Defects in Ductile Iron

Metallurgical DefectsMetallurgical Defectsin Ductile Iron in Ductile Iron

Some Problem ElementsSome Problem Elements

Common Metallurgical Defects in Ductile IronCommon Metallurgical Defects in Ductile IronCommon Metallurgical Defects in Ductile IronCompacted GraphiteLow Nodule CountChunky graphiteExploded graphiteNodule AlignmentCarbidesGraphite flotationFerrite/Pearlite - ratioSlag inclusionsShrinkage porosityGas porosity

Compacted Graphite in Ductile IronCompacted Graphite in Ductile IronCompacted Graphite in Ductile Iron

increase Mg and/or RE

reduce S in base iron

reduce fade time

better inoculation

possibly reduce Ti contamination from CGI returns

increase Mg and/or RE

reduce S in base iron

reduce fade time

better inoculation

possibly reduce Ti contamination from CGI returns

POSSIBLE CUREPOSSIBLE CURE

Titanium in Ductile Ironcauses compacted

graphite structures

combines with and removes nitrogen

leads to poor nodule shape, with flakes branching out from nodules

causes a need for more magnesium to counteract this

causes compacted graphite structures

combines with and removes nitrogen

leads to poor nodule shape, with flakes branching out from nodules

causes a need for more magnesium to counteract this

Low Nodule CountLow Nodule CountLow Nodule Count

improve inoculation or reduce fade time

avoid superheating and excessive hold times

improve base iron response to inoculation (preconditioning)

avoid excessive Mg

improve inoculation or reduce fade time

avoid superheating and excessive hold times

improve base iron response to inoculation (preconditioning)

avoid excessive Mg


151 Nodules/mm151 Nodules/mm22

712 Nodules/mm712 Nodules/mm22

Chunky GraphiteChunky GraphiteChunky Graphite

reduce RE content in nodulariser or reduce addition rate of nodulariser

reduce eventual other additions of RE

add S or use a S-containing recarburiser to neutralise excess RE

improve inoculation to reduce segregation effects of RE’s


reduce eventual other additions of RE

add S or use a S-containing recarburiser to neutralise excess RE

improve inoculation to reduce segregation effects of RE’s


Exploded GraphiteExploded Graphite

reduce carbon equivalent

increase cooling rate


reduce RE vs. sulphur ratio

reduce carbon equivalent



reduce RE vs. sulphur ratio


Spiky GraphiteSpiky GraphiteSpiky Graphite


reduce amount of tramp elements such as Pb, Bi and Sb

watch for Pb-containing scrap or Pb-paints

avoid Bi-containing inoculant

increase RE addition

reduce amount of tramp elements such as Pb, Bi and Sb

watch for Pb-containing scrap or Pb-paints

avoid Bi-containing inoculant

increase RE addition

Lead in Ductile Ironwill segregate to grain

boundaries and cause intercellular flakes at levels above 0.002%

this effect is countered by the presence of rare earths in the treatment alloy (0.005 wt%)

harmful to mechanical properties

will segregate to grain boundaries and cause intercellular flakes at levels above 0.002%

this effect is countered by the presence of rare earths in the treatment alloy (0.005 wt%)

harmful to mechanical properties

Irregular GraphiteIrregular GraphiteIrregular Graphite


Improve inoculation

Avoid long hold times after inoculation

Reduce magnesium addition

Improve inoculation

Avoid long hold times after inoculation

Reduce magnesium addition

Nodule AlignmentNodule Alignment

increase carbon equivalent

use better inoculation

increase carbon equivalent

use better inoculation


Intercellular Iron Carbides (Chill)Intercellular Iron Carbides (Chill)

increase carbon equivalent and/or silicon content

reduce Mg and/or RE content

reduce content of carbide promoting traces (Mn, Cr, V, Mo, etc.)

better inoculation

avoid tellurium cups in charge

increase pouring temperature

increase carbon equivalent and/or silicon content

reduce Mg and/or RE content

reduce content of carbide promoting traces (Mn, Cr, V, Mo, etc.)

better inoculation

avoid tellurium cups in charge

increase pouring temperature


Segregation Carbides (MeSegregation Carbides (Me--C)C)

reduce content of carbide forming traces (Cr, V, Mo, etc.)

better inoculation to minimise segregation

change nodulariser to improve nucleation

reduce content of carbide forming traces (Cr, V, Mo, etc.)

better inoculation to minimise segregation

change nodulariser to improve nucleation


Chromium in Ductile IronCase Study: Sample shown had a chromium content of .42 wt%. This caused large carbides in addition to excess pearlite.

Spectrum 1: Cr-C

Spectrum 2: Pearlite

Graphite FlotationGraphite Flotation

reduce Carbon equivalent, especially C-content

reduce pouring temperature


better inoculation

reduce Carbon equivalent, especially C-content

reduce pouring temperature


better inoculation


Low Ferrite/Pearlite RatioLow Ferrite/Pearlite Ratio

reduce content of pearlite stabilising elements (Mn, Cu, Sn, Sb....)

use more high purity charge materials (pig iron)

better inoculation

increase Silicon content

avoid hot shake out

reduce content of pearlite stabilising elements (Mn, Cu, Sn, Sb....)

use more high purity charge materials (pig iron)

better inoculation

increase Silicon content

avoid hot shake out


Low Pearlite / Ferrite RatioLow Pearlite / Ferrite Ratio

increase content of pearlite stabilising elements (Mn, Cu, Sn, Sb....)

reduce Silicon content

Watch out for Boron contamination

increase content of pearlite stabilising elements (Mn, Cu, Sn, Sb....)

reduce Silicon content

Watch out for Boron contamination


Slag InclusionsSlag Inclusions

improve deslagging practice

empty ladle between treatments

improve pouring practice

improve gating design to reduce turbulence

use filter or slag traps

reduce Mg/nodulariser addition

improve deslagging practice

empty ladle between treatments

improve pouring practice

improve gating design to reduce turbulence

use filter or slag traps

reduce Mg/nodulariser addition


Flake Graphite SurfaceFlake Graphite Surface

reduce sulphur in the sanduse special mouldcoatingsincrease Mg or Mg/S ratioavoid use of long runner-systemsreduce pouring temperatureincrease pouring rateuse RE-containing inoculant

reduce sulphur in the sanduse special mouldcoatingsincrease Mg or Mg/S ratioavoid use of long runner-systemsreduce pouring temperatureincrease pouring rateuse RE-containing inoculant


Shrinkage PorosityShrinkage Porosity

increase mould strength

improve gating and feeding design

increase carbon content up to 3.8

reduce Magnesium addition

reduce alloying contents

use better inoculant

reduce inoculation fade time

increase mould strength

improve gating and feeding design

increase carbon content up to 3.8

reduce Magnesium addition

reduce alloying contents

use better inoculant

reduce inoculation fade time


Hydrogen PinholesHydrogen Pinholes

reduce moisture in sand

ensure that tools, refractory and coatings are dry

use clean and dry cover material

reduce Al and Ti content in iron

improve venting

reduce moisture in sand

ensure that tools, refractory and coatings are dry

use clean and dry cover material

reduce Al and Ti content in iron

improve venting


Hydrogen in Ductile Iron

Case Study:

Shows the two types of porositiesmentioned above. To the left is the gas related pore with the black inner surface. And to the right is the shrinkage with a metallic surface and dendrites.

Hydrogen in Ductile Iron

Hydrogen pinholing:H2O + C H2 + CO

Followed by: 2 CO C + CO2

This is the reason for the nodule depleted zone

Hydrogen pinhole: carbon layer, nodule depleted zone

Magnesium gas defect: no carbon layer

Conclusion/Summary Conclusion/Summary To avoid metallurgical defects in ductile iron the following must be emphasised:use good quality raw materials with low contents of trace elements (Mn, S, V, Mo, Ti, Cr…..use a consistent treatment process giving reproducible analyses, high recoveries and good temperature efficiencyuse high quality nodularisers with consistent analyses and sizinguse high quality inoculants specific to the requirements

To avoid metallurgical defects in ductile iron the following must be emphasised:use good quality raw materials with low contents of trace elements (Mn, S, V, Mo, Ti, Cr…..use a consistent treatment process giving reproducible analyses, high recoveries and good temperature efficiencyuse high quality nodularisers with consistent analyses and sizinguse high quality inoculants specific to the requirements

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Defects in Ductile Iron