TTT Curve - Economic Growth - and the Source Code

In last few posts, we were discussing about interesting parallels between working with metals & the code.We discussed about properties of metal (& the code) like Strength, Ductility & Malleability and  Toughness. We also talked about Case Hardening. In this post, we will discuss something more interesting - i.e. Time-Temperature-Transformation (TTT) Curve & its relation to software development.

Figure 1: source: http://www.materialsengineer.com/E-Steel%20Properties%20Overview.htm

The abstract in the above site mentions:

The traditional route to high strength in steels is by quenching to form Martensite that is subsequently reheated or tempered, at an intermediate temperature, increasing the toughness of the steel without too great a loss in strength. The ability of steel to form Martensite on quenching is referred to as the hardenability. Therefore, for the optimum development of strength, steel must be first fully converted to Martensite. To achieve this, the steel must be quenched at a rate sufficiently rapid to avoid the decomposition of Austenite during cooling to other stable forms like Ferrite, Pearlite and Bainite.

In this post we are going to discuss out Hardenability. Ability of the steel to form Martensite is called Hardenability. It can be learned plotting the Time-Temperature-Transformation (TTT) curve. Steel is heated above its Austenizing temperature & cooled down at different rates. Curve is plotted where structural transformation of the steel into more stable forms begins & ends. This results in C-shaped curve.

What does the C-shaped curve signify?

The position of "C" along the x-axis leaves a narrow neck. Steel can be converted into fully Martensite - if & only if - its cooling rate escapes the "C" region of the TTT curve. The cooling rate that's tangent to the "C" is called "Critical Cooling Rate". It is the minimum rate at which the steel must be quenched in order to get fully Martensite. If steel is cooled slower than this critical rate, then it results in other structural forms like Bainite, Pearlite, which will not give required hardness.

So what's the issue? Its possible to ensure that steel is cooled rapidly enough to have desired hardness. But the negative side effect is, rapid cooling leaves undesirable internal stresses into steel which makes it brittle. Also, rate of cooling is so rapid that some of the Austenite doesn't at all get a chance to get converted into Martensite, even if its possible. This leaves some Retained Austenite, which makes properties of steel unpredictable.

Addition of Alloying elements into Steel play a very important role here. All alloying elements except Cobalt shifts the C-curve of TTTdiagram towards right side of the x-axis. This lowers the Critical Cooling Rate, which means you can afford to cool the steel a bit slowly, while completely converting to Martensite to get desired Mechanical Properties for the steel component you are making.

I have added nothing new so far. Every Mechanical Engineer knows it & every Metallurgist breaths it. If anyone notices errors in the above technical content, appreciate if you can bring it to my notice. 

Now some other interesting thing starts here. What is the relation of this post to Economic Growth and Software Development and the Source Code? 
Well I'll put it in my next post, as this one is getting longer.