Analysis of weld-cracking and improvement of the weld-repair process of superplastic forming tools

Arnaud Duchosal (1) , Frédéric Deschaux-Beaume (1) , Philippe Lours (2) , Sergio Haro (3) , Gilles Fras (1)

1 AS - Assemblages Soudés
2 ICA - Institut Clément Ader
3 Unidad Academica de Ingeniería

Superplastic forming (SPF) dies are generally made of using heat resistant cast steels, which are very sensitive to weld cracking. In order to improve the weld-repair process of such dies to prevent weld-cracking, the microstructure and the mechanical behaviour of a typical heat-resistant cast steel was first studied, using isothermal low-cycle fatigue tests and in-situ tensile tests. The welding behaviour of such steel was also investigated, using a shielded metal arc welding (SMAW) process and welding conditions similar to those employed for weld repair industrial dies. The comparison of the aspect of weld-cracking with the fracture mechanisms observed at room temperature or during isothermal low-cycle fatigue tests suggests a similar brittle failure mechanism, due to the presence of large interdendritic carbides in the cast steel. The melting of the cast steel surface using a gas tungsten arc welding (GTAW) process allowed to refine the primary carbides, and then to reduce the weld-cracking sensitivity. The refining method with GTAW before welding has been successfully tested to weld-repair a sample representative of SPF dies, and is recommended for subsequent repairs of such dies.

Mots clés: Superplastic forming; Heat resistant cast steel; Weld-cracking; Weld-repair

Domaines: Mécanique des matériaux [physics.class-ph]; Mécanique des matériaux [physics.class-ph]

Arnaud Duchosal, Frédéric Deschaux-Beaume, Philippe Lours, Sergio Haro, Gilles Fras. Analysis of weld-cracking and improvement of the weld-repair process of superplastic forming tools. Materials & Design, 2013, 46, pp.731-739. ⟨10.1016/j.matdes.2012.11.003⟩. ⟨hal-00798986⟩