In situ tempering of martensite during laser powder bed fusion of Fe-0.45C steel
Artikel i vetenskaplig tidskrift, 2022

During laser powder bed fusion (L-PBF), materials experience cyclic re-heating as new layers are deposited, inducing an in situ tempering effect. In this study, the effect of this phenomenon on the tempering of martensite during L-PBF was examined for Fe-0.45C steel. Detailed scanning electron microscopy, transmission electron microscopy, atom probe tomography, and hardness measurements indicated that martensite was initially in a quenched-like state after layer solidification, with carbon atoms segregating to dislocations and to martensite lath boundaries. Subsequent tempering of this quenched-like martensite was the result of two in situ phenomena: (i) micro-tempering within the heat affected zone and (ii) macro-tempering due to heat conduction and subsequent heat accumulation. Hardness measurements showed that although both influenced martensite tempering, micro-tempering had the most significant effect, as it reduced martensite hardness by up to ∼380 HV. This reduction was due to the precipitation of nano-sized Fe3C carbides at the previously carbon-enriched boundaries. Lastly, the magnitude of in situ tempering was found to be related to the energy input, where increasing the volumetric energy density from 60 to 190 J/mm3 reduced martensite hardness by ∼100 HV. These findings outline the stages of martensite tempering during L-PBF and indicate that the level of tempering can be adjusted by tailoring the processing parameters.

In situ tempering

Additive Manufacturing

Carbon steel

Laser powder bed fusion

Intrinsic heat treatment

Martensite

Författare

William Hearn

Chalmers, Industri- och materialvetenskap, Material och tillverkning

Kristina Lindgren

Chalmers, Fysik, Mikrostrukturfysik

Johan Persson

Lunds universitet

Eduard Hryha

Chalmers, Industri- och materialvetenskap, Material och tillverkning

Materialia

25891529 (eISSN)

Vol. 23 101459

Ämneskategorier

Bearbetnings-, yt- och fogningsteknik

Metallurgi och metalliska material

Styrkeområden

Materialvetenskap

DOI

10.1016/j.mtla.2022.101459

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Senast uppdaterat

2024-01-03