Materials Research and Engineering Edited by B. Ilschner and N.J. Grant Julian Szekely Goran Carlsson Lars Helle Ladle Metallurgy With 137 Figures and 24 Tables Springer-Verlag New York Berlin Heidelberg London Paris Tokyo Prof. JULIAN SZEKELY GQRAN CARLSSON Department of Materials Science MEFOS, The Metallurgical Research Plant and Engineering P.O. Box 812 Massachusetts Institute of Technology S 951 28 Lulea, Sweden Cambridge, MA 02139/USA LARS HELLE OVAKO STEEL Oy Ab SF 55100 Imatra, Finland Series Editors Prof. BERNHARD ILSCHNER Laboratoire de Metallurgie Mecanique Departement des Materiaux, Ecole Poly technique Federale CH -1007 Lausanne/Switzerland Prof. NICHOLAS J. GRANT Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge, MA 02139/USA Library of Congress Cataloging-in-Publication Data Szekely, Julian, 1934- Ladle metallurgy/Julian Szekely, G6ran Carlsson, Lars Helle. p. cm.-(Materials research and engineering) Bibliography: p. ISBN-13: 978-1-4612-8147-4 e-ISBN-13: 978-1-4612-3538-5 DOl: 10.1007/978-1-4612-3538-5 I. Inoculation (Founding) 2. Steel founding. I. Carlsson, G6ran. II. Helle, Lars. III. Title IV. Series. TS233.s981988 671.2-dc19 88-20017 Printed on acid-free paper. All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer-Verlag, 175 Fifth Avenue, New York, NY 10010, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use of general descriptive names, trade names, trademarks, etc. in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone. © Springer-Verlag New York Inc. 1989 Softcover reprint of the hardcover I st edition 1989 Typesetting by Asco Trade Typesetting Ltd., Hong Kong. Editors' Preface This book seeks to provide a comprehensive coverage of the important and growing field of ladle metallurgy, including theory, practice, and economics. During the past decade, major advances have been made in the secondary metallurgy of steel and other metals; indeed, secondary metallurgy, that is, the ladle treatment of molten metals, following the melting and refining steps, has become an important and inevitable part of the overall processing sequence. Ladle metallurgy is attractive because it can provide an effective means for adjusting and fine-tuning the composition and temperature of the molten products prior to solidification processing. Ladle metallurgy allows us to produce materials of very high purity and will become increasingly an essential process requirement. Indeed, many of the novel casting techniques will mandate steels of much higher cleanliness than those in current practice. Of course, ladle metallurgy or secondary metallurgy is not limited to steel; indeed, major advances have been made and are being made in the secondary processing of aluminum, aluminum alloys, and many specialty metals. This book provides, for the first time, a comprehensive treatment of the subject, which includes both the science base and the many practical, real-world considera tions that are necessary for the effective design and operation of ladle metallurgy systems. The aim of the theoretical chapter is to provide insight and to develop the fundamental basis of ladle metallurgy systems. The chapter concerning practice reflects the many years of practical experience with the operation ofladle metallurgy systems. Finally, the chapter on economics provides a discussion on both the capital costs and the operating costs of secondary metallurgy systems. This book should be helpful to students of materials processing and to practicing metallurgists, in both the steel and the specialty metals fields. Cambridge, MA, USA, July 1988 N.J. Grant Lausanne, Switzerland, July 1988 B. Ilschner Contents 1 Overview of Injection Technology G6ran Carlsson .............................................. . 1.1 Introduction ................................................ 1 1.2 Apparatus .................................................. 1 1.3 Hot Metal Pretreatment ...................................... 4 1.4 Steel Refining ............................................... 8 1.5 Foundry.................................................... 23 1.6 Copper..................................................... 23 1.7 Aluminium ................................................. 24 1.8 Ferro Alloy ................................................. 24 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2 The Fundamental Aspects of Injection Metallurgy Julian Szekely ................................................ 27 2.1 Introduction ................................................ 27 2.2 Thermodynamics ............................................ 27 2.3 Gas and Solids Delivery ...................................... 40 2.4 Injection of Particles into Melts ................................ 50 2.5 The Kinetics of Ladle Metallurgy Operations .................... 54 2.6 Fluid Flow and Mixing in Ladle Metallurgy Systems .............. 56 2.7 Convective Mass Transfer and Kinetics ......................... 64 2.8 Heat Transfer ............................................... 68 References ................................... . . . . . . . . . . . . . . . . . . . . 71 3 Injection Practice in the Secondary Metallurgy of Steel Lars Helle .................................................... 73 3.1 Introduction ................................................ 73 3.2 Description of the Process .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 3.3 Theoretical Approach to Powder Injection ....................... 101 3.4 Discussion of the Results Obtained with Powder Injection . . . . . . . . . . 110 3.5 Costs and Productivity ....................................... 145 3.6 Future Aspects .............................................. 145 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 4 Economic Considerations G6ran Carlsson ............................................... 151 viii Contents 4.1 Introduction ................................................ 151 4.2 Unit Price .................................................. 151 4.3 Consumption ............................................... 151 4.4 Capital Costs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 4.5 Economic Interactions with Other Processes ..................... 152 5 Testing Technique for Powder Injection Goran Carlsson ............................................... 154 5.1 Dry Blowing Tests ........................................... 154 5.2 Screen Analysis .............................................. 155 5.3 Hand Test of Powder Material ................................. 157 5.4 Water Model Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 5.5 Angle of Repose ............................................. 162 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 Subject Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 1 Overview of Injection Technology Goran Carlsson 1.1 Introduction Treating steel in the ladle is as old as the use of ladles in steelmaking. The main purposes for ladle treatment of hot metal and liquid steel include desulphurization, deoxidation, alloying, and inclusion shape control. One of the first ordinary ladle metallurgical processes was the Perrin process [1], in which steel was tapped into a ladle containing premelted slag. The kinetic energy of the steel was used to produce a large reaction surface and intensive stirring in the ladle. A very efficient method for the treatment ofliquid metal is injection of a powdered reagent or alloy. Already in his time, Sir Henry Bessemer [2] suggested that powdered material should be added to the steel. In the 1930s and 1940s, injection of powdered material was used in many different ways. One example from the iron and steel industry is lime powder injection into hot metal for desulphurization. Petersen and co-workers [3] have reported on the use of burnt lime for desulphuri zation. In the 1950s, the injection technique was introduced in foundries. The main purpose was desulphurization and alloying with magnesium. During that decade, injection metallurgy was not yet a great success, mainly owing to technical problems. A new era for injection metallurgy started in the late 1960s. The technique was developed and improved in many ways and in many countries, for example, in Sweden, the Federal Republic of Germany, and France, at the same time. The advantages of adding powdered material deeply into liquid metal are that metal lurgical operations can thereby be carried out faster, with higher yields, with better reproducibility, and to meet special requirements for the products. In this chapter, some ideas will be given on how injection techniques are used in different metal industries. 1.2 Apparatus An injection equipment system consists schematically of a powder dispenser, trans portation hose, and lance (Fig. 1.1). In the industry, it is usually completed with containers and silos for rational handling of the powder. The powder dispenser is a high-pressure vessel with a conical lower part. The powder-gas mixture is pressed through a small hole and into an ejector, where the carrier gas is added. The fluidization of the powder is done in order to break up the powder so that the transportation of it from the dispenser will be uniform. The carrier gas used for 2 1 Overview of Injection Technology D Fig. 1.1. Skeleton sketch of an injection in stallation: 1, powder dispenser; 2, transpor tation hose; 3, lance; 4, ladle or furnace; 5, 3 carrier gas; 6, powder containers; and 7, buffer 2 5- container. [ J D 5 -----,.,..-11 Fig. 1.2. Examples of ways to use two dis pensers connected to the same hose and lance. Reprinted with permission from ref. 5 (Fig. 1, p. 22: 14) . .. .", .", .", .".., SeQuentf '" .", ;) 0 0.. '0 C :> 0 «E Sequence Treatment time (minI steel is argon or nitrogen, while in hot metal nitrogen, air, or in some cases oxygen, is used. A modern injection station usually contains more than one dispenser, allowing a very flexible treatment [4, 5]. With an injection installation consisting of two dispensers connected to the same hose and lance, either simultaneous or sequence powder additions can be made (Fig. 1.2). The former method can be used for mixing of powders in order to avoid more expensive prepared mixtures and to enable flexible mixing, and for minimizing the vaporization of elements with a high vapour pressure at steelmaking temperatures. Sequence injection can, on the other hand, 1.2 Apparatus 3 TORPEDO CAR E.A.F. LADLE , \ ! 11 ': : II I " ~I I" I II " : " I, II" ,, """" I"I,I ;':.,, 'I[ " a b a a d Fig. 1.3. Different kinds of lance designs: (a) straight lance, (b) hockey-stick lance, (c) T-hole lance, and (d) 3-hole lance; note that E.A.F. stands for electric arc furnace. be used for refining, starting with one powder and finishing with another that has a higher affinity to the undesirable element; alloying, made directly after refining without raising the lance (in this way, the precision of the addition will be high); and adding poisonous elements with the lance immersed into the steel. It has been proven that desulphurization can be carried out in two steps with two reagents, giving the same degree of desulphurization compared with refining, which uses only the more expensive reagent, at a cost saving of 25-50% [5]. The injection lance can be constructed in two ways: 1. For the monolithic lance, the ceramic material is cast onto a steel tube. 2. For the sleeve lance, refractory sleeves are piled onto a steel tube. The outlet of a lance can be constructed in many different ways, according to the type of vessel in which the treatment is carried out (Fig. 1.3). In order to ensure that a lance will stand the treatment, the following points must be taken into consideration: 1. There is no nozzle blockage. 2. The refractory material has a high thermal shock resistance. 3. The refractory material can withstand high mechanical strain. 4. Slag erosion on the refractory material is controlled. Today's problems with high costs for lances might be solved in the future by injection through a tuyere in the ladle wall or bottom. Schnurrenberger et al. [6] have developed a system in which a slide gate is used for injection of lime-fluorspar or CaSi (Fig. 1.4). Results have shown that for the same degree of desulphurization the specific quantity of calcium consumed was 0.2 kg less per tonne of steel when using a slide gate than that required for lance treatment. Benefits of using the ladle slide gate nozzle are largely seen as lowered costs for consumption of refractory lining and injected material. Other systems of tuyeres, slide gates, etc., have been developed in the United Kingdom, the United States, Sweden, France, and the USSR. It looks as if there will be a break-through for injection through the ladle wall or bottom in the near future, but this will of course depend on the economics involved in substituting a 4 1 Overview of Injection Technology Well block Short 'nJector nozzle for lime-spar and (as, ,nJeclion Slider platp Fig. 1.4. Slide gate for injection. Reprinted with permission from ref. 6 (Fig. 3, p. 30: 14). complex ladle tuyere arrangement for a simple lance with high specific refractory costs. 1.3 Hot Metal Pretreatment 1.3.1 Desulphurization Treatment of hot metal in a ladle or a torpedo car is done today mostly for the purpose of desulphurization. This is due to the fact that the sulphur content of the steel has an important bearing on the surface quality and mechanical properties of the end product. Therefore, in many integrated steel mills, even for plain carbon steel production, hot metal with no more than 0.020% sulphur is charged into the steelmaking converter. Apart from a qualitative improvement in the steel product, external hot metal desulphurization may constitute a relief for the melting shop permitting a more favorable mode of operation with less basic slag. In the interests of the blast furnace, this allows the use of fuels (coke, coal powder, and oil) with higher sulphur content and the achievement of a lower silicon content in the hot metal, which permits the coke rate to be reduced and the performance to be increased. Desulphurization reagents can, for economical reasons, be limited to lime, cal cium carbide, soda ash, or magnesium. The latter could be salt-coated magnesium granules, in which the salt gives a damping of magnesium evaporation. All of these reagents can be injected into the hot metal. Consumptions of different desulphuriza tion reagents are listed in Table 1.1. The effectiveness of the reaction between the desulphurization reagent and the