Accelerated Carbon Atoms Diffusion in Bearing Steel Using Electropulsing to Reduce Spheroidization Processing Time and Improve Microstructure Uniformity

Abstract

Herein, the thermodynamic and kinetic limitations of carbide dissolution behavior during the traditional heat treatment process are broken through the external field treatment. The difference in electrical conductivity between the matrix and the carbide affects the electric current distribution, which ultimately results in electric field distortion. The numerical calculation results show that under the coupled field of heat and pulsed electric current, the distribution of the current density around the particles is related to the size of the particles. The selective distribution of current caused the energy difference to eventually promote the preferential dissolution of coarse network carbides at grain boundaries. The redistribution of carbon atoms between the grain boundaries and the grain interior provides a good initial structure for the subsequent precipitation process, and finally, uniform precipitation of cementite is achieved in the matrix. Meanwhile, the electromigration of carbon atoms under pulsed electric current increases the diffusion rate of carbon atom and shortens the processing time (traditional heat treatment is about 20 h, and the electropulse‐based method in this study is about 4 h).

An accelerated aging assisted by electric current in a Fe-Mn-Al-C low-density steel

“…According to the theory of electromigration, fast-moving electrons can increase the diffusion rate of atoms when an electric current is applied [41] . The atomic diffusion flux J e caused by the electric current effect can be expressed as [41,42] :…”

Applied electric field to repair metal defects and accelerate dehydrogenation

“…The electromigration effect can efficiently lower the kinetic limit and, as a result, minimize processing time [22][23][24][25]. Hao et al [26] also verified that the electric field can increase the atomic diffusion rate and shorten the processing time. Furthermore, the pulsed electric field may efficiently regulate dislocation movement [27], with the dislocation moving back and forth following the direction of the electric field.…”

Realising carbide ultrafast homogenisation under pulsed electric current

“…Previous research show that the current can promote the precipitate dissolution, such as the Cr-rich carbide in M50 bearing steel, the secondary carbide precipitated during tempering in M2 high-speed steel, the η phase in nickel-based superalloy, and so on [23-25], thus significantly revamping the microstructure and properties in metallic materials [26,27]. Our previous study reported that network carbides in bearing steels can be dissolved under coupled fields (thermal and electric fields) [28]. Meanwhile, the spheroidising annealing process was shortened.…”