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Title: Austenitic Nitriding of Iron and Iron-Carbon Alloys
Author: Roe, B. G. F.
ISNI:       0000 0004 2696 3876
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 1979
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Some of the scientific and technological limitations in the field of austenitic thermochemical treatments involving the diffusion of nitrogen have been investigated. New'methods of accurately analysing the nitrogen concentration gradient in surface hardened components have been evolved, using standards based on a controlled nitriding process. As a result of this work, (a) emission spectrometry is now being used as a quality control tool in industrial austenitic carbonitriding and (b) quantitative electronprobe microanalysis for nitrogen is now a powerful tool for physical metallurgical research into nitrogen-rich iron-based systems. In addition, methods of accurately determining the residual ammonia level in heat treatment atmospheres have been evolved using both infra-red gas analysis and gas chromatography. Using the analytical methods just described, an investigation of the iron-carbon-nitrogen system was undertaken. This has resulted in the following information about the system: (a) the diffusion coefficient of nitrogen in austenite is compositionally dependent, in a similar manner to that for carbon in austenite, (b) using existing DY data for very low nitrogen levels, it is possible to estimate nitrogen concentration gradients in surface hardened components, by means of equations based on compositionally dependent diffusion coefficients, (c) Dy, at a fixed nitrogen level, increases with increase in base carbon level of iron-carbon alloys,(d) the iron-carbon-nitrogen ternary system at temperatures in the range 748°C to 845°C has been investigated and the austenite phase field partly delineated, (e) the mechanism of gas void formation in the austenitic nitriding of pure iron, which has in the past restricted its application, has been investigated and shown to be due to overlapping of advancing austenite interfaces in thin sheet material. This has important industrial implications in. ýi. a. relatively thick components can be surface hardened with hi&t: nitrogen levels without fear of blistering due to gas void formation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available