The Formation of Acicular Ferrite and Mechanical Properties Behaviors in a Low Welding Crack Susceptibility Steel
The nucleation and crystallographic characteristics of acicular ferrite in the as-rolled and tempered steel were investigated by using an optical microscopy (OM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with electron backscatter diffraction (EBSD). The results showed that acicular ferrite forms at nucleation sites such as dislocations within austenite grains under the heavy reduction in the austensite non-recrystallization region and accelerated cooling conditions, and the inclusions such as Al2O3•MnS may have promotion effect for the formation of acicular ferrite. Acicular ferrite has high misorientation angle boundaries and a number of sub-boundaries or high density of dislocations inside, which contributes to an excellent combination of high strength and toughness. And the morphology of acicular ferrite does not show obvious change in tempering microstructure due to high temperature thermal stability, which plays an important part in keeping good mechanical properties for tempered specimens.
L. Y. Lan et al., "The Formation of Acicular Ferrite and Mechanical Properties Behaviors in a Low Welding Crack Susceptibility Steel", Advanced Materials Research, Vols. 163-167, pp. 337-341, 2011