Electropulse-induced microstructural evolution in a ferritic–pearlitic 0.14% C steel

Abstract

of pearlite are extensively used in various engineering and commercial applications since they possesses a good combination of strength and ductility as well as other useful material properties such as corrosion resistance, wear resistance, weldability and machinability. The stress-strain behaviours of ferritic-pearlitic steels strongly depend on its constituent phases: ferrite governs the ductility whereas pearlite phase controls the strength [1]. The relationship between microstructure and mechanical properties of these steels have been investigated by many researchers [1,2,3]. Various colonies of pearlite have different lamellae orientations. These cementite lamellae are frequently paralleled and curved and the interlamellar spacing varies in size from colony to colony [2]. Hence, pearlite microstructure can be tailored by variation of the interlamellar spacing which directly affects the strength [3].It is known that the application of electric current pulses to metallic materials affects materials plasticity [4], recrystallization [5], structure relaxation [6], casting microstructure [7,8] and fatigue life [9]. For Fe-3wt% Si alloys, electropulse has been found to promote the Goss-texture development during recrystallization [11,23]. Theoretically, electropulse is found affecting the kinetic barrier and free energy sequence of phases. The former includes the phase transformation at a lower than ordinary temperature [12] and the enhanced diffusivity [17]. The latter includes the electropulseinduced new phase [14] and new microstructure formations [15]. In the present work, electropulse-induced cementite plates rotation in ferritic-pearlitic steel was observed. This reveals a new mechanism that has not been covered in literature. Application of Electropulsing in the process of ferritic-pearlitic steel may provide a new way to enhance mechanical properties by altering the pearlite transformation and microstructure.The steel was prepared via the conventional ingot metallurgical routine and the chemical composition in weight percentage of the alloy was found to be 0.14 C-1.0 Si-2.1 Mn-0.03 Al-0.025 Nb and balance iron. The ingot was rolled at 800• C to Preprint submitted to Elsevier April 27, 2015 a sheet with 2.64 mm thickness and then chilled slowly in furnace. Its microstructure at ambient temperature consists of mainly the polycrystalline ferrite grains and a small amount of cementite scattered among the ferrite. The sheet was cut into many 30 mm(longitudinal length) × 3.42 mm (width) × 2.64 mm (thickness) samples and grouped randomly for subsequent electropulsing treatment. The electropulse was generated by an Avtech AV-108F-B-P Current Pulser which converted the direct current into pulsed current. The direct current power source has standard output power of 80 watts and standard output electric potential of 20 volts. The pulse width, peak current intensity, pulse frequency and pulse trigger mode are programmable. The testing steel sample was connected with two copper electrodes from both ends to form a curr...

Effect of electric current pulses on the microstructure and niobium carbide precipitates in a ferritic-pearlitic steel at an elevated temperature

“…As it is clear from this image, electropulsing has caused a remarkable change in the microstructure that produces ferrite matrix with smaller grain size and semi-transformed pearlite aligned with the current direction. This is in line with the observation identified in room temperature application of the electropulsing [11]. The average grain size of ferrite has reduced to 13 μm after electropulsing.…”

“…Experimental observation in this study has shown that the lamellar structure forms in a direction parallel to that of the electric current flow [11]. In a separated study, the authors have reported that electropulsing treatment affects the distribution of niobium carbide and hence the formation of precipitation free zones (PFZs) [12].…”

“…The total bulk free energy of the steel includes two terms which are the chemical free energy of the bulk phases ( ), and the free energy associated with the passing electric current pulses ( ). The free energy change due to electric current pulse can be determined by [11,13,14]: are the current densities at position r and , respectively. μ is the magnetic permeability.…”

Influence of κ-carbide interface structure on the formability of lightweight steels

“…4(a) is close to value of that for -carbide, but that in Fig. 4(b) is close to that of  phase [30,33]. The experimental measured values are consented to the theoretical analysis.…”

“…Schematic diagrams illustrate that the electrical resistivity of a material with microstructure (a) is larger than that of (b) when the grey phase has larger conductivity than that of the matrix. The figure was drawn following the similar concept in literature [30,33]. Matthiessen's theory, the electrical resistivity of -carbide is higher than that of  phase due to higher C, Al and Mn compositions in  than in .…”