Tungsten in Steels

Tungsten in Steels  Tungsten (W) (atomic number 74 and atomic weight 183.92) has density of 19.3 gm/cc. Melting point of W is 3410 deg C and boiling point is 5400 deg C. The phase diagram of the Fe-W binary system is at Fig 1. Fig 1 Fe-W binary phase diagram Application of W in steels started as early as in the mid-19th century and until the first quarter of the 20th century, its importance in steel has steadily increased, with the steel industry then the largest W consumer. W was among the very first alloying elements systematically studied and used to improve steel properties, for example hardness, cutting efficiency and cutting speeds of tool steels. The use of W in structural steels declined since 1940 because alloying with molybdenum (Mo) and chromium (Cr) as well as with vanadium (V) and nickel (Ni) has given better performance at lower cost. W is known mainly for its strong tendency to form extremely hard and stable carbides. This property, in fact, is the basis for the most important use of W in steels, which is as a constituent of high speed and other tool steels. Around 20 Р25 % of all W produced is used in these steels. Tungsten bearing addition agents Earlier W alloyed steels were manufactured by the addition of more or less pure W powder to the liquid steel, or, alternatively, by addition of an iron rich W pre-alloy, which was obtained from purified W ore. This rather expensive procedure limited the application of W alloyed steels because of the high price. In 1893 a new tungsten ferro alloy was introduced containing up to 80 % tungsten, called ferro- tungsten (Fe-W), which was much cheaper. Fe-W has lower melting temperatures, faster dissolution in...