From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Technical paper discussing the influence of nickel on the properties of cast iron and its various alloys.
| Identifier | ExFiles\Box 142\4\ scan0141 | |
| Date | 25th May 1928 guessed | |
| Unless stated otherwise, the nickel additions referred to are small; generally less than 3 per cent. INFLUENCE ON THE CARBON. That nickel increases the amount of graphitic carbon in cast iron has been confirmed by all workers (see, for example ¹⁰ and ³⁰) for small additions of nickel, thus indicating that nickel acts in a manner similar to that in which silicon and aluminium¹⁹, act.²⁷ Thaler³¹ has shown that carbon is progressively precipitated as graphite, when nickel up to 48 per cent. is added to the iron. Primrose²⁵ found that the graphite was in a fine curly form at 18 per cent. of nickel, but could not reproduce this effect at lower percentages of nickel. Refining of the graphite on the addition of small amounts of nickel is claimed by Smalley¹⁷ and Wickenden and Vanick,³³ but this is not confirmed by Piwowarsky,²⁹ Sawamura,³⁴ on the other hand, claims that nickel favours the formation of temper carbon in white cast iron. It is of interest to note that McWilliam and Barnes⁶ found that even in nickel steels with 3 per cent. of nickel, graphite may be precipitated by drastic annealing. INFLUENCE ON CHILL. Nickel, as would be expected from its influence on the carbon in cast iron, lessens its tendency to chill³³,³⁸, and improves the quality of cast iron by eliminating hard spots. Hardness variation between thin and thick sections is lessened.³³ INFLUENCE ON HARDNESS. Nickel may either soften or harden cast iron; for, as shown above, hard iron will be graphitized by nickel and consequently will be softened, while on the other hand many workers have found that nickel, while retning the grain of cast iron, turns the pearlite into a sorbitic form, thus hardening the matrix of the iron⁹, ¹¹, ²² and ³⁹. INFLUENCE OF MACHINABILITY. By tending to eliminate chill, nickel naturally improves the machining qualities of cast iron. The iron is said to remain readily machinable, with relatively high hardness values—up to 200-250 Brinell.⁴⁰ Parts such as cylinder liners will take on a very fine finish. INFLUENCE ON WEARING PROPERTIES. Owing to the sorbitizing of the pearlite, nickel cast iron shows exceptional resistance to wear²⁹,⁴⁰. INFLUENCE ON STRENGTH. Various workers report conflicting conclusions concerning the influence of small percentages of nickel on the strength of cast-iron. Donaldson³¹ and Trantin³⁸ claim no improvement in the strength of grey iron on the addition of nickel. Campion¹⁰ found an improvement on adding up to 1 per cent. of nickel, but above this amount strength fell off again¹³, ²⁰, ²⁹. Under this heading it is interesting to note that unusual elasticity is mentioned by Turner,¹⁹ in connection with a 2 per cent. nickel cast iron, and Smalley¹⁷ obtained a bend of 1.5⁰ in a bend test on a hematite iron with 7 per cent. of nickel. FLUIDITY AND SHRINKAGE. Below 5 per cent. nickel does not impair the fluidity of cast iron, nor increase its shrinkage (pattern contraction)²², ³³. Géry⁴ actually claimed increased fluidity for nickel cast iron, and Wüst,²¹ after detailed experiments, declared that nickel up to 25 per cent. slightly decreased the shrinkage of cast iron. GROWTH. Donaldson,³⁰ working on a 0.75 per cent nickel iron, found that the iron grew more than did other special irons on repeated heating. The growth, however, was only 15 per cent. of that of common foundry iron. This growth is attributed to nickel rendering the carbide less stable. POROSITY AND GRAIN SIZE. Wickenden and Vanick³³ found also that small additions of nickel to cast iron reduced any tendency to porosity, thus densening the iron and rendering it sound. The grain size was at the same time refined. This study of published work reveals some contradictory results obtained by various workers on adding nickel to cast iron, especially in regard to strength and hardness values. In most of the work to which reference has been made, full analyses of the irons used are not given; consequently it is inadvisable to draw conclusions of a dogmatic nature. The author believes, however, from study of this literature, that the influence of nickel will depend very largely on the initial silicon and phosphorus contents of the iron. The work on which the author is at present engaged will, it is hoped, yield a more definite conclusion on this point. Concerning the constitution of nickel cast iron, it is of interest to note that Kasé²⁸ has recently published the results of a study of the constitution of the iron-carbon-nickel ternary system. The binary system iron-nickel has been investigated by Hanson and Hanson and by Hanson and Freeman.¹⁸ Special Alloy Cast Iron. It was mentioned in reference to Guillet’s work⁵ that larger additions of nickel render cast iron austenitic. In this condition the iron is non-magnetic, and these facts have been used in the development of non-magnetic cast iron.²⁴ This special iron has been made in this, as well as other countries, for some time past, but as the addition of nickel is relatively large in this case, the final product must be considered rather as an alloy than as a true cast iron. Partridge²² has also worked on the high nickel cast irons in connection with their electrical and magnetic properties. Resistance grids for tramway motors, etc., having excellent mechanical flexibility, are being made from cast iron with additions of 5 per cent. of nickel.¹⁵ Nickel-Chromium Cast Iron. The graphitizing influence of nickel on cast iron may be retarded by the addition of small amounts of chromium.²⁹ The resulting material is hard and close-grained and with low chromium contents, readily machinable. The degree of chill is controllable, and a material suitable for such parts as rolls and rolling mill guides may thus be obtained²²,³³, as also for car wheels.¹⁶ Mayari pig iron, with its inherent small percentages of nickel and chromium, is used for making up nickel-cast iron by mixing it with the cupola charge.¹⁰ The cupola variable proportion of the chromium is lost in the cupola by oxidation and the ratio of nickel to chromium therefore becomes somewhat indefinite, a result that further additions of nickel, silicon, or chromium may be necessary before the iron is poured.⁸, ⁹ Wickenden and Vanick³³ have studied nickel-chrome cast iron in some detail, and give figures for nickel-chrome ratios for various silicon contents in the iron. In general, the chromium addition does not exceed 0.5 per cent. These authors use the addition merely to control the amount of combined carbon, for, as they say, nickel cannot strengthen the iron by sorbitizing the pearlite, if the initially combined carbon is low. The two elements in combination give, when added in the right proportions, a very dense, tough, and as yet machinable cast iron, having normal fluidity and shrinkage. Piwowarsky²⁹ mentions an improvement of 80 per cent. in the mechanical properties of iron on the addition of 0.5 per cent. Cr.{Mr Cra???ster / Mr Chichester}, and 0.7 per cent. of Ni. Moldenke¹⁰ mentions an improvement in heat and acid resistance for nickel-chrome cast iron. Henderson³⁷ has recently patented a nickel-chrome temper alloy to be added to cast iron for improving its wearing properties and strength; the final composition aimed at being Ni, 0.45 per cent.—2.4 per cent. and Cr.{Mr Cra???ster / Mr Chichester} 0.1 per cent.—0.5 per cent. Thus one may conclude that nickel additions have been shown to benefit cast iron, if the latter has in it sufficient combined carbon from which they can produce sorbite. If the iron is too graphitic and soft, it may be hardened by the addition of chromium, and then the nickel addition can have a very beneficial effect. Recently Published Work. D.{John DeLooze - Company Secretary} M.{Mr Moon / Mr Moore} Houston¹¹ emphasises the softening action of Nickel on cast iron in stating that it has been demonstrated that grey cast iron, by the use of nickel, may be made machinable with virtually no silicon present, and containing only nodular graphite. He mentions also good mechanical properties associated with hard yet machinable irons obtained by adding nickel to irons of suitable compostition. The uniformity of results obtained in irons with varying silicon, and in varying sections, by the use of nickel additions, is emphasised, and methods of adding nickel to the iron as it leaves the cupola are dealt with. Under the conditions of work performed by the present author,⁵² the ratio of nickel to silicon has been demonstrated to be nearer to four to one, rather than as given in Mr. Houston’s formula “two of nickel equals one of silicon.”³³ In a further note,¹² Mr. Houston points out that nickel is not a cure for sick iron, but is a means of obtaining better properties from iron already of high quality. He states that high phosphorus iron requires more nickel than does low phosphorus iron to secure the same machinability. R.{Sir Henry Royce} S. Poister ⁴³ reviews previous work, showing that it has been confirmed that 0.5% of chromium together with 1-2% of nickel, increases the tensile and transverse strengths, and hardness of cast iron. Nickel and chromium together give better results than does either element alone; the proportion of nickel to chromium should be three to one or two to one, depending on the silicon. This paper deals primarily with chromium in cast iron. E.{Mr Elliott - Chief Engineer} Piwowarsky⁴⁴ has experimented with nickel and chromium additions to iron specially treated by first superheating, then chill casting to obtain a white or mottled fracture, and finally by annealing to induce graphitisation. Very fine structures were obtained associated with unusually high mechanical strengths. A further increase in the tensile properties of 10 to 30% was effected under these conditions by the addition of nickel (less than 3%) or of nickel and chromium. Samples were readily machinable and good deflections were obtained in the transverse tests, while in the tensile tests strengths up to 47.6 tons per square inch were recorded, with elongations of two to four per cent. Turner⁴⁵ in the discussion of the above paper, again drew attention to the need of lowering the silicon in general iron practice if nickel additions were to have a beneficial effect. Shaw,⁴⁶ also in the above discussion, said that certain nickel cast irons appeared more brittle under shock test than those containing no nickel. He gave details of heat treatment experiments on nickel chromium cast irons. Dealing also with special cast irons, Young⁴⁷ expressed the opinion that no advantage could be obtained by a combination of alloying and the Perlit process. Sipp and Roll⁴⁸ studied the growth of cast iron when subjected to steam at 450 degrees C., and on heating to temperatures of 600 to 1,000 degrees C., and when used as fire bars. Tests were carried out on bars, among others, containing 1% of nickel. It was found that nickel had no marked influence on the growth. Notes have appeared in the press from time to time concerning special alloy additions to cast iron. Monel cast iron,⁴⁹ a non-magnetic cast iron, showing considerable resistance to corrosion, containing 20% of nickel and copper in the monel metal ratio, together with 2% of chromium, and intended as a substitute for bronzes in chemical plant, etc., must be regarded as a special alloy cast iron. Nichrome B,⁵⁰ an iron-nickel chromium alloy, with a nickel-chrome ratio of five to one is recommended as a ladle addition to cast iron. A British Patent⁵¹ relates to the addition of nickel, or of nickel with other alloying materials, such as chromium, to cast irons, etc., a favourable improvement in the properties of the cast iron is claimed. The patent covers the manufacture of nickel alloys of low melting point, as ladle additions to cast iron. Nickel-silicon-carbon alloys; silicon 1 to 10%, and carbon 0.25 to 2.5% are mentioned, together with such alloys alloyed with amounts up to 30% of aluminium, chromium, manganese, copper, tungsten, molybdenum, phosphorus and sulphur, with iron in suitable amounts as a diluting agent if necessary. A form of shot for making the additions is recommended. The fundamental influence of nickel on iron-carbon-silicon alloys has been studied by the present author with Turner and Hanson, and a paper on this subject has recently been published,⁵² this being the first report on the work in hand at the University of Birmingham on the major problem of the influence of nickel on cast iron. Houston, in his most recent paper⁵³ shows that nickel may be added as an economic proposition to cast irons, to obtain improved properties. | ||