THE 6th Seminar of Metallurgical Engineers of Serbia & Montenegro with international participation was held in Arandjelovac from 12. to 13. June. This seminar was organised by the Engineers Association of Serbian & Montenegro's Metallurgists and the Institute "Vinča", and it was sponsored by the Ministry for Science, Technology and Development of Serbia, "U.S. Steel Balkan", "Termit" Domžale, "Scan group", "Metalfer" Belgrade, "Novoterm" Belgrade, "Eurokabl" Novi Sad, "Livnica MP" Niš, "Knjaz Miloš" Arandjelovac, "Eurovix Radanov" Novi Bečej and "Gauder group" from Belgium.

Over 150 national and foreign leading experts in this field attended the Seminar. In the Proceedings were printed 4 keynote papers and 91 abstracts and over 70 papers were presented on the Seminar. Two round tables were held with the topics concerning transition, social ownership transformations and metal scrap recycling.

The President of the Program Board Professor dr Karlo Raić from the Faculty of Technology and Metallurgy opened the Seminar. Thomas Kelly, general manager of the "U.S. Steel Balkan" as a general sponsor, held a welcome speech.

The participants of "The 6^th Seminar of Metallurgical Engineers of Serbia & Montenegro " presented their latest results realized in production in the fields of: processing of iron, steel and nonferrous metals, metal forming, casting, materials engineering, physical metallurgy, heat treatment and metal recycling. The papers were presented in two sessions: the session for metallurgy of nonferrous metals and the session for iron and steel metallurgy.

In regard of a large number of presented papers and different fields of interest, this paper will present the abstracts of key lectures, a few most interesting papers and four papers of the authors from the Military Technical Institute.

Key lectures

DEVELOPMENT STRATEGY IN THE PRODUC-TION OF IRON, STEEL AND NONFERROUS ME-TALS UNTIL 2010 (S. Milošević, ITNMS, Belgrade)

The government of the Republic of Serbia in coordination with the Ministry for Science, Technology and Development and in cooperation with experts from institutes, universities and industry, presented "Strategy of economic development in Serbia until the year of 2010" as well as "Selected development programs". In order to understand development trends in production of iron, steels and nonferrous metals it is necessary to gain insight into circumstances, directions and aims of economic development in Serbia until 2010. The average annual growth rate of the overall Gross Domestic Product (GDP) is predicted to reach 8.55%, export prediction is 40-45% GDP, with the prospects of structural harmonising with EU and a GDP of 2830 $ until 2010.

To reach these goals of development in Serbia, as well as the goals of development in the sector of metal production in the future, basic tendencies in world economy development have to be accepted - in the future, the forming of the world GDP by 80 % will belong only to free economies capable to accept a new logic of the world market.

The industry of iron, steel and nonferrous metals is viewed in "Strategy of economic development in Serbia until 2010" as a sector in the group A, with the main goal to maximize export up to 40-50% of the GDP.

A possible GDP until the year of 2010 in the industry of iron and steel could be approximately 407 million dollars, in nonferrous industry approximately 600 million dollars, export 60 % of production, investment of 120 and/or 450 million dollars, participation in total domestic production of 1.79 or/and 2.64%, participation in overall investments in economy of 0.49 or/and 1.84%, etc.

FACTS AND FUTURE OF THE STEEL INDUSTRY IN SERBIA & MONTENEGRO (S. Marković, Association of Ferrous Metallurgy, Belgrade)

A review of steel production in the world and in our country for the last 50 years and the capacity and production of steel in Serbia and Montenegro nowadays were presented in this paper. Technical capacity for steel production in the "Sartid" are on the level of 1 100 000 tons and in the "Željezara Nikšić" are approximately 200 000 tons. Last year, production was effectively 60% of the Sartid capacity and 40% of the "Željezara Nikšić" capacity. The future of these steelwork factories is in privatization, as it was recommended in "British Steel Consultants" and "Usinor Consultants" studies. The Factory "Sartid" has been taken over by the company "US Steel " Kosice.

Session: Nonferrous Metallurgy

MANUFACTURING OF Ti-6Al-4V ALLOY FOR ARTIFICIAL HIPS, WHY AND HOW? (S. Tadić, I. Bobić, M. Jovanović, Institut of Nuclear Sciences, Vinča)

          In this paper the authors attempted to answer why Ti alloys are used as biomaterial instead of stainless steel and cobalt-based alloys. Both advantages and difficulties of application and production of Ti alloy were described. It was considered that a direct bond between metal and a bone is not allowed in clinical practice. Most implant operations of artificial hips are based on the application of cement as an intermediate layer between metal and tissue. Experience has shown that in a post-operative period it was very successful, but after longer time cement became brittle, and/or fractured, causing pain and finally resulting in need of a new operation. To avoid this inconvenience, two new techniques were developed. They are both based on bonds between the artificial hip and the tissue without cement. Metallurgical and material science aspects of these methods were very important.

          Ti and Ti alloys have the highest bond strength and the highest rate of osteointegration in the post-operative period. On the other hand, a required surface of implant is not easily achieved.

Many experiments have shown another positive property of Ti: not only Ti-implant is inert in the body, but the human body does not recognise it as a strange part.

          The authors of this paper have tried to give an answer to a question how to produce an artificial hip with required high quality i.e. the weight of 110 g, the strength of 900 MPa, good formation and crack propagation resistance, properly manufactured surface and, of course, competitive price.

STUDY OF 8xxx ALUMINIUM ALLOYS FOR FOILS APPLICATION (K. Delijić, M. Mišović, Faculty of Metallurgy and Technology Podgorica and D. Milić, S. Fatić, Aluminium Company Podgorica)

The main characteristics of 8xxx aluminium alloys that are used for sheets, bands and foils were presented. On the basis of strength and plasticity, some Al alloys have been chosen (AA1200, AA8079, AA8006, AA8011). They satisfy required characteristics. The production of 8xxx aluminium alloys is a significant production program for the Aluminium Company Podgorica. A part of testing was done during production. It has been shown that the production of 8xxx aluminium alloys could be done on the same production line used for 1xxx, 3xxx and 5xxx aluminium alloys.

TI-AL NEW MATERIAL FOR A TURBINE ROTOR (M. T. Jovanović, I. Bobić, S. Tadić, Institut for Nuclear Science, Vinča)

Intermetallic alloys based on g-TiAl represent a new class of structural materials with operating temperatures between 500 and 800°C. In comparison with commercial Ti-alloys wich are usually used up to 550°C, g-TiAl alloys have higher creep, oxidation and hydrogen embrittlement resistance. Furthermore, this material is lighter than Ti-alloy and has twice lower density than superalloys. On the other hand, as in other intermetallic compounds, ductility of g-TiAl is low (about 3%).

This material is considered to be close to commercial application, because it has achieved a significant improvement over the last few years.

The aim of this work was to produce a prototype of a turbine wheel made of g-TiAl intermetallic alloy using precision investment casting.

The obtained casting had a flat and smooth surface without porosity, but short pourds were observed in a few fins of the wheel. It was not possible to remove them completely. The hardness of 360 HV10 is according to the literature results. The microstructure of as-cast material consists of alternating laminae representing a₂ and g phases identified by X-ray diffraction.

MICROSTRUCTURAL CHARACTERIZATION OF COMPLEX ALUMINIUM ALLOYS (V. Maksimović, M.T. Jovanović, S. Zec, Institute for Nuclear Science, Vinča)

The structure of solution heat-treated and quenched commercial aluminium-copper alloy 2219 (ASTM), is modified by adding silicon, or both silicon and germanium. The content of other elements (Fe, Mn, Zn, etc.) remained unchanged. Further treatment − precipitation hardening-de-pends on the amount of copper in the solid solution. The characterization of the quenched alloy was the aim of this work.

In both alloys, a few phases of different morphology were achieved after quenching from the temperature of solution heat-treatment.

Adding silicon to aluminium-copper alloy results in the formation of Al₂Cu globular precipitates and the (Fe, Mn, Cu)₃Si₂Al₁₅ complex phase. But adding both silicon and germanium to aluminium-copper alloy results in the formation of Al₂Cu and Al₇Cu₂Fe particles. It was shown that lattice parameters of these solid solutions (alloys) are different. The reflection of the face-centred cubic phase (Al-base) for high angle values (2q>75°), shows that lattice parameters are different for these two alloys. On the basis of these results we can conclude that there are different supersaturating levels, especially of copper, in the solid solution.

POSIBILITY OF FORMING LARGE CONICAL THIN-WALLED PARTS BY SPINNING (Lj. Radović, M. Nikačević, Military Technical Institute, Belgrade and M. Hršum, ALPO Rogatica)

The purpose of this paper is to study a possibility of forming large conically shaped parts with thin walls and a curvilinear generating line by spinning.

          The blank was an extruded tube with a wall thickness of 6mm, a length of 700 mm and an inside diameter of 258 mm, made of AlMgSi1 alloy (series 6000).

          Spinning has been performed in multiple passes with a total reduction of 66.7 %. Heat treatment, annealing, quenching and ageing were carried out before and artificial ageing after forming the finished part.

          The finished workpiece was a cone with a curvilinear generating line and a radius of curvature of 6615.5 mm, length of 1400 mm, inside diameter of 258 mm and wall thickness of 2 mm.

Mechanical properties of blanks and finished parts were determined.

On the basis of testing industrial parts and laboratory examination of spinnability, the required structural and mechanical state of the AlMgSi1 alloy necessary for cone spinning was determined.

NEW PLANTS FOR ALUMINIUM SCRAP PRO-CESSING (B. Milović, M. Milović, Impol Seval, Aluminium Rolling Mill, a.d. Sevojno)

The recent achievements in remelting aluminium scrap products have been presented in this paper. The characteristics and advantages of multiple chamber furnaces (with two or three chambers) were presented. They are used for remelting aluminium scrap (primary metal, scrapings and mixed scrap).

There are a few advantages of these furnaces:

aluminum scrap can be combined with primary metal, scrapings or mixed scrap,

preparing of aluminum scrap is not necessary (cutting, separation from other kinds of materials, e.g. plastic, paint, etc.),

minimization of remelting energy using regenerated heat of flue gases,

homogeneity of obtained metal using magnetic pumps, and

maximum control of the melting process by the application of the PLC system.

Also, the modern tilting furnaces URTF were presented, together with all advantages in comparison with conventional rotary furnaces RSF (decrease of energy, faster charging, minimum oxidation of metal during melting and lower environment pollution).

Session: Ferrous Metallurgy

APPLICATION OF THE ULTRASONIC METHOD FOR MONITORING STRENGTH CHANGES IN A HEAT RESISTANT SPECIMEN UNDER THERMAL SHOCK (T. Volkov-Husović, R. Jančić, K. Raić, Faculty of Technology and Metallurgy, Belgrade, V. Djordjević, V. Stojadinović, Šamot, Arandjelovac)

          Thermal shock in heat resistant material causes quasi-static and dynamic crack propagation and leads to strength decrease. It is well known that macro and micro cracks in material influence longitudinal and transversal sound velocity and Young¢s modulus of elasticity. This was used for monitoring levels of specimen damage during thermal stability testing. In spite of the significance of monitoring crack propagation in a specimen under thermal shock from the aspect of integrity and safety of constructions, there were no reports in the literature about the application of nondestructive methods for these purposes.

          A possibility to apply one nondestructive method – ultrasonic method, for monitoring strength changes in a heat resistant specimen under thermal shock was the aim of this work. The method of determining Young¢s modulus of elasticity (JUS.D.B8.121) was used and then sound velocities, V_p and V_s were determined. Strength changes were being monitored as well.

          The results have shown that there is a correlation between the decrease of sound velocity and the number of cycles during fast cooling of material. On the basis of the equation which connects the sound velocity changes and the specimen strength a clear correlation between the specimen strength decrease and the increase of the number of cycles during rapid cooling has been obtained.

EFFECTS OF PRODUCTION CONDITIONS ON STRUCTURE STABILITY OF DUPLEX STAINLESS STEEL FOR CASTING (B. Dimčić, Z. Cvijović, Faculty of Technology and Metallurgy, Belgrade and G. Radenković, Faculty of Mechanics, Niš)

The results of the structure investigation of duplex stainless steel of 27Cr-7Ni-2Mo-3Cu type, formed under different processing conditions, are presented in this paper. The stability of the structure of duplex casting stainless steels, under service conditions, needs a special attention. Satisfactory properties of these steels, the cause of their wide application, are a result of their microstructural characteristics. The optimum microstructure obtained by a certain heat treatment is unstable and contains unstable delta ferrite.

The process of delta ferrite decomposition in these steels is analysed during isothermal tempering in a temperature region from 800 to 980^oC for previously obtained structural conditions. It is shown that the steel is sensitive to the formation of secondary phases. The formation of carbides M₂₆C₆ in a cast structure, which could not be suppressed by rapid cooling, is a consequence of high alloying. The dual phase structure consisted of austenite and ferrite and was obtained after resolving tempering at 1150^oC. The intensive decomposition of delta ferrite to secondary austenite (g₂), M₂₃C₆ and s phase occurred during isothermal tempering at the temperature range of stability of these phases. The reaction rate depends on the initial microstructure and tempering temperature.

ESTIMATION OF WELDABILITY OF "PIVA 150B" ELECTRODE FOR ARC WELDING (V. Grabulov, Z. Odanović, Military Technical Institute, Belgrade, Factory of Electrodes Piva, Plužine)

The investigation of weldability of the electrode for arc welding under a commercial name of PIVA 150B (type E 515 B 120 262H according to JUS C.H3.011) was performed. As there is no strict methodology or test for defining weldability, the investigation methodology, consisting of a few standard and non-standard tests, was applied. For the estimation of crack susceptibility in a welded joint, technological tests such as "CTS" and "Y" for cold cracks, "FISKO" test for hot cracks and "TANAKA" test for reheat cracks were applied. The instrumented Charpy test was applied for the determination of toughness and transition temperature of welded joints as well as standard tests for testing joint mechanical properties. Metallurgical changes in a welded joint were analysed by the optical metallography and by hardness changes through the weld cross section.

The results have shown that the electrode PIVA 150B has good weldability regarding the performed tests. It was shown that the electrode has good balance of the chemical composition of the wire and the coat and that an adequate production process had been applied. The results of these investigations present recommendations for defining optimum welding parameters.

ANALYSIS OF HEAT TREATMENT EFFECTS ON THE PROPERTIES OF MARAGING STEEL 18Ni1800 (Z. Odanović, V. Grabulov, Military Technical Institute, Belgrade)

The investigation of heat treatment effects on mechanical properties and steel resistance to crack propagation by the fracture mechanics methods in static and dynamic conditions was presented.

The tests were performed on maraging steel of 18Ni1800 (UHF 10) type. Steel was produced combining induction melting and by electric slag remelting (ESR). Steel was ingot-cast and forged to the square bars of 55 mm. Heat treatment after forging was performed by the following procedures: T1) austenitising at a temperature between 810 and 830^oC for 1 hour followed by air cooling and ageing at a temperature between 480 and 500^oC followed by air cooling and T2) three times austenitising at 910-930^oC followed by water cooling, then ageing at 480^oC for three hours followed by air cooling.

The chemical composition of the investigated steel was: C-0.015%, Mo-4.88%, Ni-18.19%, Co-7.42%, Ti-0.46%, Al-0.09%, S-0.008% and P-0.004%.

The tensile testing results have shown a tensile strength of 1795 to 1710 MPa and a yield strength of 1740 to 1670 for heat treatment T1. For heat treatment T2 tensile strength was from 1710 to 1670 MPa and yield strength was between 1660 and 1625 MPa. The effects of heat treatment on hardness were not visible distinctly and the hardness was between 49 and 51 HRc. The results of the absorbed energy tests (KV300/2) show the values of 22 to 12 J for heat treatment T1 and between 19 and 11 J for T2 in longitudinal direction. The fracture toughness in static conditions (K_Ic) was between 91 and 71 MPa m^0.5 for T1 and between 94 and 74 MPa m^0.5 for T2. The fracture toughness for dynamic condition (K_Id) was between 48 and 44 MPa m^0.5 for T1 and it was between 52 and 42 MPa m^0.5 for T2.

The investigation results have shown that the steel treated by both heat treatment procedures has a good combination of strength, strain and energy properties. It satisfies conditions for the production of highly loaded components with a combination of high values of absorbed energies and fracture toughness in static and dynamic conditions.

The tensile strength and yield strength values were only a little higher after heat treatment T1, while fracture toughness K_Ic and dynamic fracture toughness K_Id were better after heat treatment T2.

FORMING OF PRECISION THIN-WALLED ULTRA-HIGH STRENGTH STEEL TUBES (M. Nikačević, Lj. Radović, Military Technical Institute, Belgrade and M. Hršum, ALPO Rogatica)

The purpose of this paper is to study a possibility of forming thin, precision tubes using medium-alloy ultra high-strength steel, quenched and tempered, Č.4734S and Č.SP-28T, by tube spinning. The quality of these steels is defined by standards SNO 0411 and SNO 4072.

          Precision thin walled ultrahigh-strength steel tubes, (R_m=1400 MPa), with the ratios length/diameter (L/D)>10 and diameter/thickness D/S>50, are used for hydraulic parts, batteries, high-pressure tanks in automotive industry and for aircraft and aerospace applications.

The blank was a cylindrical cup with a spherical bottom, with an outside diameter of 76 mm, wall thickness of 3.5 mm and hight of 250 mm, obtained by deep drawing. The forming was performed by tube spinning in three or four passes with intermediate heat treatment. The last pass was carried out after annealing or quenching and tempering. The total reduction was 82%.

          Microstructural and mechanical properties of the blanks and the finished parts were examined. Residual stresses and hydrostatic pressure were determined as well.

          The results have shown that the strength, fracture resistance and precision of dimensions of such tubes, clearly depend on the thermo-mechanical treatment of tube spinning.

During the Seminar national and foreign firms had presentations of their production programmes from the field of metallurgical processing.

According to the opinion of the participants and the Programme Board of the 6^th Seminar of Metallurgical Engineers of Serbia & Montenegro, the meeting was valuated as very successful. It was the biggest meeting in the field of metallurgy in the country with a large number of presented innovations, realized in practice in the previous period. Some of the papers will be printed in the Journal of Metallurgy.