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This paper analyses the performance of the cryogenically treated En 52 valve steel. This steel is processed with cryogenic treatment by varying parameters. The factors selected for the analysis are soaking period, temperatures of soaking and tempering. The trials derived from design of experiments L9 (33) orthogonal array with Taguchi technique were executed. The mechanical properties are measured for the cryogenic-treated En 52 material as per standard method. The tensile strength and hardness of the treated cryogenic En 52 steel have been selected as the responses. Combination of optimum parameters for cryogenic treatment was achieved from response parameters of Taguchi approach. The analysis of variance was used to recognize the most effective determinant for cryogenic process of En 52 steel. Soaking period was found to be the most influencing factor for both tensile strength and hardness outputs. Soaking temperature was the second-best parameter followed by tempering temperature. [ABSTRACT FROM AUTHOR]

Abstract: The cyclic oxidation behavior of DIN 1.4871 austenitic valve steel was investigated after plasma nitriding. For this, nitriding cycle of 450°C for 7h was carried out. Cyclic oxidation of nitriding samples and base metal were evaluated at 750°C. The results of this investigation indicated that plasma nitriding strongly affected the oxidation resistance of the samples. The nitrided layer which is comprised predominantly a “S” phase, offered superior oxidation resistance. The mechanism of oxidation is explained by outward diffusion of metallic cations (Cr and Fe) and reaction with oxygen on the surface of specimens. This mechanism is confirmed by EDX analyses. [Copyright &y& Elsevier]

This study investigated the optimization of the deep cryogenic treatment for En 52 valve steel using the Taguchi method in combination with the Grey relational analysis. The factors considered for the optimization are the cooling rate, soaking temperature, soaking period, and tempering temperature, each at three different levels. The mechanical properties such as the tensile strength, hardness, and wear resistance were selected as the quality targets. Nine experimental runs based on L9 (34) orthogonal array of the Taguchi method were performed. An optimal parameter combination of the deep cryogenic treatment was obtained via the Grey relational analysis. The analysis of variance is applied to identify the most influential factor and it is found that the soaking period is the most influential factor for the deep cryogenic treatment of En 52 valve steel. A confirmation experiment is performed to verify the optimal result. The results of the confirmation tests prove that the tensile strength, hardness, and wear resistance of the deep cryotreated En 52 valve steel samples improved simultaneously through the optimal combination of the deep cryogenic treatment parameters obtained from the proposed method. The improvement in the tensile strength, hardness, and wear resistance of the deep cryotreated samples at the optimized treatment condition on the samples without deep cryogenic treatment is 7.84, 11.16, and 46.51%, respectively. Through the deep cryogenic treatment the wear resistance of the En 52 valve steel has improved more compared to the other responses. [ABSTRACT FROM AUTHOR]

This experimental study investigates the wear resistance improvement in En 52 and 21-4N valve steels through shallow and deep cryogenic treatment using a reciprocatory friction and wear monitor as per the ASTM standard G-133. It has been observed that the wear resistance of En 52 and 21-4N has improved by 81.15% & 13.49% respectively, due to shallow cryogenic treatment, 86.54% & 22.08% respectively, due to deep cryogenic treatment, when compared to the conventional heat treatment. The microstructural study suggests that the improvement in wear resistance and hardness is attributed to the conversion of retained austenite into martensite, along with precipitation and distribution of the carbides brought in by the cryogenic treatment. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the tribology and cyclic oxidation behavior of plasma nitrided DIN 1.4871 austenitic valve steel were investigated. For this purpose plasma nitriding treatments were carried out in nitrogen and hydrogen with ratio N2/H2: 1/3 at 10 Torr pressure. Nitriding cycles of 400, 450, 500 and 550 °C for 7 h were selected. To remove oxide layer and to enhance diffusion, an effective sputter cleaning procedure was applied in argon and hydrogen gases. The pin-on-disc sliding wear experiments were performed at a load of 6 N and sliding velocity of 0.1 m/s in normal atmosphere under dry condition. Cyclic oxidation tests used to evaluate the oxidation characteristics of the samples consisted of 50 cycles each 30 min at 750 °C. The structure and properties of the samples were examined by optical and scanning electron microscopy (SEM), microhardness measurements and X-ray diffraction. The results indicated plasma nitriding at all temperatures increased the wear resistance of valve steel when sliding against bearing steel. The 550 °C nitrided layer, with CrN, Fe4N and Fe2–3N on the surface, was most effective in improving wear resistance. In the case of cyclic oxidation, the results showed that oxidation resistance depends strongly on nitriding temperature. Nitriding at 450 °C produced a layer of predominantly “S” phase which was more effective in improving the oxidation resistance of valve steel. [Copyright &y& Elsevier]