Influence of Strain Path Changes on Microstructure Inhomogeneity and Mechanical Behavior of Wire Drawing Products

Abstract

Cold drawn low carbon steel wires are widely used in several engineering applications where a proper combination of strength and ductility is of the paramount importance. In the present paper, the multi-pass angular accumulative drawing (AAD) is proposed as a new forming process where the high strain accumulation is used as a way to achieve much higher microstructure refinement level compared to the conventional wire drawing process. This process is characterized by a complex strain path history, being an effect of wire diameter reduction, bending, tension and torsion, what directly affects the microstructure changes in the final product. This process also evolves high inhomogeneity of microstructure, that if properly controlled, can lead to further properties improvement - what can be especially beneficial for alloys that are not characterized by complex compositions. In the present paper, special emphasis is given on the inhomogeneity of both deformation and microstructure and resulted mechanical properties. After drawing and annealing (at 500oC) mechanical properties measurements and microstructure analysis on the longitudinal sections of the wires were performed to assess the differences existing with respect to the conventional wire drawing process.

Modelling of deformation inhomogeneity in the angular accumulative drawing process—multiscale approach

“…The present and previous results, for low carbon steel [4], confirmed that the strain path applied in the AAD process affects directly the microstructure and texture changes in the final product. The reason is that the strain accumulation in the drawn wires are direct results of combined effect of: reduction of the area, strain accumulation in the outer part of the wire due to bending/unbending process, and desired shear deformation.…”

“…Although, the AAD design allows for various combinations of die positioning to be used [4], the present study was concentrated on the stepped die positioning (Fig. 1c), in which the offset from the drawing line between successive dies was equal to 101.…”

“…Angular Accumulative Drawing (AAD) process has been developed and proposed as a new wire drawing method that introduces controlled microstructure inhomogeneity [3,4]. In this process, complex strain path is applied and large strain accumulation is introduced to refine the microstructure of a drawn wire.…”

Multiscale Analysis of Processing‐Microstructure‐Mechanical Behavior Interrelationships of UFG Microalloyed Steels

“…In order to study the effect of more complex deformation route on microstructure refinement and inhomogeneity, room temperature wire drawing tests were performed using the Accumulative Angular Drawing process presented in Figure . The study was performed on microalloyed (Y) steel supplied as a wire rod, with recrystallized polygonal ferrite microstructure and the mean grain size of 15–20 µm.…”

“…Total strains of 0.45 and 0.38 were applied in first and second pass, respectively, followed by the calibration pass with the strain of 0.14. Although, the AAD design allows for various combinations of die positioning to be used, the present study was concentrated on the stepped die positioning (Figure c), in which the offset from the drawing line between successive dies was equal to 10°. Additionally, after first pass, the wire was rotated by 180° to obtain axi‐symmetrical distribution of strain accumulation at the cross‐section of a final product.…”