MOLYBDENUM.
Molybdenum was once thought of as being somewhat in a class with tungsten, but its use in high speed tool steels is being generally discontinued. The reason for this is that it was found that in rapid steels this element caused irregular performance, such as large variations in the cutting speeds which they would stand. This element is also likely to make the steels seamy and contain physical imperfections. Molybdenum steels were also found to crack on quenching, and possess decided variations in internal structure.