The Effect of Austenitizing Temperature on Prior Austenite Grain Size in Martensitic Cast Steel

Abstract

The GX12CrMoVNbN9-1 (GP91) cast steel belongs to a new group of high-temperature creep resistant cast steels being introduced to the power industry. The cast steel is characterized by higher mechanical properties in comparison with the low alloy Cr – Mo or Cr – Mo – V cast steels used so far. The mechanical properties of martensitic cast steels depend on the parameters of heat treatment, such as the temperature of austenitizing. The paper is to present the results of research on the influence of austenitizing temperature ranging from 980 to 1100oC and hold time of 12 hours on the growth of austenite grain. The tests were carried out on test samples taken from a test coupon. Description of the influence of austenitizing temperature on the austenite grain size was made using the mean diameter of grain. Performed tests have shown that the distributions of mean diameters are of normal character, on the significance levels α = 0.05 and α = 0.04. For the investigated temperature range, the ν coefficient of non-homogeneity of the mean diameter of prior austenite grain was determined. The achieved results have proved that in the temperature range of 1010 to 1070°C the mean diameters stay within the same grade of grain size and the considerable grain growth is visible at the temperature of 1100°C.