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[en] The damping capacity of high manganese austenitic stainless steel with a two phase mixed structure of deformation-induced martensite and reversed austenite was studied. Reversed austenite with an ultra-fine grain size of less than 0.2 μm was obtained by reversion treatment. The two phase structure of deformation-induced martensite and reversed austenite was obtained by annealing treatment at a range of 500-700 °C and various times in cold rolled high manganese austenitic stainless steel. The damping capacity increased with an increasing annealing temperature and time. In high manganese stainless steel with the two phase mixed structure of martensite and austenite, the damping capacity decreased with an increasing volume fraction of deformation-induced martensite. Thus, the damping capacity was strongly affected by deformation-induced martensite. The results confirmed that austenitic stainless steel with a good combination of strength and damping capacity was obtained from the two phase mixed structure of austenite and martensite.
[en] After recalling physico-chemical properties of austenitic steels and permeability solubility and diffusion of hydrogen in metals, mechanical properties of hydrogen-charged austenite are examined and parameters of variation of these properties: testing temperature, rate of plastic deformation, internal hydrogen concentration, austenite grain size, equivalent nickel content, sensitising of the austenite, influence of the different phases
[fr]Apres avoir rappele les proprietes physico-chimiques des aciers austenitiques, ainsi que la permeabilite, la solubilite et la diffusion de l'hydrogene dans les metaux, on examine les caracteristiques mecaniques de l'austenite chargee en hydrogene et les parametres de variation de ces caracteristiques: temperature d'essai, vitesse de deformation plastique, concentration en hydrogene interne, diametre du grain d'austenite, teneur equivalente en nickel, sensibilisation de l'austenite, influence des differentes phases
[en] An introduction of the principles of the Moessbauer effect, and its utilization in materials science as Moessbauer spectroscopy is given. A special metallurgical application of the Moessbauer spectroscopy in phase analytical studies, the analysis of residual austenite phases in hardened steels is presented. (R.P.) 25 refs.; 18 figs
[en] Nanoindentation has been used to study the effects of thermal-aging and hydrogen on the mechanical property of the metastable austenitic stainless steel. Thermal-aging at 473 K decreases the nanohardness of austenite, while it increases the nanohardness of strain-induced ɑ′ martensite. Hydrogen-charging at 473 K increases the nanohardness of austenite, while it decreases the nanohardness of strain-induced ɑ′ martensite. The opposite effect on austenite and ɑ′ martensite is first found in the same pre-strained sample. This abnormal evolution behavior of hardness can be attributed to the interaction between dislocation and solute atoms (carbon and hydrogen). Carbon atoms are difficult to move and redistribute in austenite compared with ɑ′ martensite. Therefore, the difference in the diffusivity of solute atoms between austenite and ɑ′ martensite may result in the change of hardness. (paper)
[en] Austenite-martensite transformation influence on the dimensional stability of a new experimental tool steel alloyed with niobium (0.08% wt.) and vanadium (0.12% wt.) has been studied. The dimensional stability of this new steel was compared with the dimensional stability of commercial steel, after and before two thermal treatments, T1 (860 degree centigrade) and T2 (900 degree centigrade). The thermal treatments consisted on heating and cooling, at 1 atmosphere of pressure, in N2 atmosphere furnace, following by heating in a conventional furnace at 180 degree centigrade during 1 hour. Initially, the experimental steel composition and Ac1 and Ac3 transformation temperatures were determined by glow-discharge luminescence (GDL) and dilatometric tests, respectively, in order to select the austenization temperatures of T1 and T2 treatments. After hardness measurement, the microstructure of both steels was characterized by X-Ray Diffraction (XRD) and optical metallography, before and after of T1 and T2 thermal treatments. Finally, longitudinal and angular dimensional stability analyses were realized for both commercial and experimental steels. After a contrastive hypothesis analysis, the results showed that the longitudinal relative variation of the experimental steel calculated was around 0.2% and the angular relative variation was not significant. (Author)
[en] Medium Mn steel (MMnS) is the good choice for car manufacturers to meet the requirements of reducing the weight of automobiles. Quenching and Partitioning (Q and P) process is an effective method to stabilize austenite in advanced steel, thus prompting the comprehensive mechanical properties of advanced steel. In this article, the Q and P process is applied to the MMnS to explore potential mechanical properties. The effect of austenitizing temperature, one of the significant parameters of Q and P process, on the microstructure and mechanical properties of MMnS was investigated. According to microstructural analyse results, all of the MMnS specimens processed by Q and P treatment with different austenitizing temperatures could obtain multi-phase microstructure, including α′-martensite, ε-martensite and austenite. Furthermore, the highest volume fraction of austenite was observed in the MMnS processed by Q and P treatment at the austenitizing temperature of 920 °C. Due to the facilitated transformation-induced plasticity effect resulted from the high volume fraction of austenite with the austenitizing temperature of 920 °C, the MMnS obtained the high strength, high plasticity and sustaining work-hardening rate. (paper)
[en] This investigation highlights the creep deformation and rupture behaviour of Nb and Cu added 18Cr-8Ni austenitic stainless steel and compared with those of commercial 18Cr-8Ni steel. Uni-axial creep tests were performed at (288–320) MPa/600 °C and (80–110) MPa/750 °C on Nb and Cu added 18Cr-8Ni austenitic stainless steel. Accelerated creep tests predicted that creep characteristic of the alloy was insignificant or anelastic type below the stress level of ∼166 MPa at 600 °C and ∼57 MPa at 750 °C. True creep exponent value of 8 at (288–320) MPa/600 °C and 4 at (80–110) MPa/750 °C, exhibited that the alloy followed high temperature climb controlled power law creep in the specified creep test condition. The alloy was more creep brittle in nature than that of commercial 18Cr-8Ni austenitic stainless steel. The brittleness was attributed to the presence of Nb(C, N), nano-sized Cu precipitation along the transgranular region and occurrence of Cr23C6 secondary carbides along the grain boundaries. Fractographic features revealed that the alloy was prone to intergranular fracture due to creep cavitation and their linkages. (paper)
[en] The precipitation behavior of copper-rich phase in an austenitic stainless steel and the interface structure between the precipitates and the matrix have been investigated combining transmission electron microscopy and coarsening analysis. The fine dispersed Cu precipitates were spherical and highly stable in the austenite matrix, with the size being only 32 nm in diameter even after a long time 10,000 h aging at 650 °C. The average size of Cu precipitate was increasing with aging time, as predicted by the Lifshitz–Slyozov–Wagner theory. The coherent relationship between the precipitates and the matrix was preserved during the whole aging process, even at the later stage. The interfacial energy of Cu in the austenitic matrix has been independently derived from the data on coarsening experiment based on two kinds of approximations: γ-Fe and Fe–18Cr–9Ni–3Cu matrix were considered separately instead of complex austenite in this study. It was 0.086 J/m2 for Cu/γ-Fe and 0.017 J/m2 for Cu/Fe–18Cr–9Ni–3Cu. Both values are satisfied with the range of coherent interfacial energy. The coherent interfacial structure and highly stable microstructure play a key role on strengthening materials
[en] The paper treats studies of TIG gas-shielded arc welding using pure nitrogen, N2+ 5-20 % Ar gas mixtures and N2 + 2-10%H2 gas mixtures. A weld root shielding was provided by nitrogen gas.Welding in N2 requires by 40%lower welding current than welding in argon. The study showed that porosity was an issue due to over alloying of N2 in the weld pool; it can, however, be avoided with adequate welding parameters, particularly sufficiently high welding speed and controlled low heat input. The microstructure of all-weld metal is fully austenitic (γ). Hydrogen reduces nitrogen solubility in the weld pool and produces an austenitic-ferritic (γ+δ) microstructure. Titanium increases nitrogen solubility in the weld pool and strongly reacts with nitrogen. Consequently, there is a high fraction of TiN inclusions in the weld metal. (Author) 25 refs.
[en] Instrumented microindentation (IM) on two Ni–Ti shape memory alloys (SMAs), where one is austenitic and the other is martensitic at room temperature, were conducted from 40 to 150 ° C. Results show that the depth and work recovery ratios, ηd and ηw respectively, are complementary to each other. While ηd decreases gradually with temperature for austenite, it drops markedly for the martensite in the martensite-to-austenite transformation regime. These results affirm the utility of IM for characterizing SMAs. (technical note)