I have two 4140 bolts with the same size but different microstructures. One is pearlitic and one is martensitic. The bolts are under high stress cyclic loading conditions. Which one is expected to perform better?
Dear Dr. Mehdi Taherishargh,
generally, in precipitation-hardened alloys, thermo-mechanical processing which gives jagged grain bound-aries improves the fatigue resistance. Cast steels with a martensitic structure generally exhibit a better fatigue strength at long lives than obtained from a pearlitic structure, although this may be reversed at short lives (< 103 cycles) where life is growth dominated. This is again related to the higher strength of the martensite. Considering cast irons, fatigue resistance appears to be more affected by the size of graphite flakes than the hardness of the matrix, although the best performance derives from fine graphite and pearlitic matrices. Where the graphite is in spheroidal form an even better fatigue resistance can be obtained.
Source:
Optimising the fatigue resistance of materials
M. N. James
N&O JOERNAAL SEPTEMBER 1992, p. 34
Available at: https://cdn.ymaws.com/www.saimeche.org.za/resource/collection/A7C87EB6-455C-4212-AAAB-0BAD8C523267/James-1992_05__600_dpi_-_1992__8_3___34-42.pdf
Best regards, Pierluigi Traverso.
Hi. Usually fatigue crack growth rate decreased with an increase in martensite content. But it has optimum value.This paper would be helpful.
you should read following article
https://www.jim.or.jp/journal/e/pdf3/54/09/1570.pdf
best regards
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