Fracture Micro Mechanism of Cryogenically Treated Ledeburitic Tool Steel

0560104 - ÚFM 2023 RIV SG eng C - Conference Paper (international conference)
Jurči, P. - Ptačinová, J. - Dlouhý, Ivo
Fracture Micro Mechanism of Cryogenically Treated Ledeburitic Tool Steel.
Lecture Notes in Mechanical Engineering. In: PROCEEDINGS OF THE 9TH INTERNATIONAL CONFERENCE ON FRACTURE, FATIGUE AND WEAR, FFW 2021. Singapore: Springer, 2022 - (Wahab, M.), s. 67-84. Lecture Notes in Mechanical Engineering. ISBN 978-981-16-8809-6. ISSN 2195-4356. E-ISSN 2195-4364.
[FFW 2021 - IN9th International Conference on Fracture, Fatigue and Wear /9./. Ghent (BE), 02.08.2021-03.08.2021]
Institutional support: RVO:68081723
Keywords : Cryogenic treatment * Ledeburitic steel * Microstructure * Fracture toughness * Fracture micro mechanism
OECD category: Materials engineering

Fracture micro mechanism of cryogenically treated Cr-V ledeburitic tool steel was studied on fracture toughness testing specimens, by using the scanning electron microscopy and microanalysis. Experimental steel has been processed at different combinations of cryogenic temperatures (from the range75 to269 degrees C) and tempering regimes, producing different microstructures (martensite, retained austenite, carbides), hardness- and fracture toughness values (from the ranges 700-1000 HV and 13-20 MPa x m(1/2), respectively). Conventionally quenched the same steel was considered as a reference. Generally, the obtained fracture surfaces manifest combined low-energetic ductile/cleavage crack propagation mode. The low-energetic ductile mode is associated with the presence of small globular carbides (size < 0.3 mu m) that are produced by cryogenic treatments. On the other hand, cleavage mode is more pronounced with increased matrix stiffness, which is caused by the precipitation of nano-scaled transient carbides within the martensite. Also, differences in role of crack propagation between various carbides were determined. These differences are caused by crystallography of these phases as well as by their size. While small globular carbides (cementite) and dominant amount of the eutectic carbides (cubic MC-phase) assist more probably (by 50-60%) in ductile micro mechanism the coarser secondary particles (hexagonal M7C3-phase) are much more prone to cleavage cracking. This tendency increases with decreasing steel hardness since the matrix becomes more plastic, and the carbides cannot deform together with the matrix as they are much more brittle.
Permanent Link: https://hdl.handle.net/11104/0333303