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Zhangjiagang, China

Fang F.,Nanjing Southeast University | Hu X.-J.,Nanjing Southeast University | Hu X.-J.,Jiangsu Sha Steel Group | Zhang B.-M.,Nanjing Southeast University | And 2 more authors.
Materials Science and Engineering A | Year: 2013

In this paper, extremely high strength was obtained in medium carbon steel having a carbon content of 0.35% by weight through cold drawing. Experimental results showed that the tensile strength of the steel increased by nearly three folds from the original value ~615. MPa to 1810. MPa corresponding to drawing strain of 3.0. To reveal the mechanisms that govern the strengthen increase, the microstructural evolution was analyzed during cold drawing, with respect to the change of the deformation resistance (measured by micro-hardness) of micro-constituents (i.e., primary or proeutectoid ferrite and pearlite) in the material. The proeutectoid ferrite became elongated and, at the same time, increasingly hardened while the pearlite maintained equiaxed shape after initial drawing. With the increase of the drawing strain, the pearlite was stretched parallel to drawing direction, accompanied by an increase in the 〈110〉 texture intensity and dislocation density in the ferrite phase. Under heavy drawing, a laminate structure formed, consisting of alternating pro-eutectoid ferrite and pearlite both parallel to the drawing direction. The 〈110〉 texture intensity in the ferrite phase became saturated as ε>1.2. High density dislocation zones further spread in the ferrite phase. The interlamellar spacing between ferrite and cementite phases in the pearlite decreased. Based upon these observations, mechanistic models were constructed to provide insight into the deformation and strengthening mechanisms of this steel. © 2013 Elsevier B.V. Source


Fang F.,Nanjing Southeast University | Zhao Y.,Nanjing Southeast University | Zhou L.,Nanjing Southeast University | Hu X.,Jiangsu Sha Steel Group | And 2 more authors.
Materials Science and Engineering A | Year: 2014

In this paper, microstructure and mechanical properties of cold drawn pearlitic steel wires were investigated by combining SEM and XRD analysis with tensile testing. Experimental results show that the tensile strength of wires increases from 1250. MPa to 3280. MPa with increasing drawing strain of 3.2. When the strain is greater than 2.0, the rate of work hardening has increased rapidly. The original steel rods have a weak 〈110〉 texture. With the increase of the drawing strain, the orientation of 〈110〉 intensified and became dominant. The 〈110〉 texture became saturated when drawing strain reaches 2.0. In addition, for low strain (. ε=1.1) pearlite wires, the intensity of 〈110〉 texture decreased sharply after austenitization at 820. °C for 5. min. With the increase of austenitization time, the intensity of 〈110〉 texture decreased continually, and eventually no dominant texture existed. For high strain (. ε>1.6) steel wires, though the intensity of 〈110〉 texture decreased in the beginning, the 〈110〉 texture remained dominant after prolonged austenitization treatment. The observed texture inheritance can be exploited in the development of steel wires with unprecedented strength. © 2014 Elsevier B.V. Source


Fang F.,Nanjing Southeast University | Zhou L.,Nanjing Southeast University | Hu X.,Jiangsu Sha Steel Group | Zhou X.,Nanjing Southeast University | And 5 more authors.
Materials and Design | Year: 2015

Pearlitic steel rods with inherited texture (IT) were prepared from pre-drawing followed by austenitization treatment. Effects of inherited texture on the microstructure and mechanical properties of cold-drawn pearlitic wires were investigated. The 〈1. 1. 0〉 texture of ferrite increased with drawing strain and became saturated when strain reached about 2.0. However, wires with IT showed a higher 〈1. 1. 0〉 texture intensity. The ratio of bent over straight pearlite colonies in wires with IT were about 20% lower than that of wire without IT in drawing. Additionally, Wires with IT showed a greater work hardening rate. Tensile strength of wires without IT increased from 1260. MPa to 3010. MPa as drawing strain increased to 3.5, while wire with IT exhibited an 7% increase in tensile strength (i.e., up to 3230. MPa). Torsion angle of wires with IT were about 13% higher than that of wires without IT. Differential scanning calorimetry (DSC) analysis showed that wires with IT have higher thermal stability. © 2015 Elsevier Ltd. Source


Fang F.,Nanjing Southeast University | Zhao Y.,Nanjing Southeast University | Liu P.,Nanjing Southeast University | Zhou L.,Nanjing Southeast University | And 3 more authors.
Materials Science and Engineering A | Year: 2014

Nanostructural evolution of cementite lamellae in pearlitic steel wires subjected to cold drawing remains elusive, making it difficult to understand the origin of remarkable ductility in cementite. Using high-resolution transmission electron microscopy (HRTEM), the mechanisms underlying the inelastic deformation of cementite in pearlitic steel wires were examined and elucidated. Deformation of cementite in drawing should be included in two mechanisms: (1) Dislocation mechanism: deformation in low strain pearlite should rely on the movement of dislocation. Flat-crystal cementite was broken up into several different orientation cementite particles. (2) Grain rotation mechanism: the deformation mechanism should be by the rotation of cementite particles. Cementite still keeps lamellar shape, but it was divided into a multilayer structure: central nano-crystal and outermost amorphous cementite. © 2014 Elsevier B.V. Source


Fang F.,Nanjing Southeast University | Hu X.-J.,Nanjing Southeast University | Hu X.-J.,Jiangsu Sha Steel Group | Chen S.-H.,Jiangsu Sha Steel Group | And 2 more authors.
Materials Science and Engineering A | Year: 2012

Spheroidization of lamellar cementite often occurs in cold-drawn pearlitic steel wires during galvanizing treatment, leading to the degradation of mechanical properties. Therefore, it is important to understand effects of galvanization process on microstructure and mechanical properties of cold-drawn wires. In this paper, cold-drawn steel wires were fabricated by cold drawing pearlitic steel rods from 13. mm to 6.9. mm in diameter. Thermal annealing at 450 °C was used to simulate galvanizing treatment of steel wires. Tensile strength, elongation and torsion laps of steel rods and wires with, and without, annealing treatment were determined. Microstructure was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition, differential scanning calorimetry (DSC) was used to probe the spheroidization temperature of cementite. Experimental results showed that tensile strength of wires increased from 1780. MPa to 1940. MPa for annealing <5. min, and then decreased. Tensile strength became constant for annealing >10. min. Elongation of wires decreased for annealing <2.5. min, and then recovered slightly. It approached a constant value for annealing >5. min. Tensile strength and elongation of wires were both influenced by the strain age hardening and static recovery processes. Notably, torsion laps of wires hardly changed when annealing time was less than 2.5. min, and then decreased rapidly. Its value became constant when the hold time is greater than 10. min. Lamellar cementite began to spheroidize at annealing >2.5. min, starting at the boundary of pearlitic grains, and moving inward. A broad exothermic peak was found at temperatures between 380 °C and 480 °C, resulting primarily from the spheroidization of lamellar cementite, which is responsible for the degradation of torsion property of cold-drawn wires. © 2012 Elsevier B.V. Source

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