scholarly journals Metastability and fatigue behavior of austenitic stainless steels

2018 ◽  
Vol 165 ◽  
pp. 04010 ◽  
Author(s):  
Marek Smaga ◽  
Annika Boemke ◽  
Tobias Daniel ◽  
Matthias W. Klein
Keyword(s):  
Phase Transformation ◽  
Strain Rate ◽  
Cyclic Deformation ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Austenitic Steels ◽  
Threshold Temperature ◽  
Martensite Formation ◽  
Transformation Behavior ◽  
Phase Transformation Behavior

This study presents the results of a detailed investigation of metastability and susceptibility to deformation induced α’-martensite formation of several austenitic steels (AISI 304, AISI 321, AISI 348 and two batches from AISI 347) in the solution-annealed state. Besides conventional characterization of metastability by calculating stacking-fault energy and threshold temperature (designated as MS and Md30), the present work introduced a new method for determining susceptibility to α’-martensite formation. The method was based on dynamically applied local plastic deformation and non-destructive micro-magnetic measurement of α’-martensite content. The parameter Iξ was established, which correlated very well with the grade of α’-martensite formation during cyclic loading. The cyclic deformation and phase transformation behavior of cyclically loaded specimens from different metastable austenitic steels were investigated in total-strain and stress controlled fatigue tests with load ratio R = -1 at ambient temperature. The influence of the strain rate on the cyclic deformation and phase transformation behavior was also examined. During the fatigue tests, besides stress-strain hysteresis and temperature measurement, in situ micro-magnetic measurements were performed. Using the compressive measured data, the influence of plastic induced self-heating of the specimen and the strain rate on α’-martensite formation was analyzed.

Influence of Cyclic Deformation Induced Phase Transformation on the Fatigue Behavior of the Austenitic Steel X6CrNiNb1810

2014 ◽  
Vol 891-892 ◽  
pp. 1231-1236 ◽  
Author(s):  
Andreas Sorich ◽  
Marek Smaga ◽  
Dietmar Eifler
Keyword(s):  
Phase Transformation ◽  
Fatigue Life ◽  
Austenitic Steel ◽  
Cyclic Deformation ◽  
Deformation Behavior ◽  
Fatigue Behavior ◽  
Cyclic Hardening ◽  
Martensite Formation ◽  
Destructive Testing

The austenitic steel X6CrNiNb1810 (AISI 347) was investigated in isothermal total strain-controlled tests at ambient temperature and T = 300 °C in the LCF-and HCF-range. The phase transformation from paramagnetic austenite (fcc) into ferromagnetic α´-martensite ́(bcc) leads to cyclic hardening and to an increase in fatigue life. At 300 °C no α´-martensite formation was observed in the LCF-range and the cyclic deformation behavior depends basically on cyclic hardening processes due to an increase of the dislocation density, followed by cyclic saturation and softening due to changes in the dislocation structure. In the HCF-range an increase in fatigue life was observed due to ε- and α´-martensite formation. Measurements of the mechanical stress-strain-hysteresis as well as temperature and magnetic properties enable a characterization of the cyclic deformation behavior and phase transformation in detail. The changes in the physical data were interpreted via microstructural changes observed by scanning-and transmission-electron-microscopy as well as by x-ray investigations. Additionally electromagnetic acoustic transducers (EMATs) developed from the Fraunhofer Institute of Non-destructive Testing (IZFP) Saarbrücken were used for an in-situ characterization of the fatigue processes.

Biaxial fatigue behavior of a powder metallurgical TRIP steel

2015 ◽  
Author(s):  
S. Ackermann ◽  
T. Lippmann ◽  
D. Kulawinski ◽  
S. Henkel ◽  
H. Biermann
Keyword(s):  
Phase Transformation ◽  
Trip Steel ◽  
Cyclic Deformation ◽  
Fatigue Behavior ◽  
Shear Loading ◽  
Mode I ◽  
Mode Ii ◽  
Martensite Formation ◽  
Biaxial Fatigue ◽  
Shear Fatigue

Multiaxial fatigue behavior is an important topic in critical structural components. In the present study the biaxial-planar fatigue behavior of a powder metallurgical TRIP steel (Transformation Induced Plasticity) was studied by taking into account martensitic phase transformation and crack growth behavior. Biaxial cyclic deformation tests were carried out on a servo hydraulic biaxial tension-compression test rig using cruciform specimens. Different states of strain were studied by varying the strain ratio between the axial strain amplitudes in the range of -1 (shear loading) to 1 (equibiaxial loading). The investigated loading conditions were proportional due to fixed directions of principal strains. The studied TRIP steel exhibits martensitic phase transformation from ?-austenite via ?-martensite into ?‘- martensite which causes pronounced cyclic hardening. The ?‘-martensite formation increased with increasing plastic strain amplitude. Shear loading promoted martensite formation and caused the highest ?‘-martensite volume fractions at fatigue failure in comparison to uniaxial and other biaxial states of strain. Moreover, the fatigue lives of shear tests were higher than those of uniaxial and other biaxial tests. The von Mises equivalent strain hypothesis was found to be appropriate for uniaxial and biaxial fatigue, but too conservative for shear fatigue, according to literature for torsional fatigue. The COD strain amplitude which is based on crack opening displacement gave a better correlation of the investigated fatigue lives, especially those for shear loading. Different types of major cracks were observed on the sample surfaces after biaxial cyclic deformation by using electron monitoring in an electron beam universal system and scanning electron microscopy (SEM). Specimens with strain ratios of 1, 0.5, -0.1 and -0.5 showed mode I major cracks (perpendicular to the axis of maximum principal strain). Major cracks after shear fatigue had partially mode II orientation (tilted 45° to the loading axes) and afterwards bifurcated into two pairs of mode I cracks. Another shear test revealed a major crack of mode I orientation (parallel to the loading axes). These results are in good agreement to the literature. Micro cracks after shear fatigue were longer than those after biaxial fatigue with strain ratios of 1 and 0.5. Major and minor cracks after equibiaxial and shear loading showed crack branching and crack coalescence. The results on fatigue crack behavior support the assumption that the period of stage I (mode II) crack propagation is much longer under shear loading than under other biaxial conditions due to absence of tensile stress normal to the planes of maximum shear strain under shear loading.

Evolution of Phase Transformation Behavior in Li(Mn1.5Ni0.5)O4 Cathodes Studied By In Situ XRD

2011 ◽  
Vol 158 (8) ◽  
pp. A890 ◽  
Author(s):  
Kevin Rhodes ◽  
Roberta Meisner ◽  
Yoongu Kim ◽  
Nancy Dudney ◽  
Claus Daniel
Keyword(s):  
Phase Transformation ◽  
Transformation Behavior ◽  
Phase Transformation Behavior ◽  
In Situ Xrd

Cracking and Phase Transformation in Silicon During Nanoindentation

2003 ◽  
Vol 795 ◽  
Author(s):  
Jae-il Jang ◽  
Songqing Wen ◽  
M. J. Lance ◽  
I. M. Anderson ◽  
G. M. Pharr
Keyword(s):  
Raman Spectroscopy ◽  
Phase Transformation ◽  
Single Crystals ◽  
Transformation Behavior ◽  
Amorphous Phases ◽  
Phase Transformation Behavior ◽  
Wide Range ◽  
Load Displacement ◽  
Indenter Geometry

ABSTRACTNanoindentation experiments were performed on single crystals of (100) Si using a series of triangular pyramidal indenters with centerline-to-face angles in the range 35.3° to 85.0°. The influences of the indenter geometry on cracking and phase transformation during indentation were systematically studied. Although reducing the indenter angle reduces the threshold load for cracking and increases the crack lengths, c, at a given indention load, P, the frequently observed relation between P and c3/2 is maintained for all of the indenters over a wide range of load. Features in the nanoindentation load-displacement curves in conjunction with Raman spectroscopy of the crystalline and amorphous phases in and around the contact impression show that the indenter geometry also plays a role in the phase transformation behavior. Results are discussed in relation to prevailing ideas about indentation cracking and phase transformation in silicon.

Sign in / Sign up

Export Citation Format

Share Document