Processability and cracking behaviour of novel high-alloyed tool steels processed by Laser Powder Bed Fusion

Concerning tooling applications, Laser Powder Bed Fusion (LPBF) enables new features such as internal cooling channels that can be implemented in cutting or shaping tools. Thus, higher cutting speeds are feasible thanks to the more efficient cooling that could not be obtained by channels fabricated with conventional methods. However, the alloys exploited for the cutting tools production usually contain high levels of carbon, which makes their LPBF processability challenging due to their high crack-susceptibility. In this work, an approach based on the use of basic physical/empirical indicators has been employed to map the processability of six novel high-alloyed tool steel grades. A large experimental campaign with variable energy densities, single and double passes, as well as different focal points was designed. The results exhibit highly dense but cracked parts. In particular, the LPBF processability deteriorates with increasing carbon content, suggesting that mostly chemistry, rather than process parameters, plays a key role in the determination of the LPBF feasibility. The cooling rate, cooling time between 800 °C and 500 °C, equivalent carbon content, solidification interval, martensite start temperature and volumetric energy density were employed as indicators to provide a rapid classification of processability. The work demonstrates that the combined use of the indicators can better explain the cracking behaviour of carbon-containing tool steels. At a screening level, this approach based on complementar use of physical/empirical tools, may significantly shorten the experimental effort during the design of new compositions, especially when dealing with crack susceptible alloys like carbon-containing tool steels.