Expert Analysis for Gray Iron Microanalysis
Expert is a large step forward where additional information available for the first time in the world is added to the micro-Thermoanalysis. This level adds fraction solid, and the heat of fusion of the sample by integrating the area between the rate of cooling curve and the baseline curve. Then each segment of solidification is integrated and ratioed against the total heat of fusion. Reporting these values as a percent of the heat of fusion corrects for slight changes in sample size. In addition, the various derivative curves can be displayed, and their data put into an excel format.

Expert Option Curves
⦁ Zero Curve or Baseline Curve is the cooling rate if no crystallization or solidification occurred. The area between this curve and the cooling rate bounds the heat of fusion.
⦁ Color integration adds color to the individual zones for quicker identification.
⦁ % Solid includes the percent fraction solid curve to the temperature curve. This is useful for solidification modeling. A detailed list of the fraction solid is included in the data drop if requested.

Information and Variables of Gray Iron Expert Microanalysis
⦁ Nucleation is the point at which heat energy first begins to slow the cooling of the sample. It can be missed if there is insufficient superheat in the sample. This point anchors the left side of the zero curve and is required for the calculation of the heat of fusion.
⦁ Pre-eutectic activity is the measure of gas in the sample. Internal reduced pressure pulls the gas into bubbles early in solidification before stress-initiated shrinkage is formed so the endothermic arrests before eutectic are classified as gas related. Gas can be seen where turbulence aspirates air into the molten metal.
⦁ Eutectic activity is the measure of micro-shrinkage occurring in the metal. This is sum of the endothermic arrests occurring between the eutectic and the start of solidus.
⦁ Eutectic Acceleration is a feature not yet fully understood. It is a measure of how fast the eutectic recalescence starts and it varies greatly between the metal types of Gray, Ductile and CGI. It is the maximum slope leading into the eutectic undercooling.
⦁ Eutectic deceleration is another feature not yet fully understood. It is a measure of how fast the eutectic reaction ends. It is the average slope of the recalescence or how fast the energy production is falling off.
⦁ Heat of Fusion is the total area between the zero curve and the rate of cooling. It is the sum of the distance between the two curves for each data point. Note: all area integrations are based on the background mathematical values and not based on screen pixels.
⦁ % Liquidus is the area between the baseline curve and the rate of cooling from the Start of Nucleation to the Rigidity Point. It includes the Early Liquidus and the Late Liquidus.
⦁ % Early Liquidus is the area between the baseline curve and the rate of cooling from the Start of Nucleation to the Liquidus Point. This is the energy from the initial growth of dendrites.
⦁ % Late Liquidus is the area between the baseline curve and the rate of cooling from the Liquidus Point to the Rigidity Point. This energy covers dendritic thickening and any late secondary branching.
⦁ % Graphite Liquidus is the area of the graphite liquidus if it occurs. Graphite is a very low energy producer and so a Graphite Liquidus is small. No austenite is being formed during this arrest which also means it is very low energy. But it has a strong and undesirable effect on shrinkage.
⦁ % Pre-eutectic carbides are the carbides that form around the rigidity point from lower silicon irons commonly used in pump housings to mitigate wear. They form in thin sections leaving the thinker sections machinable.
⦁ % Deceleration into Eutectic zone is the area between the baseline curve and the rate of cooling from the Rigidity point to the maximum acceleration into the eutectic point. During this zone carbon is concentrating to eutectic levels.
⦁ % Early Eutectic Zone is the area between the baseline curve and the rate of cooling from the maximum acceleration point to the Eutectic Point. This is still a zone where most of the eutectic forms. Depending on the type of iron, and percent dendrites, some micro-shrinkage can form in this zone.
⦁ % Late Eutectic Zone extends from the Eutectic Point to the End of Eutectic Growth Point. Here is where much of the micro-shrinkage occurs.
⦁ % Eutectic Recalescence Zone is the energy released due to the previous undercooling. The less undercooling (better inoculation) the smaller this value will be.
⦁ % Eutectic is the sum of the eutectic deceleration zone, the early eutectic zone and the late eutectic zone.
⦁ % Gas is the energy absorbed in forming gas bubbles in the metal.
⦁ % Eutectic Contraction zone starts with the point of maximum stress in the casting (End of Eutectic Energy Formation) and the start of Solidus. During this zone the hardness of the casting is determined, and macro shrinkage can occur.
⦁ % Shrink (Macro) is the integrated % of energy that was absorbed by the various macro shrinkage arrests. These do not include micro-shrinkage or suck-in defects.
⦁ % Stress is the endothermic energy absorbed by the grain boundaries as they solidify. For a given grade of iron, the larger this number, the less shrinkage will be found in the finished castings. Stress will always be present due to the reduction in volume that occurs from liquid form to solid form. It will be reduced by gas holes, micro-shrinkage, macro-shrinkage or by suck-in. Or it can be stored in the grain boundaries. As the casting cools from Solidus to Eutectoid temperatures, roughly 2,000 F to 1,400 F, additional graphite will form increasing the internal volume of the casting. This increase can tighten the grain boundaries if they are loose, or can cause mold wall movement if there is not enough looseness in the grain boundaries to absorb the expansion.

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