scholarly journals Fatigue Crack Initiation and Propagation at High Temperature of New-Generation Bearing Steel

Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 25
Author(s):  
Zhiwei Wu ◽  
Maosheng Yang ◽  
Kunyu Zhao
Keyword(s):  
Fracture Surface ◽  
Failure Mode ◽  
Electron Backscatter Diffraction ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Optical Microscope ◽  
Bearing Steel ◽  
Fatigue Properties ◽  
New Generation ◽  
Scanning Electron

The new generation of bearing steel has good comprehensive properties, which can satisfy most of the requirements of bearing steel in a complex environment. In the presented work, fatigue properties of 15Cr14Co12Mo5Ni2 bearing steel have been investigated by means of rotating bending fatigue tests on smooth bar specimens after carburization and heat treatment. Optical microscope, scanning electron microscopy, electron backscatter diffraction, and Image-Pro Plus software were used to analyze the fracture, microstructure, and carbides. The results suggest that the fatigue strength at room temperature and 500 °C is 1027 MPa and 585 MPa, respectively. Scanning electron micrographic observations on the fracture surface of the fatigue specimens at 500 °C show that fatigue cracks usually initiate from voids in the carburized case and oxide layer on the surface of steel. The failure mode in the carburized case is a quasi-cleavage fracture, and with the increase of crack propagation depth, the failure mode gradually changes to fatigue and creep-fatigue interaction. With the increase of the distance from the surface, the size of the martensite block decreases and the fracture surface shows great fluctuation.

scholarly journals Quantitative Analysis of Inclusion Engineering on the Fatigue Property Improvement of Bearing Steel

Metals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 476 ◽  
Author(s):  
Chao Gu ◽  
Min Wang ◽  
Yanping Bao ◽  
Fuming Wang ◽  
Junhe Lian
Keyword(s):  
Fatigue Life ◽  
Quantitative Analysis ◽  
Critical Size ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Fatigue Property ◽  
Bearing Steel ◽  
Fatigue Properties ◽  
Bearing Steels ◽  
Inclusion Distribution

The fatigue property is significantly affected by the inner inclusions in steel. Due to the inhomogeneity of inclusion distribution in the micro-scale, it is not straightforward to quantify the effect of inclusions on fatigue behavior. Various investigations have been performed to correlate the inclusion characteristics, such as inclusion fraction, size, and composition, with fatigue life. However, these studies are generally based on vast types of steels and even for a similar steel grade, the alloy concept and microstructure information can still be of non-negligible difference. For a quantitative analysis of the fatigue life improvement with respect to the inclusion engineering, a systematic and carefully designed study is still needed to explore the engineering dimensions of inclusions. Therefore, in this study, three types of bearing steels with inclusions of the same types, but different sizes and amounts, were produced with 50 kg hot state experiments. The following forging and heat treatment procedures were kept consistent to ensure that the only controlled variable is inclusion. The fatigue properties were compared and the inclusions that triggered the fatigue cracks were analyzed to deduce the critical sizes of inclusions in terms of fatigue failure. The results show that the critical sizes of different inclusion types vary in bearing steels. The critical size of the spinel is 8.5 μm and the critical size of the calcium aluminate is 13.5 μm under the fatigue stress of 1200 MPa. In addition, with the increase of the cleanliness of bearing steels, the improvement of fatigue properties will reach saturation. Under this condition, further increasing of the cleanliness of the bearing steel will not contribute to the improvement of fatigue property for the investigated alloy and process design.

Fatigue and Corrosion Fatigue Failures

2005 ◽  
Author(s):  
Fred V. Ellis
Keyword(s):  
Fracture Surface ◽  
Corrosion Fatigue ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Applied Loading ◽  
Root Area ◽  
Waterwall Tube ◽  
Two Factors ◽  
Fracture Appearance ◽  
Thread Root

A metallurgical failure analysis was performed for a hanger rod and a waterwall tube sample. The hanger is a rigid type and supports a long vertical run of piping. The fracture is in one of the threaded ends and the fracture surface consists of three regions. The outermost portion adjacent to the thread root has ratchet marks that are an indication of fatigue crack initiation. The center portion has concentric, oval shaped beachmarks. The oval shape is consistent with an applied loading due to two bending moments. The inner portion is the final fracture and is approximately 1/4 of the thread root area indicating relatively low remote stresses. The failure mechanism is fatigue based on the beachmarks on the fracture surface and the transgranular cracking. The lower slope waterwall tube failure had a window opening fracture appearance. The axial fractures forming the window are located at the edge of the membrane welds on the cold or backside. There are shallow toe cracks at the membrane weld on the tube outside surface. The fracture surface had multiple, thumbnail-shaped fatigue cracks connected to the inside surface. These fatigue cracks are due to the corrosion fatigue mechanism based on two factors: (1) the stress responsible for their growth is related to the unit thermal cycling and the welded panel geometry near the corner of the boiler, and (2) they are oxidized indicating a corrosion contribution.

Aqueous Corrosion of Deformed Steel Under Simulated Diluted Bitumen

CORROSION ◽  
10.5006/3121 ◽  
2019 ◽  
Vol 75 (10) ◽  
pp. 1194-1206
Author(s):  
Hongxing Liang ◽  
Rebecca Filardo Schaller ◽  
Edouard Asselin
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Photoelectron Spectroscopy ◽  
Electron Backscatter Diffraction ◽  
Pipeline Steel ◽  
Optical Microscope ◽  
Circular Ring ◽  
Aqueous Corrosion ◽  
Backscatter Diffraction ◽  
Scanning Electron

The effect of predeformation on corrosion of ASTM A106B pipeline steel exposed to 1.7 mM sodium chloride droplets covered by simulated diluted bitumen was evaluated. The microstructures of ASTM A106B pipeline steel with and without predeformation were examined by electron backscatter diffraction and optical microscope. Corrosion of pipeline steel under the chloride droplet covered by simulated diluted bitumen for 5 min was studied with and without predeformation using scanning electron microscopy. Corrosion was initiated at the surface of ASTM A106B pipeline steel after 5 min of exposure. The predeformation increased the number of pits initiated at the steel surface and the number of partially dissolved inclusions. Scanning electron microscopy, profilometry, and x-ray photoelectron spectroscopy measurements were used to characterize the corrosion of the specimens with and without prior deformation after 24 h of exposure to an oil-covered droplet. The corrosion products coalesced and formed a small circular ring which deviated from the geometric center of the droplet. The diameters of the circular rings for the unbent and pre-bent specimens were 2.371±0.125 mm and 2.465±0.046 mm, respectively; the distances between the circular ring centers and droplet centers were 0.599±0.124 mm and 0.620±0.190 mm, respectively. The average corrosion penetration of the predeformed specimen was 1.18±0.09 times higher than that of the specimen without predeformation.

Fatigue Properties for Sinter-Hardened Fe-Ni-Mo-Cu Materials

2007 ◽  
Vol 534-536 ◽  
pp. 677-680
Author(s):  
Chong Lin Wang ◽  
Ping Wang ◽  
Zai Min Shi
Keyword(s):  
Plastic Deformation ◽  
Fracture Surface ◽  
Endurance Limit ◽  
Fatigue Cracks ◽  
Axial Loading ◽  
Raw Material ◽  
Fatigue Properties ◽  
Fatigue Striation ◽  
Pulse Pump ◽  
Fatigue Endurance

Fe-4Ni-0.5Mo-1Cu powder was selected as raw material, pressed and sinter-hardened at 1135°C for 30 min with rapid cooling. The density varies in the range of 7.24-7.29 g/cm3. Its fatigue properties have been tested in axial loading of alternating tensile/compressive stress at R=-1 with a servo-pulse pump. The fatigue endurance limit was measured to be 260 MPa. The microstructure showed more homogeneous bainite and martensite. Neither Ni nor Mo rich areas were detected. Fractography displayed the fatigue cracks initiated from the pore areas near the surface. A nontypical ductile fatigue striation was found. More dimples occurred on fracture surface due to the plastic deformation, which can prohibit cracking propagation and improve its fatigue properties.

scholarly journals Low-Temperature Strengths and Ductility of Various Tungsten Sheets

2011 ◽  
Vol 2011 ◽  
pp. 1-7 ◽  
Author(s):  
Yutaka Hiraoka ◽  
Hiroaki Kurishita
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Electron Microscope ◽  
Low Temperature ◽  
Fracture Surface ◽  
Optical Microscope ◽  
Transgranular Fracture ◽  
Bend Tests ◽  
Point Bend ◽  
Scanning Electron

We used three kinds of tungsten sheets in this study. First, we examined microstructure such as grain size distribution using an optical microscope. Secondly, we carried out three-point bend tests at temperatures between about 290 and 500 K. Then, we examined fracture surface of a failed specimen using a scanning electron microscope. Lastly, by analyzing all these results, we evaluated apparent intergranular and transgranular fracture strengths and discussed strengths and ductility of tungsten. Additionally, we compared mechanical properties of tungsten with those of molybdenum.

Hydrogen Accumulation during Fatigue Deformation of Al-Mg-Si Base Alloys

2006 ◽  
Vol 519-521 ◽  
pp. 1053-1058
Author(s):  
Keitaro Horikawa ◽  
Hidetoshi Kobayashi
Keyword(s):  
Fracture Surface ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Fatigue Properties ◽  
Frequency Effect ◽  
Slip Lines ◽  
Surface Hydrogen ◽  
Testing Frequency ◽  
Slip Planes ◽  
Hydrogen Accumulation

Hydrogen accumulation during fatigue of bake-hardened Al-Mg-Si alloys was investigated by means of hydrogen microprint technique. As a result of S-N curve relation as a function of testing frequency, effect of environmental hydrogen on fatigue properties was not clearly identified. Based on the low cycle fatigue test with 60MPa stress amplitude, it was revealed that hydrogen was preferentially accumulated on slip lines and that distribution of hydrogen emission was changed in the crack propagation direction. Hydrogen was preferentially accumulated at the coarse slip lines near the fatigue cracks where the separation of slip planes was observed in the fracture surface. On the other hand, hydrogen was observed on the slip lines arranged like steps where the fatigue striations were formed in the fracture surface. At near the final fracture area where the finer slip lines were formed on specimen surface, hydrogen was arranged on each slip lines formed by multiple slips. Morphology of hydrogen accumulation on slip lines was not changed when the testing frequency was changed from 2Hz to 15Hz.

Crack Growth Evaluation of Induction Quenched JIS-S45C Steel Based on Stress Intensity Factor Simulation

2021 ◽  
Vol 1020 ◽  
pp. 126-130
Author(s):  
Takahiro Matsueda ◽  
Ayumu Tamura ◽  
Koshiro Mizobe ◽  
Katsuyuki Kida
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Fracture Surface ◽  
Fatigue Cracks ◽  
Optical Microscope ◽  
Bending Test ◽  
Test Machine ◽  
Low Carbon ◽  
Rotating Bending

Problems lived with fatigue fracture for the safe design of the members and structures. In this study, rotating bending tests were performed to investigate the fatigue crack propagation behavior of induction quenched and tempered JIS S45C low carbon steel. Hardness distribution was checked by the Vickers hardness test machine and the microstructure in cross section and fracture surface were observed with an optical microscope and a scanning electron microscope. The depth of the hardened boundary was approximately 1 mm from the surface and formation into martensite occurred at the surface of the specimen. It was ascertained that fracture surface of notched specimens consisted of the five fracture types. In addition, the maximum stress intensity factor of fatigue cracks increased during rotating bending test on notched specimen. The relation between SIF and the fracture surface is discussed.

Influence of Tensile Pre-Strain on the Torsional Fatigue Crack Behaviors of a Structural Steel

2007 ◽  
Vol 340-341 ◽  
pp. 507-512
Author(s):  
Cong Ling Zhou ◽  
Shinichi Nishida ◽  
Nobusuke Hattori
Keyword(s):  
Fatigue Crack ◽  
Structural Steel ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Axial Direction ◽  
Strain Ratio ◽  
Fatigue Properties ◽  
Mode Ii ◽  
Torsional Fatigue ◽  
Mode Ii Crack

Structural steel is widely used in engineering even in nowadays and many new materials have been developed or are under developing. As one of the most common type, torsional fatigue properties are normally calculated from the rotating bending fatigue properties. In this study, the torsional fatigue properties of a structural carbon steel (S45C) with different tensile pre-strain ratio is investigated, especially on the effects of Mode II crack before it branches under different stress amplitudes. Based on the experimental results and microstructure observation, the main results obtained are: (1)Torsional fatigue strength is increased after tensile pre-strain deformation, and the fatigue limits increase with increasing of tensile pre-strain ratio, the highest improvement can be up to 125% of that of the plain specimen. (2) Torsioanl fatigue cracks initiate from the torsional slip lines in ferrite grains, and there is no obvious effect by the tensile pre-strain. With increasing of tensile pre-strain ratio, the fatigue crack initiation life ratio becomes later and the growth rate becomes faster. (3) The mode II crack length along the axial direction becomes longer with increasing of tensile pre-strain ratio, and the crack branch direction does not affected by the tensile pre-strain. Moreover, the length along axial direction is not affected by the stress amplitude change for specimens with the same tensile pre-strain ratio. (4) The length of non-propagating crack becomes shorter with increasing of tensile pre-strain ratio.

Effect of High Tensile Pre-Strain on the Torsional Fatigue Properties of a Structural Steel

2007 ◽  
Vol 353-358 ◽  
pp. 94-97
Author(s):  
Cong Ling Zhou ◽  
Shinichi Nishida ◽  
Nobusuke Hattori
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Structural Steel ◽  
Fatigue Limit ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Fatigue Properties ◽  
Initiation Point ◽  
Torsional Fatigue ◽  
Propagating Crack

This study is developed to investigate the effect of monotonic plastic deformation on the torsional fatigue properties of a structural steel. Five different kinds of tensile pre-strain, 2%, 5%, 8%, 12% and 22%, were applied to the specimens, respectively. And the maximum pre-strain value is near to the necking strain of the test material. The effects of tensile pre-strain on surface hardness, fatigue crack initiation and propagation behaviors, and the behavior of non-propagating cracks. The main results obtained are: The fatigue limits are 145, 160,175, 200 and 215MPa for specimens with tensile pre-strain of 2% 5%, 8%, 12% and 22%, which are improved to 104%, 114%, 125%, 143% and 153% of the fatigue limit for non-pre-strained specimens, respectively. The torsional fatigue limit increases with the tensile pre-strain increasing, until the pre-strain value being near to the necking strain ratio. However, the fatigue limit increase becomes more slowly for high tensile pre-strained specimens than the lower ones. The fatigue cracks of the tensile pre-strained specimens initiated earlier than that of the non-pre-strained specimens, and the propagation is also accelerated, but there is no effect on the fatigue crack initiation point and the branch point. Non-propagating crack length becomes shorter with increasing of tensile pre-strain until the value near the necking strain, and the quantity of non-propagating crack increases at the same time.

Low-voltage, high-resolution scanning electron microscopy of polymers

1987 ◽  
Vol 45 ◽  
pp. 466-467 ◽  
Author(s):  
S. J. Krause ◽  
W.W. Adams ◽  
S. Kumar ◽  
T. Reilly ◽  
T. Suziki
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Low Voltage ◽  
Chromatic Aberration ◽  
Image Resolution ◽  
Resolution Limit ◽  
Crossover Point ◽  
New Generation ◽  
Beam Damage ◽  
Scanning Electron

Scanning electron microscopy (SEM) of polymers at routine operating voltages of 15 to 25 keV can lead to beam damage and sample image distortion due to charging. Imaging polymer samples with low accelerating voltages (0.1 to 2.0 keV), at or near the “crossover point”, can reduce beam damage, eliminate charging, and improve contrast of surface detail. However, at low voltage, beam brightness is reduced and image resolution is degraded due to chromatic aberration. A new generation of instruments has improved brightness at low voltages, but a typical SEM with a tungsten hairpin filament will have a resolution limit of about 100nm at 1keV. Recently, a new field emission gun (FEG) SEM, the Hitachi S900, was introduced with a reported resolution of 0.8nm at 30keV and 5nm at 1keV. In this research we are reporting the results of imaging coated and uncoated polymer samples at accelerating voltages between 1keV and 30keV in a tungsten hairpin SEM and in the Hitachi S900 FEG SEM.

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