Suppression of Secondary Ferrite Formation by Boron Addition in High Carbon Steel Wires

Abstract

Heavily cold drawn pearlitic steel filaments containing small amount of micro alloying elements were investigated to stop delamination in torsional deformation. In Nb treated high carbon steel wire, the volume of secondary ferrite increased remarkably, and delamination occurred in the steel filament that was drawn up to 3.8 in drawing strain. But in Ti and boron treated high carbon steel filament, the secondary ferrite drastically decreased. And delamination did not occurr in this steel filament which was heavily drawn up to 4.2 in true strain.
From microstructural and chemical analysis, free boron seemed to suppress to generate secondary ferrite at boundary between pro-eutectoid cementite and austenite during patenting. Patenting process has very short reheating condition and very fast cooling and transformation time. The authors understood that such a very short heat treatment process is quite favorable to utilize boron to control secondary ferrite generation in high carbon pearlitic steel.