A study of microstructure and cracking behavior of H13 tool steel produced by laser powder bed fusion using single-tracks, multi-track pads, and 3D cubes

Abstract

This study investigated laser powder bed fusion (LPBF) additive manufacturing of H13 tool steel to identify how laser power (P) and scan speed (V) influenced melt pool geometry, microstructure, and susceptibility to cracking. Sequential studies from tracks, pads to 3D cubes were performed. Tracks and pads were made by laser scan on H13 build plates with and without powder addition. P-V windows were identified where keyholing, balling and under-melt occurred. The only change in melt pool geometry between the powder and no-power experiments was a slight shift of P-V window for the onset of balling. An inhomogeneous microstructure was observed for some tracks and pads, with a cellular-network microstructure and isolated-whisker microstructure at different regions in the same melt pool. Cracks were found in the regions with the isolated-whisker microstructure. Based on these observations, P-V windows of higher and lower cracking tendency were predicted. 3D-cubes built by P-V sets in different windows showed crack densities in line with the predictions. The results of this study provide guidance for LPBF process control to obtain uniform microstructure and minimize cracking of H13 steel parts.