Avoidance of detrimental nitrides in duplex stainless steels

Purpose and goal

The purposes and goals of this pre-study were fulfilled: The metallography and computational thermodynamics make it possible to give guidelines for heat treatments to achieve optimum properties. With the results, precipitation sequences and the connection between rapid phase transformations during the cooling have been studied experimentally and also predicted. Methods and tools for quantification of nitrides have been studied and developed in the project which has led to an increased understanding of possibilities and limitations with nitrogen as an alloying element.

Results and expected effects

This pre-study has successfully highlighted the complexity surrounding accuracy and precision when quantifying nitrides and has contributed with new and well-defined experiments & metallography and advanced calculations. With the organisation of the workshop good opportunities were given for open and fruitful discussions between materials producers, end users and certification bodies. The participants of the project were also given the possibility to verify and evaluate boundaries on a laboratory scale and put them into context of their production facilities.

Approach and implementation

This pre-study was run by a project committee with representatives from the participating companies and regular reporting to a steering group from Jernkontoret. A total of nine meetings were held, start-up on August 7th 2014 and final meeting on August 12th 2015, with Jan Y. Jonsson from Outokumpu Stainless as chairman. The project work was successful and efficient by making use of established knowledge on carbides as well as results, methods & models on nitrides from the previous project PREDUP within the Steel research programme 2007-2012.