In-situ observations of phase transformations during C–Mn–Al steel weld solidification

Abstract

In order to better understand the microstructural evolution in steel welds, in-situ experiments using time-resolved X-ray diffraction (TRXRD) and laser scanning confocal microscopy (LSCM) are performed and the phase transformations that occur during welding of C–Mn–Al steels are directly observed. Ferrite and austenite phases are identified and quantified in the fusion zone (FZ) using the real time TRXRD and LSCM data. The results show non-equilibrium peritectic transition during rapid cooling, in contrast to the equilibrium δ-ferrite solidification that occurs under slow cooling conditions. Austenite nucleates along δ-ferrite grain boundaries during the δ→γ transformation, whereas during the γ→α transformation, the microstructures change from Widmanstatten ferrite (WF) to intragranular bainitic ferrite in the rapidly and slowly cooled welds, respectively. Using these real time observations, important kinetic information about phase transformations during steel weld solidification can be determined.

Keywords:

• In-situ time-resolved X-ray diffraction
• Laser scanning confocal microscopy
• Welding
• Solidification
• Phase transformation

A part of this research was financially supported by Grants-in-Aid for Scientific Research A (No. 2324617). The synchrotron radiation experiments were performed at the BL46XU in Spring 8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI).