The Effect of Working on the Physical Properties of Molybdenum

Abstract

Numerical values are recorded for hardness, ultimate tensile strength and per cent elongation of molybdenum wire and sheet having had various amounts of mechanical working. The data indicate only the range that may be expected and are not exact for any given piece of metal. It is indicated that the methods of working, annealing, etc., greatly affect the strength and ductility of the metal. Molybdenum metal is inherently a moderately hard, very brittle metal and the properties of high strength and ductility found in commercial metal are properties imparted to it by mechanical working and heat treatment. INTRODUCTION Molybdenum is commercially produced by powder metallurgy methods. The metal powder obtained by reducing the oxide MoOa or other compound in hydrogen is pressed to desired shape and heated to near the melting point in a hydrogen atmosphere to produce solid, coherent metal billets. These billets are forged and rolled or drawn at temperatures higher than those used for working steel. The physical properties of the finished molybdenum depend upon these temperatures and working schedules. The object of this paper is to show how the density, hardness, tensile strength and other properties of molybdenum are altered by working or annealing and to give some average figures for commercial sheet and w i r e . DENSITY OF MOLYBDENUM Commercial molybdenum powder has a particle size of 1 or 2 microns and, when lightly tapped in a cylinder or glass graduate, has a bulk density of about 3. The density of a pressed billet is normally 6 and of heattreated ingots about 9.8. The density of the heat-treated pieces, however, depends somewhat upon the pressures used for compacting. Very high pressures on thin sections result in densities greater than 10. When the heat-treated ingot is worked into sheet metal or wire, however, there is a gradual increase in the density as shown in Fig. 1. The exact density of molybdenum should not be cited unless the amount of working is indicated. t Manuscript received February 19, 1946. This paper is based in part on work done for the Office of Scientific Research and Development under Contract OEMsr 1205 with Westinghoutm Electric Corp. t Assistant Director of Research, Westinghouse Electric Corp., Bloomfield, N. J. w Research Engineer, Westinghouse Electric Corp. 217 ~ 1 8 ] . W. MARDEN AND D. M. WROUGHTON