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Korean Journal of Metals and Materials > Volume 56(3); 2018 > Article
Korean Journal of Metals and Materials 2018;56(3): 187-196. doi: https://doi.org/10.3365/KJMM.2018.56.3.187
과공석 강선에서 공정조건이 인장파단 거동에 미치는 영향
안강석, 박정훈, 남원종
국민대학교 신소재공학과
Effects of Manufacturing Conditions on Tensile Fracture Behaviors in Hyper-Eutectoid Steel Wires
Kang Suk An, Jung Hoon Park, Won Jong Nam
School of Advanced Materials Engineering, Kookmin University, Seoul 02707, Republic of Korea
Correspondence  Won Jong Nam ,Tel: +82-2-910-4649, Email: wjnam@kookmin.ac.kr
Received: 20 November 2017;  Accepted: 2 January 2018.  Published online: 6 March 2018.
ABSTRACT
This study investigated the effects of manufacturing conditions, such as patenting temperature and drawing strains, on the tensile fracture behaviors, especially on reduction of area (RA), of hyper-eutectoid steel wire. Steel wires with the chemical compositions of Fe-0.92C-1.3Si-0.6Mn-0.3Cr (wt%), were austenitized at 900 °C for 3 min and isothermally transformed at 580 °C and 620 °C for 3 min. Patented steel wires were cold drawn from 4.90 mm to 1.49 mm in diameter with an 18% reduction per pass. The cup-and-cone fracture surfaces of the tensile specimens consisted of a fibrous zone (crack initiation zone), radial marks (crack propagation zone), and shear lips. Four types of fracture mode were found in the tensile fractured surfaces of the patented specimens: dimple (fibrous zone), shear cracking (fibrous zone), boundary fracture (radial marks), and cleavage-type fracture (radial marks). Increasing transformation temperature contributed to an increase in the area fraction and size of the shear cracking and cleavage-type fracture. The increase in RA with the reduction in transformation temperature was attributed to a reduction in the pearlite block size as well as refinement of the interlamellar spacing. Meanwhile, as drawing strain increased, the area fraction of the fibrous zone in the tensile fractured surface decreased until a drawing strain of 1.79 and then increased, while RA increased up to a strain of 1.79 and decreased. It was found that the area fraction of the fibrous zone in the tensile fractured surface is closely related to the difference in RA in hyper-eutectoid steel wires.
Keywords: hyper-eutectoid steel, strength, ductility, cold drawing, tensile properties, fracture
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