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Druga L.,ATTIS | Cojocaru M.,Polytechnic University of Bucharest | Dragomir D.,UTTIS Industries
Metalurgia International | Year: 2013

The paper approaches the evolution of the commercial heat treatments in Romania during 2005-2011. The main changes occurred in the Romanian heat treatments market during this period of time are shown on Romanian geographic areas. A quantitative approaching of the main categories of heat treatments and an estimation of the 2012-2013 evolution in the field is also given. Source


Cojocaru M.,Polytechnic University of Bucharest | Druga L.,Romanian Academy of Sciences | Dragomir D.,UTTIS Industries
UPB Scientific Bulletin, Series B: Chemistry and Materials Science | Year: 2015

The machine parts, fasteners and many other components require high fatigue resistance as well as other properties. The paper aims to determine the influence of nitriding and nitrocarburizing realized at temperatures below the eutectoid transformation temperature in the Fe-N system on the fatigue resistance of 42CrMo4 steel. The effects of performing these thermochemical treatments both on annealed as well as quenched-tempered matrixes on change of fatigue resistance under rotary bending stresses are taken into analysis. It was concluded that, independently of the matrix structural condition, the subsequent sub-critical thermochemical treatments applied after heat treatments, will lead to the fatigue resistance enhance; the nitriding is constantly providing better results than nitrocarburizing performed in ammonia/endogas mixtures. Economic reasons, recommend however the nitrocarburising in atmospheres with high ammonia contents to be applied in order to provide appropriate increase of the fatigue resistance of 42CrMo4 alloy steel components. Source


Dragomir D.,UTTIS Industries | Cojocaru M.O.,UTTIS Industries | Druga L.N.,UTTIS Industries
International Journal of Microstructure and Materials Properties | Year: 2014

The experimental research aimed at mathematical modelling of the carburising process in less common carburising media (paste and urban fuel gas) through explicitness of the mathematical correlations between the chemical-structural and mechanical properties of carburised layers obtained on a low alloy steel (21NiCrMo2) and thermochemical processing parameters. The mathematical models developed for the carbon concentration, hardness and retained austenite in the carburised layer represent the effect of the statistical processing of the experimental results using the experiment programming method and reflect with high probability the real carburising behaviour of the 21NiCrMo2 steel in the specified conditions (temperatures of 900-1000°C and holding times of 30-90 min). These models are very useful tools to those are processing this steel in less common carburising media because they allow the estimation of the carburising results in the specified conditions and the efficiency of the decisions related to the processing parameters and ensure the results reproducibility. Copyright © 2014 Inderscience Enterprises Ltd. Source

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