Influence of aging on the relaxation and internal friction properties of cold drawn pearlites

Abstract

Rolled wire of eutectoid steel containing approximately 0.8% carbon is particularly suitable for hardening by cold drawing. When drawn it acquires exceptional mechanical strength, so that it can transform int the strongest material known, apart from the thinnest metal wiskers. Lamellar pearlite is obtained by isothermally annealing (patenting) austenite at temperatures between 720 and 450/sup 0/ C, the interlamellar spacing being a decreasing function of the transformation temperature. The strength of a patented wire cold drawn to a given reduction has been the subject of almost exhaustive studies of Embury and Fischer, later re-interpreted by Langford, in terms of a modified Petch argument. Drawn pearlitic wires are used as a reinforcement in pre-stressed concrete, and, under the name of ''music wire'', to make springs. Under these conditions, the mechanical strength, though important, is not the most interesting property, which is, instead, the capacity to show a small load (or stress) relaxation rate under constant extension. The relaxation will be called parabolic, logarithmic or hyperbolic. Usually the three alternatives take place successively in the course of a sufficiently long relaxation test. It has to be appreciated that a relaxation test is similar in many respects, but by no means identical, tomore » a low temperature creep test. The work done up to 1970 in the entire field of microplasticity of steel wires has been extensively reviewed by Lehnert.« less