Periodic Reporting for period 1 - BOHNS-TV (Batch Optimization of Process Parameters for Hot Working of High Nitrogen Stainless Steels and Thermodynamic Validation)
Periodo di rendicontazione: 2019-11-16 al 2021-11-15
Against the background of rising market opportunities for high nitrogen stainless steels, nitrogen alloying systems have become increasingly diverse, resulting in incremental hot/cold forming manufacturing costs and introducing environmental concerns. To reduce manufacturing costs and pollution, it is of crucial importance to develop a suitable strategy and a database for fast formulating the hot working process of high nitrogen stainless steels. It is necessary to develop a statistical strategy for batch optimization of the hot working processes for high nitrogen stainless steels as well as for validation of the thermodynamic theories in nitrogen alloying.
The overall objectives are to develop a suitable strategy and a database for fast formulating the processing parameters of nitrogen-containing stainless steels, and develop an integrated model describing the interrelationship of nitrogen content, deformation degree and microstructure, and share with a wider research/manufactory community the databases of working process parameters for a typical selection of nitrogen-containing stainless steels.
The overall objectives are to develop a suitable strategy and a database for fast formulating the processing parameters of nitrogen-containing stainless steels, and develop an integrated model describing the interrelationship of nitrogen content, deformation degree and microstructure, and share with a wider research/manufactory community the databases of working process parameters for a typical selection of nitrogen-containing stainless steels.
A model of nitrogen-containing stainless steel with gradient nitrogen content has been developed and validated with thermodynamic calculation. High-temperature alloying processes for high carbon chromium bearing steels and austenitic stainless steels were developed. The hot working process of the gradient model was explored on austenitic steel grades; the relationship between nitrogen content, processing, and microstructure of nitrogen-containing steels was elucidated; an integrated model describing the interrelationship of nitrogen content, cold deformation degree, microstructure, and SFE was developed.
The proposed methodology and the developed model have proved valuable and in some cases transformative, in the contexts addressed by the project. For practical applications of severe surface deformation, the nitrogen content has its prime role in stabilizing austenite against strain-induced martensite formation, while plastic deformation determines the hardness profile. The important findings, the carbon and nitrogen activities, as imposed by the composition of the gas mixture associated with the applied parameters, have a decisive influence on the microstructural and compositional evolution as well as on the carbon/nitrogen diffusion kinetics, show promising applications on formulating the process of surface engineering for bearing industries. The other key exploitable result is the output of the integrated model describing the interrelationship of nitrogen content, deformation degree and deformation (micro) products.
The proposed methodology and the developed model have proved valuable and in some cases transformative, in the contexts addressed by the project. For practical applications of severe surface deformation, the nitrogen content has its prime role in stabilizing austenite against strain-induced martensite formation, while plastic deformation determines the hardness profile. The important findings, the carbon and nitrogen activities, as imposed by the composition of the gas mixture associated with the applied parameters, have a decisive influence on the microstructural and compositional evolution as well as on the carbon/nitrogen diffusion kinetics, show promising applications on formulating the process of surface engineering for bearing industries. The other key exploitable result is the output of the integrated model describing the interrelationship of nitrogen content, deformation degree and deformation (micro) products.
During the fellowship, we developed a high-temperature gaseous carbonitriding process for high carbon chromium bearing, in particular, the thermodynamics and kinetics of carbonitriding have been revealed, which can relate the changes in carbon/nitrogen activity that were imposed by the applied gas mixtures to the interactions between carbon and nitrogen and microstructure features. Excellent austenite stability and corrosion resistance were achieved in a nitrogen-stabilized austenitic stainless steel synthesized by surface alloying with nitrogen. Severe plastic deformation on the nitrogen-stabilized case can yield an austenitic nano-crystalline surface layer, which provides a promising processing solution for stainless steel bearing operating in a corrosive environment. We have developed the nitrogen content‒strain model by combining the surface nitrogen alloying with plastic deformation. The transition of phase stability and deformation modes in dependence of nitrogen content and plastic strain in a functionally graded austenitic stainless were revealed.
The main outcomes of this project involve high-efficient industrial production technology and enhanced nitrogen alloying thermodynamic theory and my acquired inter-sectoral skills will make me more appealing to employers from different sectors. The training activities I have received during the project will provide me with the independence and professional maturity necessary, which will significantly strengthen my career perspectives, both in academia and in industry.
The main outcomes of this project involve high-efficient industrial production technology and enhanced nitrogen alloying thermodynamic theory and my acquired inter-sectoral skills will make me more appealing to employers from different sectors. The training activities I have received during the project will provide me with the independence and professional maturity necessary, which will significantly strengthen my career perspectives, both in academia and in industry.