The Effect of Rapid Heating and Fast Cooling on the Transformation Behavior and Mechanical Properties of an Advanced High Strength Steel (AHSS)

Abstract

The major goal of this work was to study the effect of rapid heating and fast cooling on the transformation behavior of 22MnB5 steel. The effect of the initial microstructure (ferrite + pearlite or fully spheroidized) on the transformation behavior of austenite (during intercritical and supercritical annealing) in terms of heating rates (2.5, 30 & 200 °C/s) and fast cooling, i.e., 300 °C/s rate, were studied. As expected, the kinetics of austenite nucleation and growth were strongly related to the heating rates. Similarly, the carbon content of the austenite was higher at lower intercritical annealing temperatures, particularly when slower heating rates were used. The supercritical temperatures used in this study were similar to those used during commercial hot stamping operations, i.e., 845 and 895 °C, respectively, followed by a fast cooling rate. The prior austenite grain size (PAGS) was not strongly influenced by the nature of the initial microstructure, heating rate, reheating temperatures (845 or 895 °C), at 30 s holding time. The decomposition of austenite using fast cooling rates was examined. The results showed that 100% martensite was not obtained. The observed low temperature transformation products consisted of mixtures of martensite-bainite plus undissolved Fe3C carbides and small amounts of martensite-austenite (M-A). At higher supercritical temperatures, i.e., 1000 °C and 1050 °C, the final microstructure showed an increase in the volume fraction of martensite and a decrease in the volume fraction of bainite. The Fe3C and the M-A microconstituent were not observed. The best combination of tensile properties was obtained on samples reheated in the lower temperature range (845 to 895 °C). Interestingly, when the samples where reheated at the higher temperature range (1000 to 1050 °C) and fast cooled, the results of the mechanical properties did not exhibit significantly higher strength levels independent of heating rate or initial microstructural condition. This can be attributed to the change in the microstructural balance %martensite+%bainite as the reheating temperature increases. The results of this study are presented and discussed.

The Effect of Different Annealing Strategies on the Microstructure Development and Mechanical Response of Austempered Steels

“…The results suggest that LA regions decompose to a mixture of ferrite and possible bainite, while prior HA regions are transformed mainly to martensite due to the inhomogeneous distribution of alloying elements in austenite. These results concur with those reported for lean alloy steels subjected to ultrafast heating and fast cooling [15,49,[53][54][55].…”

Prediction of Thermal Damage upon Ultrafast Laser Ablation of Metals

“…The surface of the workpiece may reach elevated temperatures, but if the heating and cooling down cycle is rapid enough, the induced thermal stress may be temporary and return to zero once the temperature again becomes homogeneous. On the other hand, heat-induced phase transformations take place only if the time spent at high temperatures is long enough, as they often depend on the heating and cooling rates [36,37]. Therefore, knowing the maximum temperature reached may not be enough to explain or predict the thermal damage.…”

Minimisation of Heating Time for Full Hardening in Hot Stamping Using Direct Resistance Heating

“…They showed that the final martensite volume fraction changed with an increase of the holding time in the austenite temperature range of 800-900 • C. Zhang et al [12] studied the phase transformation in the hot stamping process of USIBOR 1500 high-strength steel based on the Kirkaldy-Venugopalan model during the pressure holding quenching process. Pedraza et al [13] studied the effect of rapid heating and fast cooling on the transformation behaviour and mechanical properties of 22MnB5 steel. Mori et al [14] developed smart hot stamping of ultra-high strength steel products using rapid resistance heating and mechanical servo press.…”