Solidification Characteristics and Eutectic Carbonitrides in Super 304H Austenitic Heat‐Resistant Stainless Steel

The effect of the cooling rate of liquid steel on solidification characteristics, microstructure, and microsegregation of alloying elements in Super 304H steel is studied. Both the initial and final solidification temperatures of the steel decrease with increasing the cooling rate, whereas the solidification temperature interval monotonically increases. The nucleation mechanism remains the site saturation nucleation at various cooling rates. The effective activation energies of liquid steel solidification at various cooling rates are negative values, which indicates that liquid steel solidification conforms to the anti‐Arrhenius behavior and is mainly controlled by nucleation of austenite. The functional relationship between the secondary dendrite arm spacing and the cooling rate of liquid steel is expressed as λ 2 = 325.23· v −0.54 . The area fractions and sizes of eutectic Nb(C,N) decrease with the increase in the cooling rate. The critical nucleation radius and critical nucleation energy of eutectic precipitate decrease with increasing the cooling rate, which is conducive to the nucleation of eutectic precipitate. A higher cooling rate cannot markedly alleviate the microsegregation of alloying elements C and N, whereas it significantly alleviates the microsegregation of the alloying element Nb, which is conducive to inhibiting the precipitation of eutectic Nb(C,N).