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This project aimed at developing Ti-containing structural steels with a suitable dispersion of Ti-rich particles, in order to restrict austenite grain growth and increase weld HAZ toughness. The steels examined contained Ti additions of up to 0.025%, and also microalloying additions of Nb and V. Studies were carried out on various laboratory ingots of different size, enabling the solidification and post solidification cooling rate (PSCR) conditions prevailing in continuously cast steels to be simulated. Examination of particles in as-cast ingots revealed clear differences between VTi and NbTi steels. Rolling experiments showed that increasing reheating temperatures produces a significant increase in the Ti content of the precipitates. Particle sizes are also reduced after reheating and, in the NbTi steels, complex morphologies are replaced by simpler, cuboidal types. Austenite grain sizes after heat treatment were measured as a function of PSCR and reheating temperature. The VTi steel had a finer austenite grain size than the NbTi steel, a reflection of the finer particle size in the VTi steel. A correlation was obtained between particle size and simulated austenite grain size, suggesting that particle sizes must be kept below 20 nm if a fine weld HAZ grain size is required. The maximum HAZ hardness of Ti treated steels was lower than in Ti free steels, but HAZ toughness was improved. Ti additions reduce parent-plate strength in both the as-rolled and normalised condition, but adequate properties can be maintained by the use of appropriate rolling schedules and solid solution strengthening by elements such as Ni.

Additional information

Authors: CROWTHER D N, British Steel plc, London (GB);COCHRANE R C, British Steel plc, London (GB);ROSE A J, British Steel plc, London (GB)
Bibliographic Reference: EUR 13114 EN (1990) 100 pp., FS, ECU 8.75
Availability: (2)
ISBN: ISBN 92-826-1920-6
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