Brian Yao said:What are the reasons behind the different microstructures of steel at different temperatures? I don't understand why steel at high temperatures (austenite phase) would favor an FCC crystal structure while steel at lower temperature (ferrite) would favor a BCC crystal structure.
Okay I understand that carbon in Fe strengthens the metal by creating distortions within the lattice but I don't understand how temperature plays a role in determining the preferred crystal structure.drvrm said:carbon in small quantities is added to iron and one can get steel.
the size of carbon atoms is less than the spacing between iron atoms so it goes in and forms a solid solution-thus deforming the structure of iron.
The iron-carbon equilibrium diagram (phase diagram) is a plot of transformation of iron with respect to carbon content and temperature.
this admixture of carbon leads to several changes in its properties -stress bearing and ductileness etc.
If one observes the metallurgy of steel in detail related to its various phases your question can be handled-
its better you see a site which handles your querry...
ref; <http://nptel.ac.in/courses/105106112/1_introduction/2_metallurgy_of_steel.pdf>
BCC (body-centered cubic) and FCC (face-centered cubic) are two different types of crystal structures that can exist in steel. In BCC, the atoms are arranged in a cubic lattice with one atom at each corner and one in the center of the cube. In FCC, the atoms are arranged in a similar cubic lattice, but with one atom at each corner and one in the center of each face. This results in a more tightly packed structure in FCC compared to BCC.
FCC is the preferred crystal structure for most types of steel. This is because it has a higher density and therefore provides better strength and ductility. However, BCC is also commonly found in some steels, such as low-carbon and high-alloy steels.
The crystal structure of steel has a significant impact on its mechanical properties. FCC steel tends to have higher strength and ductility, making it more suitable for applications that require these properties. BCC steel, on the other hand, is more brittle but can tolerate higher temperatures, making it suitable for high-temperature applications.
Yes, the crystal structure of steel can be changed through heat treatment processes. For example, heating and quenching can result in a transformation from BCC to FCC structure, while slow cooling can result in the opposite transformation from FCC to BCC. This allows for the manipulation of steel's mechanical properties for different applications.
The preferred crystal structure in steel is determined by factors such as composition, temperature, and cooling rate during the steel's formation. Generally, lower carbon content, higher temperatures, and slower cooling rates favor the formation of FCC structure, while higher carbon content, lower temperatures, and faster cooling rates favor BCC structure.