Bainite

About: Bainite is a research topic. Over the lifetime, 9520 publications have been published within this topic receiving 145305 citations.

Influence of carbon, manganese and nickel on microstructure and properties of strong steel weld metals: Part 3 – Increased strength resulting from carbon additions

Abstract: Neural network predictions suggested that the strength of a high strength steel weld metal with 7 wt-% nickel and 0·5 wt-% manganese could be increased significantly at moderate expense to impact toughness by additions of carbon. Based on this, three experimental weld metals were produced with carbon contents between 0·03 and 0·11 wt-%. Mechanical test results were in agreement with predictions. At low carbon content the microstructure was largely bainitic in dendrite core regions whereas martensite was found at interdendritic regions. From microstructural studies and dilatometry experiments it was found that carbon stabilised austenite to lower transformation temperatures and that the microstructure became more martensitic in nature. Effects on strength and impact toughness were explainable in terms of a refinement of the microstructure and tempering behaviour.

One-step theory of fcc-bcc martensitic transformation

Abstract: Martensitic transformation in steels is responsible for their very high strength and has thus been studied for more than one century since the first works of Martens. However, there is not yet simple physical theory. A rigorous classification of the crystallographic subgroupoids (packets) of the KS variants and the continuity between the KS, NW and Pitsch variants are introduced to represent the crystallographic intricacy associated to the martensite transformation. From this analysis, a new simple theory based on Pitsch distortion is proposed. The distortion respects the hard sphere packing of the iron atoms and implies the existence of a neutral line along the close packed directions. Its principal strains are 0, -5.8 and +15.5 %, well below the +12, +12 and -20 % values of the Bain distortion. Martensite variants nucleate by Pitsch distortion in an austenitic matrix continuously deformed by the transformation. The martensite variants grow by the same Pitsch distortion; they are locally in Pitsch orientation, and therefore are gradually oriented inside the deformation field of austenite leading to the continuum of orientations including KS and NW. Many observations reported in literature can now be re-interpreted.