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A STUDY OF SELECTIVE SURFACE AND INTERNAL OXIDATION OF ADVANCED HIGH STRENGTH STEEL GRADES

Chen, Meng-Hsien
http://rave.ohiolink.edu/etdc/view?acc_num=case1401380512

Abstract Details

2014, Doctor of Philosophy, Case Western Reserve University, Materials Science and Engineering.
Advanced high-strength steels (AHSS) have been widely used in automotive industry to improve safety and fuel economy. However, unintentional selective oxidation of alloying elements of AHSS during the thermal cycles employed on a continuous galvanizing line (CGL) complicates the coating process. Amongst the observed effects, external oxides can cause incomplete reactive wetting, resulting in bare spot defects in the zinc coating. This study focuses on developing and validating “oxidation maps” to define regions of selective oxidation for alloying elements in PO2-T space. Oxidation maps use CALPHAD method in combination with the Wagner’s model to determine regions where no oxidation, internal oxidation or external oxidation will occur. Experiments were carried out in an attempt to validate the predictions. Three types of AHSS grade steels, with variation in Mn, Si, Al contents, were used for experiments to validate the oxidation maps. Samples of selected steels were subjected to four different simulated CGL thermal cycles with two heating rates and two hold times, that bracket much of the range expected in industrial practice. Experiments were also undertaken for two of the steels under much higher dew point annealing conditions to probe the predicted boundary between external and internal oxidation. Samples were characterized by SEM, AES, XPS, and TEM to determine the oxide phases as well as the oxidation modes. Analysis results demonstrated that the formation of oxide phase on or in each steel is consistent with the thermodynamic modeling. A calculated Ellingham diagram clearly illustrates the formation sequence of oxide phases for the steels studied. For the prediction of oxidation mode, the oxidation maps are generally consistent with the analysis result. Inconsistency was observed only in one circumstance, and this is attributed to the highly heterogeneous surface caused by cold rolling. Otherwise, a kinetic model was studied to simulate the amount of atoms diffusing across steel surface and incorporated into the oxide(s). The number of oxide particles of a given size formed on a selected area was also consistent with predictions.
James McGuffin-Cawley (Advisor)
Mark De Guire (Committee Member)
Frank Ernst (Committee Member)
Jay Mann, Jr. (Committee Member)
376 p.
Automotive Materials; Engineering; Materials Science; Metallurgy
CALPHAD; AHSS; advanced high strength steel; selective oxidation; oxidation map; CGL; galvanizing

Recommended Citations

Citations

  • Chen, M.-H. (2014). A STUDY OF SELECTIVE SURFACE AND INTERNAL OXIDATION OF ADVANCED HIGH STRENGTH STEEL GRADES [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1401380512

    APA Style (7th edition)

  • Chen, Meng-Hsien. A STUDY OF SELECTIVE SURFACE AND INTERNAL OXIDATION OF ADVANCED HIGH STRENGTH STEEL GRADES. 2014. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1401380512.

    MLA Style (8th edition)

  • Chen, Meng-Hsien. "A STUDY OF SELECTIVE SURFACE AND INTERNAL OXIDATION OF ADVANCED HIGH STRENGTH STEEL GRADES." Doctoral dissertation, Case Western Reserve University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1401380512

    Chicago Manual of Style (17th edition)

case1401380512
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© 2014, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.
Release 3.2.12