The main focus of this experiment was to investigate the characterization of austenite structure prior to the transformation. This investigation is carried out with respect with grain-size distribution. The outcome of this investigation shows that different ratios of picric and hydrochloric acids were required by different alloys and different thermomechanical treatments. This can be controlled by carefully measuring pH- value. Etching techniques and quantitative metallography is used to characterize transformation structure.
The results indicate that steel A, B, and D are of same strength, whereas steel C demonstrates less strength. This different behavior is due to the structural differences. It is also found that the transformed structure consist bainite and ferrite. Where the ferrite content in steel A, B, and D is 40%, the ferrite content in steel c is 50%. The ferrite grains are much coarser which is inherited from the coarser austenite structure.
High impact energy values are found with steel A and B up to -90'C. This is caused by small and homogeneous austenite grains. There are differences in recrystallization behavior which makes is necessary to investigate the precipitation process and its influence on recrystallization.
The examination of steel B exhibit following results: some Al-rich particles found after short holding time. At longer holding V-rich particles are found. In V-Nb-Ti steel the Nb precipitates appear later and in lesser amount compared to Ti-free steel. The different recrystallization of steel D and B indicates strong tendency to recrystallization of V-Nb-Ti steel leading to inhomogeneous austenite grain structure.
All four steel specimens had undergone TM rolling treatment with varying conditions. The mechanical properties are related to the microstructures. The formation of these structures can be explained with the help of precipitation and recrystallization behavior of the austenite. Steel A and B gained best overall properties in term of strength and