42 iron phase diagram
The Fe- C phase diagram is shown in Fig 2. In pure iron, austenite transforms to ferrite on cooling to 912 deg C. This transition temperature is traditionally called the A3 temperature, and the diagram shows that adding C to Fe lowers the A3 temperature. The iron -carbon phase diagram in Fig 2 actually shows two diagrams namely (i) the stable iron-graphite diagram (red lines), (ii) and the metastable Fe-Fe3C diagram. Cementite is metastable, and the true equilibrium is to be between iron and graphite (C). The phase boundary between the different solid phases is drawn on a binary phase diagram, usually plotted as temperature versus percent iron. Adding some elements, such as Chromium , narrows the temperature range for the gamma phase, while others increase the temperature range of the gamma phase. Iron phase diagram