A New Method to Study the Effect of Cooling Rate on the Decomposition of Austenite in Advanced High Strength Sheet Steels

摘要

A new modified Jominy holder and specimen were developed to study the effect of chemical composition, intercritical annealing temperature and cooling rates on the transformation behavior of a series of Dual-Phase sheet steels. Correlations between temperature, time and the distance from the water quenched end were developed using a Lab View data acquisition program. In addition, the hardness and microstructure along the length of the sheet steel sample were determined as a function of cooling rate from the intercritical annealing temperature. Special chemical regents were used to reveal new ferrite, bainite and other microstructural components which were also evaluated by optical, scanning and transmission electron microscopy. Critical cooling rate equations, based on steel composition, volume fraction of austenite and intercritical annealing temperatures, were developed to avoid or minimize the formation of new ferrite and bainite. The results of this work show that the modified Jominy test is an effective and efficient way to evaluate the hardenability of sheet steels.