Metallurgical Defect and Hydrogen Embrittlement Failure of a Gear

2014 ◽  
Vol 548-549 ◽  
pp. 438-443
Author(s):  
Yu Zhou Gao ◽  
Zhi Wei Yu ◽  
Xiao Lei Xu
Keyword(s):  
Hydrogen Embrittlement ◽  
Fracture Surface ◽  
Crack Propagation ◽  
Casting Defect ◽  
The Core ◽  
Large Size ◽  
Ductile Shearing ◽  
Metallographic Observation ◽  
Metallurgical Defect ◽  
Upper Bainite

Circumferential cracking occurred on the spoke plate of a statically placed marine gear. Fractographic investigation indicates that two independent crack origins are present on the fracture surface. Intergranular fracture mode was mostly found in slow crack propagation region and the intergranular facets associated with ductile shearing. Metallographic observation reveals that a type of macro casting defect, spot-segregation, is generally present on the gear material. Large size macro spot-segregation defect zones just appear in two crack origin regions. Appearance of the large spot-segregation zones in the core of spoke plate supplies the favorable metallurgical condition for hydrogen-induced fracture: presence of excessive impurities of S, P and then appearance of abnormal microstructure of upper-bainite susceptible to hydrogen embrittlement. From the evidences it is concluded that the gear failed due to the hydrogen embrittlement. The possible source for hydrogen was introduced during melting and casting operating.

scholarly journals Large Bent Jets in the Inner Region of CSS

1996 ◽  
Vol 175 ◽  
pp. 71-72
Author(s):  
F. Mantovani ◽  
W. Junor ◽  
M. Bondi ◽  
L. Padrielli ◽  
W. Cotton ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Radio Sources ◽  
Ambient Media ◽  
The Core ◽  
Gaseous Environment ◽  
Radio Jets ◽  
Large Size ◽  
Superluminal Motion ◽  
Inner Region ◽  
Quasars And Radio Galaxies

Recently we focussed our attention on a sample of Compact Steep-spectrum Sources (CSSs) selected because of the large bent radio jets seen in the inner region of emission. The largest distortions are often seen in sources dominated by jets, and there are suggestions that this might to some extent be due to projection effects. However, superluminal motion is rare in CSSs. The only case we know of so far is 3C147 (Alef at al. 1990) with a mildly superluminal speed of ≃ 1.3v/c. Moreover, the core fractional luminosity in CSSs is ≃ 3% and ≤ 0.4% for quasars and radio galaxies respectively. Similar values are found for large size radio sources i.e. both boosting and orientations in the sky are similar for the two classes of objects. An alternative possibility is that these bent-jet sources might also be brightened by interactions with the ambient media. There are clear indications that intrinsic distortions due to interactions with a dense inhomogeneous gaseous environment play an important role. Observational support comes from the large RMs found in CSSs (Taylor et al. 1992; Mantovani et al. 1994; Junor et al. these proc.) and often associated with strong depolarization (Garrington & Akujor, t.p.). The CSSs also have very luminous Narrow Line Regions emission, with exceptional velocity structure (Gelderman, t.p.).

scholarly journals Crack Propagation Characteristics and Fracture Surface Energy of Boride Cermets

2002 ◽  
Vol 66 (11) ◽  
pp. 1116-1121
Author(s):  
Hiromoto Kitahara ◽  
Yasuhiro Yoshikawa ◽  
Fuyuki Yoshida ◽  
Hideharu Nakashima ◽  
Kazuo Hamashima ◽  
...  
Keyword(s):  
Fracture Surface ◽  
Surface Energy ◽  
Crack Propagation ◽  
Propagation Characteristics ◽  
Fracture Surface Energy

scholarly journals A simplified analysis of the Chernobyl accident

2021 ◽  
Vol 7 ◽  
pp. 1
Author(s):  
Bertrand Mercier ◽  
Di Yang ◽  
Ziyue Zhuang ◽  
Jiajie Liang
Keyword(s):  
Numerical Models ◽  
List Type ◽  
Flash Evaporation ◽  
The Core ◽  
Large Size ◽  
Reaction Coefficient ◽  
Pressure Tubes ◽  
Void Effect ◽  
Reactivity Coefficient ◽  
Reactivity Increase

We show with simplified numerical models, that for the kind of RBMK operated in Chernobyl: The core was unstable due to its large size and to its weak power counter-reaction coefficient, so that the power of the reactor was not easy to control even with an automatic system. Xenon oscillations could easily be activated. When there was xenon poisoning in the upper half of the core, the safety rods were designed in such a way that, at least initially, they were increasing (and not decreasing) the core reactivity. This reactivity increase has been sufficient to lead to a very high pressure increase in a significant amount of liquid water in the fuel channels thus inducing a strong propagating shock wave leading to a failure of half the pressure tubes at their junction with the drum separators. The depressurization phase (flash evaporation) following this failure has produced, after one second, a significant decrease of the water density in half the pressure tubes and then a strong reactivity accident due to the positive void effect reactivity coefficient. We evaluate the fission energy released by the accident

scholarly journals Analysis of Stress Corrosion Cracking Propagation of SS304 Stainless Steel Using Crack Shape and Etch Pits

2020 ◽  
Vol 58 (9) ◽  
pp. 583-589
Author(s):  
Byung Hak Choe ◽  
Sang Woo Lee ◽  
Jong Kee Ahn ◽  
Jinhee Lee
Keyword(s):  
Stainless Steel ◽  
Phase Transformation ◽  
Hydrogen Embrittlement ◽  
Crack Propagation ◽  
Stress Corrosion ◽  
High Hardness ◽  
Face Centered Cubic ◽  
High Concentration ◽  
Etch Pits ◽  
Tem Analysis

Austenitic stainless steel SS304 is vulnerable to Cl atmosphere SCC (stress corrosion crack). In this study, SCC phenomena related to stress and corrosion composition were analyzed to identify the mechanism for SCC initiation and propagation in SS304. The microstructure and mechanical properties resulting from crack propagation were analyzed by OM, SEM/EDS and micro Vickers hardness tests. The abnormal phase transformation induced by the SCC was analyzed by TEM and diffraction. As a result of these analyses, the shape of SCC was observed to form a branched type crack, which was related to etch pit patterns on the etched surface due to the austenitic fcc (face centered cubic) lattice slip. In addition, the high concentration accumulation of Cl and S components at the SCC site, observed by SEM/EDS, indicated that the SCC was affected by the corrosive atmosphere. The SCC crack propagation was accompanied by hardening, which is believed to be associated with the mechanism of hydrogen embrittlement. High resolution TEM analysis found abnormal satellite diffraction points in the SCC high hardness region. This means that a superlattice phase with high hardness values is formed near the SCC region. And the HIC (hydrogen induced crack) effect, a kind of hydrogen embrittlement, was also influenced by the hardened superlattice phase. It is assumed that the SCC and HIC are similar phenomena produced in the same stress and corrosive atmosphere by superlattice phase transformation.

The Comparison of Self-Compacting Rock-Filled Concrete with Large-Size Natural and Recycled Aggregate

2014 ◽  
Vol 513-517 ◽  
pp. 20-23
Author(s):  
Hai Chao Wang ◽  
Xue Hua Wang ◽  
Xue Hui An
Keyword(s):  
Fracture Toughness ◽  
Crack Propagation ◽  
Fracture Energy ◽  
Fracture Mechanism ◽  
Recycled Aggregate ◽  
Propagation Process ◽  
Fracture Characteristics ◽  
Three Point Bending ◽  
Large Size ◽  
Crack Propagation Process

The different fracture characteristics of self-compacting rock-filled concrete with large-size natural and recycled aggregate are analyzed by three-point bending experiment. According to the analysis of the crack propagation process, the fracture mechanism differences of self-compacting rock-filled concrete with large-size natural and recycled aggregate are discussed. The further analysis of the differences of fracture toughness, fracture energy, and are gain

Low Toughness and Embrittlement Phenomena in Steels

2015 ◽  
pp. 439-485
Keyword(s):  
High Temperature ◽  
Hydrogen Embrittlement ◽  
Fracture Surface ◽  
Liquid Metal ◽  
Surface Characteristics ◽  
Low Alloy Steels ◽  
Contributing Factors ◽  
Tempered Martensite ◽  
Alloy Steels ◽  
Strength And Ductility

This chapter describes the causes of cracking, embrittlement, and low toughness in carbon and low-alloy steels and their differentiating fracture surface characteristics. It discusses the interrelated effects of composition, processing, and microstructure and contributing factors such as hot shortness associated with copper and overheating and burning as occur during forging. It addresses various types of embrittlement, including quench embrittlement, tempered-martensite embrittlement, liquid-metal-induced embrittlement, and hydrogen embrittlement, and concludes with a discussion on high-temperature hydrogen attack and its effect on strength and ductility.

Evaluation of Hydrogen Embrittlement of Cr-Mo Low Alloy Steel by Slow Strain Rate Technique With Cathodically Charged Specimen

2017 ◽  
Author(s):  
Daichi Tsurumi ◽  
Hiroyuki Saito ◽  
Hirokazu Tsuji
Keyword(s):  
High Pressure ◽  
Hydrogen Embrittlement ◽  
Fracture Surface ◽  
Strain Rate ◽  
Current Density ◽  
Cleavage Fracture ◽  
Hydrogen Gas ◽  
Low Alloy Steel ◽  
Slow Strain Rate Technique ◽  
Pressure Hydrogen

As an alternative method to slow strain rate technique (SSRT) under high-pressure hydrogen gas evaluation, SSRT was performed with a cathodically charged specimen. Cr-Mo low alloy steel with a tensile strength of 1000 MPa grade was selected as a test material. Cathodic charging was performed in 3% NaCl solution and at a current density in the range of 50–600 A/m2. The effect of specimen size on the hydrogen embrittlement properties was evaluated. Relative reduction of area (RRA) values obtained by tests at a cathode current density of 400 A/m2 were equivalent to those performed in hydrogen gas at pressures of 10 to 35 MPa. Fracture surface observations were also performed using scanning electron microscopy (SEM). The quasi-cleavage fracture surface was observed only after rupture of small specimens that were subjected to hydrogen charged tests. It was also necessary for the diameter of the specimen to be small to form the quasi-cleavage fracture surface. The results indicated that to simulate the high-pressure hydrogen gas test, a specimen with a smaller parallel section diameter that is continuously charged until rupture is preferable.

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