Therefore, it was necessary to develop a new kind of steel to meet a new and severe condition and accordingly the mother of experiment and invention gave birth to the now famous "High Speed" Steel.
The general principles applying to the hardening and drawing of High Speed Steel are in many ways the same as described above for the simple carbon steel, except that as we begin to add various elements other than carbon to the melt, the resulting alloy becomes more and more complex in its form and reactions and therefore its heat treatment causes greater and greater study and skill in its successful undertaking.
It is generally known among tool hardeners that it is necessary to heat the tool to a higher degree of temperature in order to secure proper hardness when using High Speed Steel than it is when a simple Carbon Tool Steel is employed. We are told that the introduction of certain elements into the melt of a simple Carbon Tool Steel has the tendency to change the critical range. Of course, the formulas used in the manufacture of any high grade High Speed Steel contain very appreciable amounts of various elements other than Carbon which materially effect the property which the steel will have when hard. The effect which these elements appear to produce in the period of critical range can be seen from figure 7.
In this case an experiment was made with a piece of High Tungsten High Speed Steel similar to the experiment which was described in detail above with the test piece of simple Carbon Tool Steel. The readings of the pyrometer were carefully recorded and when plotted on the graph sheet produced the picture under discussion.
Here it will be noticed that the vivid reaction, which we might have expected would occur as the temperature indicating the first critical range was reached, was materially reduced. This might lead us to suspect that the desired allotropic change had not completely taken place at this point. In fact we noticed that the pyrometer needle did not record a vivid critical point until a very much higher temperature was reached. All of these observations serve as a possible explanation or indication of why it is necessary to employ very much higher temperatures in the hardening of High Speed Steel than it is in the hardening of a piece of simple Carbon Tool Steel.
In a later chapter of this little volume we define Carbon Steels as those which do not contain enough of any element other than carbon to materially affect the physical properties which the steel will have when hard. High Speed Steels which are one of a very important group of special alloy steels, are those steels to which some element other than carbon has been added in sufficient amount to materially effect the physical properties which the steel will have when hard.
The element which stands out alone as the most vital and important one as affecting the wonderful and highly desirable features looked for in High Speed Steels is Tungsten. We will discuss the various effects which the different elements give to the different alloy steels in a later chapter, but for the present we will confine ourselves to a brief discussion of the heat treatment of the now famous modern High Speed Steel.
High Speed Steel. Carbon .58%. Structure: Very fine pearlitic condition, with particles of free carbide. Mag. 500x