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The project is focused on the production of thick high strength steel plates and sections, based on a low carbon bainitic steel metallurgy with requirements in terms of tensile properties, resistance to brittle fracture, weldability, homogeneity. Plate activities. Laboratory rolling of various compositions based on Mo,Cr,Cu,Ni,B alloying of low C Nb steels has been made. The laboratory rolling simulation of plates has allowed the effect of alloying and plate processing conditions on the formation of various bainite microstructures to be analysed. The best strength-toughness compromise was achieved with a relatively coarse lath bainite microstructure from a boron-free concept. It has been shown that a MoCr- and CuNi-system equals in their strength properties. A lower alloyed Boron-variant has even a higher strength but reacts more sensitively to changes in cooling conditions. A higher final rolling temperature and a higher cooling stop temperature improve toughness. A low cooling stop temperature is favourable when annealing. Welding followed by PWHT reduces toughness in the heat affected zone. The best results can be found for the CuNi alloyed steel. Beam activities. The laboratory experiments have shown the benefit of the grades with the lowest carbon contents and bainite promoters (B, Nb, Cr) for developing homogeneous microstructures and hardness through the thickness. However, the most homogeneous bainitic transformation is not associated with optimised properties and the best combination of resistance, toughness and weldability was obtained on the 0.09 % C with 0.2 % Cu. The toughness of the 0.02 % C boron alloyed steels was particularly sensitive to the cooling conditions whatever the rolling reduction is. Increasing the Cu content for a given carbon level does not reduce the hardness gradient. On the 0.09 % C, a reduction of the self tempering temperature from 600 to 550 °C, which leads to a more important quenching during the rolling, brings a gain in impac

Additional information

Authors: DE RO A, European Commission, DG Research, Brussels (BE);SCHWINN V, European Commission, DG Research, Brussels (BE);DONNAY B, European Commission, DG Research, Brussels (BE)
Bibliographic Reference: EUR 22434 EN (2007), 187 pp. Euro: 25
Availability: Katalogue Number: KI-NA-22434-EN-S The paper version can be ordered online at:
ISBN: ISBN: 92-79-03796-X
Record Number: 200718830 / Last updated on: 2007-02-26
Original language: en
Available languages: en