Abstract
SEM, TEM characterizations, in combination with tensile tests, provided an intriguing observation that ultra-high-strength and good ductility could be achieved simultaneously by changing the ratio of large and small precipitates in high-carbon steel (1.0C-1.5Cr-0.31Mn-0.20Si, wt %). The high yield strength of 670 MPa, tensile-stress of 740 MPa, and good ductility (elongation of 26%) were obtained by adopting spheroidization annealing, cold rolling, recrystallization annealing, and cold drawing. This led to nanosized precipitates with a large ratio of big size to the small size of 0.28, promoting high dislocation storage of 1.39 × 1014 m−2. In addition, the finite element (FE) method was used to simulate the cold-rolling process, and the largest stress and strain were 830 MPa and 0.6 at a depth of 3 mm after the fourth pass of the 0.10C-1.50Cr steel, respectively. The stress and strain accumulation in the top layer was potentially caused by severe plastic deformation, as well as attrition rendered by the rollers. This explained the emergence of dense low-angle grain boundaries in the region close to the surface of the cold rolled steel.
Highlights
Cold drawn high carbon steel wires have wide industrial applications, such as steel cords for automobile tires, cable wires for suspension bridges, ropes, and springs [1,2,3]
Two different types of structures appeared in pearlite, namely coarse lamellar structure (CLS) and fine lamellar structure (FLS) (Figure 2a,b)
The motivation of this study was to obtain the best combination of strength and ductility by controlling the ratio of small and large cementite particles in the microstructure
Summary
Cold drawn high carbon steel wires have wide industrial applications, such as steel cords for automobile tires, cable wires for suspension bridges, ropes, and springs [1,2,3]. High strength mainly results from the specific microstructure consisting of soft ferritic matrix and hard cementite lamellae. The spheroidization of cementite lamellae is beneficial to the cold formability of steels; the pearlite steel is usually to be subjected to spheroidization annealing [4,6]. The cementite lamellae gradually change their shapes into spherical particles to produce a mixed microstructure, in which globular cementite particles are uniformly distributed throughout the ferrite matrix [7,8,9]
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