In this lesson we're going to describe how you go about heat treating a plain carbon steel whose composition is the Eutectoid. What we see on the diagram are the regions where Pearlite forms, and Pearlite is forming as a result of holding the Austenite below the Eutectoid temperature for a certain period of time. And what you do is to produce the Pearlite, which is the two phase microstructure of ferrite and cementite and that is occurring by a diffusional process. When we quench to a lower temperature and hold. For example, if we were to quench the 300 degrees and hold it for various periods of time, we would see that up until we reach that first line that separates the Austenite from the Austenite, Bainite phase field, what we find is we have 100% Austenite. When we reach the line at 300 degrees, we begin to form structure that we refer to as Bainite. Again, FE3C plus ferrite and it continues on and the Austenite continues to decompose, forming more and more Bainite until we reach the dotted line where we have 50% Bainite and then eventually we have 100% Bainite. Now, if we were to quench from above the Eutechtoid temperature, this time down to the Lower temperature. We would wind up producing the structure that we refer to as martensite. Now remember, martensite is a single phase material. It occurs by a diffusionless transformation. And it's referred to as an athermal transformation. In other words let's quench the Austenite Down to the 50% line. When we hold it at the 50% line, we can hold it indefinitely and what we should have after we've held it for that period of time is still 50% Austenite that has not decomposed plus the 50% martensite that did. So, we have those horizontal lines. Now when we look at the various temperatures to which we quench. Starting up there with the Austenite transforming into these various decomposition products, what we see is that there becomes a progressively finer micro structure that develops and ultimately when we quench down and product Martensite. We're going to get a very fine microstructure that has a very high strength. Thank you.