In Situ Observations of the Formation of Fine‐Grained Mixed Microstructures of Acicular Ferrite and Bainite in the Simulated Coarse‐Grained Heated‐Affected Zone

Abstract

The formation of fine‐grained mixed microstructure of acicular ferrite and bainite in the simulated coarse‐grained heated‐affected zone was investigated by means of in situ observation and EBSD analysis. Single, multiple, and sympathetic nucleation of acicular ferrite were observed. Acicular ferrite laths or plates were formed prior to bainite and effectively partitioned austenite grains into many smaller and separated regions. The later formed bainite at lower temperature was confined in those smaller regions, thus resulting in the fine‐grained mixed microstructures of acicular ferrite and fine bainite plate.

In situ observation of acicular ferrite formation and grain refinement in simulated heat affected zone of high strength low alloy steel

“…In addition, the broad faces of acicular ferrite laths or plates were also observed to provide nucleation sites for acicular ferrite and bainite microstructures. 5 The acicular ferrite and bainite plates formed at lower temperature were confined in those small regions. Therefore, the later formed microstructure can only achieve a limited size.…”

“…Therefore, the later formed microstructure can only achieve a limited size. 3,5,26 The final crystallographic grain size was in the same range for both the specimens austenitised at 1300uC (smaller prior austenite grain size) and 1350uC (larger prior austenite grain size).…”

In-situ Observations of Acicular Ferrite Growth Behavior in the Simulated Coarse-grained Heat-affected Zone of High-strength Low-alloy Steels

“…9,10) Extensive work has been carried out on the nucleation of acicular ferrite. [11][12][13][14][15][16][17][18][19][20][21][22][23] Therefore, the present work focused on the growth behavior of acicular ferrite using in-situ observation in conjunction with thermodynamic calculations.…”

In Situ Observation of Grain Refinement in the Simulated Heat‐Affected Zone of Al–Ti‐0.05% Ce‐Deoxidized Steel

“…The specimens were heated at a rate of 5 °C s −1 , then isothermally held at 1350 °C for 150 s, and immediately cooled at a rate of 5 °C s −1 . It should be noted that the heating and cooling rates (±5 °C s −1 ) are designed to be slower than that of actual thermal cycle with a high heat input for the observation of the grain boundary migration and acicular ferrite transformation at high/intermediate temperature during the simulated welding process . In addition, the difference in temperature between the top surface of specimen and the bottom of crucible is about 10–15 °C during the heat treatment .…”