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The present study has considered the possibilities of annealing in reactive atmospheres during the continuous annealing of various steel grades, especially Ti-IF steels. The work was mainly focused on a carburising treatment with CO-H(2)-N(2) gas mixtures performed in a hot wall and a cold wall technology simulator. Furthermore, the possibilities of a nitriding treatment were investigated too.

Concerning the carburising treatment, annealing cycles with different gas mixtures of CO-H(2)-N(2)-H(2)O were set up. The annealing temperature for IF steel was set at 810 degrees Celsius, and in most cases was close to the industrial process. For example, IF steel was submitted for 10s in weak carburising atmospheres leading to carbon concentrations of 100 mass ppm to 10 micro-m depth. If strong carburising atmospheres are applied the total carbon content was increased up to 650 mass ppm after 60s.

Introducing interstitials into ULC steel after recrystallization led to higher strength combined with high formability. Bake hardening of 40MPa is possible, but connected with age hardening. The r-value of carburised Ti-IF steel is still at a high level, greater than two. Moreover, a favourable r(o) value of two measured even if an austenite layer (3 000- 8 000 mass ppm C) of 20 micro-m was formed. The carburising treatment, necessary to produce DDQ-BH steels from Ti-IF grades, lowered the reactivity during galvanizing and galvannealing. However, a perlitic skin led to a higher reactivity. This could be a good way to increase or decrease the reactivity during the alloying process of critical steel grades such as high P and high Si

Additional information

Authors: WILLEM J-F, CRM, Liege (BE);BLECK W, RTWH Hochschule Aachen (DE);AHRENS M, RTWH Hochschule Aachen (DE)
Bibliographic Reference: EUR 19890 EN (2001), pp. 220. Euro: 32.50
Availability: Available from EUR-OP sales agent URL:
ISBN: ISBN 92-894-1545-2
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