Simulation of Dimensional Effects on Strain Inhomogeneity an‎d Mechanical Properties of Thermex-Processed Rebars

4/28/2026 12:00:00 AM

This research investigates the influence of roll an‎d rebar dimensions on strain inhomogeneity, microstructure evolution, an‎d mechanical properties of rebars produced by the Thermex process, utilizing numerical simulation an‎d the analysis of extracted data. The effective strain distribution across the 18 mm rebar section demonstrates that the central regions are subjected to a biaxial compressive mode, while the surface regions undergo biaxial plane strain. During eight rolling passes, the maximum effective strain is observed at the center, an‎d the minimum at the surface. The Strain Inhomogeneity Factor (SIF) is maximized along the Z-direction in odd passes an‎d along the Y-direction in even passes, with the magnitude of strain inhomogeneity increasing in both directions with an increasing number of passes. Specifically, the strain inhomogeneity along the Y-direction increases from 0.355 in the second pass to 0.47 in the eighth pass, an‎d for the Z-direction, it increases from 0.30 in the second stan‎d to 0.45 in the eighth pass. Concurrently, the difference in strain inhomogeneity between the two directions decreases; the absolute percentage difference in strain inhomogeneity in the second pass is 16%, which reduces to an absolute value of 5.29% in the eighth pass. Analysis of the effect of roll diameter reveals that increasing the roll diameter from 337.5 mm to 562.5 mm results in an increase in the central effective strain an‎d a decrease in the surface strain, consequently leading to an increase in strain inhomogeneity. This increase is more significant in the 18 mm rebar compared to other rebar sizes, accompanied by an increase in the SIF from 0.36 to 0.53 along the Z-direction an‎d from 0.37 to 0.57 along the Y-direction. However, with a reduction in cross-sectional area an‎d an increase in the number of passes, the difference between strain inhomogeneity in the two directions diminishes. For the 32 mm rebar, with the least reduction in cross-sectional area, the difference in strain inhomogeneity between the two directions at a constant roll diameter of 562.5 mm is 9.93%, whereas for the 18 mm rebar, with the greatest reduction, it is 6.21%. Microstructural investigation indicates that increasing the rebar diameter leads to an increase in the thickness an‎d area fraction of the martensitic layer an‎d a decrease in the thickness of the transition layer. Furthermore, increasing the rebar diameter promotes the growth of pearlitic phase grains from 28.8 μm in the 18 mm rebar to 43.95 μm in the 32 mm rebar, an‎d the ferritic grain size increases from 8.45 μm in the 18 mm rebar to 11.75 μm in the 32 mm rebar due to a reduced cooling rate. The results of tensile an‎d hardness testing demonstrate that as the rebar diameter increases from 18 mm to 32 mm, the ultimate tensile strength decreases from 741 MPa to 702 MPa, the yield strength decreases from 645 MPa to 520 MPa, an‎d the elongation increases from 14.25% to 15.9%, while the core hardness remains approximately constant, but the surface hardness decreases, mirroring the trend in strength. Additionally, the hardness inhomogeneity decreases, indicating a more uniform hardness distribution in thicker rebars. The findings of this research underscore the importance of geometric parameters in the precise control of the thermal, structural, an‎d mechanical behavior of Thermex-processed rebars during the hot rolling process.

نورد داغ ميلگرد، نورد كاليبر، كرنش موثر، ناهمگني كرنش، سيستم ترمكس

Hot bar rolling , Caliber rolling , Effective Strain, Strain Inhomogeneity, Thermex process

Nima Moradi

Alireza Eivani & Hamidreza Jafarian