Strain Aging in Boron Alloyed Multi-Phase С- Mn – Si – Steel Wire Rod

The specimens of C – Mn – Si - steel wire rod 5.5 mm in diameter with 0.005% B and without B additions from Moldova Steel Works had been studied. It was been established by crystallographic-geometrical analysis, that the boron atoms could be allocate in B – alloyed a – Fe only in the positions of a sub-interstitial solid solution. By study a static strain aging (SSA) and a dynamic strain aging (DSA) specimens of wire rod by C – Mn – Si - steel with B and without B (both with multi-phase (ferrite- martensite (bainite)-pearlite) microstructures) more expressed decreasing of strengthening properties and higher characteristics of ductility had been determined for C – Mn – Si - steel specimens with B. These results could be explained by “de - nitrogenous” and “de - carbonaceous” mechanisms, when boron atoms from a – Fe sub-interstitial solid solution by producing wire rod and by its strain aging thermal treatment with temperatures 150 - 450 °С generate boron- nitrogenous and boron - carbonaceous – nitrogenous precipitations. By realizing these mechanisms nitrogen and carbon atoms are partly excluded from the dislocation pinning’s process. This, in fact, explains to inhibit the development of strain aging (SSA and DSA) in boron- micro-alloyed C – Mn – Si - steel.