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This collaborative project aimed to evaluate the feasibility and potentiality of a carburising treatment in the continuous annealing furnace to produce deep-drawing quality steel grades with bake hardening (DDQ-BH). A section composed of two radiant muffle furnaces made of Inconel 600 was implemented on the CRM pilot line. The total length of the section (3.4 m) insured a treatment of 14 s at a line speed of 15 m/min (about 1.4 t/h). Sealing gates were placed at the two section extremities. Differential pressure measurements at the gate extremities allowed the prevention carburising gas flowing into neighbouring sections while limiting HNx dilution. The continuous annealing was carried out in the following sequences:
- strip recrystallisation under HNX;
- carburising treatment under high concentrations of CO and H2;
- post-diffusion treatment under HNX;
- hot-dip galvanising or galvannealing.

The use of a 33% CO- 66 %H2 type gas mixture with carbon potential controlled by water vapour addition has enabled more than 70 ppm of carbon in the strip in less than 15 s. Bake hardening values of 40 MPa associated the introduction of an excellent formability were obtained. Denting properties were similar to conventional BHsteel grades. Yield point elongations of 0.4 - 0.9 % were observed after aging treatments of 10 h at 75°C. Due to the carbon profile in the strip thickness, this aging sensitivity is difficult to avoid. Nevertheless, this route remains attractive due to its flexibility and to the low constraints on the upstream process. Industrial perspectives are discussed.

Additional information

Authors: HENNION A, CRM, Liège (BE);NOVILLE J F, CRM, Liège (BE);LEPRINCE G, IRSID - Groupe Arcelor, Maizières-lès-Metz (FR);SENET E, SOLLAC - Groupe Arcelor, La Défense (FR);SOLER M, SOLLAC - Groupe Arcelor, La Défense (FR)
Bibliographic Reference: EUR 20910 EN (2003), 39pp. Euro: 15
Availability: EUR-OP reference: KI-NA-20910-EN-S Available from EUR-OP sales agents URL:
ISBN: ISBN: 92-894-6436-4
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