SEM Study of the Influence of Microstructure on Low Cycle Fatigue Crack Growth in Martensitic Steel I

2018 ◽  
Vol 774 ◽  
pp. 96-100 ◽  
Author(s):  
Tamaz Eterashvili ◽  
Temur Dzigrashvili ◽  
M. Vardosanidze
Keyword(s):  
Room Temperature ◽  
Martensitic Steel ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Cycle Fatigue ◽  
Slip Bands ◽  
Sem Study ◽  
Austenite Grains ◽  
Plastic Zones ◽  
The Impact

Distribution of fatigue cracks in chromium martensitic steel after low cycle fatigue (LCF) tests at room temperature has been studied using SEM, and the experimental evidences of localized plastic flow (LPF) are presented. The influence of the location of LPF and the microstructure elements on the trajectory and growth of microcracks is also considered. The dimensions of plastic zones ahead of macrocrack tip as well as at its edges were measured in the process of crack propagation inside of the sample. The processes occurring in plastic zone, particularly ahead of macrocrack tip, were analyzed. Distribution, orientation and the reasons of slip bands’ formation as well as the microstructure elements at which they were nucleated have been studied. The impact of the slip bands’ orientation on the process of macrocrack growth was also analyzed. In addition the interactions of a crack with the boundaries of former austenite grains, martensitic packets, martensitic laths, slip bands and precipitates have been discussed.

Short Crack Initiation during Low-Cycle Fatigue in SAF 2507 Duplex Stainless Steel

2007 ◽  
Vol 345-346 ◽  
pp. 343-346 ◽  
Author(s):  
M.C. Marinelli ◽  
Suzanne Degallaix ◽  
I. Alvarez-Armas
Keyword(s):  
Stainless Steel ◽  
Duplex Stainless Steel ◽  
Room Temperature ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Surface Strain ◽  
The Other ◽  
Cycle Fatigue ◽  
Cyclic Tests ◽  
Characteristic Microstructure

In this work, the formation of fatigue cracks is considered as a nucleation process due to the development of a characteristic microstructure formed just beneath the specimen surface. Strain controlled cyclic tests were carried out at room temperature at total strain ranges εt = 0.8 and 1.2% in flat specimens of SAF 2507 Duplex Stainless Steel (DSS). The results show that for this DSS, at εt = 0.8%, the correlation between phases (Kurdjumov-Sacks crystallographic relation) plays an important role in the formation of microcracks. On the other hand, at εt = 1.2%, microcracks initiate in the ferritic phase and the K-S relation does not seem to affect the formation of the cracks.

Structure Changes in Stainless Steels Used in Nuclear Reactors and Turbo Generators after Minor Low Cycle Fatigue Deformation

2005 ◽  
Vol 475-479 ◽  
pp. 3505-3508
Author(s):  
Tamaz Eterashvili ◽  
T. Dzigrashvili ◽  
M. Vardosanidze
Keyword(s):  
Room Temperature ◽  
Nuclear Reactors ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Slip Bands ◽  
Structure Changes ◽  
Before And After ◽  
Number Of Cycles ◽  
Local Plastic Deformation

The structure of austenitic steel before and after 25% of total number of cycles of low cycle fatigue tests conducted at room temperature is studied using TEM. It is shown that the cyclic deformation of the steel proceeds heterogeneously. The microstructure of the steel is investigated in the area between the deformed and undistorted parts of the samples. The crystallography of the observed twins and the slip bands is specified. The value of local plastic deformation within a micro area of a grain is measured, and the influence of microstructure on crack initiation is discussed.

Low cycle fatigue properties and microstructure of P92 ferritic-martensitic steel at room temperature and 873 K

2019 ◽  
Vol 157 ◽  
pp. 109923 ◽  
Author(s):  
Zhen Zhang ◽  
Zhengfei Hu ◽  
Siegfried Schmauder ◽  
Baosen Zhang ◽  
Zhangzhong Wang
Keyword(s):  
Room Temperature ◽  
Martensitic Steel ◽  
Low Cycle Fatigue ◽  
Fatigue Properties ◽  
Cycle Fatigue

Low-Cycle Fatigue Behavior of TP347H Austenitic Stainless Steels at Room Temperature

2013 ◽  
Vol 815 ◽  
pp. 875-879 ◽  
Author(s):  
Hong Wei Zhou ◽  
Yi Zhu He ◽  
Yu Wan Cen ◽  
Jian Qing Jiang
Keyword(s):  
Fatigue Life ◽  
Stainless Steels ◽  
Room Temperature ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Austenitic Stainless Steels ◽  
Fracture Morphology ◽  
Cycle Fatigue ◽  
Response Curves

Low-cycle fatigue (LCF) tests were performed with different strain amplitudes from 0.4% to 1.2% at room temperature (RT) to investigate fatigue life and fracture morphology of TP347H austenitic stainless steels. The results show that there is initial cyclic hardening for a few cycles, followed by continuous softening until fatigue failure at all strain amplitudes in stress response curves. The fatigue life of the steels follows the strain-life Coffin-Manson law. Fracture morphology shows that fatigue cracks initiate from the specimen free surface instead of the interior of the specimen, and ductile fracture appears during LCF loading. More sites of crack initiation and quicker propagation rate of fatigue crack at high strain amplitudes than those at low strain amplitudes are responsible for reduced fatigue life with the increasing of strain amplitude.

scholarly journals Low-cycle Fatigue and Fracture Behaviour of 9%Ni Steel Flux Cored Arc Welding joint at Cryogenic Temperature

2019 ◽  
Vol 269 ◽  
pp. 03008
Author(s):  
Weidong Mu ◽  
Yuzhang Li ◽  
Yan Cai ◽  
Min Wang
Keyword(s):  
Fatigue Life ◽  
Low Temperature ◽  
Arc Welding ◽  
Cryogenic Temperature ◽  
Room Temperature ◽  
Weld Seam ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Cycle Fatigue ◽  
Flux Cored Arc Welding

In the present work, low-cycle fatigue (LCF) test and crack tip opening displacement (CTOD) test were performed for 9% Ni steel flux cored arc welding (FCAW) joint at room temperature (296 K) and cryogenic temperature (80 K). At cryogenic temperature, the strain amplitude had a far greater impact on fatigue life of 9%Ni steel welded joint and it decreased dramatically lead to a significant increase in fatigue life. It was found that most fracture initiation of joints located in fusion area at room temperature, while it occurred in weld seam at low temperature. The fracture toughness of weld seam was higher than that of fusion zone no matter the testing temperature. The effect of precipitated phase was the true reason. The fatigue cracks propagated in transgranular mode at room temperature, ultimately, and intergranular mode at low temperature in both LCF specimens and CTOD specimens.

Structure Changes in Stainless Steels Used in Nuclear Reactors and Turbo Generators after Minor Low Cycle Fatigue Deformation

2005 ◽  
Vol 475-479 ◽  
pp. 1487-1490 ◽  
Author(s):  
Tamaz Eterashvili ◽  
T. Dzigrashvili ◽  
M. Vardosanidze
Keyword(s):  
Room Temperature ◽  
Nuclear Reactors ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Slip Bands ◽  
Structure Changes ◽  
Before And After ◽  
Number Of Cycles ◽  
Local Plastic Deformation

The structure of austenitic steel before and after 25% of total number of cycles of low cycle fatigue tests conducted at room temperature is studied using TEM. It is shown that the cyclic deformation of the steel proceeds heterogeneously. The microstructure of the steel is investigated in the area between the deformed and undistorted parts of the samples. The crystallography of the observed twins and the slip bands is specified. The value of local plastic deformation within a micro area of a grain is measured, and the influence of microstructure on crack initiation is discussed.

scholarly journals Investigating the Interaction between Persistent Slip Bands and Surface Hard Coatings via Crystal Plasticity Simulations

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1012
Author(s):  
Mohammad S. Dodaran ◽  
Jian Wang ◽  
Nima Shamsaei ◽  
Shuai Shao
Keyword(s):  
Crystal Plasticity ◽  
Coating Thickness ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Hard Coatings ◽  
Fatigue Performance ◽  
Shear Stresses ◽  
Cycle Fatigue ◽  
Slip Bands ◽  
Persistent Slip Bands

Fatigue cracks often initiate from the surface extrusion/intrusions formed due to the operation of persistent slip bands (PSBs). Suppression of these surface topographical features by hard surface coatings can significantly extend fatigue lives under lower stress amplitudes (i.e., high cycle fatigue), while cracks initiate early in the coating or in the coating–substrate interface under higher stress amplitudes (i.e., low cycle fatigue), deteriorating the fatigue performance. However, both beneficial and detrimental effects of the coatings appear to be affected by the coating–substrate material combination and coating thickness. A quantitative understanding of the role of these factors in the fatigue performance of materials is still lacking. In this study, crystal plasticity simulations were employed to elucidate the dependence of the coating’s effects on two factors—i.e., the coating thickness and loading amplitudes. The results revealed that the thicker coatings more effectively suppress the operation of the PSBs, but generate higher tensile and shear stresses, normal and parallel to the interfaces, respectively, promoting interfacial delamination. The tensile stresses parallel to the interface within the coating, which favors coating fracture, are not sensitive to the coating thickness.

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