Search

The role of vanadium content in hydrogen diffusion behaviour in X80 pipeline steel has been investigated. The results show that the hydrogen diffusion coefficient decreases from 1.54 × 10−6 cm2 s−1 in 1# steel with 0.03 wt-% vanadium to 9.97 × 10−7 cm2 s−1 in 3# steel with 0.14 wt-% vanadium due to the increase in irreversible and reversible traps. With the increase in vanadium content, more vanadium carbides precipitate in tested steels. The length (or number) of the low angle grain boundaries and special grain boundaries increase because of grain refinement, making the number of reversible traps increase. The dynamic condition of diffusible hydrogen in 3# tested steel with the largest number of hydrogen traps is the weakest. To weaken hydrogen-induced cracking dynamic condition, it is recommended to add 0.14 wt-% vanadium to X80 pipeline steel. [ABSTRACT FROM AUTHOR]

Reversible temper embrittlement has been frequently observed in many different low alloy steels serving at high temperature, e.g. order of 500 °C. This type of embrittlement can change the brittle transgranular fracture mode to intergranular decohesion with subsequent change in fracture stress and fracture toughness. The present paper deals with the influence of the prior austenite grain size and isothermal aging time on the degree of embrittlement of 2.25Cr-1Mo steel, which is very popular for its use in power generating and other petrochemical industries. In this research work, the specimens of 2.25Cr-1Mo steel were treated in three different austenitizing temperatures along with different isothermal embrittling time periods. Then the induced degree of embrittlement was characterized by the fracture stress values at -196 °C and area fraction of intergranular failure. The outcome of the experimental results shows that the increase in austenite grain size and/or isothermal embrittling time severely weakens the grain boundary cohesive strength leading to brittle intergranular failures and thus to a greater degree of temper embrittlement. [ABSTRACT FROM AUTHOR]

The influence of bulk microstructure (grain size distribution, grain boundary length) on the oxygen transport properties of permeation membranes has been investigated. For this purpose, La0.5Sr0.5FeO3-δ samples with different microstructures were prepared by varying sintering time and temperature. Average grain sizes, which ranged from 0.20 to 1.43 μm, were determined by SEM analysis. The oxygen transport properties of the samples were characterised by permeation measurements as a function of temperature in an air/argon oxygen partial pressure gradient. The fluxes presented a change in activation energy, which was attributed to a change in the rate limiting step, from bulk diffusion at lower temperature (< 850°C) to surface limitation at higher temperature (> 900°C). Only transport through the bulk was influenced by the microstructure, with the highest flux for the smallest grains. At 800°C, the fluxes were respectively 0.06, 0.03 and 0.01 μmol cm-2 s-1 through ≈ 1 mm thick samples with average grain sizes of 0.20, 0.63 and 1.43 μm respectively. This would imply that oxygen transport occurs more rapidly along grain boundaries than through the bulk. Grain boundary structure and composition were analysed by TEM. [ABSTRACT FROM AUTHOR]

• Changing grid from triangular into hex improves boundary reconstruction accuracy. • Marching squares algorithm is 5 times more accurate than a simple square grid. • Average error values may be used as correction coefficients. This paper presents methods to calculate the length overestimation errors which are being made when approximating a discrete line by edges of triangular tessellation and marching squares algorithm. The maximum error and its average value are 15.47 % and 10.27 % for the triangular tessellation, while for the marching squares approach they are 8.24 % and 5.49 %, respectively. Mathematical calculations were compared with experimental results obtained by the Electron Backscatter Diffraction technique showing their usefulness as correction coefficients to obtain more accurate boundary length estimates. [ABSTRACT FROM AUTHOR]