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Monday 23 January 2006
HOT INDUCTION BENDING: METALLURGICAL EVALUATIONS AND HOT DEFORMABILITY BEHAVIOUR OF Q&T SEAMLESS PIPES
E. Anelli, G. Porcu, G. Cumino, A. Mannucci, M. Tivelli.
Referee: P.E. Di Nunzio, M. Pontremoli
Paper presented to Proceedings of the International Symposium on Microalloyed Steels for the Oil & Gas Industry,
Araxà (Brasil), 23-25 January 2006.
Hot bending process of pipes is usually performed by means of rapid heating by induction, bending to a given radius, external cooling by water spray. After bending operation, bends are usually tempered off-line. This process is expected to change the microstructure and precipitation of the mother quenched and tempered (Q&T) seamless pipe. Since the reheating stage causes austenitizing and partial dissolution of fine precipitates, high bending temperatures, useful to reduce the energy required for the deformation, will promote austenite grain growth. Coarse grains help in the achievement of the final strength level on the bend through the improvement of hardenability, but can be detrimental to final toughness and hot ductility during bending operation. Therefore, the chemical composition of the steel and the hot bending conditions have to be tailored to the specific bend grade to be produced. In this work a systematic investigation of microstructure and strength-toughness combination of bends in low-C micro-alloyed steels deformed using low and high bending temperatures was performed. Also hot tensile tests reproducing the typical deformation conditions of hot bending operation were carried out on specimens taken from the mother Q&T seamless pipes. Results were interpreted in terms of microstructure and precipitation evolution.
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