One concept that can be difficult to understand intuitively is that the hardness or strength of steel does not change its stiffness. Meaning, “flexing” steel without permanently bending it is not changed by its hardness. I have heard many people swear up and down that they can tell a difference, so I found a great Youtube video that illustrates this [1]:
There are many modifications to a straight high temperature austenitize for a given hold time followed by quenching. I am covering a few of them in this article.
Preheating
Preheating is performed to minimize size change, distortion, and cracking during heat treatment. Often a single preheating is recommended, but for some grades two preheating temperatures are recommended. For example, the Vanadis 4 Extra datasheet recommends a first preheat temperature of 600-650°C and a second of 850-900°C, such as in the following schematic [1]:
Carbide Volume
As covered in Part 1, carbide volume decreases with increasing temperature. As an example, here are micrographs showing carbides in a spray-form version of the original Vanadis 4 (non-Extra) [1]:
Update 7/6/2018: Since the writing of the original article I found some excellent micrographs that show austenitization very well and serve as a good supplement to the schematic diagrams. Go to the bottom of the article to see them.
I enjoy reading patents from steel companies, it reveals information about new products and research often not available otherwise. One thing I’m surprised there isn’t more talk about is a steel Crucible patented but never sold – an improved 3V: https://www.google.com/patents/US7615123
