Abstract
Longitudinal grooves of various depths ranging from 0.001 in to 0.011 in were machined on the cylindrical surface of steel slugs prior to carrying out an automatic two-stage transfer heading operation. The longitudinal grooves were used to estimate the ‘critical groove depth’, which was defined as the depth of longitudinal groove that contained a ductile fracture crack just on the point of ‘opening out’ at the end of the heading process, thus giving a measure of the ductility of the wire.
A half-replicate of a two-level factorial experiment was carried out to assess the effects and interactions of annealing temperature, annealing time, cooling rate and ageing temperature on the ductility of four different types of 1/2 in diameter cold heading steel wire.
The results show that certain types of steel wires have optimum ductility in the ‘as-received’, cold-drawn, state. Other types of steel are shown to respond favourably to process annealing treatments, in which case annealing at 700°C for 1 hour followed by air cooling should give optimum ductility. It is shown that there is no general correlation between decreasing hardness and increasing ductility for steel wire.
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