Enhanced Characterization of Non-Metallic Inclusions for (Sub) Micro Steel Cleanness Evaluations

Alexander Mayerhofer

Research output: ThesisDoctoral Thesis

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Abstract

A central part of research and development in metallurgy are analyses of steels´ microstructure and containing phases. Due to ever-increasing demands on steel cleanness, the evaluation of endogenous and exogenous non-metallic phases with decreasing sizes is more and more important in research and industry. The current thesis deals with the limits and potentials of scanning electron microcopy and energy dispersive spectrometry (SEM/EDS) of non-metallic inclusions (NMI) to handle future demands on inclusion analytics. Comprehensive literature research of different approaches for steel cleanness evaluations and particle analysis reveals SEM/EDS as one of the most essential measurement systems for steel research and secondary metallurgical process development. Constantly improving image resolution and detectors’ accuracy enables a wide range of chemical and morphological information of non-metallic inclusions. A thesis’s main task is to develop sound guidelines for a standardized inclusion detection and instructions for interpreting manual and automated SEM/EDS measurements in steel cleanness demands. Besides the influence of fundamental physical phenomena on the result, data post-processing and interpretation limits are discussed. The Potentials of SEM/EDS analysis are elaborated and summarized, leading to different approaches, guidelines, and innovative evaluation methods. Electron interaction simulations are used to better understand X-ray interaction volumes in non-metallic inclusions. As one result a particle size-depending mathematical model of the theoretical information share of matrix and inclusion composition is established. Comparing simulation of performed analysis and measurements, the potential of digital approaches dealing with metallurgical research problems is shown. A guide to manual point measurements and methods of electrolytic and chemical extraction are described to optimize SEM/EDS analysis experimentally. With the correct application of the procedures shown, composition and morphology evaluations, including matrix element contents in particles down to 300 nm in size, can be realized. First non-metallic inclusion standard samples for metallurgical demands are produced. To determine the iron content falsification at automated inclusion analysis, reference and standard samples are correlated, resulting in 80 % Fe overestimation for 0.3 - 0.5 µm sized inclusions. Additionally, a mathematical correction of matrix interaction based on standard and reference samples has been developed to improve particle analysis’s general output and evaluate particles´ Fe contents at steel cleanness evaluations. Furthermore, in addition to a new morphological categorization method, a size-dependent and direction-independent cluster identification method is developed based on inclusions´ morphology and position data of automated measurements. This methodology of morphological particle evaluation and categorization can be applied to all inclusion classes of all product types. The work concludes with a guideline for proper correction, classification, and typification of typical non-metallic inclusions at steel cleanness evaluations. The particle categorization methodology, defined as objective as possible, can be used to develop, evaluate and interpret particle populations or detailed analyses of specific metallurgical issues. Finally, the application of data evaluation and interpretation is demonstrated using various industrial samples. The interpretable result of measurements is optimized and improved by enhanced data correction and evaluation. The potential of properly evaluated automated analyses is shown and discussed. By basic treatment of SEM/EDS - analytics in metallurgical applications, further knowledge is generated leading to an essential work for future research projects and industry developments.
Translated title of the contributionErweiterte Charakterisierung nichtmetallischer Einschlüsse für (Sub) Mikro Reinheitsgradbestimmungen
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Michelic, Susanne Katharina, Supervisor (internal)
  • Pogatscher, Stefan, Assessor A (internal)
  • Clemens, Helmut, Co-Supervisor (internal)
  • Dippenaar, Rian, Assessor A (external), External person
Publication statusPublished - 2021

Bibliographical note

embargoed until null

Keywords

  • SEM/EDS
  • steel cleanness evaluation
  • electron interaction
  • interaction volume
  • simulation
  • manual SEM/EDS analysis
  • automated SEM/EDS analysis
  • X-ray interaction volume
  • electrolytic extraction
  • sequential chemical extraction
  • twin jet-polishing
  • inclusion standard production
  • NMI standard
  • Fe Quantification
  • matrix interaction quantification
  • sample selection
  • thermodynamics
  • kinetics
  • (Fe
  • Mn)Oxides
  • oxide morphology
  • Matrix Correction
  • morphology categorization
  • M-factor
  • NMI spatial distribution
  • feature evaluation
  • correction
  • classification
  • typification
  • iron correction
  • cluster identification
  • spatial distribution
  • distance distribution
  • influences on experiments
  • phenomena EDS
  • cutting position
  • image
  • artefacts
  • composition evaluation
  • Improvement Potentials
  • inclusion formation
  • simulated automated measurements
  • homogenity
  • heterogenity
  • dissolution
  • inclusion reference production
  • NMI interpretation
  • NMI evaluation
  • data representation

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