Numerical Simulation of Wire Rod Cooling in Eutectoid Steel under Forced-Convection

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.

Effects of Wire Drawing and Annealing Conditions on Torsional Ductility of Cold Drawn and Annealed Hyper-Eutectoid Steel Wires

The effects of microstructural features on torsional ductility of cold drawn and annealed hyper-eutectoid steel wires were investigated. The patented wire rods were successively dry drawn to ε = 0.79 (54.7%) ~ 2.38 (90.7%). To examine the effects of hot-dip galvanizing conditions on torsional ductility, steel wires with ε = 1.95 were annealed at 500 °C for 30 s for ~1 h in a salt bath. In cold drawn wires, the number of turns to failure increased steadily, showing the maximum peak, and then decreased with drawing strain. During the post-deformation annealing at 500 °C, torsional ductility of steel wires decreased with annealing time, except for the rapid drop due to the occurrence of delamination for 10 s annealing. The decrease of the number of turns to failure would be attributed to the microstructural evolutions, accompanying the spheroidization and growth of cementite particles and the recovery of ferrite in cold drawn steel wires. From the relationship between microstructural evolution and torsional ductility, it was found that among microstructural features, the shape and orientation of lamellar cementite showed the significant effect on torsional ductility of cold drawn and annealed hyper-eutectoid steel wires.

Post Solutionising Rolling Sway on the Precipitation Behaviour of Eutectoid Steel Powder Reinforced Al7075 Ternary Alloy Composites

The solitary distinguished thermal treatment to aluminium alloy matrix of nonferrous group with uniformly dispersed reinforcement particles is precipitation or age hardening with or without mechanical working. Al7075 ternary alloy composites belongs to Al-Zn-Mg group and bulk properties can be enhanced by the formation of the immensely small consistently spread out precipitates of solute rich second phase within the matrix phase. The treatment comprises solutionising (550°C) supported by controlled aging (100 and 180°C) below the solvus temperature of the given alloy. Aging expedites the diffusion of solute atoms to form secondary particles (intermetallics) from the room temperature super saturated solid solution. This process is supported by deformation known as rolling as post activity, develops strain hardening in matrix and reinforcement. The present work shows the distinction in the aging phenomenon on alloy and alloy matrix composites (reinforced with 3 and 6 wt% of eutectoid steel powder, 10-30 micron size) upon undergoing cold rolling prior to aging i.e., after solution treatment. The variation in the hardness distribution with aging kinetics for both aging temperatures with and without cold deformation (10 and 20%) in between the consecutive stages like, solution treatment and aging were investigated and peak hardness values were noted in each aging temperatures and results were analysed. In every hardness test 10 trials were performed and the average of 6 consistent readings are taken as the outcome. 20 to 40% improvement in peak hardness is observed with intentional deformation over without deformation. The composite may be used for light duty cold working dies where bulk hardness and frictional characteristics are very important.

In Situ EBSD Observation of Pearlite-Austenite Reverse Transformation in Eutectoid Steel

The reverse transformation of austenite from pearlite was observed in-situ by using a sophisticated EBSD system. Quantitative information on the nucleation sites and orientation selection of the austenite was obtained. Initially, the nucleation sites were restricted to high-angle grain boundary (HAB) and all the austenite orientations were selected by Kurdjumov-Sachs (K-S) orientation relationship. Latterly, the constraints were relaxed as new nucleation sites were involved. The γ growth was preferentially into the pearlite grains without K-S relation. Nucleation and growth at HAB edge may contribute to γ coarse grains, whereas nucleation at pre-existing γ boundary is important to grain refinement of γ structure.