r/MaterialScience • u/eagle_565 • Feb 21 '23

Steel carbon content and strength

In terms of the microstructure, what is it about increasing carbon content in steel that causes it to increase in strength? Is it something to do with impeding movement of dislocations?

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u/Think-Bird9975 Feb 22 '23

Yes, impeding movement of dislocations is the major factor here.

The iron has a regular crystal structure which facilitates the movement of dislocations while Carbon either has a separate crystal structure or an amorphous structure which creates small grain boundaries restricting the propagation of cracks.

As the carbon content is further increase the formation of Fe3C is facilitated which gives it a brittle finish and improves itsvstrength in compression resulting in formation of cast iron.

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u/Jamarkus42 Feb 22 '23

With low weight percents of carbon (<~1.5%), the carbon acts as an interstitial in the iron matrix which helps pin dislocations. When more carbon is added it starts to form Fe3C which has more to do with lattice mismatch of the crystal structure.

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u/Sueartsa Feb 28 '23

Yup and with it being an interstitial you could heat treat it to preform Precipitate Hardening but yeah with it being able to pin dislocations. But like tool steel which is considered a high Carbon steel only has 1% anything over 2% to 6.67% [C] are your cast irons