After the processes of hardening and drawing our sample of simple carbon tool steel have become thoroughly mastered, it might seem that all which was desired had been accomplished and that we could go on indefinitely making and using our simple carbon steel tools. However, when the extraordinary demands of modern industry required faster and faster cutting speeds, and deeper and deeper cuts, we commenced to realize that our familiar carbon tool steels would not fill the bill. This was due to the fact that as the tools became pressed with the faster speeds and deeper cuts, they could not do their work without becoming over-heated by the friction caused by the work of upsetting the chip and therefore the critical temperature was rapidly approached. Of course we know that if this temperature should be reached the steel would quickly lose its hardness and its cutting edge would therefore be completely ruined. 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. [Illustration: ≈HEATING AND COOLING OF HIGH SPEED STEEL SHOWN IN FIG. 12.≈] 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.