The optimum patenting conditions for hypereutectoid steel to obtain a high drawability and a high work hardening rate were studied by metallographic examinations and laboratory drawing. Based on the present results, higher strength steel wire with small diameter has been manufactured on a production basis.
1) Provided that an appropriate cooling rate corresponding to carbon content is secured, the precipitation of thick proeutectoid cementite can be prevented.
2) In the practical patenting temperature range, the cementite plate thickness as well as the pearlite lamellar spacing decreases as the carbon content increases.
3) The work hardening rate during drawing and the delamination resistance are enhanced through elimination of the upper bainite in pearlite.
4) The maximum strength of 0.04 mm wire manufactured from 0.96%C-0.2%Si-0.3%Mn-0.2%Cr steel without delamination occurrence has reached to as high as 5.70 GPa.