{"id":5256,"date":"2026-08-26T11:51:09","date_gmt":"2026-08-26T11:51:09","guid":{"rendered":"https:\/\/aboutfoundry.com\/eutectic-temperature\/"},"modified":"2026-08-26T12:40:45","modified_gmt":"2026-08-26T12:40:45","slug":"eutectic-temperature","status":"publish","type":"post","link":"https:\/\/aboutfoundry.com\/en\/eutectic-temperature\/","title":{"rendered":"Eutectic Temperature"},"content":{"rendered":"\n

The eutectic temperature is the single, fixed temperature at which a liquid alloy of a specific composition solidifies directly into a solid mixture, without passing through a pasty two-phase range.<\/strong><\/p>\n\n\n\n

The Eutectic Point in the Iron-Carbon System<\/h2>\n\n\n\n

In the iron-carbon system, the eutectic reaction takes place at a carbon content of roughly 4.3%. Two versions of the diagram give slightly different values: the stable system, where carbon separates as graphite, places the eutectic at about 1153°C; the metastable system, where carbon stays bound as cementite and forms ledeburite, places it at about 1147°C. Both numbers describe the same alloy family, cast iron, just under different cooling conditions.<\/p>\n\n\n\n

Why the Eutectic Point Matters in Foundry Practice<\/h2>\n\n\n\n

Foundries design cast iron close to the eutectic composition because it gives the lowest possible melting and pouring temperature for the whole iron-carbon series. A melt at or near the eutectic point also solidifies over a very narrow temperature interval instead of a wide pasty range, which keeps the liquid channel open longer while filling the mold. That is one reason eutectic and near-eutectic cast irons show better mold-filling behavior than alloys further from the eutectic composition. Compositions with less carbon than the eutectic point are called hypoeutectic and form primary austenite dendrites on cooling; compositions with more carbon are hypereutectic and form primary graphite before the eutectic reaction sets in.<\/p>\n\n\n\n

Stable and Metastable Eutectic Compared<\/h2>\n\n\n\n
System<\/th>Approx. Carbon Content<\/th>Approx. Eutectic Temperature<\/th>Solid Product<\/th><\/tr><\/thead>
Stable (graphite)<\/td>4.26% C<\/td>1153°C<\/td>Austenite + graphite<\/td><\/tr>
Metastable (cementite)<\/td>4.3% C<\/td>1147°C<\/td>Ledeburite (austenite + cementite)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Frequently Asked Questions About Eutectic Temperature<\/h2>\n\n\n\n

What is the difference between the eutectic point and the eutectic temperature?<\/h3>\n\n\n

The eutectic point is the combination of composition and temperature at which the eutectic reaction occurs. The eutectic temperature is just the temperature value of that point, always paired with a specific composition.<\/p>\n\n\n\n

Is eutectic cast iron the strongest cast iron?<\/h3>\n\n\n

No. Eutectic composition gives the best castability and fluidity, not the highest strength. Hypoeutectic irons with more primary austenite often reach higher mechanical properties, at the cost of a higher melting and pouring temperature.<\/p>\n\n\n\n

Why does an alloy at the eutectic composition melt at a lower temperature than either pure component?<\/h3>\n\n\n

Mixing two components lowers the freezing point of the mixture below that of either pure substance. The eutectic composition is the single mixing ratio where this depression reaches its minimum for the whole system, which is why it marks the lowest point on the phase diagram.<\/p>\n\n\n\n

Standard Reference<\/h2>\n\n\n\n

No DIN standard sets the eutectic point itself; it is a materials-science constant of the iron-carbon system, not a specification value. DIN EN 1561:2024-03<\/strong> (grey cast iron) and DIN EN 1563<\/strong> (ductile cast iron) build on it indirectly, because both standards classify iron grades that foundries keep close to the eutectic carbon content for castability.<\/p>\n\n\n\n

Further Terms<\/h2>\n\n\n\n