Effect of Cooling Rate on the As-Cast Microstructure of a High Strength Steel Produced in a Large Size Ingot

This paper presents an experimental study on the influence of solidification cooling rate on the evolutions of microstructural morphologies of a high strength low alloy steel. To this end, solidification samples (cylindrical form with 10 mm diameter and 120 mm length) were prepared from 30 cm below the ingot/hot-top interface, at the center, of a 40 MT (Metric Ton) ingot. Solidification experiments were carried out by using Gleeble ® 3800 thermo-mechanical simulator. Two solidification cooling rates of 1 and 50°C/s were chosen. For microstructural characterization, samples were prepared by mounting, polishing and etching with 3% Nital solution. Also, an optical microscope was employed for microstructural observations. The obtained results showed that for 1°C/s, the microstructure is composed with dendrites and grains. Here, the grain morphology is the dominant one. In the case of 50°C/s, the dendrites were localized at the sample surface and the grains were present more into the depth of the sample. Moreover, the increase of solidification cooling rate results in finer dendrites. The results are discussed in the framework of solidification mechanisms.