Elucidation of void defects by soft reduction in medium carbon steel via EBSD and X-ray computed tomography

Abstract

In this work, void formation in medium carbon ferrite-pearlite steel is investigated with soft reduction (SR) technology as regards its initiation sites and governing factors: prior austenite grain size, grain boundary ferrite (GB-α) precipitation, pearlite block size and sub-grain boundaries misorientation. The small and tightly packed pearlite colonies attached with GB-α and irregular broken cementite lamellae provide an easier path for void initiation at prior austenite grain boundary (PAGB) and pearlite colony boundary respectively. 3-dimensional void morphology and void size including porosities with different SR parameters were characterized via X-ray computed tomography (XCT). The total number of voids, their sizes, and shape complexity are increased by increasing reduction amount, and serious void defects are evident without the implementation of SR technology. The size of shrinkage void increases with increasing reduction amount, which is twice without implementation of SR technology as compared with the high reduction amount of 6 mm. The total number of voids and their sizes was less along with porosities at minimum reduction amounts of 2 mm and 4 mm, which are small enough to compensate the solidification shrinkage voids.

Keywords

• Microstructure
• Void initiation
• Grain size
• Soft reduction
• X-ray computed tomography