Analytical investigation of grain size dependence of microhardness in high nickel-containing reheated weld metal

Grain size dependence of microhardness has been addressed in the bainitic reheated weld metals by in situ observation of morphological evolution and characterization of microstructural development. A higher cooling rate promotes the boundary of smaller prior austenite grains to provide more effective sites for primary bainitic ferrite nucleation, yet a lower cooling rate is increasingly beneficial to sympathetic nucleation as well as impingement of secondary bainitic ferrite. The microstructures, obtained by cooling at a higher rate and composed of abundant lath bainite, are closer to the microstructures in the raw weld metal than those cooled at a lower rate, including lath bainite, acicular ferrite and intercritical ferrite. Microhardness is decisive by prior austenite grain size mainly, as well as microstructures. Smaller grains contribute notably to microhardness, and it is worth stressing that the sizes of smaller grains lie on prior austenite grain boundaries rather than the subboundaries generated by intragranular acicular ferrite and intercritical ferrite.

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Opracowanie ze środków MNiSW w ramach umowy 812/P-DUN/2016 na działalność upowszechniającą naukę (zadania 2017)