Comportement mécanique d'assemblages en acier 27CD4 et 100C6 soudés rapidement par soudage-diffusion-dynamique

Abstract
A new process, dynamic-diffusion-bonding (DDB) was improved in our laboratory (1). It offers the advantages of both classical diffusion-bonding and rapidity, which is consistent with mass production. It was proven possible to carry out high strength bonds in a very short time : 60 seconds with specimens of 27CD4 steel (diameter=16mm). After bonding, the specimens were heat treated in order to homogeneize the structure along the piece. With the optimal bonding conditions, namely a few seconds at 1060°C, in a nitrogen with 5% hydrogen gas, with a proper surface preparation (Ra=0,04 µm) and under a modulated pressure during the whole bonding process (2,3) : - deformation of the bonded specimens is limited to about 2% of the heated length, - tensile and torsion behaviour is very good : failure occurs out of the interface. No defect remains across the weld interface, - the failure energy of joints measured with impact tests is lower than that of the base metal, because of the flatness of the interface and because of the presence of very fine oxide particles in the bond, - fatigue behaviour (rotating beam tests) of bonded pieces is very good : their fatigue strength (720 MPa : stair case estimation for 5 .10⁶ cycles) is very closed to those of unbonded specimens (780 MPa), and the crack initiates out of the interface near a big inclusion. With the 100C6 steel, bonds of the same quality were obtained, and with higher roughness of specimens (Ra=0,15 µm), high quality joints were achieved with a duration of 60 seconds at 1050°C.