*4.2. Coarsening of Prior Austenite Grain Size*

Average austenite grain sizes as a function of reheating temperature for all six alloys are shown in Figure 11. Error bars represent 95% confidence intervals about the mean grain size. In general, austenite grain sizes increase with increasing the reheating temperatures. The Nb-bearing steels show a higher tendency for abnormal grain growth, a characteristic of microalloyed steels [25–27]. As an

example, a series of microstructures of L8 is depicted in Figure 12, and it can be seen that abnormal grain growth occurs at/or close to 1100 ◦C.

**Figure 11.** Mean austenite grain size as a function of reheating temperature.

**Figure 12.** Light optical micrographs of prior austenite grains for steel L8 after soaking to the temperatures indicated.
