150 BELL SYSTEM TECHNICAL JOURNAL 



not be fabricated cold and this appeared at first to limit seriously the 

 applications for the otherwise promising material. Brittleness in 

 cold-rolling was overcome through the addition of approximately 2.5 

 per cent of vanadium, whereupon the alloy can be cold rolled after a 

 quench from a high temperature. Fortunately the vanadium does not 

 materially impair the useful magnetic characteristics. The alloy 

 finds its chief application in the form of .010 inch sheet in the telephone 

 receiver diaphragm. 



Substantial tonnages of permanent magnet materials are also used 

 in telephone apparatus per year. Of this most is 3.5 per cent chromium 

 and other permanent magnet steels of low cost and low maximum 

 energy product (B X H maximum for the demagnetization curve). 

 Much of the remainder used is a material with high maximum energy 

 product for receivers and other applications where space and weight 

 limitations prevail. For this purpose 36 per cent cobalt steel has been 

 used but it is now replaced in new apparatus by an iron-cobalt- 

 molybdenum alloy, remalloy, which has superior magnetic properties 

 and is of lower cost. 



This iron-cobalt-molybdenum alloy, which contains approximately 

 12 per cent cobalt and 17 per cent molybdenum, has no intentional 

 carbon addition and is of a dispersion hardening type. The hardening 

 heat-treatment consists of quenching from 1180°-1300° C. in oil 

 (after which the material is mechanically and magnetically soft) fol- 

 lowed by aging at 670°-700° C. for one hour (which induces mechan- 

 ical and magnetic hardness). The material can be hot-worked and 

 machined except in the hardened condition, and welds readily, but is 

 somewhat brittle. 



' Magnets of the iron-nickel-aluminum type are increasingly used in 

 telephone apparatus. These alloys may be ternary compositions or 

 may be modified by a number of additional elements; cobalt and 

 copper additions have been found advantageous. The high coer- 

 cive force, high maximum energy product, and light weight make 

 them attractive. Disadvantages are non-workability and lack of 

 machinability. 



In addition to magnetic purposes, ferrous alloys are used extensively 

 in other applications. Considerable quantities of carbon and alloy 

 steels are used for structural purposes, and high alloy steels for installa- 

 tion and maintenance tools. 



Prospective Developments 



In concluding a discussion of metallic materials in telephone equip- 

 ment interest naturally is directed toward the future developments. 



