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Vol.37, No.5, 539 ~ 543, 1999

Title

Research Paper / Mechanical Behavior : Nueleation of Low Cycle Fatigue Crack at High Temperature in Nitrogen Alloyed Type 316L Stainless Steel

김대환Dae Whan Kim, 류우석Woo Seog Ryu, 김우곤Woo Gon Kim, 국익현Il Hiun Kuk

Abstract

The effect of nitrogen on the nucleation of a low cycle fatigue (LCF) crack was studied at high temperature using type 316L stainless steel with different nitrogen contents (0.04-0.15%). Strain-controlled LCF tests were conducted in the temperature range of R.T. ∼600℃ and in air. The waveform of LCF was a symmetrical triangular with a total strain amplitude of 1.0% and in a constant strain rate of 2×10^(-3)/s for all tests. The sites for crack nucleation, crack population, and crack depth from the surface of the specimens were measured after LCF testing up to 40% of fatigue life. The preferred sites for crack nucleation were grain boundaries, but some of cracks also nucleated at twin boundaries and slip bands. Crack population on the surface of the specimen decreased but the maximum depth of the crack from the surface of the specimen did not change with the addition of nitrogen at high temperatures. The cycles for the nucleation (100㎛) of LCF crack increased with the addition of nitrogen. So, the increase of LCF life with the addition of nitrogen at high temperatures may be explained by the fact that nitrogen increases the resistance of crack nucleation.

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