Summary of ElementSummary of Element Effects in Ductile Iron of the Elements Effects... · Boron in Ductile Iron • Boron is noted for promoting ferrite and , when present at elevated

Summary of ElementSummary of Element Effects in Ductile Iron

Rick GundlachElement Materials Technology Wixomgy

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DIS Annual Meeting, June DIS Annual Meeting, June 7, 2012 7, 2012 Muskegon, MichiganMuskegon, Michigan

Types of Alloying Elements• Substitutional and Interstitial elements• Substitutional and Interstitial elements• Each has a distinct and unique effect on the

solidification structure and solid statesolidification structure and solid-state transformation products

– Eutectic carbon content– Stability of graphite (versus carbide)– Eutectoid carbon content– Stability of austenite and ferrite phases

Hardenability etc– Hardenability, etc.

Iron-Carbon Phase Diagram

Carbon Equivalent• Many elements raise the chemical activity ofMany elements raise the chemical activity of

carbon and, thus, they reduce the eutectic carbon content, such as Si, Al, Ni and Cu

• Some elements reduce the chemical activity of carbon and, thus, they raise the eutectic carbon content, such as Cr and Vcarbon content, such as Cr and V

• Another more comprehensive CE expression

CE = %C + %Si/3 + P/3 – Cr/6 + Ni/12

Another Carbon Equivalent Formula

%C + %Si/7 = 3.9• The formation of graphite compensates for the Liquid-Solid g p p q

contraction that occurs during solidification

• Chemical composition determines the amount of graphite that forms during solidification.g

• Combinations of carbon and silicon influence the amount of graphite that forms and the type of solidification shrinkage

V l l th 3 9 ll hibit d i f• Values less than 3.9 generally exhibit draw-in or surface sinking

• Values above 3.9 are subject to mold-wall movement and internal shrinkage porosityinternal shrinkage porosity

Fe-2%Si-C Phase Diagram


Calculating Critical Temperaturesf C itifrom Composition

UCT = 1370oF +78(%Si) – 32(%Mn) – 20(%Ni) ( ) ( ) ( )– 53(%Cu) + 4.6(%Mo) – 160(%P)

LCT = 1324oF +38(%Si) 50(%Mn) 9 6(%Ni)38(%Si) – 50(%Mn) – 9.6(%Ni) – 16(%Cu) + 1.2(%Mo) – 127(%P)

Interstitial Elements

• Oxygen, Sulfur & NitrogenOxygen, Sulfur & Nitrogen

These elements exhibit Surface Active• These elements exhibit Surface Active behavior and influence the nucleation and growth of graphiteand growth of graphite

The Role of MagnesiumThe Role of Magnesium

• Reduce the concentrations of the surface active elements S and Osurface active elements S and O

• Promote high nodularity

How Much Mg is Needed?How Much Mg is Needed?

Too little Mg produces low nodularity• Too little Mg produces low nodularity• Too much Mg leads to carbides• The Mg requirement increases with

decreasing freezing rate• Various methods used for determining an

adequate amount, including Mg:S ratioExcess Mgg

My Favorite Mg CalculationMy Favorite Mg Calculation

Mgresidual = O.75*%S + 0.018%

This calculation presumes that:

1. The level of soluble sulfur (and oxygen) must1. The level of soluble sulfur (and oxygen) must be reduced below a critical level to achieve a fully nodular structure, and

2. The reaction, Mg + S → MgS does not go to completion – excess Mg is needed to drive the dissolved S down

Solubility in Solutions

Mg + S → MgS

K = (%Mg) X (%S) / (%MgS)K (%Mg) X (%S) / (%MgS)

K = Equilibrium Constant It defines the limitK = Equilibrium Constant. It defines the limit of solubility of constituents in a solution

Solubility of Mg and S (according to thermodynamic calculation)

∆Go = RT ln K∆Go = RT ln K

where K = (αMg * αS), andαMg = activity of Mg ≈ wt-% MgMg y g gαS = activity of S ≈ wt-% S

∆Go = RT ln [(%Mg x %S) x C]

Gibb’s Free Energy for Sulfides

Solubility of MgS in Melt0.05

0.04

%

0.02

0.03

agne

sium

,

0.01

Ma

00 0.002 0.004 0.006 0.008 0.01

Sulfur, %Sulfur, %

Solubility of MgS in Melt

Rare Earth ElementsRare Earth Elements

• RE aid in achieving high nodularity

• RE are strong deoxidizersRE are strong deoxidizers

• RE are strong sulfide formers

• RE can increase nodule count

• RE react with tramp elements to form pintermetallic compounds, and neutralize the damaging influence of tramp elements



Relative Influence of Tramp pElements on Graphite NodularityOne formula for rating the damaging influence:

SG =SG = 4.4Ti + 2As + 2.3Sn + 5Sb + 290Pb + 370Bi +1.6Al

When SG <1.0, SG graphite is possible,When SG >1.0 degenerate graphite is likely

• Ce and other RE elements can neutralize these tramp elements• Amount needed to neutralize tramp elements not an exact science. • Unlike S and O reactions, the RE reactions are not well known.

Tolerances for Tramp ElementsTolerances for Tramp Elements

• Lead – 0 002%Lead 0.002%• Antimony – 0.002%• Tin – 0.002%Tin 0.002%• Bismuth – 0.002%• Tellurium – 0.02%• Aluminum – 0.04%• Titanium – 0.05%• Zirconium – 0.01%• Selenium – 0.01%


Boron in Ductile Iron• Boron is noted for promoting ferrite and , when

present at elevated levels, more Cu is required to produce pearlitic gradesproduce pearlitic grades

• The boron effect essentially reduces the hardenability of ductile iron.

• Boron is insoluble in austenite and occupies the grain boundaries

• In steels, boron is used to enhance hardenability, as long as nitrogen is tied up by Ti or Zr additions to the melt

• Is it possible that boron nitride nucleates ferrite?

• Could the boron effect be neutralized by reducing the level of dissolved nitrogen?level of dissolved nitrogen?

Solubility of Boron Nitride0.01

0.008

0.004

0.006

Nitr

ogen

, %

0.002

00 0.001 0.002 0.003 0.004 0.005

Boron %Boron, %



El t P t P litElements Promote Pearlite

• Copper• ManganeseManganese• Chromium

Ti• Tin• Antimony• Arsenic

Relative Influence of AlloyingRelative Influence of Alloying on Promoting Pearlite

• Manganese – strong• Chromium – strong• Copper – strongerCopper stronger• Tin – 10 times stronger than Cu

Sb & A t th S• Sb & As – stronger than Sn

Relative Influence of AlloyingRelative Influence of Alloying on Promoting Pearlite

One formula for rating pearlitizing power:

Alloy Factor = %Cu + %Mn + %Cr + %Mo + %V + 10x%Sn

For 80-55-06: AF must be 110 - 130For 100-70-03: AF must be 140 - 160

TRANSFORMATION ON CONTINUOUS COOLING

INCREASED HARDENABILITY WITH ALLOYING



Elements Influence Transformation to Martensite

Martensite Transformation occurs over a temperature range of 150oCtemperature range of 150oC

Martensite Transformation Start temperature isMartensite Transformation Start temperature is influenced by carbon and the alloying elements

Ms(oF) = 930 – 570C – 60Mn - 50Cr - 30Ni -20 Si – 20Mo – 20W

Interrupted QuenchInterrupted Quench

DUCTILE IRON GROWS DENDRITICALLYDENDRITICALLY


Segregation of Solute Elements S fDuring Solidification

• Alloying elements partition between the• Alloying elements partition between the liquid and solid phases according to their effect on melting point temperatureg p p

• Some elements concentrate in the growing solid phase, others concentrate g o g so d p ase, ot e s co ce t atein the remaining liquid

• Ductile iron grows dendritically and alloysDuctile iron grows dendritically, and alloys that segregate to the liquid will concentrate in the interdendritic regions

Partitioning of Solute Element at Freezing Frontat Freezing Front

Segregation of Solute Elements S fDuring Solidification

• Ductile iron grows dendritically, and alloys that segregate to the liquid will g g qconcentrate in the interdendritic regions

• The degree of segregation is dependent• The degree of segregation is dependent on freezing distance – the distance between neighboring dendrites (and often g g (neighboring nodules)

Alloying and Ductile‐to‐Brittle Transition

QUESTIONS?QUESTIONS?

For additional information, l t tplease contact:

• Rick Gundlach• Element Wixom• 51229 Century Court

Ph 248 560 4005• Phone: 248-560-4005• Email: [email protected]• Web Site Address: [email protected]


For additional information, l t tplease contact:

• Rick Gundlach• Element Wixom• 51229 Century Court

Ph 248 560 4005• Phone: 248-560-4005• Email: [email protected]• Web Site Address: [email protected]

DIS Annual Meeting, June 7, 2012 DIS Annual Meeting, June 7, 2012 Muskegon, MichiganMuskegon, Michigan

ALLOY FACTORS FOR HARDENABILITY

Documents

Summary of ElementSummary of Element Effects in Ductile Iron of the Elements Effects... · Boron in Ductile Iron • Boron is noted for promoting ferrite and , when present at elevated