NbC-Ausscheidungen in einem PH 15-5 Stahl

Translated title of the contribution: NbC-Precipitates in a PH 15-5 steel

Martina Kaufmann

Research output: ThesisMaster's Thesis

Abstract

Quality assurance and control of processed materials play a significant role, particularly in the aviation industry. One of these materials is the precipitation hardened martensitic stainless-steel PH 15-5. It exhibits a favorable combination of strength and fracture toughness, along with good corrosion properties, making it an important material in various industries, also due to its widespread availability. The favorable mechanical properties arise from a typical combination of multiple strengthening mechanisms for metallic materials. These include grain refinement strengthening, martensitic transformation, and precipitation hardening. In the latter, especially Cu-precipitates in the matrix enhances the strength. Furthermore, primary and secondary carbides exist in the iron matrix. In this process, it is crucial for the carbides to be well-distributed and have a certain size. Due to this PH 15-5 steel is normally remelted via electro slag remelting (ESR) or vacuum arc remelting (VAR). In the case of PH 15-5, niobium carbides (NbC) are dispersed in the martensitic matrix. The size of these carbides depends on the manufacturing process of the raw material and its subsequent processing (e.g., forging). Therefore, the dimensions and quantity of NbC vary depending on the supplier and the diameter of the raw material. Currently, these carbides are detected and measured using scanning electron microscope (SEM)- analysis, and the goal of this work is to establish a correlation between NbC, raw material diameter, and supplier. Additionally, the study aims to determine whether NbC distribution can also be measured using a light optical microscopy (LOM) to minimize investigation costs by avoiding SEM measurements. A total of 7 samples with four different raw material diameters from two suppliers were examined using both LOM and SEM at three positions on the round raw material: the center, half-radius, and edge. The raw material with the highest and lowest carbide content, as well as the most commonly used diameter at voestalpine Böhler Aerospace GmbH & Co KG, were selected for deformation experiments on the dilatometer to investigate the influence of forming and the associated temperature exposure. During the master's thesis, manufacturer-dependent results as well as a position dependence of the NbC distribution within pre-material bars could be determined. In addition, there were significant differences between the LOM and SEM results on the same samples.
Translated title of the contributionNbC-Precipitates in a PH 15-5 steel
Original languageGerman
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Schnitzer, Ronald, Supervisor (internal)
  • Gruber, Christian, Supervisor (external)
Award date22 Mar 2024
Publication statusPublished - 2024

Bibliographical note

embargoed until 06-02-2029

Keywords

  • NbC
  • Precipitates
  • PH 15-5
  • Pre-material characterisation
  • Distribution

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