008 pct Mg (by weight), maximum. Tables II and 111 present the mean analyses computed from at least four determinations of each constituent. B) Electrical Characteristics—The test procedures forthe determination of the thermal emf vs copper, resistivity, and the resistance-temperature relationship are given in detail in Ref. 1. It was also shown that the resistance-temperature relationship is of the form Pt = P,n + At -B/2, [1] where P, is the resistance at t C expressed in percent of a given standard resistance, P, is this per- 0 centage at 0°C, and A and B are constants for a given, properly treated, composition. The results of the electrical tests are also given in Tables II and 111. INTERPRETATION OF DATA The modified Linde2 formula, known to be valid for dilute binary solid solutions, was applied to the complex Cu-Mn-Ni-Fe type alloys. This relationship is of the form where Ap is the increase in resistivity. Zb the valence of the solute, Zn the valence of the solvent, and K and K are designations assigned by Robinson and Dorn3 to the constants for the periodic group to which solute element belongs. The units of K, are -cm per valence difference squared per at. pct; those of K2 are pa-cm per at. pct. For the sake of brevity, these units are not repeated in the following discussion. Calculations were made to determine if this formula was accurate for five-component systems. No experimental studies were made of the Cu-In and Cu-A1 binary systems. The effects of indium additions upon the resistivity of copper are given by Linde. These data, along with those of the effects of Mn and Fe, permitted the calculation of the effects of Al.

Jan 1, 1959

By Franklin H. Sharp, Kenneth L. Clifford

During the last few years the New Lead Belt of Southeastern Missouri has become the main source of lead in the United States. It also produces significant amounts of zinc, copper and silver. The mines are located on a narrow, mineralized trend extending southward from Viburnum, MG. for about 35 miles. The ore occurs as replacement deposits in the Bonneterre lime- stone formation which is about 1000 ft below the surface. In most of the mines, enough water is produced to supply the milling requirements without any reuse. There are dry areas, however, and at least two mills must rely on water reclaimed from their tailings lake to augment the mine water. These mills have no choice but to utilize recycled mill water.

Jan 7, 1973

Support design in jointed or blocky rock masses is often approached by the use of either 'rules of thumb', rock mass classification systems such as the Q-system (Barton, Lien and Lunde, 1974) or RMR (Bieniawski, 1973) or conventional wedge analysis. Generally, this requires that a number of key simplifying assumptions are made and the support system is designed to cater for either a mean, most likely, or worst case scenario depending on the risk tolerance. The design block size is often a major uncertainty and often a worst case block size based on excavation span is used. Thompson and Windsor (2007) state that it is inappropriate to base support designs on the excavation size as these size blocks rarely occur if discontinuity trace lengths are considered. Probabilistic keyblock methods can be used to determine the most likely design block sizes. A methodology is presented whereby JBlock software (Estherhuizen, 1996) is used to estimate potential block sizes as part of the support design process. Using information such as the spacing, orientation and length of discontinuities, it is possible to simulate blocks in the walls of an excavation (Esterhuizen and Streuders, 1998). Keyblock analysis methods (Goodman and Shi, 1985) are used to evaluate whether blocks are removable and whether the chosen support will be sufficient to ensure stability. Data from two mines is used to demonstrate how probabilistic keyblock analyses can be used in support design. Discontinuity data was used to generate 10 000 removable blocks and the design block size statistics were determined. For one mine this information was used to scale blocks in a conventional. Unwedge analysis whilst for the other mine, the point estimate method (Harr, 1987) was applied. The choice of appropriate design acceptance criteria in terms of factor of safety and probability of failure is also considered.

Nov 25, 2010

By David Evans, David Barnes, Robert Raponi

"The Williams Mine processes, on average, 6,450 t/d of gold bearing ore using two parallel grinding circuits, leaching and C.1.P., carbon stripping, electrowinning and refining. At present, each grinding circuit consists of a SAG mill in closed circuit with a spiral classifier and a ball mill in closed circuit with two stages of cyclones.Since grinding has always constituted the largest portion of milling costs, the Williams Mine has been proactive in trying to reduce such costs through innovative changes. One project under consideration is the replacement of one spiral classifier by a vibrating screen.This paper discusses the testwork performed to evaluate the replacement of one spiral classifier by a vibrating screen, and the preliminary engineering performed to date.IntroductionThe Williams Mine, located in northwestern Ontario, approximately 40 kilometres east of Marathon, is part of the Hernia gold camp. The mine is operated by the Williams Operating Corporation and is owned by the Teck Corporation and Homestake Canada Incorporated. Operation of the mine started in October 1985 at a rate of 3,000 t/d. After a mill expansion in August 1988, throughput increased to 6,000 t/d. Production has increased steadily since the mill expansion and in 1995, an average of 6,450 t/d of ore was processed at a recovery of 95.1 %."

Jan 1, 1997

By E. Landry, W. Naudts

"The amenability theory was developed by Alex Naudts and considers grouting operations as continuous permeability tests where Newtonian test fluid water, is replaced by a cementitious or solution grout. It utilizes hydraulic conductivity and grouting data to establish the amenability coefficient of a particular grout zone. The amenability coefficient reflects the quantity of apertures or voids accessible to the selected grout, divided by the number of apertures accessible to water, in the zone intersected by the grout hole. By calculating, in real time, the effectiveness of a particular grout at the start of a grouting operation, the most appropriate grout to match design criteria can be targeted. By incorporating the amenability theory in every grouting operation, schedule savings and an increase in productivity are typically achieved. Three short case studies illustrate different enhancements in productivity: At an underground mine during the construction of declines, a cement based suspension grouting program was highly ineffective and did not appear to affect the inflow into the mine workings. The amenability theory was utilized to evaluate the grouting program and based on this evaluation, changes to the grouting program were made which allowed the grouting to meet the project’s objectives. On another project, a pre-excavation grouting program implemented during shaft sinking operations utilized the amenability theory to select the most suitable grout for the program. Schedule constraints also influenced the selection of the grout. In the third case history presented, the amenability theory was used to select the grouting sequence of every individual grout hole for a grouting project in a highly heterogeneous soil formation. INTRODUCTION The amenability of a given soil, civil structure or rock formation for a particular grout formulation is a measure of the ability of that grout to permeate the pores, fissures and apertures water will flow through. The amenability coefficient of a particular grout for a specific zone equals the percentage of apertures, pores and fissures accessible by water that are also accessible by grout. Grouting should be viewed as a continuous permeability test, where the apparent in-situ hydraulic conductivity value for a particular grout zone is continuously evaluated, using grout instead of water as test fluid."

Jan 1, 2019

By R. C. Ku, A. J. McEvily, T. L. Johnston

The microplastic response of a series ofas-quenched Fe-Ni-C martensites has been measured at 77°K. At strains less than JO'3 the flow stress is governed primarily by the transformation-induced dislocation structure of the martensite. Only at strains in excess of 10-3 is the influence of carbon manifested in the flow stress. At these macroscopic strains, typically 10-2, the solid-solution hardening is proportional to (wt pct C)1/3, and, in an alloy containing 0.39 wt pct C, amounts to 50 pct of the flow stress. THE technological significance of high-strength ferrous martensite has stimulated many investigations of its structure and properties. Although our knowledge of the characteristics of martensite has increased immensely, especially with the advent of high-resolution techniques, an understanding of the basic strengthening mechanism still remains elusive. The purpose of the present paper is to consider certain aspects of micro-plastic behavior of Fe-Ni-C martensite which we feel can help to resolve this important problem. Such alloys are particularly suitable for experimental investigation because their compositions can be adjusted to reduce the M, to a temperature low enough essentially to eliminate the diffusion of carbon in the freshly formed martensite.1 The mechanical properties in this condition are of interest inasmuch as they reflect a state that is free of the important but complicating influence of precipitation processes. In this virgin martensite the carbon is distributed as it was inherited from the parent austenite; i.e., it is present interstitially, and gives rise to tetragonality through strain-induced ordering.' In order to determine the source of strength of such alloys, Winchell and Cohen1 investigated the low-temperature macroscopic stress-strain behavior of a series of virgin martensites of increasing carbon content but of common M, temperature (-35°C). They found that the flow stress increased rapidly with carbon content up to 0.4 wt pct; beyond this point the flow stress increased at a much slower rate. It was concluded that martensite is inherently strong. To account quantitatively for the strength of virgin or as- quenched martensite in terms of the role of carbon, Winchell and cohen3 suggested that the carbon atoms, trapped in their original positions by the diffusionless martensite transformation, interfere with dislocation motion according to a model akin to that of Mott and Nabarro. 4 In this treatment, individual carbon atoms are considered to constitute centers of elastic strain and thereby generate an average stress resisting the motion of dislocations throughout the lattice. The additional stress necessary to move dislocations, over and above that necessary for motion in a carbon-free martensite, is given by where L is an effective length of dislocation capable of motion. L was assumed to be limited to the spacing between the twins that are an essential structural element of Fe-Ni-C martensites. They assumtd the spacing to be invariant and of the order of 100A. However, recent work5 has shown that L is variable and can be in excess of 1000Å, so that the assignment of an appropriate value of L is not straightforward. In contrast to the above conclusion that there is an intrinsically high resistance to plastic flow, it has been suggested by Polakowski6 that freshly quenched martensite is in fact "soft" in the sense that dislocations are initially free to move upon application of stress. The high indentation hardness and macroscopic yield stress of ferrous martensites are then a consequence of rapid strain hardening that depends upon carbon in solution. Consistent with this point of view are the results of Beau lieu and Dubé who measured the rate of recovery of internal friction as a function of aging (tempering) temperature in a freshly quenched steel containing 0.90 wt pct C, 0.37 wt pct Mn, 0.1 wt pct Cr, and 0.07 wt pct Ni. The kinetics were clearly consistent with the idea that many dislocations are unpinned in the as-quenched state and that during aging they become progressively pinned by carbon at a rate controlled by carbon diffusion in the body-centered martensite lattice. In order to provide a basis upon which to distinguish between the "hard" and "soft" interpretations indicated above, we have made studies of the initial stages of plastic deformation in Fe-Ni-C martensites similar to those'used by Winchell and Cohen. It will be shown that the results support the contention that dislocation segments in as-quenched material are indeed

Jan 1, 1967