Cracking mechanism in a laser powder bed fused cold-work tool steel: The role of residual stresses, microstructure and local elemental concentrations
Research output: Contribution to journal › Article › Research › peer-review
Standard
In: Acta materialia, Vol. 225.2022, No. 15 February, 117570, 15.02.2022.
Research output: Contribution to journal › Article › Research › peer-review
Harvard
APA
Vancouver
Author
Bibtex - Download
}
RIS (suitable for import to EndNote) - Download
TY - JOUR
T1 - Cracking mechanism in a laser powder bed fused cold-work tool steel
T2 - The role of residual stresses, microstructure and local elemental concentrations
AU - Platl, Jan
AU - Bodner, Sabine C.
AU - Hofer, Christina
AU - Landefeld, Andreas
AU - Leitner, Harald
AU - Turk, Christoph
AU - Nielsen, Marc-André
AU - Demir, Ali Gökhan
AU - Previtali, Barbara
AU - Keckes, Jozef
AU - Schnitzer, Ronald
N1 - Publisher Copyright: © 2021 The Author(s)
PY - 2022/2/15
Y1 - 2022/2/15
N2 - Laser powder bed fusion (LPBF) facilitates economic advantages by enhancing cutting speeds of tools through the implementation of complex internal cooling channels that could not be fabricated otherwise. However, tool steels are prone to cracking during the cyclic remelting process with extremely fast cooling rates due to their high carbon and alloying element contents and related stresses. In this work, a correlation between microscopic crack patterns in a tool steel processed via LPBF, residual stress gradients, local microstructure and near-crack elemental concentrations is studied using longitudinal/transverse sectional synchrotron X-ray micro-diffraction, electron microscopy techniques and atom probe tomography. A formation of horizontal micro-cracks correlates with longitudinal/transverse sectional residual stress drops, especially at geometrically notched positions and sample edges. Remarkably, the cracks propagate predominantly along the network of eutectic intergranular carbides of type M 2C deposited at the grain boundaries of carbon martensite and retained austenite matrix. A comparison of representative carbide sizes at the crack surfaces and within the crack-free regions indicates that cracks propagate preferably through the carbides in a transcrystalline manner, whereas no correlation between the cracking and the martensite formation is observed. The observations link the crack propagation to the solidification microstructure and the prevailing eutectic network. Therefore, the stress-induced cracking of eutectic carbides, which formed during the solidification and fracture in the solid state due to tensile stress accumulations, was found as the predominant cracking mechanism of the tool steel during the LPBF process.
AB - Laser powder bed fusion (LPBF) facilitates economic advantages by enhancing cutting speeds of tools through the implementation of complex internal cooling channels that could not be fabricated otherwise. However, tool steels are prone to cracking during the cyclic remelting process with extremely fast cooling rates due to their high carbon and alloying element contents and related stresses. In this work, a correlation between microscopic crack patterns in a tool steel processed via LPBF, residual stress gradients, local microstructure and near-crack elemental concentrations is studied using longitudinal/transverse sectional synchrotron X-ray micro-diffraction, electron microscopy techniques and atom probe tomography. A formation of horizontal micro-cracks correlates with longitudinal/transverse sectional residual stress drops, especially at geometrically notched positions and sample edges. Remarkably, the cracks propagate predominantly along the network of eutectic intergranular carbides of type M 2C deposited at the grain boundaries of carbon martensite and retained austenite matrix. A comparison of representative carbide sizes at the crack surfaces and within the crack-free regions indicates that cracks propagate preferably through the carbides in a transcrystalline manner, whereas no correlation between the cracking and the martensite formation is observed. The observations link the crack propagation to the solidification microstructure and the prevailing eutectic network. Therefore, the stress-induced cracking of eutectic carbides, which formed during the solidification and fracture in the solid state due to tensile stress accumulations, was found as the predominant cracking mechanism of the tool steel during the LPBF process.
UR - http://www.scopus.com/inward/record.url?scp=85122163436&partnerID=8YFLogxK
U2 - 10.1016/j.actamat.2021.117570
DO - 10.1016/j.actamat.2021.117570
M3 - Article
VL - 225.2022
JO - Acta materialia
JF - Acta materialia
SN - 1359-6454
IS - 15 February
M1 - 117570
ER -