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Three types of steels were designed on the basis of GX40CrNiSi25-12 austenitic heat resistant steel by adding different Mn contents (2wt.%, 6wt.%, and 12wt.%). Thermodynamic calculation, microstructure characterization and mechanical property tests were conducted to investigate the effect of Mn addition on the microstructure and mechanical properties of the austenitic heat resistant steel. Results show that the matrix structure in all the three types of steels at room temperature is completely austenite. Carbides NbC and M23C6 precipitate at grain boundaries of austenite matrix. With the increase of Mn content, the number of carbides increases and their distribution becomes more uniform. With the Mn content increases from 1.99% to 12.06%, the ultimate tensile strength, yield strength and elongation increase by 14.6%, 8.0% and 46.3%, respectively. The improvement of the mechanical properties of austenitic steels can be explained by utilizing classic theories of alloy strengthening, including solid solution strengthening, precipitation strengthening, and grain refinement. The increase in alloy strength can be attributed to solid solution strengthening and precipitation strengthening caused by the addition of Mn. The improvement of the plasticity of austenitic steels can be explained from two aspects: grain refinement and homogenization of precipitated phases. [ABSTRACT FROM AUTHOR]

To improve the nitrogen-expanded crystalline structure, tribological and anti-corrosion properties in industrial field, nitrogen atoms were incorporated into 65Mn steel by plasma nitriding. In this study, 65Mn steel was processed using a plasma nitriding method at 600 °C for the improvement of tribocorrosion resistance. The structural evolutions, chemical elements and chemical bonds of obtained nitrided sample were investigated using a scanning electron microscope, electron dispersive spectroscopy and X-ray photoemission spectroscopy, respectively, and the effects of normal load on the coefficient of friction and wear rate in 0.1 mol/L Ca 3 (PO 4) 2 solution were investigated using a reciprocating ball-on-plate wear tester. The polarization and electrochemical impedance spectroscopy of nitrided sample in Ca 3 (PO 4) 2 solutions were conducted using an electrochemical workstation. The results show that the average coefficients of friction of nitrided samples are decreased from 1.047 to 0.420, and the corresponding wear rates are ranging from 6.274 to 11.250 under the normal loads of 2–10 N. The presence of nitrided layer originated from the plasma nitriding process plays roles of the high hardness and excellent tribocorrosion resistance. The wear mechanism is a combination of abrasive wear and adhesive wear, which is attributed to the formation of hard nitrides. Moreover, the corrosion resistance of nitrided sample is improved by the formation of passive film and the band gap energy of Fe 4 N. • The tribocorrosion and electrochemical properties of plasma nitrided 65Mn steel are improved by LR. • The charge transfer resistance of plasma nitrided 65Mn steel is larger compared with the original 65Mn steel. • The tribocorrosion and corrosion models of nitrided 65Mn steel are revealed by the DFT calculation. • The enhancement of wear and corrosion properties is attributed to the Fe 4 N phases with larger band gap energy. [ABSTRACT FROM AUTHOR]

Difficult-to-cut material, i.e., AISI D2 tool steel, has been widely adopted in metalworking industries to manufacture dies for piercing, blanking, drawing and thread rolling due to its excellent wear resistance and non-deforming properties. This article attempts an experimental study to determine the effect of cryogenic coolant (liquid nitrogen) on the grindability of AISI D2 tool steel as work material and its results are compared with the conventional dry and wet grinding methods. The effects of the cryogenic coolant on force components (i.e., tangential force, Ft and normal force, Fn), specific grinding energy (u), force ratio, surface roughness parameters (Ra and Rz) and microstructure were observed. The comparison results indicate a significant reduction in grindability indices such as 64% and 44% in Ft, 54% and 34% in Fn, 46% and 30% in Ra and 40% and 34% in Rz, respectively under cryogenic grinding at higher downfeed as followed to dry and wet grinding. The grinding performance in Ft, Fn, u and Ra was also improved with an increased delivery pressure of the liquid nitrogen (LN2). From the results, it is concluded that cryogenic coolant offers an influential method to improve grinding performance and surface integrity of AISI D2 tool steel. [ABSTRACT FROM AUTHOR]

For sub-sized fatigue specimens made of EUROFER97 in unconstrained contact to ceramic breeder pebbles, exposed to purge gas conditions for different durations in an oven, a chemical surface attack was observed which led to a significant reduction of fatigue lifetime [Aktaa et al., 2020]. To better reproduce the flow of the purge gas in the breeding zone of a Helium-Cooled Pebble Bed Breeding Blanket, the experiment was now repeated by placing the same kind of samples in the helium loop HELOKA HEMAT, where the gas is permanently circulated in a closed circuit, and its water content is controllable. The composition of the gas was monitored with a mass spectrometer and humidity sensors. The samples were exposed to a mixture of helium and 0.1vol% hydrogen at DEMO relevant operating conditions (550 °C, 1.2 bars abs.) for a duration of 8, 16, 32, and 64 days, respectively. New sample holders were designed which allow direct contact of the samples with the gas mixture. A special procedure for the handling of the test section was implemented to avoid contact of the hygroscopic pebbles with air humidity during the preparation phase and during the extraction of the samples from the test rig. The present contribution discusses the various considerations on which the test rig design was based, followed by a description of the experimental setup and preliminary results of the testing campaign. These are similar to the results achieved in the oven experiment. In the future, the loop will be used for tests with up to 200 Pa partial pressure of steam in helium; a mixture that is considered relevant for the DEMO purge gas composition. [ABSTRACT FROM AUTHOR]