Numerical Simulations of Concentration-Depth Profiles of Carbon and Nitrogen in Austenitic Stainless Steel Based Upon Highly Concentration Dependent Diffusivities
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Case Western Reserve University School of Graduate Studies / OhioLINK
2011
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=case1295638232 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-case12956382322021-08-03T05:33:51Z Numerical Simulations of Concentration-Depth Profiles of Carbon and Nitrogen in Austenitic Stainless Steel Based Upon Highly Concentration Dependent Diffusivities Gu, Xiaoting Materials Science Numerical Simulation Finite Difference Method Concentration Dependent Diffusion Stainless Steel Carburization <p>The typical Swagelok procedure of the low temperature carburization conducted for approximately 40 hours at 450°C can produce an interstitially hardened case in AISI 316L stainless steel with a surface carbon concentration of 10 to 15 at% and a penetration depth of 20 to 25µm. The concentration-depth profile of carbon obtained after such a treatment exhibits a very concave shape that greatly deviates from the profile defined by an error-function solution to Fick’s second law. This result provides a unique opportunity for studying the concentration dependence of the carbon diffusivity in austenite. </p><p>An extensive literature review focusing on the concentration dependence of the carbon diffusivity in austenite was performed. The model proposed by Asimow provides a very satisfactory description for the concentration dependence of the carbon diffusivity in AISI 316L stainless steel during low temperature carburization. This result indicates that the concentration-enhanced diffusion of carbon in austenite is most likely because the lattice expansion induced by carbon in solution in an austenite matrix greatly decreases the activation energy associated with the diffusion of carbon. </p><p>A numerical model for a one-dimensional diffusion in a semi-infinite system was designed using CALPHAD-based thermodynamic modeling and a fully-implicit finite difference algorithm. The numerical simulation based upon Asimow’s analytical model generated the concentration-depth profile of carbon in AISI 316L stainless steel carburized by the typical Swagelok procedure and provided an excellent agreement with the experimental results obtained from surface chemical analysis of X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). The simulation parameters, including the activity of carbon in treatment atmosphere, the maximum possible solubility of carbon, and the mass transfer coefficient at the gas-metal interface, were thoroughly discussed. </p><p>A similar numerical simulation was performed to reproduce the unusual carbon concentration-depth profile observed during a plasma carbonitriding process. The accumulation of carbon in front of the nitrogen diffusion zone was explained by the classical diffusion theory, recognizing the concentration dependence of both carbon and nitrogen diffusivities in stainless steels. The large nitrogen concentration introduced by plasma nitridation provides a significant driving force for carbon diffusion. Nitrogen greatly increases the chemical potential of carbon that corresponds to a given carbon concentration. The chemical potential gradient of carbon generated during the plasma nitridation process provides the driving force for the diffusion of carbon.</p> 2011-03-16 English text Case Western Reserve University School of Graduate Studies / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=case1295638232 http://rave.ohiolink.edu/etdc/view?acc_num=case1295638232 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |
| collection |
NDLTD |
| language |
English |
| sources |
NDLTD |
| topic |
Materials Science Numerical Simulation Finite Difference Method Concentration Dependent Diffusion Stainless Steel Carburization |
| spellingShingle |
Materials Science Numerical Simulation Finite Difference Method Concentration Dependent Diffusion Stainless Steel Carburization Gu, Xiaoting Numerical Simulations of Concentration-Depth Profiles of Carbon and Nitrogen in Austenitic Stainless Steel Based Upon Highly Concentration Dependent Diffusivities |
| author |
Gu, Xiaoting |
| author_facet |
Gu, Xiaoting |
| author_sort |
Gu, Xiaoting |
| title |
Numerical Simulations of Concentration-Depth Profiles of Carbon and Nitrogen in Austenitic Stainless Steel Based Upon Highly Concentration Dependent Diffusivities |
| title_short |
Numerical Simulations of Concentration-Depth Profiles of Carbon and Nitrogen in Austenitic Stainless Steel Based Upon Highly Concentration Dependent Diffusivities |
| title_full |
Numerical Simulations of Concentration-Depth Profiles of Carbon and Nitrogen in Austenitic Stainless Steel Based Upon Highly Concentration Dependent Diffusivities |
| title_fullStr |
Numerical Simulations of Concentration-Depth Profiles of Carbon and Nitrogen in Austenitic Stainless Steel Based Upon Highly Concentration Dependent Diffusivities |
| title_full_unstemmed |
Numerical Simulations of Concentration-Depth Profiles of Carbon and Nitrogen in Austenitic Stainless Steel Based Upon Highly Concentration Dependent Diffusivities |
| title_sort |
numerical simulations of concentration-depth profiles of carbon and nitrogen in austenitic stainless steel based upon highly concentration dependent diffusivities |
| publisher |
Case Western Reserve University School of Graduate Studies / OhioLINK |
| publishDate |
2011 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=case1295638232 |
| work_keys_str_mv |
AT guxiaoting numericalsimulationsofconcentrationdepthprofilesofcarbonandnitrogeninausteniticstainlesssteelbaseduponhighlyconcentrationdependentdiffusivities |
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