Abstract: The substitution of conventionally quenched and tempered (Q&T) plates by thermomechanically treated ultra-high strength steels is becoming widely accepted in industry. Austenite conditioning during rolling followed by Direct Quenching (DQ) might offer benefits in mechanical properties. The metallurgical mechanisms behind these different routes, though, are not clear; especially when different combinations of microalloying elements such as B, Mo and/or Nb are combined. Deformation dilatometry studies were performed with several microalloyed medium carbon grades. Their transformation behavior was analyzed when different thermomechanical strategies were applied and differences on the hardenability of each alternative were evaluated. Multipass torsion tests were also performed and the austenite conditioning before transformation studied. The relationship between austenite and final martensite microstructure was evaluated using the EBSD technique. This study aims to correlate the effect of composition and processing parameters in the final quenched structure.
Authors: I. Zurutuza, N. Isasti, E. Detemple, V. Schwinn, H. Mohrbacher, and P. Uranga
Keywords: martensite, CCT diagrams, Direct Quenching, niobium, molybdenum