Master thesis: Numerical modeling of homogenization in duplex stainless ste

Forskningsinstitutet Swerim erbjuder tillämpad forskning inom gruvteknik, processmetallurgi, material- och produktionsteknik, främst för gruv-, stål- och metallindustrin. Swerim har 190 medarbetare på två orter i Sverige - Luleå och Stockholm. Institutet är en sammanslagning av Swerea MEFOS och verksamheterna material- och processutveckling samt produktionsteknik vid Swerea KIMAB.

Background

Detrimental phases are known to form in duplex stainless steels when they are exposed to temperatures between 600oC and 1000oC for a certain period of time. These phases include s, ? and p etc., with s being the most detrimental one. Due to its brittle nature, the formation of s phase has always been a serious concern for both the manufacturers and the end users since it causes deterioration of certain properties like impact toughness and corrosion resistance. Homogenization is one of the treatments that is used for complete dissolution of sigma phase in duplex stainless steels. In this method, the material is heat treated at elevated temperature for a certain period of time to completely dissolve sigma phase and homogenize any gradients in chemical composition that may have formed due to reminiscence of sigma phase.

The intricacy of such problems due to their complex underlying physical phenomena demands the use of advanced numerical methods to model them. One such tool that is now commonly used for material research and can handle realistic microstructures is the so-called phase-field (PF) method, which is an FEM based modeling technique to model phase transformations in 2D and 3D. A generic PF model has been developed at Swerim AB and KTH, to simulate dissolution of sigma phase in a simple microstructure and is coupled to the Thermo-Calc databases to retrieve thermodynamic and kinetic quantities in real time (see figure 1). The challenge is, however, to perform efficient and trustworthy large scale simulations on complicated microstructures.

Task description
The aim of this thesis project is to improve the existing phase-field model to simulate the homogenization process in commercial alloys and validate it in order to determine the time needed to completely homogenize a material with prior sigma phase in it. Furthermore, the developed model will be applied to different commercial materials and realistic microstructures in order to determine their behavior during and after homogenization. 

Suitable background

* ? Master of Science program in Solid Mechanics, Computer Science or similar.
* ? Proficient in numerical analysis and programming languages like C/C++, Fortran etc.
* ? Some background knowledge of Materials Science is a plus.


Figure 1: Dissolution of sigma phase (green) in duplex stainless steel with austenite (blue) and ferrite (red) phases.

Location
The work will be carried out at Swerim in Stockholm.

Contact persons
Amer Malik, Senior Researcher, amer.malik@swerim.se, 08-545 274 50
Joakim Odqvist, Associate Professor (KTH), odqvist@kth.se