Observation of Nb grain boundary segregation and Nb(C,N) precipitation on the austenite grain growth by HT-LSCM

Observation of Nb grain boundary segregation and Nb(C,N) precipitation on the austenite grain growth by HT-LSCM

Brief description of the problem/assignment

In continuous casting and heat treatment processes, the monitoring of the austenite grain size and homogenous size distribution is an important factor for efficient production of high-quality steel. The austenite grain size is a precursor for the final mechanical properties. The right grain size avoids production related issues like hot tearing, creep and embrittlement mechanisms. In order to achieve these objectives, the addition of alloying elements and formation of precipitation are the most common methods.

In the course of this thesis, the austenite grain growth under isothermal annealing conditions and controlled atmospheres will be investigated. The samples will differ in chemical composition to portray the influence of Nb as a GB segregation metal, which inhibits GB movement due to the solute drag effect. Furthermore, Nb tends to form precipitations of Nb(C,N) which will inhibit the GB movement too, due to the Zener Pinning Effect. The impact of each of these influences should be investigated.

Steps of the offered master thesis:

  • Literature review (Grain growth, Solute Drag Effect, Zener Pinning Effect, Nb as alloying element)
  • Laboratory melts for various multicomponent alloys in Fe-C-N-Nb systems
    • Variation in C, N and Nb content
  • Grain growth experiments with 4 varying temperatures
  • Evaluation of austenite grain size distribution and growth, including metallography (digital microscopy)
  • Discussion of the results

Note: The preferred language is English, but German is possible too

Industry Partner

Advisors

Christian Bernhard

Ao.Univ.-Prof. Dipl.-Ing. Dr.mont.
Vice-Head of Institute - Secondary Metallurgy and Casting

Maximilian Kern

Dipl.-Ing.
High Temperature Confocal Microscopy
2022-09-19T08:12:42+02:00
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