The automotive manufacturers currently use advanced high-strength steels (AHSS) to produce lightweight vehicles with increased safety performance. While showing excellent strengthto-weight ratios, AHSS have several limitations due to the high loads required in cold forming and cutting processes, which lead to accelerated wear and premature fracture of tools. Thus, new tool materials with improved mechanical behavior ought to be developed with regard to the tool failure mechanisms. The aim of this work is to shed light on the fracture mechanisms acting in tools (i.e. crack nucleation and propagation) applying the acoustic emission (AE) technique. Bending tests using two different tool steels were monitored in order to establish a relationship between AE signals and fracture events.