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Adding the optimal amount of inoculant as a function of the nucleation properties in the base iron

ATAS Dynamic Inoculation

Version: 020131

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Why dynamic inoculation?

• Too much inoculant increases risk for shrinkage in grey iron and slag defects

• Too little inoculant increases risk for chill and shrinkage in ductile iron

• Amount and type of inoculant influences the precipitation of eutectic graphite

• The nucleation properties can vary considerably even with constant chemistry

• Reduces cost for inoculants

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Efficient inoculation is essential!

• Most frequently used treatment to cast iron• Provide initial nucleation sites• Control crystallization• Influence nodule count / cell size• Control chill and intercellular carbides• Influence shrinkage tendency• Influence physical properties

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Problem 1 - Selecting Inoculant

• Influencing factors: Base iron status, type of graphite (flake, CG, DI), pouring temperature, casting modulus, quality requirement, price etc.

• At least 20 different basic types of inoculants to choose from

Question: How to select and evaluate?

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Problem 2 - How much to add?

Too much: • increases cost• increases shrinkage in grey iron• increases endogenous slag a.o.Too little:• decreases cell size / nod. count• increases chill tendency• reduces some physical propertiesQuestion: How to evaluate?

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Chemistry is not enough!

• Weight % of each element - that´s all !!!• No info about compounds• No info about oxides, silicates or nitrates• No info about amount or size of graphite• No info about interactions• No info about behaviour during solidification• In summary no info about nucleation!

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ATAS shows the integrated effects of all components!

A spectrometer analysis shows the elemental amount of each element, so e.g. 0.04% Mg can mean different things!

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White eutectic temperature

1% Si reduces TE approx 12 C

1% P reduces TE approx 30 C

1% Cr increases TE approx 27 C

The white eutectic temperature shows the “silicon equivalent”, which is the lower limit for chill formation.

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Grey eutectic temperature

The grey eutectic temperature (TElow) shows the actual, lowest temperature during the eutectic part of solidification.

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Factors influencing Metallurgical Quality

• Chemical composition• Charge materials and mixture (Combined & Free C)• Charging sequence and temperature / time ratios• Iron handling and treatment practice• Pouring temperature and inoculation practice • Presence and amount of reaction products • Thermal properties of alloy, mould and core(s)• Mould / core hardness / weighting• Methoding (gating, feeding, feeding paths, etc.)• Shake-out time

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Nucleation properties in the base iron do vary although chemistry is constant!

Nucleation properties

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White and grey curves

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Under cooling

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Chill & Inverse Chill

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Chill

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Inverse Chill

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Effects of inoculation

• Can reduce TL• Increase TElow• Increase TEhigh• Reduce recalescence• Increase GRF 1• Decrease GRF 2• Deeper dT/dt_TS

Conclusion: Different applications require different inoculants!

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0.08% Inoculant

Sample taken from the Quik-Cup. Note R and GRF 2

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Inoculation Index = Undercooling uninoculated sample / Undercooling inoculated. Undercooling = TEgray - TElow (actual)

Recalescence - R

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Testing Inoculants

The effect of different inoculants can easily be studied using ATAS and the most optimal inoculant for the actual application can be selected.

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Dynamic Inoculation

The optimal amount of inoculant during a day as evaluated by ATAS. Without ATAS the foundry had to add 0.3% all the time in order to take the ”worst” case into account.

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Dynamic Inoculation

In most cases the iron is over-inoculated (often 30-40%) as the chemical analysis does not give any indication of the nucleation status.

ATAS can measure the nucleation status and suggest optimal additions of inoculants.

The dynamic inoculation approach reduces problems with micro shrinkage, chill, slag and reduces costs.

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Calibration

The Dynamic Inoculation module in ATAS is calibrated by taking samples from uninoculated iron and iron with different amounts of inoculant. A formula for inoculation is created based on these data.

The main factors influenced by inoculation are:

TL, TElow, R, GRF1, GRF 2, TS and dT/dt_TS

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Alloy Database - Learning

The results from all tests are stored and used with a statistical method to fine-tune the threshold values.

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Alloy Database - Limits

The threshold values for different alloys and/or casting categories are stored in a database.

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Alloy Database Inoculation

The system can be used “off-line” where the recommended amount is displayed on the screen or “on-line” connected to an inoculation dosing device.

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Benefits with ATAS Dynamic Inoculation

• Reduced shrinkage problems• Reduced chill problems• Reduced expansion penetration• Less variations in cell size• Less variations in Brinell Hardness• Less variations in machinability• Less consumption of inoculant• SPC test of base iron