MODELING OF METALLURGICAL PROCESSES

A.K. LAHIRI

Department of MetallurgyIndian Institute of Science, Bangalore – 560 012

Metallurgical processes are very complex and our understanding of them is far from adequate

for proper first principle models. At present, first principle models require tuning or adjustable

parameters to get proper result. So physical models and empirical models are often used for

practical solutions.

Experience in modeling of Corex process, Hot Rolling Mill and Foaming will be discussed.

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MY EXPERIMENTS WITH THE IMPRESSION CREEP TECHNIQUE

D.H. SASTRY

Department of MetallurgyIndian Institute of Science, Bangalore – 560 012

Impression creep technique is a modified indentation creep test wherein the conical or ball

indenter is replaced by a cylindrical, flat bottomed punch. The usefulness of this technique is

illustrated by application to a variety of investigations. The high temperature creep behavior

of a number of metals and alloys, with emphasis on the estimation of the thermal activation

parameters aiding the identification of the rate controlling mechanisms of creep, has been

investigated. The technique has also been exploited to assess the ‘single crystal’ creep

behavior vis-à-vis that of a polycrystalline sample. Utilizing the impression creep test, the

creep behavior of individual zones in steel weldments has been examined. The simplicity and

the utility of the impression creep test has been further demonstrated by its application to the

study of superplastic behavior in alloys. This talk presents a cross section of the results

obtained in the above investigations. It is concluded that this novel creep technique is capable

of yielding much of the information that can be obtained from the normal tensile creep testing.

Furthermore, the test method can provide data which are either impossible or extremely

difficult to obtain with conventional creep testing.

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RECENT DEVELOPMENTS IN IRONMAKING

AMIT CHATTERJEE

Adviser to the Managing Director, Tata Steel, Jamshedpur – 831 001

The blast furnace has continued to be the principal means of producing hot metal. Its

superiority has not been challenged for more than 100 years. Therefore, although it is an old

process the fact that it continues to reign supreme as far as bulk hot metal production is

concerned may not be surprising.

This has happened because of several innovative changes in blast furnace technology, the

most important of which are: increased use of coal injection to replace more than 50% of

metallurgical coke, and suitable re-engineering to make the process applicable to even small

scale production (100 – 300 tpd compared with the earlier range of 1000 – 10,000 tpd).

However, because of the shortage of coking coal, no matter how much coal is injected, a

certain amount of high-grade coke has to be used in blast furnaces. Alternative methods of

iron production under the generic names Direct Reduction and Smelting Reduction have been

evolved to complement blast furnace iron making.

Although these alternative processes have not yet made a substantial impact on the overall

ironmaking scenario, they have made it possible to make hot metal without using any coke.

These processes are also more ecologically friendly. Because of these reasons, it is

anticipated that these alternative processes will play an increasingly more important

complementary role.

India has made a good beginning by becoming the world’s largest producer of DRI and

having established SR technology via the COREX route at JSW Steel Limited, Toranagallu,

Bellary district, Karnataka.

This talk will discuss these issues, give details of the promising alternative processes, and take

a peep into the future.

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INTERPLAY BETWEEN EXPERIMENTS AND THEORETICAL DEVELOPMENTSIN MATERIALS SCIENCE AND ENGINEERING

PLACID RODRIGUEZ

Vice- President Indian National Academy of Engineering, New Delhi, andDAE- BRNS Senior Scientist and AICTE-INAE Distinguished Visiting Professor,

Department of Metallurgical and Materials Engineering,Indian Institute of Technology Madras, Chennai – 600 036

Theory or Experiment, "Episteme or Techne": The question: "Which of the two is more

important or which comes first?" has been debated from the time of the ancient Greek

philosophers. The main message of this paper is that both are equally important and that it is

the interplay between experimental research and theoretical developments that lead to path-

breaking science and revolutionary technologies. An allied question is the relationship

between Science and Technology. The linear model that

SCIENCE → TECHNOLOGY → ECONOMIC WEALTH

which was postulated by Adam Smith and Francis Bacon is found to be not totally valid when

we closely examine the history of the sciences and technologies. In science, more often

experimental research reveals new phenomena and new facts, for the explanation of which, a

new theory needs to be developed. Quite often, an already well-known phenomenon needs

modifications in the existing theory to fully explain all the experimental observations

including some of the anomalies. We also find similarly that most of the technologies

preceded the related science in the sense that the technologies were developed based on

empirical knowledge, common sense and ingenuity and the scientific principles underpinning

the technologies were understood or developed only later.

The above thesis is illustrated by examples taken from the author's own fields of

specialization: Materials Science and Engineering and Nuclear Science and Technology. The

scientific basis of the extraction of metals was fully developed only in the 19th and 20th

century with the concepts of Gibbs free energy, Arrhenius rate equation and Eyring’s absolute

reaction rate theory which were postulated in 1876, 1889 and 1935 respectively. However by

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1935 almost all the chemical elements except the Lanthanides (the rare earths) and the Trans-

uranium elements were isolated and separated. It is also pertinent to point out that commercial

production of many of the common metals also was achieved much before the science of

extractive metallurgy, as we know it today was developed. On the other hand, the subject of

crystallography was developed fully and comprehensively much before an experimental

technique like X-ray diffraction was available for probing and determining the crystal

structure of materials. We also have examples that many of the scientific discoveries have

depended on advances in technology. Advances in technology in the form of scientific

instruments and techniques like X-ray diffraction and electron microscopy have resulted in the

new science of Materials Science and Engineering with its scientific basis emanating from

new insights into chemistry and physics embracing the old technologies of metallurgy and

ceramics and the new technology of polymers.

Another example is the scientific basis of the strength of materials. The concept of

dislocations which was postulated in 1934 was a classic example of the need felt for a new

theory to explain a large body of experimental observations. Most of the strengthening

mechanisms in metals and alloys were all observed and discovered as phenomena and

experimental facts much before 1934. But the theory of crystal dislocations for the plastic

information of materials had to wait nearly three decades before it received universal

acceptance; the direct observation of dislocations under the electron microscope became

possible only in 1956 with the interplay between electron microscopy as an experimental

technique and the kinematics of electron diffraction as a theoretical development. The paper

gives a few more examples of the interplay between experiments and theory and between

science and technology with examples taken from the impact of Nuclear Technology on

Materials Science and Engineering.

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CHARACTERIZATION OF STRUCTURAL METALS USING NONDESTRUCTIVEBALL INDENTATION (ABI) TECHNIQUE

K. LINGA (KL) MURTY

North Carolina State University, Raleigh NC 27695-7909, USA

The talk summarizes our work on the mechanical and fracture characterization of various

metals using a stress-strain microprobe (SSM) based on automated ball indentation technique.

The ball indentation technique is uniquely suited in cases where there is a limited amount of

material (nuclear, microelectronics, nanostructures, etc) and in cases where gradient properties

are expected such as in welds. The automated ball indentation (ABI) technique of the SSM

system is based on strain-controlled multiple indentations (at a single penetration location) of

a polished surface by a spherical indenter (e.g. 0.25 to 1.57 mm diameter) and the indentation

depth is progressively increased to a maximum user-specified limit with intermediate partial

unloadings. The technique permits measurement of yield strength, stress-strain curve, strength

coefficient, and strain-hardening-exponent (uniform ductility). From tests at varied

temperatures, estimates can be made on energy to fracture. We present results on gradient

properties of reactor pressure vessel steels, effect of cold-work on mechanical and fracture

characteristics, effect of thermal aging in a cast SS and a superalloy, mechanical anisotropy of

textured Zr alloy tubing, strain-rate effects in microelectronic solders and mechanical

properties of nanograined metals. We demonstrate here the usefulness of the technique for in-

situ condition monitoring of structural metals.

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EXPERIMENTAL DESIGNS TOWARDS AN UNDERSTANDING OF PROCESSPHENOMENA IN STEEL MAKING

A. KAPILASHRAMI1, E. KAPILASHRAMI2, M. GÖRNERUP1 ANDS. SEETHARAMAN1

1 Division of Materials Process Science, Royal Institute of Technology,SE-100 44 Stockholm, Sweden

2 Blast Furnace-Iron Making Department, SE-631 80 Oxelösund, Sweden

An understanding of process phenomena is essential in the optimization of metallurgicalprocesses. With respect to steel making processes, the process models need be based on theprocess fundamentals in order to develop models of the existing processes as well as to findnewer process solutions. Experimental designs to understand the reaction mechanismsunderlying the processes are receiving increasing attention during recent years. Examples ofsuch experimental designs are presented in the present paper. Thermal diffusivities of the cokesamples from different depths in the experimental blast furnace have led to very interestingobservations with respect to the degree of graphitization of coke during its descent in the blastfurnace and thereby, its reactivity. Thermal diffusivity measurements were also used tomonitor the behavior of mould flux slags and their crystallization. These results are alsoconfirmed by X-ray diffraction studies.

The reduction behaviour of iron oxide pellets by CO/CO2 gas mixtures was monitored by X-ray image analysis method. The heating rate of the pellet and the presence of elemental carbonin contact with the pellet seem to have significant impact on the reduction phenomenon.

Studies of bubble formation experiments using cold modeling and monitoring of slag foamingphenomenon under an ongoing reaction have been carried out in collaboration with IndianInstitute of Science. Wetting of refractories by liquid iron under dynamic conditions by X-rayradiography is an area that gives insight into the refractory reactions.

X-ray visualization experiments were designed and carried out in the case of four differentfluxes used in various Swedish steel companies in order to understand the melting behavior ofmould fluxes The observations show unique results illustrating the differences in the meltingbehavior of different fluxes with apparently similar compositions. The surface- and interfacialtensions of the mould flux slags were also measured as part of this study.

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LTCC TECHNOLOGIES FOR HARSH-ENVIRONMENT AUTOMOTIVEAPPLICATIONS UTILIZING SOLDERED INTERCONNECTIONS

D.H.R. SARMA

Delphi Electronics and Safety, Kokomo, Indiana 46904-9005, USA

This paper summarizes the results from an extensive study designed to evaluate LTCC (Low-

Temperature Co-fired Ceramic) technology for automotive ECM (Engine Control Module)

applications and to demonstrate the design advantages that it offers. Test and demonstration

parts were prepared from the DuPont 951 green tape system using various tape thicknesses,

compatible conductor materials and surface resistors. Conventional performance tests such as

solderability, aged adhesion, dielectric voltage breakdown and crossover shorting were carried

out, as well as solder-joint based thermal-cycling tests of components including, full array and

perimeter bump flip chips. In situations where individual materials demonstrated

unacceptable performance, improvements were made or new materials developed.

Packaging advantages of LTCC including flip chip on via, backside resistors and constrained

sintering (zero shrinkage in the x- and y-directions to improve positional tolerance) are

discussed. In addition, material and design solutions to thermal issues that enable single

board LTCC designs for ECU's (Electronic Control Unit) are presented. The results of a

concurrent project in which a functional engine control product emulator was built and

successfully tested are referenced and discussed in the context of the results from this work.

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KINETICS OF INCLUSION ENGINEERING, SOLIDIFICATION AND PHASETRANSFORMATION OF STEELS

TOSHIHIKO EMI

Emi TechnologyFormerly Professor, Tohoku University and

Member of the Board, Kawasaki Steel Corp. (Now JFE Steel)

Contact Address: Takasu 5-1, B1905Urayasu-shi, Chiba 279-0023, Japan

In-situ dynamic observations have been accomplished of the phenomena associated with

refining and solidification of liquid steel for producing super performance steels. A confocal

scanning laser microscope (CSLM) combined with infrared image furnace (IIF) has been

developed for the observations at elevated temperatures (~1873K) with high resolution

(0.5µm). The phenomena include the process of (1) agglomeration of alumina inclusion

particles into clusters, (2) kinetics of disintegration and transformation of the clusters into

lime-aluminate particles by lime treatment, (3) pushing and engulfment of the inclusions by

advancing solid/liquid interface, (4) development of the perturbation of the interface to

transform planar crystals into cellular and dendritic morphology, (5) kinetics of the peritectic

solidification, (6) characteristic behavior of δ→γ phase transformation and (7) determination

of interfacial energy of δ/γ boundaries, and (9) kinetics of the crystallization of mineral phases

in molten silicates. Theoretical interpretation and technological significance of these

observations will be presented together with promising areas of application of the CSLM-IIF

combination in metallurgical research.

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ISOTHERMAL MULTIPLE HEAT STRESS RUPTURE CORRELATIONS

S.K. RAYMaterials Technology Division, Metallurgy and Materials Group

Indira Gandhi Centre for Atomic Research, Kalpakkam – 603 102

The author and his coworkers developed [1-3] a generic method, henceforth called RSR (after

Ray-Sasikala-Rodriguez) method, to account for the heat-to-heat variations in stress rupture

properties of structural steels. Specifically, it was proposed that in any stress rupture

correlation, ln (σ/µ) and ln tr could be substituted respectively by the corresponding “heat-

corrected” terms P1 and P2. For the k -th heat, with αk and βk as the corresponding heat-

indexing constants, the “heat corrected” terms are defined as P1≡ ln(σ/µ)+ βk and P2≡ln tr −αk.

Graphically, this “heat correction” means that for any chosen temperature, plots of ln tr

against ln(σ/µ) for different heats can be superposed by translations parallel to the axes by

amounts that varies with the heat, but is independent of temperature. This also necessitates

that for the (arbitrarily selected) “first” or “reference” heat, the heat indexing constants are

assigned pre-fixed values; it is convenient to take α1 ≡ β1 ≡ 0. This overview presents a

summary of the work carried out by the author and his colleagues [4-11] using this heat

indexing method for isothermal multiple heat stress rupture correlations.

The only other method in the literature using pair if indexing constants for each heat, is that of

Manson and Park (MP) which differs from the RSR method in the definition for the “heat

corrected” stress term: P1 ≡ βk . ln(σ/µ). The two HCs were compared for their efficacies in

isothermal multiple-heat stress rupture correlation using literature data for a number of ferritic

and austenitic steels (0.5Mo-0.15C steel, a 9Cr-1Mo steel, two grades of 2.25Cr-1Mo steels,

and two grades of AISI type 316 stainless steels). While both MP and RSR correlations

provide viable means for accounting for heat-dependence of creep rupture life, in general the

HC used in RSR correlation is significantly superior to that in MP correlation for the non-

austenitic grades considered, and marginally superior for the austenitic grades. Further, it was

shown that for type SS 316 (tubes and bars) and 2.25Cr-1Mo steel (tubes and plates), robust

isothermal correlations can be derived from combined analysis of stress rupture data for

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multiple heats of different product forms. It was concluded that mechanism(s) for creep

damage evolution remains unchanged in the various heats of the various product forms for the

same generic grade; these heats differ only with respect to quantitative aspects of creep

damage kinetics.

Similarly, it was demonstrated that it is possible to consider heats of SS 316 L(N) base metal

as variants of the SS 316 grade; robust isothermal “reference” correlations were generated by

pooling the extensive body literature stress rupture data for large number of heats SS 316 and

SS 316L(N) base metals and using RSR heat indexing method. For 99.73% confidence

interval, the uncertainty in predicted rupture life decreased from a factor of ~39 without any

HC, to a factor of ~ 6 using RSR heat correction method. The reference correlations can be

utilised to (i) predict the rupture life of any of the heats included in the analysis at these

temperatures, (ii) to economically generate long-term data to extend the validity range for

extrapolation, and (iii) to characterize a “new” heat of SS 316 or SS 316L(N) base metal with

from limited body of (short duration) rupture data. The last point has been illustrated, not only

for an SS 316 L(N) base metal, but also for an SS 316(N) weld metal. For the latter material,

the complex effects of in situ transformation of the initial δ - ferrite into embrittling phases

during creep necessitated rejection of rupture data for relatively short durations.

1. Ray S K, Sasikala G, and Rodriguez P, Trans Ind Inst Metals 48 (1995) 453.2. Ray S K, Sasikala G, and Rodriguez P, Trans Ind Inst Metals 48 (1995) 467.3. Ray S K, Sasikala G, and Rodriguez P, Trans Ind Inst Metals 48 (1995) 483.4. Sasikala G, Ray S K, and Rodriguez P, Int J Pressure Vessels and Piping 75 (1998) 287.5. Sasikala G, Ray S K, and Rodriguez P, Scripta Metall 39 (1998) 1353.6. Sasikala G, Ray S K,and Rodriguez P, Mater Sci Engg A260 (1999) 284.7. Sasikala G, Ray S K, Mannan S L, and Rodriguez P, in Proc. Int. Symp. Materials Ageing

and Life Management, October 3-6, 2000, (eds.) Baldev Raj, K. Bhanu Sankara Rao,T. Jayakumar and R.K. Dayal, Allied Publishers, (2000) pp.186-192.

8. Ray S K, Sasikala G, and Rodriguez P, Trans Indian Inst Metals 55 (2002) pp.31-41.9. Sasikala G, Ray S K, Mannan S L, and Rodriguez P, HNS 2001, Trans Indian Inst Metals

55 (2002) pp.329-335.10. Sasikala G, Ray S K, Mannan S L, and Rodriguez P, Mater. Sci. Technol. 19 (2003) pp.

626-631.11. Sasikala G, Ray S K, Mannan S L, and Rodriguez P, Mater. Sci. Technol. 19 (2003) pp.

632-636.

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NON-CONVENTIONAL METAL PROCESSING

T.V.L.N. RAO

Advance Engineering, Die Casting Division, Sundaram Clayton Ltd, Chennai – 600 050

Processing of components play a predominant role for meeting the performance requirements

especially while being applied for critical applications. Metals and alloys developed for

aerospace applications should meet the stringent quality norms stipulated as per the end

application. Aerospace components are critical and complicated, as they have to meet a

combination of properties of tensile strength at low and elevated temperature, creep, stress

rupture, Low cycle fatigue at low temperature and at elevated temperatures, etc. As these

components are subjected to variable stresses and temperatures during service, they are

exposed to a situation of a complex thermomechanical environment. Hence, the components

experience random loading conditions with a varying atmosphere. An evaluation of structure

property correlation in this case would be of creep fatigue interaction. In view of this complex

requirement for such applications, components designers and manufacturers have evolved at

designing components and their processing as per their functional requirements. This

presentation elucidates the experience we had in designing processes for the manufacture of

components of superalloys, titanium alloys and special steels at MIDHANI employing

innovative processes which include superplastic forming, roll forming and spinning.

The automotive industry is fast growing in the country. There is a great potential for

developing automobile components to meet the demand from the automotive industry.

Pressure die-casting of aluminum based automobile components are widely used in this

industry. This presentation shows a science-based approach being followed by the industry for

the evolution of technologies for component development by die-casting.

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EVALUATION OF TIN-BASED LEAD FREE SOLDERS BY IMPRESSION CREEPTECHNIQUE

G.S. MURTHY

Department of Metallurgical Engineering, Andhra University, Vishakapatnam – 530 003

Soldering technology plays a key role in modern electronics, telecommunication, automobile

and aircraft industries. Tin-Lead alloys have been conventional solders for a long time due to

their low cost combined with good solderability. The harmful and toxic effects of lead on

human health and environment have spurred the search for suitable alternative alloys. Creep,

due to heating in service, is a major cause of solder joint failures in electronic and other

applications.

In the present study, the creep behaviour of some tin-based lead free solders has been

investigated by Impression Creep technique in comparison with that of conventional Tin-Lead

solders.

The study reveals that binary Sn-3.5Ag, Sn-9Zn and Sn-58 Bi alloys exhibit better creep

resistance while the ternary Sn-57 Bi- 1.3 Zn alloy shows similar creep behaviour and the

binary Sn-0.7 Cu shows much lower creep resistance compared to conventional Sn-Pb

solders.

Based on the studies, it can be concluded that Sn-3.5 Ag, Sn-9 Zn and Sn-58 Bi alloys can be

suitable substitutes at higher operating temperatures with improved solder joint reliability. For

normal applications the ternary Sn-57Bi – 1.3 Zn alloy can be an effective non- toxic

replacement for Sn-Pb solders.

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STUDIES ON INDENTATION CREEP BEHAVIOUR OF NUCLEAR GRADESTAINLESS STEEL WELDS

BHEEMARAJ UDAPUDI AND K. RAJENDRA UDUPA

Department of Metallurgical and Materials Engineering,National Institute of Technology Karnataka, Surathkal - 575 025

Experiments have been carried out to investigate the indentation (impression) creep on TIG

welded nuclear grade AISI 316 austenitic stainless steel. Samples were selected from the

plates which had been welded by implantation technique by introducing Cr during welding in

order to maintain ferrite level in 2-6 FN. The samples of both weld and parent metal region

were aged at various combinations of time and temperature in the range of 300°C to 500°C for

the period of 500 to 2500 hrs.

Impression creep behavior of samples aged in different conditions was tested using tungsten

carbide indenter at various stress levels in room temperature. From the indentation depth vs.

time plot, impression creep rates were calculated. Creep rates for welded metal and parent

metal are compared.

Results of the experiments on impression creep behavior suggest that creep resistance of

welded region is superior to those of parent metal. It is found in the present investigation that

there is a dependency of creep on the hardness of the materials for all the cases, both in weld

and parent metal portion of the weldment. Dislocation creep mechanism seems to be

dominating under the conditions of the present investigation.

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DIFFUSION BONDING OF TITANIUM AND ITS ALLOYS

M. SUJATHA

Materials Science Division, National Aerospace Laboratories, Bangalore-560 017

The paper presents an overview of the diffusion bonding technique and the usefulness of the

technique in the fabrication of various components used in the aerospace sector. The evolution

of this technique and the recent advances in the diffusion bonding of titanium alloys and its

aluminides is presented. Preliminary results obtained from diffusion bonding studies on

commercial pure titanium and other (α+β) titanium alloys with γ titanium aluminide Ti-48Al-

2V-2Nb are presented. Bonds were prepared under vacuum at pressures 40 –56 MPa and in

the temperature range of 800-9000C for times ranging from 1800-3600 s. Microstructural

studies showed formation of a diffusion zone of width 0.5-1.0 µm at the bond line depending

on the bonding parameters.

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JSW STEEL: AN OVERVIEW

D. GUPTA

DGM (R&D, Process control-Iron zone), Jindal Vijayanagar Steel Ltd., Hospet – 583 123

Jindal Vijayanagar Steel Ltd (JVSL) is a relatively new company. Present steel capacity is 2.5

MT and by March-06 it’s going to be 4.0 MT. JVSL started hot metal production in 1999,

pellet plant in 2000. Since then it has grown both in size and activities. It has added a blast

furnace and a coke oven. One more blast furnace and a coke oven and a sinter plant are also

coming up shortly. This paper discusses about the transition of JVSL to JSW Steel, which

includes, Steel plants, port, mining and power facilities. Some of the unique features of JSW

Steel are its COREX Ironmaking facilities, non-recovery Coke Oven, COREX Gas based

Pellet Plant etc. Its synergistic combination of COREX and Blast Furnace offers specific

operational flexibility. Technological details of COREX and non-recovery Coke Oven have

been discussed at length in this paper.

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BLAST FURNACE: MODELLER’S PARADISE

N.N. VISHWANATHANDepartment of Metallurgical Engineering and Materials Science,

Indian Institute of Technology Bombay, Mumbai – 400 076

Blast furnace is a highly efficient counter current heat and oxygen exchanger wherein iron ore

is converted to liquid iron in large quantities. The present understanding of the blast furnace

is primarily from the dissection studies carried out in 70’s. However, it is very difficult to

know internal state of a furnace in operation. Even with the present advanced instrumentation,

it is possible to collect only limited information from a working blast furnace. In this context,

mathematical model can be of great help in understanding the internal state of blast furnace,

which further can aid in operation and control.

National Metallurgical Laboratory, Jamshedpur through Ministry of Steel has initiated

national level project on Blast Furnace Modelling involving steel industries, research labs and

academic institutions. As a part of this project IIT-Bombay is involved in the crucial part of

developing a mathematical model to simulate gas flow, solid flow, composition and

temperature profiles inside the furnace from the throat to the slag level in the hearth.

Blast furnace being a complex heterogeneous reactor involving solid, liquid and gaseous

phases it poses a great challenge for a modeller. In this paper, various aspects of model

building along with some of results obtained from the model will be presented.

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MATHEMATICAL MODEL OF COREX MELTER GASIFIER

S. PAL

John F. Welch Technology Centre, GE, Bangalore – 560 066

COREX is an alternative process of producing liquid iron using pure oxygen and non-coking

coal. The process is physically divided into two reactors, namely, the reduction shaft and the

melter gasifier. Iron ore gets reduced in the solid state in the reduction shaft. This partially

reduced iron (DRI) is reduced completely and melted in the melter gasifier. In this

presentation, three different mathematical models of melter gasifier, namely 2D steady state,

dynamic and 3D model will be discussed.

The 2D steady state model is developed to obtain a better understanding of the COREX melter

gasifier. The model aims at predicting the temperature, concentration and velocity fields of

different phases inside the furnace. During plant operation, after blow-in, the furnace passes

through a transient period before it reaches steady state. Besides, often, it is required to

shutdown the furnace for routine maintenance, which leads to an unsteady state for a

significant period of time. In this context, a dynamic model is developed to study the transient

behavior of the furnace. Finally, we discuss a 3D model to describe the furnace behavior when

one of its tuyeres is blocked.

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INTERFACIAL SHEAR STRENGTH OF THE PERFLUOROCYCLOBUTANE(PFCB) FILMS ON SILICON

B. SRINIVASA RAO

Materials Science and Engineering, University of Washington, Seattle, WA 98195-2120, USA

The debonding behaviour of perfluorocyclobutane (PFCB) films on Silicon (Si) has been

investigated using indentation as a function of cure temperature and film thickness. PFCB

films on Si were processed by spin coating (1-4 micron) and solution casting (20-60 micron).

The interfacial shear strength of PFCB/Si was independent of film thickness, however, the

strength increased with cure temperature. The PFCB/Si cured at 225oC exhibited interfacial

shear strength of 137 MPa and the strength increased to 165 MPa when the cure temperature

was raised to 275oC. The increase in interfacial strength as a function of temperature has been

attributed to the enhancement of the bonding between PFCB and Si due to increase in the

density of cross-links. Spin coated films exhibited better adhesion than the solution cast films.

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A CRITICAL DAMAGE CRITERION FOR CREEPING SOLIDS

C. PHANIRAJ

Metallurgy and Materials GroupIndira Gandhi Centre for Atomic Research, Kalpakkam - 603 102

Creeping solids fail as a result of initiation and growth of damage that manifests as increase in

deformation rate during tertiary stage leading to failure. Before reaching tertiary creep, the

material deforms at a minimum creep rate and this stage is desirable to avoid failures. The

product of minimum creep rate and time to failure, generally found to be constant as proposed

by Monkman and Grant, is the total secondary strain contribution of creep ductility and is

referred to as 'Monkman-Grant Ductility' (MGD). A new concept of time to reach MGD is

introduced as the time at which MGD is reached along the creep curve and 'true tertiary creep'

sets in. It is put forward that the time to reach MGD is the time at which the creep damage

attains a critical level. This is shown for a typical case of cavitation mechanism in α-iron

where the time to attain critical cavity size matches well with the time to reach MGD. A

critical damage criterion is proposed as a unique relationship between time to reach MGD and

time to failure that depends only on the tolerance of material to resist creep damage. The

validity of the proposed creep damage criterion is demonstrated for a wide range of materials

from pure metals to complex engineering alloys. Further it is shown that the damage criterion

has useful implications in engineering creep design of high temperature components.

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PERSPECTIVES IN RESEARCH IN THE AREA OF POWDER METALLURGY

A.O. SURENDRANATHAN

Department of Metallurgical and Materials Engineering,National Institute of Technology Karnataka, Surathkal - 575 025

In this paper, the perspectives in research in the area of powder metallurgy for the last decade

are briefly dealt with. The topics covered in some detail are microwave sintering, mechanical

alloying, electrical discharge texturing (EDT), bonded abrasives, and application of artificial

neural networks. Mention is also made of high-energy production of materials, production of

metallic foams, etc.

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CORROSION INHIBITION OF AL–SIC(P) COMPOSITE IN HYDROCHLORIC ACID

SUMA A. RAO1, PADMALATHA1, J NAYAK2, A.N. SHETTY2, K.R. HEBBAR2 ANDH.V.S. NAYAK2

1 Manipal Institute of Technology, MAHE, Manipal-576 1042 Department of Metallurgical and Materials Engineering,

National Institute of Technology Karnataka, Surathkal-575 025

Aluminium matrix composites look very promising and are expected to overtake conventional

Al-base alloys. One of the main drawbacks of aluminium matrix composites is decrease in

corrosion resistance compared to the base alloy for which a protective oxide surface film

imparts corrosion resistance. Addition of reinforcing phase (a function of reinforcement

proportion and particle size) can lead to inhomogeneities and cause discontinuities in the

surface film, increasing the number of sites where corrosion can be initiated and making the

composite more vulnerable.

In this study the inhibitive behaviour of Pyridinium salts of 1,3-Thiadiazole-2,5-dithiol

and1,2,4-Trizole-3,5-dithiol on the corrosion of 6061 Al reinforced with 15 vol. pct. SiC

particulate composite in 0.01, 0.1and 1.0 N HCl solution has been investigated by

potentiodynamic polarization techniques in the temperature range of 303K–323K. The

concentration of inhibitors used lies in the range up to 500 ppm. The results indicate that

Pyridinium salts of both 1,3-Thiadiazole-2,5-dithiol as well as 1,2,4-Triazole-3,5- dithiol

function as moderate inhibitors for the corrosion of Al–SiC composites in HCl environment. It

is also observerved that both the organic compounds act as anodic inhibitors. The values of

∆Gads are low and negative indicating the process of physisorption but spontaneous and

exothermic. The values of ∆Gads decrease with increase in inhibition efficiency indicating the

spontaneity of adsorption process and stability of the adsorbed layer. Physisorption of these

compounds as well as Al-complexes follow Temkin’s model. The inhibition efficiency

increases with increase in inhibitor concentration and also with increase in temperature for

both the compounds. The corrosion potential shifts to more positive values indicating the

inhibitors are affecting the anodic metal dissolution process.

ABSTRACT

31

EFFECT OF MATERIAL CONDITION ON THE CORROSION BEHAVIOUR OFMARAGING STEEL IN ALKALINE MEDIA

J. NAYAK, A.O. SURENDRANATHAN, K.R. HEBBAR ANDH.V. SUDHAKER NAYAK

Department of Metallurgical and Materials Engineering,National Institute of Technology Karnataka, Surathkal-575 025

Corrosion behavior of 18Ni 250 grade maraging steel (under four conditions viz. Annealed,

Aged, Weld and Weld-Aged) in sea water [pH=8.00 ± 0.05], neutral medium [pH=7] and

alkaline medium (pH=10, pH=12 and pH=14), at three levels of temperatures (30oC, 40oC and

50oC) was investigated.

Corrosion potentials and corrosion current densities were measured by Linear polarization

technique and Tafel extrapolation technique using a very high input resistance 352 model

Versastat (EG and G make).

The results of investigation indicate that corrosion rates are influenced by material condition

(i.e. annealed, aged, weld and weld-aged) and the medium (type of the medium, temperature

of the medium and pH of the medium). Among the four conditions of the material under

investigation, annealed samples show the least corrosion rates and weld-aged samples show

the highest corrosion rates in all the media and at all temperatures. The corrosion rates of weld

samples were close to those of annealed samples but on the higher side and the corrosion rates

of weld-aged samples were close to those of aged samples but on the higher side. Aged

samples show higher corrosion rates than annealed samples in all the media and at all

temperatures. Corrosion rates of the material under all the four conditions increase with

increase in temperature in all the media except in NaOH of pH=14 where it first increases and

then decreases at 323 K. The main mechanism of corrosion in sea water was found to be

pitting by chloride ions. The material develops corrosion resistance in alkaline media, as

compared to the acid media, due to the formation of hydroxide film. As the pH of the alkaline

media increases, corrosion rate decreases and at highly alkaline condition (pH=14), the

corrosion rate again increases except at 323 K.

ABSTRACT

32

MICROSTRUCTURAL EVOLUTION IN MODEL QUATERNARY SYSTEMS -A MONTE CARLO SIMULATION STUDY

R. SANKARASUBRAMANIAN AND R. BALAMURALIKRISHNAN

Defence Metallurgical Research Laboratory, Hyderabad - 500 060

Atomistic Monte Carlo (MC) simulations are those involving sampling of distributions of

atoms at certain positions. In this presentation, the use of MC to simulate microstructures of

model Ni-Al-Cr-Re quaternary alloys will be described. The simulations have been done on a

three dimensional rigid fcc lattice with more than a million atoms. Starting from an initial

random configuration, the system energy is minimised through successive exchange of

positions of randomly selected nearest neighbouring pair of atoms. Each of these exchanges

is carried out based on the change in system energy upon exchange, which is calculated by

considering (Lennard-Jones type) pair interactions up to third nearest neighbours. Quantitative

analysis of the simulated microstructures has been carried out to obtain the partitioning of the

constituent alloying elements into the ordered γ/ and disordered γ phases.