Bainitic hardenability - effective use of expensive and strategically sensitive alloying elements in high strength steels (BainHard)

The main objective of this project was to determine the bainitic hardenability for alloying elements, both singly and in combination and develop a bainitic hardenability model for use in steel design to ensure optimum use of expensive or strategically sensitive additions in high and ultra-high strength bainitic strip, plate and long products. The work has been concentrated on a low carbon base alloy with the composition of 0.05wt-% C, 1.5wt-% Mn, 0.3wt-% Si and small amounts of Cu, Ni, Cr, V, Ti and Mo where the different alloying systems were divided among the partners where test materials were made based on reference material manufactured by SZMF. The work was progressing in steps first with a detailed mapping of alloy influence on structure development with TTT, CCT and DCCT diagrams. The information from dilatometer tests, mechanical tests and micro structural analysis has been gathered in the Bainhard database which was exclusively developed for the project to facilitate the development of models for bainitic hardenability. This was done in two ways, based on thermodynamic inverse calculations for thermo mechanically treated materials as well as on experimental results based on Jominy tests and CCT-diagrams. The modelling work based on the large amount of data generated was also used for regression analysis which gave information of the hardenability effect from the alloy elements which was studied within the project both as single element as well as in combination with others. Finally a number of full-scale tests were made at three steel plants in order to validate the models and get more practical information regarding the hardenability of bainitic steels of real steel products.