Iron-Steel Diagram : Comprehension 1

[FredTechWelding]

According to the Iron-Steel Diagram, over a certain temperature, the initial Iron/Steel structure is complete transformed in Austenite.

My question is :
For the Steel with very low carbon content (for example for pure ferrite steel), where does the carbon come from to complete the transformation of each austenite structure ?
By definition, ferrite structure only possess a body-centered cubic structure with only 1 carbon element, as the autenite structure (face-centered cubic) possess 6 carbon elements....

Thanks in advance !

 

[TVP]

Fred,

Iron does not require the presence of Carbon to transform into austenite (FCC structure). Pure iron will transform from ferrite (alpha, BCC) into austenite (gamma, FCC) above ~ 930 C. Here is a link with some additional information:

http://web.utk.edu/~prack/MSE 300/FeC.pdf

 

[OGMetEngr]

To get all technical, many sources state the definition of austenite as a solid solution of C in gamma-Fe. By this definition with no carbon, it is not austenite. You speak of low carbon steels. If there is any carbon the Fe-C binary phase diagram applies and the phase can be seen at equilibrium. Notice the sliver of alpha-Fe on the left side for extremely low amounts of C. This accounts for concentrations and temperatures where there isn't enough carbon to transform to austenite (FCC).

 

[OGMetEngr]

Also, the link TVP pointed to came from the University I graduated from. I remember the class that included this presentation, it was an intro to materials science and engineering lab class that all engineering majors were required to take. A little over the heads of most other engineering majors I think.