{'fraction_non_alphanumeric': 0.01710914454277286, 'fraction_numerical': 0.0, 'mean_word_length': 5.523076923076923, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Microstructural Change during the Hot Working of As-Cast Austenite

The direct hot rolling of the as-cast austenite of thin slab castings requires the microstructural changes within the austenite phase field that are necessary for a satisfactory product to be accommodated within a smaller degree of total reduction, within a smaller number of passes, and within a shorter time scale. Particularly in the case of microalloyed steel, the constitution of the as-cast austenite prior to rolling differs from that of austenite of thick slabs reheated for conventional hot rolling. Consequently, the models developed for conventional rolling employing reheated austenite cannot be relied upon for predicting microstructural change during the rolling of as-cast austenite. The as-cast austenite of microalloyed steels has larger grains, is segregated, and carbonitride precipitates may be present that are not in equilibrium with their solid solution. These factors are discussed in the light of recent research. It is suggested that recrystallisation kinetics should be linearly, rather than quadratically, related to austenite grain size, and that above a limiting carbon content the addition of Nb and Ti results in excess, eutectically precipitated, Nb-rich carbonitride due to segregation during freezing. The former leads to more rapid recrystallisation than would be predicted by the conventional models, and helps to ensure that plain C-Mn steels can be satisfactorily processed. The presence of eutectic carbonitrides means that the supersaturation of the austenite with respect to microalloy constituents is unknown, and recrystallisation-stop temperatures cannot be modelled satisfactorily.