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Influence of laser polishing on surface roughness and microstructural properties of the remelted surface boundary layer of tool steel H11

 
: Temmler, A.; Liu, D.; Preußner, J.; Oeser, S.; Luo, J.; Poprawe, R.; Schleifenbaum, J.H.

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Volltext ()

Materials and design 192 (2020), Art. 108689, 25 S.
ISSN: 0264-1275
ISSN: 0261-3069
National Natural Science Foundation of China NSFC
51527901
National Natural Science Foundation of China NSFC
51575298
National Natural Science Foundation of China NSFC
51705284
National Natural Science Foundation of China NSFC
51705285
National Natural Science Foundation of China NSFC
11890672
Englisch
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer IWM ()
Fraunhofer ILT ()
laser polishing; AISI H11; surface roughness; decarburization; micro hardness; martensite formation

Abstract
This work investigates the influence of multi-step laser polishing on microstructural properties of the remelted surface layer of tool steel H11. Four different laser polishing process parameter sets were selected that lead to a significant reduction in roughness. In a sequential process using continuous and pulsed laser radiation (Nd:YAG) a significant reduction of surface roughness was achieved on an initially annealed H11 sample. The remelted layers were analyzed using roughness measurements, white light interferometry, X-ray diffractometry, electron backscatter diffraction, glow discharge emission spectroscopy, and nanoindentation hardness measurements. Laser polishing leads to a grain refinement and a significant increase in hardness. A surface roughness of Ra 50 nm was achieved in an Argon process atmosphere with an additional 6 vol% CO2. In particular the carbon concentration was more than halved within the remelted layer. The lower carbon concentration is correlated with a decreased maximal surface hardness down to 366 HV. High residual tensile stresses of up to 926 MPa can be introduced by laser polishing. Overall, high temperature gradients and, in particular, decarburization due to carbon diffusion processes were identified to be the major driving force for significant changes in surface micro-roughness and microstructural properties.

: http://publica.fraunhofer.de/dokumente/N-593198.html