Original article "75 years of inoculation techniques", written by D.O.Morton and M.D.B.Bryant of Foseco International Limited. Published in British Foundryman 1979, pp.183-186.
Inoculation techniques 1900-1980
The good old days.
In charting the progres of 75 years of inoculation, it is first of all necessary to look back to the state of affairs at the dawn of the 20th century.
The Empire was at its height, and the high noon of the Edwardian era was about to begin. Iron founders were, in general, cupola melting with charges consisting of pig iron and castr iron scrap, and tapping metal of high carbon equivalent and low mechanical properties. the effects of most of the major elements on the structure and properties of cast iron were understood, including carbon, silicon from the work of Turner and of wood, phoforus from that of Stead, manganese and aluminium from the effords of Keep. The metallurgical microscope and the art of metallography had been perfected by Sorby, and tensile and hardness testing apparatus was available.
In the ordered, but insular, Edwardian world where contact between individual investigators was often minimal, it seems to have escaped serious notice than
in 1906 in America, A.E.Outerbridge added ferrosilicon to a ladle of iron which already had the required silicon content, improved the properties of the iron, and so began the technique of inoculation(1). At that time there was probably litle incentive to develop the idea and it was to be another 20 years or so before inoculation became of any importance. Not untill the First World war and the newly emergent automobile industries made ever increasing demands on the foundry industry was progress stimulated.
Figure 1, The effect of inoculation on chill in grey iron. Wedge on the left uninoculated. Wedge on the right inoculated.
The beginnings.
The search for high strength cast irons was based on the knowledge that the reduction of carbon and silicon to lower levels was essential for high strength development. Steel additions were made to the cupola charge from about the time of the outbreak of the war, and the confusing term "semi-steel" was coined for any cast iron where more thean about 15 % of steel had been included in the charge. The term remained in vogue for some 30-40 years before its eventual disappearance.
In the early days, poor control over the cupola and the iron analysis resulted in many disappointments, and even in the 1930's many foundry managers would still not tolerate steel in the cupola. Processes were developed which produced cast irons with special properties by using heated or chill moulds,
jolting or shaking the iron, or using special charges. Although they florished for a while, they just as quickly faded away. Who now remembers Diefenthalers 1916 patent for Lanz-Perlit iron, or Emmel iron, Schuz Iron, Corsalli Iron and dechnesne Iron? All of these processes were in fact german, but it was in the USA and in Great Britain in the early 1920s-the era of the flapper, the Charleston, and the Model T-that inoculation began to emerge, although not yet so called.
The 1920s.
In the early years of the 1920s, a number of foundrymen investigated the effects of ladle additions on cast irons. Some of this work was done in secret, some of it was published, and some of it formed the basis of a variety of patents. Silicon control was in the forefront of everyone's minds. Strong iron was dependant on obtaining the lowest possible silicon content consistent with a grey fracture and machineability of thin sections. Crosby at the Studebaker Foundry added graphite and ferrosilicon (1922-1923)(2), Meehan added calcium silicide and magnesium silicide (1922)(3), Smalley used ferrosilicon, calcium silicide, and zirconium silicon (1922-1924)(4), and Moldenke added aluminium (1921)(2).
The objects of all these various additions to the ladle were to control the graphite size and shape in low carbon equivalent iron, to promote A-type flakes instead of fine under-cooled forms, to obtain freedom from chill in thin sections, to opromote uniformity throughout different section sizes, and to improve machineability. These are exactly the same objectives for which inoculants are still used today. In the 1920s, the process was seen as one of scavenging, refining, and deoxidising the melt, and it was not yet understood as one of nucleation. The metallurgy of the solidification of cast irons was as yet imperfectly understood, and much argument raged over wether graphite solidified directly from the melt, or wether it was always a decomposition product of primary solidification of cementite.
The later years of the decade were taken up with consolidation. For instance, the Meehanite Corporation specifications showing the use of ferrosilicon or calcium silicide additions first appeared in the U.K. in 1928(6). There was no mention of the word inoculation in the 1920s, and the treatments were simply referred to as ladle additions. The terms inoculation and inoculants belong to the next period in history, and their originator is unknown.
The 1930s.
The years of the depression, of appeasement with Germany, and of eventual rearmament saw steady progress in the art of inoculation.
The interest of the automobile and agricultural equipment manufacturers, the railways, and not least the armament industries, ensured a ready market for high strength cast irons. It was a time of advancement in knowledge on the solidification of cast irons, and the investigations of Boyles (5),Eash(7),Norbury and Morgan(8),Flinn and Reese(9),Massari(10), von Keil(11),Piwowarsky(12), and Lorig(13) were crucial to the development of of metallurgical theory. The new certainty that A-type flakes grew directly from the melt enabled these investigators to settle on nucleation of graphite as being the principle mode of action of inoculants. Surprisingly, some 40 years later we still cannot be certain how this nucleation occurs and on the precise compositions of the nuclei formed.
Much emphsis was placed on how to gain proper control of the effects of inoculation.Ferrosilicon containing 75-80% silicon became established as the most common inoculant. The control of calcium and aluminium in ferrosilicon had been far from satisfactory in the early days, which probably helped the initial success of calcium silicide. It was not. until 1938 that Lorig Kinnear and Barlow(14) suggested that calcium and aluminium were the vital elements in ferrosilicon, and it was left to McLure et al(15) in 1957 and Dawson(16) in 1961 to indicate the optimum contents. Graphite itself was proved to be a valuable inoculant by both Norbury and Morgan(8) and Massari and Linsay(10). The latter pair allowed a lump of graphite electrode to float and gradually dissolve in the ladle of iron, and not unnaturally discovered that the effectwas altogether too potent. They then had to compensate by adding carbide stabilisers to the iron. Complex inoculants became fashionable, and Eash did much work with nickel plus silicon additions which resulted in the introduction of Ni-tensyl iron by International Nickel(7). The earliest of the complex proprietary inoculants was introduced just before the Second war in the form of SMZ from Union Carbide, based on the work of Burgess. Stabiliising inoculants, which were a mixture of chromium and silicon, were first produced by the Vanadium Corporation in 1939(2).
The 1940s.
Just as the first war had been the parent of high strength cast irons, so the Second war was the inspiration for the greatest innovation in cast iron metallurgy of this century. The making of ductile iron by a magnesium treatment was a direct consequence of the shortage of chromium in America due to the War. The magnesium method pioneered by International Nickel and the cerium method of Morrogh and Williams were both announced at a historic AFS Congress in Philadelphia in 1948(17).Because both magnesium and cerium are carbide stabilisers and the manufacture of ductile iron requires an inoculation step, so inoculation received another boost. Ferrosilicon rapidly became the almost universal product to be applied in ductile iron.
In grey iron the 1940s was a time of considering the best methods of adding the existing selection of inoculants. It was soon proved that the most effective method was into the stream of metal entering the ladle, and a number of simple devices were invented to do this (2,18).
The 1950s.
In contrast to the previous decades, and to those to follow, the 1950s was a quiet period. However, further modifications to inoculation theories were proposed, e.g. Hurum in 1952(19), and the solidification of undercooled graphite was finally proved to be just as much a product of solidification from the liquid during the eutectic reaction as are random flakes. The most notable suggestion for a new inoculant was the use of barium in a silicon-manganese alloy base by Kessler in 1956(20).
Figure 2. Effect of inoculation on graphite and microstructure in grey iron. Structure on left uninoculated showing undercooled graphite and cementite. Structure on right showing random flake graphite and absence of cementite.
The 1960s.
While the Beatles shook up music scene, the inoculation world was enlived by the steady emergence of what may be considered as the second phase of complex inoculants. Commercial bariom-containing inoculants were developed by the Vanadium Corporation and Baranov(22), and strontiom ferrosilicons were prepared by BCIRA and Union Carbide after the work of Dawson(23) and Clark and McCluhan(24).
Cerium-bearing inoculants were proposed, and appeared from the Vanadium Corporation. Mixed inoculants giving good control over the very potent effects of graphite were introduced by Foseco.
The problem of fading had been recognised very early on, and it was acknowledged that inoculated metal had to be poured in 10 minutes or less to avoid this. The big advantage claimed for barium alloys, for example, was their supposedly better fade resistance. In the mid-1960s, the problem was tackled in a different way, and inoculation of the metal directly in the mould was attempted. In this position there would be no further problem with fading. The investigations of Dell and Crist(25), Trager and Kaune(26), Hall(27), Bakkerus and Gaertman(28), and Ryzhikov(29) proved that the concept was viable by using a variety of inoculants either as fines, lumps, pellets, or tablets. Karsay used a different technique and inoculated in the spout of the ladle with atube filled with inoculant(30).
Figure 3. Effect of inoculation on graphite and microstructure in a nodular graphite iron.
Structure on left uninoculated showing low nodule count, high pearlite content, and cementite.
Structure on right inoculated showing high nodule count, low pearlite content, and no cementite.
The 1970s and beyond.
The last decade has seen environmental considerations leading to mechanisation and automation of foundries, and this in turn has brought many refinements of in-mould techniques. These extend now to the complete treatment of ductile iron in the mould following the successful experiments of Moore and Kessler(31) and Dunks and mcCaulay(32).
Two recent inoculation methods which may be mentioned are the CQ Process where a wire with an inoculant core is fed into the mould downsprue(33), and the BCIRA stream inoculator where a carefully monitored addition is made to the stream of metal entering the mould 934). No completely new inoculants have been introduced, but improvements in scientific techniques and the application of modern equipment such as the scanning electron microscope and micro probe analyser have taken us closer to a final understanding of the nucleation and growth process in cast iron and of the process of inoculation. It is these advantages as exemplifierd in the work of Jacobs, Lux and Hitchings, McSwain and Bates, and many others which probably hold out the greatest hope for the development of new inoculants and methods for the future. Release from some of the constrictions of inoculant fade would be one of the greatest benefits which research may yet provide. The in-mould and in-stream methods are capable of further developments, and the introduction of new types of cast iron, such as compacted graphite iron, opens up new fields for inoculation.
In 75 years, the cast iron industry has seen major changes in techniques and methods of manufacture and in the understanding of its basic metallurgy. Despite severe challenges from light metals and plastics the 75th anniversary celebrations of the Institute are held at a time when the industry is very active technologically and forward looking. Inoculation has a vital role to play in the continuing progress of cast iron.
References.
(1)T.Turner: The Metallurgy of Cast iron. Griffin Co.Ltd. London, 1920.
(2) V.H.Patterson and M.J.Lalich: Proceedings of the 44th International Foundry Congress, 1977, Firenze, paper I.
(3)Augustus F.Meehan:US Patent 1 499 068, 1924.
(4)O.Smalley:Transactions of the American Foundrymens Society, 1926, v.34, pp.881-895.
(5)A.Boyles:The Structure of Cast iron.American Society for Metals, Cleveland, 1947.
(6) Augustus F.Meehan:US Patents 1683086 and 1683087, 1928.
(7)J.T.Eash:Transaction of the American Foundrymens Society, 1941, v.49,pp.887-910.
(8)A.L.Norbury and E.Morgan:Journal of the Iron and Steel Institute, 1930, v.121,pp 367-392. Also, Foundry trade Journal, 1936, June 11th, pp.453-455.
(9)R.A.Flinn and D.J.reese:Transactions of the American Foundrymens Society, 1941,v.49,pp559-607.
(10)S.C.Massari and R.W.Lindsay:Ibid.,pp.953-985.
(11)O.von Keil:Archiv fur das Eisenhuttenwesen, 1934, v.7,pp.579-584.
(12)E.piwowarsky:Ibid.,431-432.Also Transactions of the American Foundrymens Society, 1926,v.34,pp914-985.
(13)A.Boyles and C.H.Lorig:Transactions of the American Foundrymens Society, 1941,v.49,pp769-781.
(14)C.H.Lorig,H.B.Kinnear and T.barlow:Summary report on Electric Furnace melting, Batelle memorial Institute,1938.
(15) N.C.McClure et al.:Transactions of the American Foundrymens Society, 1957,v.65,pp.340-351.
(16)J.V.Dawson and S.Maitra:The British Foundryman, 1967, v.60,April,pp117-127.
(17)H.Morrogh and W.J.Williams:Transactions of the American Foundrymens Society, 1948,v.56,pp.72-90.
(18)H.P.Hughes and W.Spenceley:Proceedings of the Institute of british Foundrymen,1943-1944, v.37,pp.A71-A85.
(19) F.Hurum:Transactions of the American Foundrymens Society, 1952,v.60,pp.834-848.
(20)H.Kessler:US Patent 2810639, 1956.
(21)Vanadium Corporation and R.L.Mickelson: US Patent 3137570, 1962.
(22)O.Baranov: USSR Patent 169548, 1964.
(23)BCIRA and J.V.Dawson:British Patent 1002107, 1963.
(24)R.A.Clark and T.K.McCluhan:Transactions of the American Foundrymens Society, 1966,v.74,pp.408-416.
(25)W.J.Dell and R.J.Christ:Transactions of the American Foundrymens Society, 1964,v.72,pp.408-416.
(26)H.Trager and A.Kaune:German Patent OLS 1458899, 1965.
(27)Foseco International Limited and C.Hall:British Patent 1105028, 1966.
(28) H.Bakkerus and J.Gaertman: Metalen, 1964, V.19, April, p.94.
(29) A.A.Ryzhikov et al: Russian castings production, 1965, October, p.423.
(30) S.I.Karsay: US Patent 3367395, 1965.
(31)W.H.Moore and H.H.Kessler: US Patent 3746078, 1971.
(32) C.M.Dunks, J.L.McCaulay and Materials and Methods Limited: British Patent 1278265, 1968.
(33) J.R.Nieman and L.W.McFarland: US Patent 3991808, 1976.
(34 G.F.Sergeant: Conference on Modern Inoculating Practices for Grey and Ductile Iron, Cast metals Institute, American Foundrymans Society, 1979, pp. 237-266.
