Abstract
A coupled thermal-microstructural simulation model was developed to estimate the thermal history in a eutectoid steel wire rod under continuous cooling and forced-convection. The model coupled the phenomena of heat transfer, phase transformation and estimation of the cooling boundary condition. The thermal histories were analyzed at different cooling rates to emulate the forced-convection conditions by air-jet as in the controlled cooling conveyor. The thermal histories were acquired and used to calculate the forced-convection heat transfer coefficients through the solution of the Inverse Heat Conduction Problem, while the phase transformation was approximated with the Johnson–Mehl–Avrami–Kolmogorov (JMAK) kinetic model. From the heat transfer coefficients and the kinetic parameters, a user-defined function (UDF) was coded and employed in the ANSYS Fluent® software. The model results were compared and validated with the experimental histories, obtaining a good agreement between both responses, while the microstructural evolution of the pearlite was validated using Scanning Electron Microscopy (SEM) and Vickers microhardness. It was found that specimen diameter and air velocity are the main variables to modify the undercooling and therefore the pearlite interlamellar spacing.
Highlights
Pearlitic high carbon steels are employed in applications that demand high tensile strength and ductility such as tire reinforcements, saw cables, prestressed concrete, and piano wires [1,2]
These mechanical properties are closely related to the interlamellar spacing between the ferrite and cementite which compose the pearlite; as this parameter decreases, the plastic limit and the maximum yield stress increase [3,4,5,6]
The continuous cooling that takes place in the controlled cooling conveyor is one of the most complex processes for the industrial production of high carbon steel wire rod. This process starts in the laying head, where the rod from hot rolling is looped continuously into coils and placed on the line where temperatures between 850 and 950 ◦C are measured
Summary
Pearlitic high carbon steels are employed in applications that demand high tensile strength and ductility such as tire reinforcements, saw cables, prestressed concrete, and piano wires [1,2]. These mechanical properties are closely related to the interlamellar spacing between the ferrite and cementite which compose the pearlite; as this parameter decreases, the plastic limit and the maximum yield stress increase [3,4,5,6]. The continuous cooling that takes place in the controlled cooling conveyor is one of the most complex processes for the industrial production of high carbon steel wire rod. The geometry of the coil as well as the cooling air flow pattern generate a variation in the heat transfer coefficient in the different areas of the conveyor, which is governed by convection and radiation heat transfer [9,10,11,12,13]
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