Effects of Manufacturing Conditions on Tensile Fracture Behaviors in Hyper-Eutectoid Steel Wires

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 degrees C for 3 min and isothermally transformed at 580 degrees C and 620 degrees C for 3 rain. 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.