The mechanics of drawing wire at elevated temperatures

Abstract

Although elevated temperature drawing of wire has been an industrial process for a number of years it has not been investigated systematically and many facets of the process have not been understood. Consequently a continuous in-line heat treatment draw process was developed. The technique of drawing mild steel, medium carbon steel and M2 'high speed' steel wires up to 700°C and about 45% area of reduction was established. The mechanics of wire drawing at elevated temperatures has been studied in depth theoretically and practically. An upper bound solution was derived, and solved numerically, to establish the draw stress and other data, for a range of variables. The stress, strain, strain rate and temperature were related mathematically by the power law and the velocity-modified temperature respectively. This enabled the flow stress distribution in the deformation zone to be calculated, after taking into consideration the temperature rise due to deformation and frictional work. Based on the flow stress distribution, a mean flow stress was calculated and used in the upper bound solution. Adiabatic conditions were assumed to prevail. A special computer program was written to plot the strain, strain rate, temperature and flow stress distributions. The effects of draw temperature, area of reduction and lubricant were investigated experimentally. For a constant draw speed of 20 ft min -1, the strain-ageing region was found in the approximate temperature range of 200 ̊ - 400 ̊ C. In general, the experimental draw stresses required at elevated temperatures were lower than those developed in cold drawing. The experimental and theoretical results for medium carbon-steel were in satisfactory agreement, except for draw temperatures of 600°C and above. The results of mild steel and M2 'high speed' steel could not be verified theoretically due to a lack of suitable stress-strain data but such evidence as is available leads to the conclusion that the theory is in agreement with the experimental results