High Cycle Fatigue Strength of Modified 9Cr-1Mo Steel at Elevated Temperatures

2014 ◽  
Author(s):  
Motoyuki Ochi ◽  
Ken Suzuki ◽  
Isamu Nonaka ◽  
Hideo Miura
Keyword(s):  
Fatigue Strength ◽  
Fatigue Limit ◽  
Room Temperature ◽  
High Cycle Fatigue ◽  
Elevated Temperatures ◽  
Fatigue Loading ◽  
Bending Test ◽  
Cycle Fatigue ◽  
Intergranular Cracking

In order to clarify the characteristics of high-cycle fatigue of the modified 9Cr-1Mo steel, a high temperature rotary bending test was carried out. As a result, the fatigue strength of this alloy decreased monotonically at elevated temperatures. It decreased from 440 MPa at room temperature to about 350 MPa at 400°C. This decrease of the fatigue strength was attributed to the temperature dependence of the yielding strength of this alloy. The fatigue limit appeared near 107 cycles at 400°C, whereas it appeared around 106 cycles at room temperature. The most important result is that the fatigue limit disappeared up to 108 cycles at temperatures higher than 500°C. Thus, the number of cycles at which the fatigue limit appeared shifted to higher cycles with increasing the testing temperature. Clear striation was observed in the stable crack growth region on the fracture surface of all the specimen tested at room temperature, 400°C, 500°C, 550°C, and 600°C. Intergranular cracking, which have been observed in creep-fatigue tests, was not observed. Since the estimated operating temperature of FBR is 550°C, it is very important to consider this fatigue strength in the structural and reliability design of the modified 9Cr-1Mo steel. In this study, the change of crystallinity of this alloy under fatigue loading was also analyzed by applying an EBSD method. The image quality (IQ) value obtained from the analysis was used for the quantitative evaluation of the crystallinity in the area where an electron beam of 20 nm in diameter was irradiated. The quality of the atomic alignment was found to degrade under the cyclic loading, and a crack started to occur on the surface of the alloy when the quality of the atomic alignment decreased to a certain critical value.

High Cycle Fatigue Properties of Modified 9Cr-1Mo Steel at Elevated Temperatures

2012 ◽  
Author(s):  
Yoshiaki Matsumori ◽  
Jumpei Nemoto ◽  
Yuji Ichikawa ◽  
Isamu Nonaka ◽  
Hideo Miura
Keyword(s):  
Fatigue Strength ◽  
Fatigue Limit ◽  
Room Temperature ◽  
Structural Reliability ◽  
High Cycle Fatigue ◽  
Elevated Temperatures ◽  
Fatigue Behavior ◽  
Cyclic Softening ◽  
Fatigue Properties ◽  
Cycle Fatigue

Since high-cycle fatigue loads is applied to the pipes in various energy and chemical plants due to the vibration and frequent temperature change of fluid in the pipes, the high-cycle fatigue behavior of the alloys used for pipes should be understood quantitatively in the structural reliability design of the pipes. The purpose of this study, therefore, is to clarify the high-cycle fatigue strength and fracture mechanism of the modified 9Cr-1Mo steel at temperatures higher than 400°C. This material is one of the effective candidates for the pipes in fast breeder demonstration reactor systems. A rotating bending fatigue test was applied to samples at 50 Hz in air. The stress waveform was sinusoidal and the stress ratio was fixed at −1. The fatigue limit was observed at room temperature and it was about 420 MPa. This value was lower than the 0.2% proof stress of this alloy by about 60 MPa. This decrease can be attributed to the cyclic softening of this material. The limited cycles at knee point was about 8×105 cycles. All fracture was initiated from a single surface crack and no inclusion-induced fracture was observed in the fracture surface by SEM. Thus, the high-cycle fatigue design based on the fatigue limit may be applicable to the modified 9Cr-1Mo steel at room temperature. The fatigue limit of about 350 MPa was also observed at 400°C, and it appeared at about 107 cycles, while it appeared at around 106 cycles at room temperature. Thus, it was confirmed that the fatigue strength of this alloy decrease with temperature. However, the fatigue limit didn’t appear at 550°C up to 108 cycles. The fatigue limit may disappear in this alloy at 550°C. It is very important, therefore, to evaluate the ultra-high cycle fatigue strength of this alloy at temperatures higher than 400°C.

Elucidation of the High Cycle Fatigue Damage Mechanism of Modified 9Cr-1Mo Steel at Elevated Temperature

2015 ◽  
Author(s):  
Takuya Murakoshi ◽  
Motoyuki Ochi ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Fatigue Strength ◽  
High Cycle Fatigue ◽  
Elevated Temperatures ◽  
Surface Hardness ◽  
Diffraction Method ◽  
Fatigue Loading ◽  
Damage Mechanism ◽  
Fatigue Tests ◽  
Electron Back Scatter Diffraction ◽  
Cycle Fatigue

Modified 9Cr-1Mo steel is one of the heat-resistant steels developed for steam generator in a FBR (Fast Breeder Reactor). When it is used in a FBR, the lifetime of the steel under HCF (High Cycle Fatigue) and V-HCF (Very-High Cycle Fatigue) caused by flow-induced vibration has to be considered for assuring its long-term reliability up to 1011 cycles. Since previous studies showed that the fatigue limit did not appear up to 108 cycles, it is necessary to investigate the fatigue strength of this alloy in cycles higher than 108 cycles. In this study, in order to clarify high cycle fatigue strength and fracture mechanism of the modified 9Cr-1Mo steel, the change of the lath martensitic strengthening structure was observed in detail on the surface of specimens fractured by rotary bending fatigue tests by using EBSD (Electron Back-Scatter Diffraction) method. The Kernel Average Misorientation (KAM) value obtained from the EBSD analysis was used for the quantitative evaluation of the change of the lath martensitic texture. It was found that the average KAM values clearly decreased on the surface areas of the fractured specimens after the application of 107-108 cycles of fatigue loading at temperatures higher than 550°C. This result indicates that degradation of the lath martensitic texture occurred around the surface of specimens tested at the temperature higher than 550°C. In order to quantitatively evaluate the decrease of its strength, a hardness test was performed at room temperature by using a nanoindentation method. It was confirmed that the surface hardness of specimens decreased drastically in the specimens fractured at temperatures higher than 550°C. From these results, it was concluded that the effective 0.2%-proof stress decreased during the fatigue tests by the degradation of the lath martensitic texture caused by the fatigue loading at elevated temperatures. Further analyses are indispensable for explicating the damage mechanism more in detail.

OS1514 High-Cycle Fatigue Strength of Modified 9Cr-1Mo Steel at Elevated Temperatures

2013 ◽  
Vol 2013 (0) ◽  
pp. _OS1514-1_-_OS1514-3_
Author(s):  
Motoyuki OCHI ◽  
Ken SUZUKI ◽  
Isamu NONAKA ◽  
Hideo MIURA
Keyword(s):  
Fatigue Strength ◽  
High Cycle Fatigue ◽  
Elevated Temperatures ◽  
Cycle Fatigue

Fatigue Performance of Low Rigidity Titanium Alloy for Biomedical Applications

2004 ◽  
Vol 449-452 ◽  
pp. 1265-1268
Author(s):  
Toshikazu Akahori ◽  
Mitsuo Niinomi ◽  
Hisao Fukui ◽  
Akihiro Suzuki
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Fatigue Limit ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Tangential Force ◽  
Solution Treatment ◽  
Beta Phase ◽  
Fretting Fatigue ◽  
Cycle Fatigue

Microstructures of Ti-29Nb-13Ta-4.6Zr (TNTZ) aged at temperatures between 573 and 723 K after solution treatment at 1063 K have super fine omega phase, or􀀂 both super fine alpha and omega phases, respectively in beta phase with an average grain diameter of 20 µm. Plain fatigue strength of TNTZ aged after solution treatment is much greater than that of as-solutionized TNTZ in both low cycle fatigue and high cycle fatigue life regions. This is due to the improvement of the balance of strength and ductility by the precipitation of alpha phase. Fretting fatigue strength of TNTZ conducted with various heat treatments decreases dramatically as compared with their plain fatigue strength in both low cycle fatigue and high cycle fatigue life regions. In this case, the decreasing ratio of fretting fatigue life increases with increasing the small crack propagation area where both the tangential force and frictional force at the contact plane of pad exist. In fretting fatigue in air, the ratio of fretting damage (Pf/Ff), where Pf and Ff stand for plain fatigue limit and fretting fatigue limit, respectively, increases with increasing elastic modulus. In fretting fatigue in Ringer’s solution, the passive film on specimen surface is broken by fretting action in TNTZ, which have excellent corrosion resistance, and, as a result, corrosion pits that lead to decreasing fretting fatigue strength especially in high cycle fatigue life region, are formed on its surface.

scholarly journals The Effect of Baking Heat Treatment on the Fatigue Strength and Life of Shot Peened 4340M Landing Gear Steel

Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5711
Author(s):  
Seok-Hwan Ahn ◽  
Jongman Heo ◽  
Jungsik Kim ◽  
Hyeongseob Hwang ◽  
In-Sik Cho
Keyword(s):  
Heat Treatment ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Fatigue Limit ◽  
Shot Peening ◽  
High Cycle Fatigue ◽  
Landing Gear ◽  
Cycle Fatigue ◽  
Heat Treated ◽  
Ultrasonic Fatigue

In this study, the effect of baking heat treatment on fatigue strength and fatigue life was evaluated by performing baking heat treatment after shot peening treatment on 4340M steel for landing gear. An ultrasonic fatigue test was performed to obtain the S–N curve, and the fatigue strength and fatigue life were compared. The micro hardness of shot peening showed a maximum at a hardened depth of about 50 μm and was almost uniform when it arrived at the hardened depth of about 400 μm. The overall average tensile strength after the baking heat treatment was lowered by about 80–111 MPa, but the yield strength was improved by about 206–262 MPa. The five cases of specimens showed similar fatigue strength and fatigue life in high cycle fatigue (HCF) regime. However, the fatigue limit of the baking heat treated specimens showed an increasing tendency rather than that of shot peening specimens when the fatigue life was extended to the very high cycle fatigue (VHCF) regime. The effect of baking heat treatment was identified from improved fatigue limit when baking heat was used to treat the specimen treated by shot peening containing inclusions. The optimum temperature range for the better baking heat treatment effect could be constrained not to exceed maximum 246 °C.

scholarly journals High Cycle Fatigue Performance of Inconel 718 Alloys with Different Strengths at Room Temperature

Metals ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 13 ◽  
Author(s):  
Liqiong Zhong ◽  
Hao Hu ◽  
Yilong Liang ◽  
Chaowen Huang
Keyword(s):  
Solid Solution ◽  
Fatigue Limit ◽  
Fatigue Fracture ◽  
Inconel 718 ◽  
Room Temperature ◽  
High Cycle Fatigue ◽  
Aging Treatment ◽  
Cycle Fatigue ◽  
Inconel 718 Alloy ◽  
Solution State

In this paper, the high cycle fatigue performance of solid solution state and aged Inconel 718 superalloys was studied at room temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the original structural features and fatigue deformation features of two kinds of alloys. SEM, laser scanning confocal microscopy, and electron backscatter diffraction (EBSD) were used to analyze the secondary fracture features of the fatigue fracture morphology and fatigue fracture profile. The results showed that the aging treatment significantly affected the strength and plasticity of the alloy, which in turn affected the fatigue performance of the alloy. After the aging treatment, the yield strength σs and the tensile strength σb of the Inconel 718 alloy increased by 152% and 65.9%, respectively, compared with those of the solid solution state, but the rate of elongation δ and rate of contraction in the cross-section area φ decreased by 63.7% and 52.3%, respectively. The fatigue limit of the aged state was lower than that of the solid solution state by 6.3%. The quadratic function relationship between the high cycle fatigue limit σ−1 and the tensile strength σb of the Inconel 718 superalloy at room temperature was σ−1 = σb · (0.869−3.67 × 10−4 · σb). An analysis of the fatigue fracture mechanism showed that the fatigue fractures before and after aging were all initiated in the grains oriented relatively unfavorably on the surface of the sample, with a mixture of intergranular and transgranular propagation after the transgranular propagation of several grains. The higher plasticity of the solid solution state Inconel 718 alloy resulted in a large number of slip deformation zones under high cycle fatigue loads, and the plastic deformation was relatively uniform. The lengths of the secondary fractures were as high as 120 μm, which formed the single-source plastic fatigue fracture that promoted an increase in the fatigue limit. After aging treatment, the higher strength of the Inconel 718 alloy made dislocation slip difficult under high cycle fatigue loads, and the plasticity compatible deformation capability was poor. When local dislocations slipped to the intragranular γ” phase, γ’ phase, or interfaces with nonmetallic compounds (NMCs), plugging occurred. The degree of stress concentration increased, causing the initiation of fatigue fracture; the secondary fracture was approximately 20 μm. Brittle cleavage due to multiple sources significantly reduced the fatigue limit.

scholarly journals Validation of Multiaxial Fatigue Strength Criteria on Specimens from Structural Steel in the High-Cycle Fatigue Region

Materials ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 116
Author(s):  
František Fojtík ◽  
Jan Papuga ◽  
Martin Fusek ◽  
Radim Halama
Keyword(s):  
Fatigue Strength ◽  
Structural Steel ◽  
High Cycle Fatigue ◽  
Fatigue Loading ◽  
Multiaxial Fatigue ◽  
Experimental Results ◽  
Prediction Methods ◽  
Cycle Fatigue ◽  
Strength Criteria

The paper describes results of fatigue strength estimates by selected multiaxial fatigue strength criteria in the region of high-cycle fatigue, and compares them with own experimental results obtained on hollow specimens made from ČSN 41 1523 structural steel. The specimens were loaded by various combinations of load channels comprising push–pull, torsion, bending and inner and outer pressures. The prediction methods were validated on fatigue strengths at seven different numbers of cycles spanning from 100,000 to 10,000,000 cycles. No substantial deviation of results based on the selected lifetime was observed. The PCRN method and the QCP method provide best results compared with other assessed methods. The results of the MMP criterion that allows users to evaluate the multiaxial fatigue loading quickly are also of interest because the method provides results only slightly worse than the two best performing solutions.

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