1. D AY 11 – I NTERMETALLIC COMPOUNDS AND THE I RON -C ARBON P HASE DIAGRAM

2. f20_09_pg284 Note the MG2Pb line. Intermetallic compounds show up as vertical lines. Their bonding predicts that they will be hard britlle, “rock-like” phases

3. M ATERIALS E NGINEERING – D AY 11 T HE I RON C ARBON ( OR I RON -I RON C ARBIDE )

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5. Ferrite (  ) Low temperature form of Fe – it is BCC. Can only hold up to 0.022% C by weight. This carbon is interstitial. It is very soft ductile material. Austenite (  ). High temperature form of Fe – not in equilibrium below 727C. It is FCC. Can hold up to 2.14% C by weight. This is also very soft ductile material. Cementite (Fe 3 C). A compound of Fe and C which always has 6.70% C by weight. The crystal structure is complicated. It is very hard brittle material.

6. V OCABULARY Ferrite (  ) Low temperature form of Fe – it is BCC. Can only hold up to 0.022% C by weight. This carbon is interstitial. It is very soft ductile material. Austenite (  ). High temperature form of Fe – not in equilibrium below 727C. It is FCC. Can hold up to 2.14% C by weight. This is also very soft ductile material. Cementite (Fe 3 C). A compound of Fe and C which always has 6.70% C by weight. The crystal structure is complicated. It is very hard brittle material.

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8. U SING THE F E -C D IAGRAM We can use the diagram to predict microstructure, and thereby mechanical properties in equilibrium (i.e. slow) cooled steels. This depends on a reaction known as the Euctectoid Reaction. Here is that reaction As we cool below 727C The resulting microconstituent is called Pearlite, P.

9. P EARLITE Here are some micrograph images.

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12. Hypoeutectoid – Below Eutectoid Composition, i.e. less than 0.77% carbon. Hypereutectoid – Above Eutectoid Composition, i.e. greater than.77% carbon

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15. F INDING THE R ELATIVE A MOUNT OF P EARLITE Steel has 0.30% C by wt. Use the Fe-C diagram to predict microstructure if we cool it slowly. 0.30 %C W P at low temp = W  at 727

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19. W HAT IS STEEL ? A vast family of materials Usually composed of ferrite + cementite. There are some exceptions. The way that the cementite is distributed in the ferrite is very important. For example, 1. Very coarse roundish cementite particles widely separated  soft ductile steel. 2. Very fine roundish cementite particles closely spaced  hard strong steel. (Has some ductility) 3. And so on – there are many ways to distribute cementite in ferrite.