Avoidance of sigma phase in high performance stainless steels

Purpose and goal

This project aimed to develop a state-of-the-art modeling tool to identify, analyze and eventually eradicate the factors concerning the composition of alloying elements that result in the formation of sigma phase. The model has been developed and tested for a range of alloying element compositions and thermal history. Within the project we have identified the elements and the conditions that support the formation of sigma phase.

Expected results and effects

The project has resulted in developing a model that offers predictive capabilities for production process parameters of high performance stainless steels in terms of i) composition (Cr, Mo, Ni, N, Al, Mn) and ii) thermal history to avoid precipitation of sigma phase. The use of a realistic and efficient modeling tool will give production excellence both technically and economically to Swedish stainless steel industries by having faster development cycles and by having the possibility to offer improved products to the world market with a wide range of applications.

Planned approach and implementation

The project was divided into three stages. The first stage comprised the development of a phase-field model coupled to the CALPHAD databases. In the second stage the developed model was verified against the experimental data from literature and from experiments performed within the project. In the final stage, a number of simulations were performed to analyze the effect of different alloying elements on the precipitation of sigma phase and a strategy for the alloying elements was developed that would reduce the possibility of sigma phase precipitation in the given SDSS alloy.