Papers by Keyword: Embrittlement

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Authors: Hyoung Seop Kim, Sun Ig Hong, Min-Seok Sohn
Authors: Yu Hong Yao, Jian Feng Wei, Jiang Nan Liu, Zheng Pin Wang, Yao Hua Jin
Abstract: The microstructure and property of 15Cr1Mo1V steel welded joints after 70,000h service have been researched by OM, SEM, Vickers hardness test and small punch test (SPT). The microstructure of 15Cr1Mo1V steel welded joints after service became coarse and the grain boundary became vague. More carbide particles were observed in welded joints after service. The microhardness gradient curve of 15Cr1Mo1V steel welded joints before service was higher than that after service. The SPT properties gradient curves, including yield strength gradient curve and tensile strength gradient curve by SPT, had the same shape and trend as the microhardness gradient curve before and after service. The SEM fracture appearance of SPT specimens was the characteristic of ductile fracture, irrespectively of before or after service, though the dimple size was a little bit big and deep before service and some cluster particles were observed after service for the ripening of carbides.
Authors: A.F. Armas, Suzanne Degallaix, Gérard Degallaix, S. Hereñú, C. Marinelli, I. Alvarez-Armas
Abstract: The cyclic behavior of type DIN 1.4460 duplex stainless steels in as-received and aged conditions was investigated at room temperature and at 500°C. At room temperature, the aged samples showed embrittlement effects such as loss of toughness and reduction of fatigue life. At 500°C, beneficial effects of the synergy between temperature and strain cycling were observed. It is proposed that at high temperature in the ferrite the strain cycling can decompose the chemical composition fluctuations, promoting a demodulation of the spinodal decomposition formed by aging.
Authors: Ehsan Mahdavi, Mahmoud Mosavi Mashhadi
Abstract: An analytical procedure is developed to design and predict the behavior of a pressure vessel. If a pressure vessel contains hydrogen, it is difficult to predict what will happen in the future. In this study, this is accounted for and the stress intensity factor for mode-Ι is calculated because the main factor controlling mass diffusion, as a driving force, is related to the stress in this mode. Also, it is known that the stress intensity factor depends upon concentration. The main challenge in hydrogen embrittlement is the prediction of crack growth and the estimation of lifetime for a pressure vessel. This paper investigates the effect of hydrogen diffusion upon crack in a pressure vessel by using numerical finite-element simulations. The fracture behavior of the alloy as related to hydrogen embrittlement was also studied. The computational simulations involved sequentially-coupled stress and mass-diffusion concentrations at the crack tip. Although there have been various previous works in this area, most of them have been experimental estimates of hydrogen diffusion. In this paper, we calculate the stress intensity factor by using the finite-element method (FEM) and use mathematical analysis simultaneously. The analytical method alone could not be used because the mass diffusion has special characteristics. That is, the treatment of diffusion is different at each step. We conducted finite-element modeling simulations of the intergranular fracture of alloy X-750 due to hydrogen embrittlement. Sequentially coupled stress and mass diffusion determinations were carried out in order to determine crack tip stresses and hydrogen diffusivity in the crack-tip region. Good qualitative agreement between the FEM modeling and the analysis was observed.
Authors: Gomathy Sasikala, Matcha Nani Babu, Bhyravajoshulu Shashank Dutt, Shreedhar Venugopal
Abstract: This paper summarizes the results of the studies on fracture mechanics characterisation of SS 316L(N) and its welds. The results presented include the fracture toughness and FCG properties of the base and weld materials at different temperatures. Influence of nitrogen content on the base material properties is discussed. Further, the effects of long-term ageing at different temperatures on the fracture and FCG behaviour of the welds are presented and discussed. The weld metal has been subjected to extended thermal ageing, and a detailed study has been undertaken to characterize the (i) FCG properties and (ii) quasistatic J-R curves for the indigenously developed SS 316(N) weld material at both ambient and service temperatures. The ageing conditions covered include the advanced ageing according to the RCC-MR design code, i.e, > 4000 h at 923 K and the low temperature ageing, i.e., 643-823 K the operating range for the SS 316L(N) components in PFBR. The results are discussed in detail in the light of microstructural changes taking place in the weld metal and their influence on the operating micromechanisms.
Authors: V.N. Vilane, R.D. Knutsen, J.E. Westraadt
Abstract: A thermohydrogen process promoting metastable phase decomposition (THP-MD) treatment was performed on wrought Ti-6Al-4V to determine the effects of microstructure evolution on tensile ductility. Tensile ductility was affected by the nature of phase and morphology evolution in which dissolved hydrogen played a key role. Hydrogen reduced the beta transus and stabilised more beta phase at aging/tempering temperature. A reduced beta transus in a similar heat treatment resulted in a bimodal morphology (in non-hydrogenated samples) or a fully acicular morphology (in hydrogenated samples). It also reduced the volume fraction of alpha at aging/tempering temperature which resulted in the extensive enrichment of reduced alpha with aluminium (Al) during tempering. The increased Al content in the reduced alpha promoted ordering of the HCP lattice to the brittle titanium aluminide (Ti3Al) phase. In addition to Ti3Al embrittlement, the acicular morphology of Ti-6Al-4V tempered hexagonal martensite (ά) offers limited resistance to crack propagation. The highest degree of embrittlement was observed in prior hydrogenated samples because of the combined effect of the acicular morphology and Ti3Al embrittlement.
Authors: V. Voyevodin, O. Borodin, V. Bryk, A. Kalchenko, A. Parkhomenko, G. Tolstolutskaya
Abstract: Mechanisms of degradation of physical-mechanical properties of PVI steels during irradiation are studied. Microstructure evidence of influence of irradiation temperature, dose and dose rate on processes of low-temperature swelling and embritllement of pressure vessel internal materials, 18Cr-10Ni-Ti steel, of reactor WWER 1000 are presented. Micro mechanisms of plastic deformation and steel failure in wide range of temperatures and irradiation doses are described. Analysis of influence of subsequent and simultaneous irradiation with beams of gas and heavy ions is carried out for investigation of influence of gaseous impurities that form through transmutation nuclear reactions on defected structure evolution under irradiation.
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