**1. Introduction**

The continuous demand of using AHSS and UHSS steels, particularly Press Hardenable Steels (PHS), during hot stamping operations requires a systematic and fundamental understanding of the physical metallurgy of these steels. According to recent report on the use of AHSS and UHSS in North America, light weight vehicles are predicted to increase from the current 332 pounds per vehicle to 483 pounds by the year 2025 [1]. To achieve the desired performance of AHSS many studies are being conducted by universities and steel companies around the world. For example, Figure 1 shows the different pathways currently being studied to increase the strength and ductility of AHSS [1]. In addition, this figure also presents actual coating data for AHSS GEN 1 and 3 steels. It seems that the major research trends to increase the performance of AHSS strength-ductility are strongly related with the ability to control composition, microstructure and dislocation motion.

**Figure 1.** Different pathways to increase strength-ductility of AHSS [1].

## *Rapid Austenitization*

According to Stahl Zentrum Stahl fur nachhaltige Mobilitat [2] hot stamped parts used in autos represent approximately 30% of all the body components. Mori et.al. [3], suggest that the use of high energy input during the process of hot stamping becomes an interesting proposition due to the effects of rapid heating on; (1) the transformation behavior of austenite; (2) oxidation behavior; (3) limited decarburization; (4) fine and/or coarser austenite grain sizes depending on reheating temperatures, holding times and heating rates; (5) localized non-uniform microstructures with substantial chemical heterogeneity; and (6) good hot workability. In summary, rapid heating and cooling during hot stamping seems to provide both a robust processing scheme and more cost effective approach than traditional reheating methods. Furthermore, the use of high input energy also opens the door to the potential development of new AHSS with higher strength and better total elongation.

Rapid heating technology is not new, the concept was initially developed to increase the mechanical properties of Armor plates for the US Army in 2010 [4]. Later on, the process was patented as a Micro-treatment of Iron-Based Alloy and Microstructure Resulting Therefrom [4]. It seems that by using rapid heating it is feasible to produce significant grain refinement of the decomposition products of austenite. There is substantial evidence that rapid hot forming based on high power and process integrated heating methods is an attractive proposition for the development of high strength steels with good formability [5–9]. Despite these claims, the state-of the-art in the development of AHSS steels using rapid heating seems to lack a better understanding on the effect of the starting microstructural condition and ultra-fast heating techniques. This is important because permits the better understanding of the formation and subsequent transformation behavior of austenite. To explore the effects of low and high input energy, starting microstructural condition, rapid cooling and resulting mechanical properties, the present study was conducted on a conventional 22MnB5 AHSS steel grade.
