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The orientation relationship (OR) between the bcc and fcc phase in the plessite microstructure of the iron meteorites Watson, Agpalilik and Gibeon has been analysed in a scanning electron microscope using electron back-scattered diffraction (EBSD). A very strong OR exists, independently on the analysed plessite type and the observed spreading of single orientation data. The agreement between the experimental orientation distribution and existing models varies for each meteorite. The black plessite in the Agpalilik corresponds to the Nishiyama-Wassermann model whereas the Duplex plessite of the Gibeon meteorite shows an OR close to the Kurdjumov-Sachs model. The Watson meteorite is strongly deformed so that a general OR is difficult to determine due to the blurred experimental orientation distribution.
The hydrogen influence on the microstructure of the austenitic-ferritic Cr22-Ni5-Mo3 stainless steel was investigated. Cathodic hydrogen charging was performed electrochemically from aqueous solution of 0.1M H2SO4 with hydrogen entry promoter addition. The aim of this study was to reveal microstructural changes appearing during the hydrogen charging and particularly to clarify the occurrence of phase transformations induced by hydrogen. The specific changes in both phases of steel were observed. In the ferritic phase, strong increase of dislocation density was noticed. Longer time of hydrogen charging leaded also to the strips and twin plates formation in ferrite phase. In the austenitic phase, the generation of stacking faults, followed by the formation of α' martensite was remarked.
Fatigue crack propagation investigations have been performed in austenitic-ferritic duplex stainless steel H22N5M3 in air and during hydrogen charging, using various frequencies of loading. Strong differences of crack propagation velocity depending on the test conditions were noticed. Lower frequency with applied hydrogen charging led to the huge increase of crack propagation velocity compared to the tests performed in air. To understand such a behaviour in each case and characterize crack mode, the samples were observed using electron back-scattered diffraction (EBSD). It was shown that in air, the fatigue crack propagation involved plastic deformation and the resulting cracks had ductile character. The presence of hydrogen led to more brittle mode of cracking. This effect was also connected with frequency of loading: lower frequency, which assured longer time for hydrogen-crack tip interaction, resulted in the highest crack propagation velocity and the brittle cracking mode with lower amount of plastic deformation. The performed observations indicated that the path of the crack went mostly transgranularly through both austenite and ferrite phases. Phase and grain boundaries were not the preferred paths for crack propagation.
Interphase boundary characterization in duplex steel and iron meteorites using EBSD technique
(2006)
The properties of materials are mainly described by the orientation distribution of the crystalline phases in a material. Beside the so considered anisotropy also the grain as well as phase boundaries are of extreme importance for a whole string of properties, e.g. the strength of a material. On the example of the interface between fcc and bcc iron the discovered and derived models are discussed. Although the common models are based on the crystal lattice description, the atomic configuration on the interface is analysed. Since experimentally a wide spread of orientations data appears the consideration of the frequency distribution is proposed to find at least the main orientation relationship between fcc and bcc. High-indexed pole figures as well as the Euler subspace are introduced in order to increase the accuracy and to compare different measurements. For the sake of simplicity EBSD measurements on iron meteorites are used since they commonly consist of large fcc single crystals which transformed to a low and very specific number of bcc grains. In special cases the described procedure could also be used for steels.
Downsizing (power-to-weight ratio) and higher speeds lead to a rise in Hertzian contact pressures in combination with an increase in surface or oil temperatures. Under such conditions, commonly used bearing steels, such as 100Cr6, reach their limits, creating a demand for alternative slip-rolling resistant steel alloys. The present work therefore compares the slip-rolling performance of various steel types with Maraging- and PM-type steel alloys such as e.g. CSS-42L™, ASP2012, BIMAX42+, in the Hertzian contact pressure range up to P0max of 4 GPa. Through-hardened 100Cr6H (AISI 52100), case-hardened 20MnCr5 (AISI 5120H) and nitrogen alloyed Croni-dur30 (AMS 5898) still compete in terms of slip-rolling and wear resistance and load carrying capacity, whereas Maraging- and PM-type steel alloys offer superior strength and toughness properties.
The metal magnetic memory (MMM) technique relies on the measurement of stress-induced self-magnetic leakage fields (SMLFs) at the stress concentration zones (SCZs) of ferromagnetic materials during mechanical loading. However, there is an associated change in geometry of the specimen along with the stress due to plastic deformation. This paper presents a three-dimensional finite element (3D-FE) analysis of the stress-induced geometry effect on SMLFs in notched specimens during tensile deformation. The tangential (Hx) and normal (Hy) components of the SMLF signals have been predicted from the deformed specimens caused by different levels of tensile stress. Key parameters from the SMLF signals are determined for the possible estimation of damage in the specimen under tension. Studies reveal that the stress-induced geometry effect has a great influence (about 20%) on the SMLF signals, especially in the plastic deformation stage. The results show that the peak amplitude could be used for the estimation of different deformation stages under tension. The study also reveals that the SMLF signal is influenced by the thickness of the tensile specimen. The model-predicted thickness profile has also been experimentally validated.
Properties of pipe steels for CCS (carbon capture and storage) technology require resistance against the corrosive environment of a potential CCS-site (heat, pressure, salinity of the aquifer, CO2-partial pressure). The influence of austenitzing in heat treatment routines of two different injection pipe Steels (1.4034, X46Cr13 and 1.4021, X20Cr13) was evaluated. Steel coupons were austenitized at different temperatures (900- 1050 °C) for different lengths of time (30-90 min) before quenching and annealing prior to long term corrosion experiments (60°C, 100 bar, artificial brine close to a CCS-site in the Northern German Basin, Germany). In general, fewer pits are found on X46Cr13. Comparing steels with 13% chromium each the higher carbon content of X46Cr13 (0.46% C) results in a lower number of pits compared to X20Cr13 (0.20% C). It is found that neither the carbon content of the steels nor austenitizing temperature has much influence, but local corrosion behaviour is most susceptible towards austenitzing time.
Properties of pipe steels for CCS (carbon capture and storage) technology require resistance against the corrosive environment of a potential CCS-site (heat, pressure, salinity of the aquifer, CO2-partial pressure). The influence of austenitzing in heat treatment routines of two different injection pipe steels (1.4034, X46Cr13 and 1.4021, X20Cr13) was evaluated. Steel coupons were austenitized at different temperatures (900-1050 °C) for different lengths of time (30-90 min) before quenching and annealing prior to long term corrosion experiments (60°C, 100 bar, artificial brine close to a CCS-site in the Northern German Basin, Germany). In general, fewer pits are found on X46Cr13. Comparing steels with 13% chromium each the higher carbon content of X46Cr13 (0.46% C) results in a lower number of pits compared to X20Cr13 (0.20% C). It is found that neither the carbon content of the steels nor austenitizing temperature has much influence, but local corrosion behaviour is most susceptible towards austenitzing time.