Characterization of Dislocation Evolution in Cyclically Loaded Austenitic and Ferritic Stainless Steels via XRD Line-profile Analysis

Abstract

Dislocations in austenitic and ferritic stainless steels (SSs) under cyclic loading were quantitatively evaluated via X-ray diffraction line-profile analysis to determine the relationship between the dislocation density and low-cycle fatigue (LCF) life in both SSs. The dislocation density of the austenitic and ferritic SSs varied linearly with respect to the LCF life in a double-logarithmic graph, with different slopes of the line. The dislocation density normalized by the maximum work hardening for both SSs exhibited a log-log linear relationship with the LCF life. The fraction of screw dislocations in the ferritic SS decreased with decreasing LCF life owing to the easy cross-slip of dislocations. Because of the difficulty of the cross-slip of dislocations in the austenitic SS, the fraction of screw dislocations remained almost constant throughout the LCF life. Analysis of the crystallite size and the dislocation arrangement with respect to the dislocation density under tensile and cyclic loading revealed that the dislocation arrangement for cyclic loading was smaller than that for tensile loading. Thus, the dislocation arrangement was related to the cyclic loading. In the plot of the dislocation evolution versus the number of cycles, two stages were observed in the variation of the dislocation characteristics for both SSs. In the first stage, the dislocation density increased, and the crystallite size decreased. The dislocation arrangement parameter of the ferritic and austenitic SS decreased and remained the same, respectively, in the first stage. In the second stage, the dislocation density, dislocation arrangement parameter, and crystallite size remained constant.

Effect of Work‐Hardening Mechanisms in Asymmetrically Cyclic‐Loaded Austenitic Stainless Steels on Low‐Cycle and High‐Cycle Fatigue Behavior

“…The peak profiles were analyzed by convolution multiple whole profile (CMWP) fitting procedure. [25,[35][36][37][38] The peaks for α 0 -martensite phase in type 304SS can be analyzed by CMWP method when there are four peaks, which would be available in high fatigue stress amplitudes. The XRD patterns were fitted by a theoretical profile, which is the convolution of the instrumental profile, the profiles corresponded to the diffraction domain size and strain due to dislocations.…”

Impact of Dislocation Density and Mobility on Yielding Behavior in Quenched Medium-carbon Martensitic Steel Tempered at Low Temperature

“…19,21,22) In addition to well-reported physical quantities, such as dislocation density and crystallite size in the analysis, other indicators of dislocation arrangement and character can be obtained. [23][24][25][26] Thus, in the LPA for as-quenched and tempered middlecarbon steel, we focused on the dislocation density and on the aforementioned parameters that are expected to suggest dislocation structures. The impact of the microstructural features determined by LPA on the yield stress is discussed.…”

Constitutive Model of the Surface Roughening Behavior of Austenitic Stainless Steel

“…Dislocation density, F MPT , and F GMO increase proportionally with the strain level [24][25][26][27][28][29]. For fine grains, the FMPT and dislocation density in a grain become much higher than for coarse grains because the slip band intersection probability becomes much higher in fine grains than in coarse grains [24,27].…”

“…MPT occurs as a result of the slip band intersection. The slip band intersection is the place of the martensitic embryo and then becomes MPT [23][24][25][26][27][28][29][30][31][32][33][34][35].…”

“…The deformation of interior crystal grains from the surface to the second layer could affect the surface unevenness in some kinds of metal [6][7][8][9][10][11][12][13][14][15]. The previous studies concluded that the surface roughening should be expressed as a function of plastic strain as ∆Ra = Ce p , where ∆Ra is the increase in surface roughness, C is a constant, and e p is the plastic strain level [25][26][27][28][29][30][31][32][33][34].…”