TY - THES

T1 - Microscopical and sub-microscopical characterization of a heavy plate made of a micro-alloyed HSLA steel

AU - Felfer, Peter

N1 - embargoed until null

PY - 2008

Y1 - 2008

N2 - In this diploma thesis, the microstructure and the atomic assembly of a micro-alloyed HSLA trial heavy plate has been investigated and compared to the materials mechanical behavior. This has been conducted in thermo-mechanical rolling condition and four additional heat treatment conditions. The aim was to find the influence of austenite conditioning (''pancaking''), annealing (precipitation hardening, etc.) and ''normalizing'' (slow air cooling) on the material properties and microstructure. The micro- and sub-micro structures have been investigated using optical microscopy (LM), electron microscopy (SEM, TEM, HRTEM) and atom probe analysis (3DAP). An etchant that is suitable for distinguishing the individual constituents in the optical microscope has been found. Atom probe analysis revealed the local enrichment and general distribution of the chemical elements in shipping condition. The behaviour of various elements during annealing has been investigated. The evolution of precipitations during annealing has been traced by X-ray diffraction (XRD). The chemical composition of the middle segregation zone has been studied using a laser assisted local electrode atom probe (LEAP), a method for site-specific preparation in steel materials has been developed for this purpose. The measured mechanical properties have been compared to the corresponding values, calculated based on microstructural features.

AB - In this diploma thesis, the microstructure and the atomic assembly of a micro-alloyed HSLA trial heavy plate has been investigated and compared to the materials mechanical behavior. This has been conducted in thermo-mechanical rolling condition and four additional heat treatment conditions. The aim was to find the influence of austenite conditioning (''pancaking''), annealing (precipitation hardening, etc.) and ''normalizing'' (slow air cooling) on the material properties and microstructure. The micro- and sub-micro structures have been investigated using optical microscopy (LM), electron microscopy (SEM, TEM, HRTEM) and atom probe analysis (3DAP). An etchant that is suitable for distinguishing the individual constituents in the optical microscope has been found. Atom probe analysis revealed the local enrichment and general distribution of the chemical elements in shipping condition. The behaviour of various elements during annealing has been investigated. The evolution of precipitations during annealing has been traced by X-ray diffraction (XRD). The chemical composition of the middle segregation zone has been studied using a laser assisted local electrode atom probe (LEAP), a method for site-specific preparation in steel materials has been developed for this purpose. The measured mechanical properties have been compared to the corresponding values, calculated based on microstructural features.

KW - HSLA

KW - heavy plate micro-alloy electron microscopy atom probe phase characterization segregation precipitation vanadium carbide seperations middle segregation

KW - site-specific sample preparation local electrode atom probe

KW - HSLA

KW - Grobblech mikrolegieren Elektronenmikroskopie Atomsonde Phasencharakterisierung Seigerung Ausscheidungen Vanadiumkarbid Seperations Mittenseigerung Zielpräparation Atomsonde Lokalelektrodenatomsonde

M3 - Diploma Thesis

ER -