| Title |
Low-Temperature Strain-Age Hardening Behavior and Cementite Crystallinity Evolution in Cold-Drawn Pearlitic Steel Wires |
| Authors |
이승희(Seunghee Lee) ; 박형준(Hyeongjun Park) ; 이진우(Jinwoo Lee) ; 정진영(Jin Young Jung) ; 강신곤(Singon Kang) |
| DOI |
https://doi.org/10.3365/KJMM.2026.64.5.422 |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Keywords |
Pearlitic steel wire; Strain-age hardening; Low-temperature annealing; Cementite nanocrystallization; Interlamellar spacing; Delamination |
| Abstract |
The effect of low-temperature annealing on strain-age hardening in severely cold-drawn high-carbon
(0.92 wt.% C) pearlitic steel wire was systematically investigated, with particular emphasis on the role of
cementite crystallinity. Pearlitic wire subjected to severe cold drawing (true strain ε = 2.41) was annealed at
150 oC for 30 min, and the resulting microstructural and mechanical changes were analyzed using transmission
electron microscopy (TEM), X-ray diffraction (XRD) of both electrolytically extracted cementite and bulk ferrite,
and mechanical testing. Cold drawing markedly refined the interlamellar spacing (ILS) from ~100 nm to ~20
nm and induced strong colony alignment. Subsequent low-temperature annealing did not cause a statistically
significant change in ILS or lamellar morphology. This indicates that the annealing-induced strengthening is
not associated with further lamellar refinement. TEM and selected area electron diffraction (SAED) analyses
revealed extensive amorphization of cementite during cold drawing, followed by localized nanocrystallization
of cementite (?10 nm) during annealing. This crystallinity recovery was corroborated by partial recovery of
cementite diffraction peaks in XRD patterns obtained from electrolytically extracted cementite powder. XRD
analysis of the bulk ferrite showed lattice expansion after cold drawing due to carbon redistribution into the
ferrite, followed by partial contraction after annealing. This is consistent with re-partitioning of carbon back
to cementite. Meanwhile, peak broadening analysis indicated that the high dislocation density introduced by
cold drawing was largely retained after annealing. Mechanically, low-temperature annealing increased tensile
strength by ~4% while further reducing tensile elongation. It also deteriorated torsional ductility, accompanied
by longitudinal delamination. These results demonstrate that strain-age hardening at 150 oC is governed
primarily by nanocrystallization of amorphized cementite and associated carbon re-partitioning, rather than
by ferrite solid-solution strengthening, dislocation density changes, or lamellar refinement. |