Magnetic induced re-dissolution and microstructure modifications on mechanical properties of Cr4Mo4V steel subjected to pulsed magnetic treatment

Abstract

Cr4Mo4V steel (similar to M50 steel) is widely used for the manufacture of shaft bearing in aerospace fields, and its rolling contact fatigue life is of great importance to service reliability. Both high fracture toughness and fatigue fracture resistance are required to improve its fatigue life, and enhancement of these mechanical properties of Cr4Mo4V steel subjected to pulsed magnetic treatment (PMT) at 0.8 T was achieved. Kernel Averaged Misorientation (KAM) maps and Image Quality (IQ) maps were constructed by Electron Backscatter Diffraction (EBSD) data along with X-ray diffraction (XRD) in this research to display the changes in microstructure induced by magnetic field. A slight decrease in the IQ and the shift of the diffraction peak were observed. The dissolution of some carbon clusters in Cottrell atmosphere resulting in a higher lattice distortion rate was proposed as a possible reason, and the mechanism from intersystem crossing was discussed. Decreases and increases of local KAM indicating dislocation motion were also observed, and the mechanism was deemed to be closely related to the carbon re-dissolution. The homogenization of microstructure resulted from these changes is in favor of the mechanical properties. In addition, frequencies of low-angle boundaries with smaller misorientation angle and coincidence site lattices (CSL) boundaries increased after PMT 0.8 T, leading to a stronger barrier and a lower nucleation rate for dislocations during deformation, which is another reason of the enhancement of mechanical properties.