Cast Iron Inoculation English

7/28/2019 Cast Iron Inoculation English

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CAST IRON

INOCULATION

ISO 9001 ISO 14001 ISO/TS 16949

THE TECHNOLOGY OF GRAPHITE SHAPE CONTROL


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Elkem manufactures and markets a

series of high quality inoculants to treat

cast iron and ensure the production ofan ideal graphite shape, distribution

and freedom from chill (cementite). All

inoculants are available in sizes suit-

able for ladle or in-stream additions.

This brochure describes some of theconditions in the production of cast iron

that call for the addition of an inoculant

to ensure the reliable production of a

sound, strong, tough, machinable cast-

ing. The mechanism of inoculation andgraphite nucleation in cast iron during

solidification is also described.

CAST IRON INOCULATION

What is Inoculation of Cast Iron?

THE TECHNOLOGY OF GRAPHITE SHAPE CONTROL

Inoculation is the means of controlling

structures and properties of cast iron

by minimizing undercooling and

increasing the number of nucleationsites during solidification. An inoculant

is a material added to the liquid iron

just prior to casting that will provide

suitable sites for nucleation of graphite

during the subsequent cooling. Tradi-

tionally, inoculants have been based

on graphite, ferrosilicon or calcium

silicide. Almost exclusively, inoculants

today are ferrosilicon based containing

small quantities of active elements

such as Al, Ba, Ca, Sr, Zr and RE (Rare

Earth metals).

The purpose of inoculation is to assist

in providing sufficient nucleation sites

for dissolved carbon to precipitate

as graphite rather than iron carbide

(cementite, Fe3C). This is done by pre-

venting undercooling below the meta-

stable eutectic temperature where

carbidic (white) structures are formed.

The iron solidification mechanism is

prone to form chilled iron structures

when the inoculation is inadequate.There are several reasons why chilled

structures are normally undesirable.

They are hard and brittle and interfere

with machining, necessitate additional

heat treatment operations, resulting in

nonconformance with specifications

and, in general, increase the total cost

of production.

Inoculation changes the structure of

cast iron by altering the solidification

process. A look at the solidification

process for hypoeutectic grey iron

(iron with a carbon equivalent less

than 4.3) helps in understanding the

effect of inoculation.

The first metal to solidify in hypoeutec-

tic grey iron is primary austenite. As

cooling continues, the remaining irongrows richer in dissolved carbon. Even-

tually, the liquid reaches the eutectic

composition of 4.3% carbon equivalent,

at which final or eutectic solidification

would start under equilibrium conditions.

However, equilibrium solidification does

not occur under practical foundry con-

ditions. Due to variations in chemistry,

pouring temperature, solidification rate,

section thickness and other conditions,

the metal will cool below the eutectic

temperature before the start of finalsolidification.

If the undercooling is slight, random

graphite flakes form uniformly in the

iron matrix, see Figure 1. This is known

as Type A graphite. As the undercooling

increases, the graphite will branch,

forming abnormal patterns. This isknown as Types B, D and E graphite.

A further increase in undercooling will

suppress the formation of graphite

and results in a hard white iron carbide

structure.

The role of the inoculant is to produce

nuclei in the liquid iron melt which

enhance the graphite nucleation with

a low degree of undercooling. This will

in turn, promote the formation of Type

A graphite structures in grey iron,and a high number of small graphite

nodules in ductile iron.

1. Structure and Phases in Cast Iron

The structure of cast iron has a

dominant influence on strength and

machinability, and in order to obtain a

machinable grey iron structure for thin

sections, the addition of an inoculant

to molten iron is widely practiced

and often absolutely necessary. For

convenience, potential difficulties with

machinability can be determined by

carrying out a hardness test (Brinell

hardness) on iron castings and, in

general, machinability improves with

decreasing hardness. The cast iron

structure can be influenced at two

distinct stages in the production route:

during solidification

during heat treatment

However, for economic reasons, the

desired structure should be achieved

during solidification without the neces-

sity for heat treatment.

Figure 1: Graphite type versus under-

cooling.


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2. Structure Stability

The microstructure of an iron casting

consists of several phases, each having

varying levels of carbon, iron and other

elements present. Table 1 shows the

analysis and specific densities of the

solid and liquid phases which take

part in the solidification process. When

solidification is complete, the following

combination of phases may be found:1) Austenite + Graphite

= GREY structure

2) Austenite + Graphite + Cementite

= MOTTLED structure

3) Austenite + Cementite

= WHITE structure

This review demonstrates that solidifi-

cation results in a minimum of two solid

phases; and austenite is present in all

the phase combinations. As the casting

cools, the austenite subsequently trans-

forms to pearlite and/or ferrite in solid

state (eutectoid transformation).

Of all the solid phases listed above,cementite has the highest hardness

(~660 HB), whilst graphite is a rela-

tively soft material of low density, which

can act as a lubricant. Hardness and

machinability of the as-cast structure

are, therefore, influenced by the relative

amounts of cementite and graphite, with

austenite playing only a minor role.

A metastable white or mottled structure

can be transformed into a stable greystructure by annealing, but the reverse

transformation is not possible as the

stable structure represents the lowest

possible energy level (at a given

temperature and composition). The

graphite produced by annealing will

have a different structure to that formed

during solidification. Cementite,

austenite and liquid iron have similar

densities and all contain carbon in

solution, see Table 1. No major redistri-

bution of the atom species is requiredfor a white structure to be produced

during solidification. However, the

formation of a stable grey structure

containing graphite is quite different.

Graphite precipitated from molten iron

is virtually pure carbon, and since it

has a lower specific density than the

alternative phases; a major redistri-bution of atoms is required to develop

a stable structure. A slow rate of soli-

dification is therefore more likely to

produce a grey iron structure.

The precipitation of cementite, re quiring

less atom redistribution than graphite,

will be more likely during rapid solidi-

fication. This can be demonstrated by

examining a typical wedge test speci-

men. The narrow tip of the wedge soli-

difies at a faster rate than the thickersection at the base of the wedge, and

will show a white structure whilst the

area of slow cooling at the base will

display a grey structure, see Figure 2.

Consequently, a slow rate of solidifi-

cation (slow cooling rate) and a small

value of undercooling encourages the

formation of a grey structure with goodmachinability and discourages a hard

white structure.

Within the composition of cast iron,

graphitizing elements will promote the

carbon-carbon bond to produce graph-

ite in the as-cast structure, whereas

carbide stabilizing elements promote

the carboniron bond and cementite will

appear in the structure. Table 2 lists a

number of such stabilizing elements.

As an example, in malleable cast irons

the need for the as-cast structure to

solidify white determines that the silicon

level is much lower than in grey irons.

Also, since chromium is a carbide

promoting element, it has to be kept at

a low level to allow transformation to a

graphitic structure during subsequent

heat treatment. In normal furnace

charge materials, steel and external

cast iron scrap may be heterogeneous

materials, especially on different delive-

ries, with contents of Cr, Cu, Sn, Sb, V,

Mo, Ti, etc., depending on the original

source and ultimately on the ability of

the scrap dealer.

Pig iron produced from steel scrap can

also display a similar variable response

to inoculation due to fluctuating trace

element contents. A more consistent

response to inoculation is attainable by

adopting a charge containing a reason-

able proportion of ore-based pig iron

due to its low level of trace elements of

the carbide stabilising type.

Controlling the concentration of trace

elements allows the foundryman a means

of promoting grey as-cast structures

and, also, helps in avoiding other un-

desirable effects of trace elements on

microstructure and properties.

Table 1:Approximate analysis and

specific densities of phases in the

solidification range of cast iron with

2.4% Si.

Figure 2:Chill Wedge with fast solidifying

white tip and slowly cooled grey base.

Table 2: Graphitizing and carbide

promoting elements.

3. Influence of Elements on As-Cast Structure


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4. Influence of Nuclei on Solidfication Structure

When crystallisation of eutectic cast

iron in chilled specimens is studied,

a gradual advance of the solidification

front is revealed. Transformation does not

take place instantaneously or uniformly

over a cross section. Initial solidification

occurs at the surface from distinct

crystallization centres and after some

time a solid/liquid interface forms. Other

isolated crystallisation centres are

active in the remaining melt and initiate

the formation of solid, see Figures 3

and 4. These isolated areas are called

eutectic cells.

Eventually, cells grow at the expense

of the liquid, and a solid cast structure

develops. Each eutectic cell consists ofgraphite and austenite with graphite as

the primary phase.

Precipitation is initiated by randomly

distributed crystallisation centres, called

nuclei. These nuclei offer favourable sites

for the deposition of carbon atoms and,

subsequently, precipitation of graphite

and austenite onto existing graphite

continues. The morphology of these cells

for grey iron shows a marked difference

with that for nodular iron, as can be

seen from Figure 3.

Grey iron: graphite lamellae start

growing from a common centre and

stays in contact with the melt as aus-

tenite fills the spaces between

the lamellae.

Nodular iron: a graphite nodule forms

first and is surrounded by austenite at

a later stage.

In eutectic nodular iron, the nodule

number is virtually identical with the

number of eutectic cells.

The mechanism described is for eutectic

solidification and is not influenced by

the presence of kish (primary) graphite

or austenite dendrites.

The nuclei substances can be more easily

observed in nodular graphite iron than

in grey iron, since it is easy to locate the

centre of a graphite spheroid. Measure-

ments have shown that the nuclei are

between 0.5 to 2.0 microns in diameter,

with a bulk chemical composition of

magnesium sulphide and magnesium

silicate. A similar investigation of nuclei

composition for grey iron has shown that

the nucleus has a core of a complex

aluminium-X-oxide where X can be

Ca, Ba, Sr, Ce, Zr surrounded by the

manganese sulphide.

5. Prerequisites for Successful Inoculation

5.1 Number of Nuclei

About 2.4wt% graphite and 97.6wt%

austenite are formed during the crystal-

lization of eutectic (nodular) cast iron,which corresponds to approximately

8 vol% graphite and 92 vol% austenite.

The mean diameter of graphite nodules

is usually between 10 80 microns,

although lower and higher values are

possible. This leads to about 3000 to

30,000 nodules per cubic millimetre

depending on the section size (cooling

rate) of the casting. The total number of

possible nuclei for graphite (inclusions)

will be at least one order of magnitude

larger than this graphite nodule density.This means that the number of inclusions

or possible nuclei for graphite is at least

100,000 per cubic millimetre and that

only a small fraction of these nuclei

actually nucleates graphite during

solidification1. Table 3 gives examples

of number densities and mean particle

sizes for nuclei and graphite nodules inductile cast iron under various inocula-

tion conditions. As can be seen from

the table, the number and mean size of

nuclei particles are unaffected by the

inoculant addition, although the nodule

characteristics obtained after solidifi-

cation are strongly dependent on the

type of inoculant used. These findings

will be discussed below.

The calculations used to generate these

figures contain certain assumptions,but one can safely conclude that:

The number of nuclei per volume of

melt is extremely high, and approxi-

mately one order of magnitude larger

than the number of graphite nodules

actually nucleated;

The ability of the particles to nucleate

graphite is strongly affected by theinoculant addition.

In order to obtain a nucleation event, a

certain degree of undercooling during

solidification is required. But since

different nuclei phases initiate graphite

nucleation at different undercooling

levels, it is preferable to have a large

number of nuclei particles which can

initiate nucleation at very small under-

cooling. This is achieved by the addition

of an inoculant to the melt just prior tocasting.

Figure 4:Solidification of near eutetic

iron2.

Figure 3:Eutetic cells: lamellar (top),

nodular (bottom) graphite .

Austenite

Graphite

Graphite

Austenite


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5.2 Constituents of an inoculant

Most of the inoculant material is so-

called carrier material that is doped

with a minor additive (nucleant),

which produces nucleating particles

in the iron melt. These particles will, in

turn, initiate the crystallization of graph-

ite. The carrier (e.g. silicon and ironcombined as ferrosilicon) should have

the following characteristics:

provide fast and homogeneous distri-

bution of the nucleant in the melt

have a composition that is compatible

to the analysis of the melt

form an alloy between the nucleant

and the carrier

be cost efficient

Trials using very pure ferrosilicon as aninoculant have demonstrated that it

does not have any nucleating effect for

graphite1,3,4 as shown in Table 3.

The nucleant, e.g. Ca, Sr, Ba or Al only

needs a limited presence and it is

beneficial if the nucleant forms an alloy

with the carrier. Also, the nucleant must

have a limited solubility in cast iron,

and form stable compounds with the

other elements forming the nuclei par-

ticles (e.g. sulphur and oxygen). Good

nucleation effect may be achieved ifthe ferrosilicon contains small but con-

trolled amounts of calcium, strontium or

barium in the range of 0.6 to 2.0%.

Table 3:Example of nuclei and nodule

number densities, average

diameters and volume fractions1.

5.3 Composition of the Nuclei

in Ductile Iron

Laboratory test results are used in this

section to explain the role of calcium

as an example of a trace element

behaving as the nucleant in ferrosilicon.

Calcium will occur in ferrosilicon as a

silicide (CaSi2). Calcium has virtually no

solubility in iron, and reacts with com-

ponents in the melt to form sulphides

and oxides.

In magnesium treated cast irons, the

inclusions contain mainly magnesium,

calcium, sulphur, silicon and oxygen.

These are primary reaction products

of the magnesium treatment. The

inclusions are composed of a sulphide

core and a faceted outer silicate shell.

The sulphide core contains both MgS

and CaS, while the outer shell con-

sists of complex magnesium silicates

(e.g. MgOSiO2, 2MgOSiO

2). These

phases will not act as potent nucleation

sites for graphite during solidification

because of a large nucleus/ graphite

interfacial energy barrier. The interfacial

energy barrier is the controlling factor in

heterogeneous nucleation behaviour.

Figure 5: Transmission electron

micrograph of duplex sulphide/oxide

inclusion in ductile iron (left).

Schematic representation of an inclu-

sion after inoculation by a calcium

containing ferrosilicon. The surface

layer of calcium silicate is the effective

phase for graphite nucleation (right).1


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After inoculation with a Ca-containing

ferrosilicon, hexagonal silicate phases of

the CaOSiO2and the CaOAl

2O

3 2SiO

2

type will form at the surface of the exis-

ting oxide inclusions produced during

nodularisation. These silicates will act

as very favourable nucleation sites for

graphite during solidification, due to

their hexagonal crystal structure, whichmatches the graphite crystal lattice

very well (i.e. low energy interface).

Figure 5 shows a typical inclusion in

ductile cast iron which is formed after

nodularisation (left), and a schematic

representation of the inclusion compo-

sition after inoculation (right). The sur-

face shell contains hexagonal calcium

silicates formed during inoculant addi-

tion, while the bulk particle is a product

of the nodularisation treatment. Hence,

the inoculation does not increase thetotal number of nuclei particles in the

melt, but rather modifies the surface of

the already existing products from nod-

ularisation. This explains why the num-

ber density of particles in uninoculated

and inoculated ductile iron melts are

the same (Table 3), while the resulting

nodule numbers will differ greatly due

to the inclusion surface modification.

When inoculation is carried out with

a strontium or barium containing ferro-

silicon inoculating hexagonal silicatesequivalent to the calcium silicates

(CaOSiO2and CaOAl

2O

32SiO

2) will

be formed (i.e. SrOSiO2, SrOAl

2O

3

2SiO, BaOSiO2and BaOAl

2O

32SiO

2)

5.4 Composition of nuclei in grey iron

Recent research results have identified

a three step nucleation process for

generating graphite flakes in grey iron.

By means of electron microscope in-vestigations, it has been revealed that

a nucleus for a graphite flake consists

of a particle with a body of manganese-

and calcium-sulphide surrounding a

nucleus core of complex Al2O

3XO

oxides, see Figure 6. The core oxide

contains elements such as calcium,

barium, strontium, zirconium, and rare

earth elements. Towards the surface

of the manganese/calcium-sulphide

body, even more complex compounds

have been observed on which thegraphite has grown.

The hypothesis is that the oxides form

as stable elements in the iron melt first.

Secondly, manganese and calcium

sulphides grow on these oxides until

a desired size and a more complex

faceted compound appears on the sur-face. The third step is that the graphite

starts to grow on this faceted surface

and grows along its base planes of

hexagonal structure.

One interesting observation was that

aluminium seems to play a key role in

the nucleation process in conjunction

with other elements. Testing of iron with

very low levels of aluminium showed

poorer performance than iron with a

certain level of aluminium. It can beconcluded that final content of alu-

minium in grey iron should be between

0.005 and 0.010% in order to maximise

eutectic cell count in grey iron. This

aluminium content range is and has to

be less than the 0.015 0.25% Al, as

this range for pin-hole susceptibilityinfluenced by aluminium.

As a result of these observations, Elkem

has invented the Preseed precondi-

tioner that contains zirconium and

aluminium, to be added to the iron melt

in the furnace or well ahead of inocula-

tion, in order to increase the potency

of the melt for inoculation

Figure 6: Transmission electron micrographs of complex sulphide/oxide inclusion in grey iron and profile of chemical

composition through the nucleus.


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Table 4:Elkem preconditioner, inoculants and inserts for grey and ductile irons.

5.5 Specification of Inoculants

The chemical composition and reliability

of the analysis from lot to lot is important

if a ferroalloy is to be considered as a

good and consistent inoculant. Many

foundrymen insist on silicon and phos-

phorus analyses in pig iron, but pay little

attention to the analysis of the inoculant,or vice versa. The preceding paragraphs

indicate quite clearly that the minor

constituents in ferroalloys, not the major

constituents (usually silicon), are critical

for the performance as inoculants. All the

Elkem inoculants are alloys that have

been smelted and alloyed to the quoted

specifications, and with the exception

of Ultraseed inoculant, no further addi-

tions have to be mechanically blended

with the alloy. The analysis guaranteed

by the specification ensures consistentinoculant properties from lot to lot. The

inoculants listed in Table 4 differ by

analysis, price and application. The

foundry experts of Elkem can give

detailed information on each inoculant

and its individual features, and also

suggestions as to the most suitable alloy

for a specific foundry condition.

5.6 Addition Technique

Chemical considerations alone will not

ensure satisfactory results since equal

attention must be paid to addition tech-

nique. For ladle inoculation this means

a continuous addition of inoculant to the

stream of iron (normally added between

one third and two thirds of ladle filling)

so that the high turbulence encourages

fast and homogeneous distribution of

the alloy. Stream inoculation may be

practised, in conjunction with automaticpouring furnaces, using finer sized

grades of the above inoculants at lower

addition rates. Similarly, inoculant fade

can be overcome by reducing the time

interval between the inoculant addition

and solidification by placing the ino-

culant piece, or insert, into the gating

system. The reaction with liquid iron

occurs within the mould and this is

known as in-mould inoculation.

Fading is the reduction in inoculation

effect with increasing time taken to pour

inoculated iron. Elkem inoculants have

been assessed against untreated refer-

ence melts and even after 10 minutes

the inoculation effect of the treated melt

proved to be good. Provided ladle in-

oculation has been carried out in a satis-

factory way and the ladle is not delayed

for an excessive period before pouring,

the need for mould inoculation can beavoided in most cases.

Alinoc, Barinoc, Elcast, Foundrisil,Reseed, SMZ, Superseed, Ultraseed, Vaxon and Zircinoc

are registered trademarks owned by Elkem AS. Preseed is a trademark of Elkem AS.


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6. Control of Inoculation

6.2 Chill Testing

The traditional method to determine the

tendency of a melt to solidify grey or

white is by examining chill wedges.

The larger the zone of white iron, the

fewer the number of nuclei that were

active in initiating a grey solidification.

Figure 8 shows chill wedges from a

foundry which had an average 11.2 mm

of chill for a period of two week on un-

inoculated cupola iron. By adding 0.2%

FeSi (85% Si), the average chill depth

was reduced and with 0.125% Super-

seed inoculant addition, the chill depth

was reduced even further.

6.3 Eutectic Cell Count

The number of eutectic cells in grey iron

can be determined on etched micro-

specimens. If an effective inoculant has

been added to the melt, there will be a

large number of active nuclei to promote

graphite precipitation at low under-

cooling during solidification. This will

be represented on the micro-specimen

by a high cell count for grey iron and

a high nodule count for ductile iron.

Table 5 shows the result of cell counts

after inoculation. The eutectic cell

number increases as the inoculant

addition to the base melt is increased.

Other factors, such as over-inoculation

leading to shrinkage proprensity, will in-

fluence the optimum inoculant addition.

Although nuclei cannot be observed

directly at solidification temperatures,

they have an effect on some properties

which can be measured by:

recording cooling curves

measuring depth of chill in chill

wedges

counting the number of eutectic cells

counting the number of graphite

nodules

6.1 Cooling Curves

Cooling curves record the changes

in temperature with time as a conse-

quence of a change of energy within

the system. A deviation from normal

cooling indicates the occurrence of a

source of heat such as the heat of

crystallization released by a precipitating

phase. The location of the inversion

points on the generally S-shaped

cooling curve in the region of eutectic

crystallization indicates the tendency

of the melt to solidify grey or white.

A high level of nucleation promotes a

higher arrest temperature which, by

avoiding the white eutectic, will result

in less risk of carbide formation.

Conversely, when the inversion point is

at a low level on the cooling curve, there

will be a tendency for cementite to

precipitate instead of graphite giving a

white structure. An increased cooling

rate, as found in thin sections, will in-

crease the degree of undercooling that

must be balanced by an increased

number of active nuclei to avoid the

formation of white iron. In the iron-carbon

system there is only a 7 C interval

between grey solidification and suffi-

cient undercooling to cause white

solidification. In Figure 7 the cooling

curve for an uninoculated reference

melt is compared with a curve from a

melt inoculated with 0.25% inoculant

addition.

The uninoculated melt shows inversion

at 1145 C whereas inversion occurs

at 1162 C for the inoculated melt. This

means that the uninoculated melt is

undercooled by 20 C and the inoculated

melt by 3 C, which gives white and

grey solidification, respectively.

Figure 7:Solidfication curves for

uninoculated ductile iron (a), and

inoculated ductile cast iron (b)

(30 mm section size).


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7.1 Principle Effects

The effects of inoculation are at a maxi-

mum immediately after the addition of the

inoculant. The rate of inoculant fading,

which depends upon the composition

of the inoculant and the condition of the

iron to which it is added, may be very

rapid and much of the inoculating effect

may be lost in the first few minutes after

the addition. The principal effects of

fading are:to cause greater undercooling to take

place during eutectic solidification

and to lead to a greater tendency to

chilling in grey and ductile cast irons,

particularly in thin sections;

to reduce the number of nodules

formed in ductile iron and to cause a

deterioration in their shape. If sufficient

ly severe, the deterioration in shape

may affect the mechanical properties

of the casting;

to reduce the number of eutectic cells

growing in flake graphite irons result

ing in a less uniform size distribution

of graphite in the casting and a

reduction in mechanical properties.

There are some well established facts

concerning fading which are of practical

significance:

all inoculants fade;

there is no period after inoculation

during which fading does not occur.

To obtain the maximum effect, metal

should be cast as soon as possible

after the addition of inoculant;

some inoculants fade more slowly

than others;

inoculating effects vary according to

inoculant composition. It is desirable

that foundries should carry out tests

to determine which is the most suitable inoculant for their purpose.

Table 5:Eutectic cell count (30 mm round bars). Figure 8:Cupola melted grey iron; no

inoculation (left), inoculated with 0.2%

FeSi85% (centre), and inoculatedwith

0.125% Superseedinoculant (right).

7. Fading of Inoculation


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9. Inoculation and Shrinkage

The solidification of grey iron is charac-

terized by the formation of a skin type

array of eutectic cells at the mould/metal

interface, followed by the development

of eutectic cells ahead of the advancing

solidification front. Newly formed graphite

compensates partly or fully for the liquid

iron contraction, provided it precipitates

within a relatively rigid skin, which is

characteristic of uninoculated grey iron.

However, if the mode of solidification is

changed, the good shrinkage character-

istics can be jeopardized, especially if

a rigid skin cannot be developed at the

mould/metal interface leaving the mould

directly exposed to ferrostatic pressure.

Eventually, the mould may yield under the

ferrostatic pressure from the remaining

liquid, and the increased volume of the

mould cavity becomes too high for com-

pensation by graphite precipitation at the

end of solidification. Some shrinkage may

occur as a result of excessive dilation of

the mould although mould geometry

will have an influence.

Unfortunately, inoculation changes the

mode of solidification in such a way that

the rigidity of the skin is decreased.

Inoculant additions should not become

excessive to avoid shrinkage and yet the

addition should be adequate to ensure

grey solidification. Test specimens,

Figure 13, show that for an equivalent

chill depth, the eutectic cell count will be

lower when using Superseed inoculant

in place of foundry grade ferrosilicon.

The lower cell count reduces the ferro-

static pressure on the mould and impro-

ves the tendency to avoid shrinkage

defects.

Since the eutectic cell count for nodular

cast iron is much higher than for grey iron,

one would expect a greater shrinkage

tendency, and it is interesting to see

that the solidification pattern is in fact

similar to over-inoculated grey iron.

Ultraseed inoculant has proven highly

successful in providing fresh nucleation

sites to ductile irons of long holding time

where the base iron or magnesium

treated iron have been held for pro-

longed times before addition of the

post inoculant. Such long hold times

are well known to reduce the overall

capabilities of the iron prior to inocula-

tion resulting in so-called dead iron.

Ultraseed inoculant will thus reinstall

good nucleation effectiveness from

reactions with its sulphur and oxygen

content forming new nucleation sites.

Due to the powerful effects of Ultraseed

inoculant on raising nodule count and

improving chill protection, it has been

found that the tendency to shrinkage

formation is also reduced with this ino-

culant. Especially, the type of shrinkage

that often occurs as small porosities in

hot-spot sections of the complex cast-

ings; appear to be effectively reduced

or even eliminated by Ultraseed inocu-

lant. Figure 14 shows an example of

microshrinkage porosity that has been

minimized by the use of Ultraseed

inoculant.

Figure 13: Comparison of the eutectic

cell count in 5 mm sections at about

equalchill depth (from BCIRA).

Figure 14: Example of micro-shrinkage prorosity in ductile iron part that has been

minimized by Ultraseedinoculant (left), compared to manganese-zirconium

containing inoculant (right).


12/12

Elkem AS

Foundry Products

Hoffsveien 65B

P.O. Box 5211

Majorstuen

N-0303, Oslo, Norway

Telephone : +47 22 45 01 00

Telefax : +47 22 45 01 52

www.foundry.elkem.com Revised April 2012 Copyright Elkem AS

Based on a comprehensive understan-

ding of the mechanisms of inoculation

described in this brochure, Elkem has,

over the years, evaluated many alterna-

tive alloy analyses to develop the current

range of inoculants which includes the

well established Superseed,Ultraseed,

Reseed and Alinoc inoculants.

Development of new improved alloys

goes on continuously.

Recently, Preseed preconditioner

has been added to the portfolio as a

novel preconditioner to enhance ino-culation effect.

For further information on Elkems

extensive range of inoculants, please

contact your local representative. The

success of Elkem products worldwide

justifies their elaborate development

and provides a sound base for the

foundryman to select the appropriate

inoculant for his foundrys particular

requirements.

10. Product Development

References:

1) Skaland, T.: Ph.D Thesis, The Norwegian Inst. of Tech., 1992

2) Engler, S.: Giesserei, techn.-wiss.Beih., 17(1965), p 169/202

3) Moore, A.: Brit.Foundrym. 68 (1974) March, p59/69 Patterson, V.H; Foundry 100 (1972) June, p 68/71

4) Riposan et al: Investigation of the Effect of Residual Aluminium on Solidification Characteristics of Un-inoculated Ca/Sr-Inoculated Gray Irons. AFS 2004

Documents

Cast Iron Inoculation English