IL36594A - Additive alloy for the treatment of spheroidal-graphite cast irons - Google Patents

Description

Additive alloy for the treatment of cast irons EY 34449 This whioh io outcome of research Toy Messrs Joan Claude and Sep relates to a novel additive alloy intended for the treatment of graphite cast of the effect which magnesium has upon the structure of the graphite precipitated in cast considerable progress has been made in the manufacture of cast It is now common practice to nodularise cast irons by means of often based on containing magnesium as the nodularising The use of alloys of this kind has the advantage over the introduction of pure magnesium of better distribution of the active element and far less violent actions whatever the method of introduction By adjusting the quantity of magnesium to be introduced in known manner to the oxygen and sulphur contents of the cast iron and by working in the absence of mente example on cast the graphite is nodularised fairly easily in cases where it is merely re matrix of the hardened cast By problems arise where it is desired to produce a cast iron with a ferrite matrix which is distinguished both by its outstanding and its high This is because the additional graphiting required is inter a function of time whilst the nodularising effect of the disappears after about 10 to 15 According to one known proposal which has been adopted on a wide the is subjected to two successive ments just before it is namely to the nodularising nodularieer disappears The inoculants used are generally Bilicon alloys which can doped with rare earths or with alkaline earths for example and which can be made heavy through the incorporation of They are introduced at a moment in time as close as ible to final for example in the mould inter alia by projection on to the walls of the mould when there is a danger hardening more particularly at those places where the casting comprises thin zones which solidify into a white and hence brittle In spite of the precautions the conventional stage treatment often produces unsatisfactory it has to be completed by a heat treatment of the solid namely by annealing above the It will be obvious to any expert that annealing such as this gives rise to surface faults which in turn produce such pecially in the case of castings comprising zones of highly variable that permanent deformation The object of the present invention is to provide an additive alloy by which it is possible to obtain through a ingle in the crude cast a spheroidal graphite cast iron with an accentuated ferrite The use of the alloy according to the invention thus affords considerable It simplifies the handling of and reduces the losses of heat from the liquid pig The losses of magnesium are reduced which allows substantial quantities of this nodularising element to be saved and much tighter control of its final It is known that what results in magnesium stabilises the ductile transition temperature of the cast iron with the result after it has been nodularised with magnesium by virtue of the addition of expensive This is by virtue of the novel additional it is possible to adjust the silicon content in the blast furnace or in the cupola furnace by means of less expensive starting The additive alloy to which the present invention relates is of the type and contains the the nitrogen being introduced for example by The composition is as Si 40 3 and nitrogen in a quantity such the ratio by weight of Ba to N is between 5 and the remainder being iron apart from the inevitable impurities introduced during its more particularly Ca and in a total concentration of less than The is further characterised by a ratio by weight of of from 1 to The various constituents of the alloy according to the invention are balanced to produce not only a ferrite matrix but also a regularisat ion of the size of the ted and a level of resistance to troublesome elements carbide which is reflected in the ance during manufacture of the cast iron of a recycling rate of scrap and which can reach and In its preferred the alloy according to the invention is characterised by the following Si 45 Mg 7 Rest iron and the inevitable impurities from manufacture in a total concentration of less than So far as the proportions are the research invention revealed the following preferred ratios by 10 i 2 The residual magnesium content of the cast iron after it has been treated with the alloys claimed is governed both by the initial iron and also by the type of cast iron It is usually greater than more between and by In this the quantity of alloy to be used is such that the magnesium is usually present in a quantity of from to of the weight of the cast iron to be It is known December page that although the introduction of nitrogen by bubbling can produce appreciable inoculation in spheroidal graphite cast this technique does not result in the formation of ferrite matrix in the crude cast According to another prior publication States Patent Specification cast irons are nodularised with additive alloys of the type in which some of the nitrogen is present in the form of a suspension of calcium the calcium associated with the mentioned elements only produces a far more incomplete level of ferritisation than that which can be obtained with barium using the alloys to which the present invention This surprising result is illustrated in Tables 1 2 in which A treatment with an alloy according to the invention B substantially identical treatment except that alloy contains Ca instead of C conventional treatment comprising ion followed by Liquid cast iron is in an ola from a batch comprising of new cast iron and of being subsequently desulphurised with GaCj known The cast iron is then transferred to a induction Passage through this furnace enables the silicon content of the cast iron to be adjusted before treatment A and B so as to after a cast iron whose composition is comparable with that of a cast iron which has been subjected to treatment of type Treatments A and B comprise introducing in into the cast iron to be treated a quantity of approximately by weight of this cast iron of an alloy containing for Si by weight Mg weight Ba by weight Ca by Al by weight N by we ight Pe making up the rest to For Si by Mg by we ight Ga by Al by we ight Treatment C to the comprises troducing in form the be treated first a quantity equivalent to about by of this cast iron of a alloy Si by weight g by weight Ba traces by weight Al by weight N traces making up the rest to 100 and then a quantity equivalent to approximately of the weight of the cast iron obtained of an inoculating alloy which is a ferrosilicon with a silicon content of After castings eciraens are The three comparative treatments with alloys B and C are carried out on the same basic cast iron made in an induction Three batches each of 600 kg are removed from the furnace for each of the treatments In every the temperature of the cast iron during treatments B and C is between and the ings and the control specimens are produced at the end of ladle the period of time elapsing between the treatment and casting of the specimens under examination is between 10 and 15 Tables 1 and 2 show respectively the results obtained from micrographic structural examinations and mechanical tests on the crude cast TABLE MicrographiO examination and results Analysis of of ferr Ref Appearance of upon the the C Si Mn e 50 A perfectly 95 spheroidal spheroidal B but with 80 numerous per ectly C spheroidal 70 Mechanical properties of standard test specim of three test Elastic limit Tensile strength 65 S A C The tables show that the castjirons treated with the alloys according to the invention show properties substantially different from the properties of the cast irons obtained in accordance with the prior especially as regards the degree of ferritisation and elongation at I it is apparent from the residual magnesium contents that the use of the alloys according to the invention considerably the yields of nodularising The following Examples are intended to illustrate the application of the alloys according to the Example A quan ity of kg of an additive according to the invention in addition to iron and the usual by weight of weight of by weight of barium and by weight is introduced by means of known type of plunger into a ladle containing 75 kg of and cast iron kept at a temperature of The resulting cast iron has the following C Si g 12 minutes after treatment the castings the control specimens show a precipitation of perfectly spheroidal No carbide is present in the even in the thin In the control the matrix has a ferrite Example 4 kg of anJaddttive alloy according to the invention taining in addition to iron and the usual urities of silicon of ma nesium of barium of plunger into a ladle containing kg of cast iron at a temperature of After the cast iron has the following C Mg 12 minutes after the castings show a tion of perfectly spheroidal No carbide is present in the even in the thin In the control the matrix has a ferrite content of 85 to Example kg of an additive alloy according to the invention containing by weight of of of of the remainder to consisting of iron and are introduced by the technique into a ladle containing 600 kg of a cast iron made in an arc furnace from a batch comprising of scrap and 60 spoiled castings at a temperature of the the mother alloy is initially placed at the bottom of a treatment covered with scrap iron and then the cast iron to be treated is poured into the After the cast iron contains of of Si and of 14 minutes after micrographic examination of the castings reveals a perfectly spheroidal graphite a ferrite matrix and the total absence of carbide even in the thin parts of the Example 600 kg cast iron with temperature of are of of of the remainder to 100 consisting of iron and Casting is finished 12 minutes after the All the castings obtained consist of spheroidal graphite cast Examination reveals a ferrite structure in the crude cast The average composition is as C Si Mn Mg Pe the rest to Example kg of an alloy containing of of of of the rest to consisting of iron and are introduced by means of an adequate plunger into a ladle containing 250 kg of cast iron of suitable o position at n temperature of 1460 The castings are produced over a period of 8 The cast iron obtained is of the spheroidal graphite It is free from carbides in the crude cast state up to nesses of 6 The composition of the cast iron in each casting is as C Si Mn Mg the insufficientOCRQuality

Claims (1)

1. CLAIMS An additive alloy the treatment of spheroidal graphite cast the alloy having the following composition by Si 40 3 14 and nitrogen in a quantity such that the ratio by weight of is from to the ratio by weight of being from to and the of the alloy being apart from less than of the inevitable impurities during An additive alloy according to Claim with the following composition by 45 7 Ba the remainder being iron apart from less than of the said An additive alloy according to Claim 1 or with the following ratios by An alloy according to 1 substantially as herein described with reference to any of the soecific Λ process for treatment of spheroidal graphite cast iron comprising the atep of adding thereto an alloy according to any of Claims 1 to A process according to Claim 5 substantially as herein described with reference to any of the A spheroidal graphite iron containing an and nitrogen when made by a process according to 5 or insufficientOCRQuality