Abstract: In order to obtain sheets made of a nickel-based superalloy of type 718 having properties of superplasticity, the sheets are manufactured with a final cycle comprising the steps of: a) solution treatment at 1060° C. for 15 minutes; b) precipitation at 730° C. to 800° C. for 1 to 2 hours; c) cold rolling at a ratio greater than 60%, and d) recrystallization at 900° C. for 30 minutes. Superplastic deformation of such sheets is carried out at about 970±10° C. and under pressures inducing stresses between 45 and 60 MPa.

Abstract: The process measures a characteristic (X) which is difficult to measure of a continuously produced product and comprises:choosing at least one easily measurable second characteristic (Y) whose variations are correlated to the variations of the first characteristic;modifying, by means acting on the product in a given zone of the production line, the first characteristic so as to put it into a known predetermined reference state (X.sub.o);taking at least in said zone a measurement of the second characteristic, and;processing said measurement for determining a variation in the first characteristic relative to the reference state (X).Application in the measurement of the flatness of a strip continuously travelling through a levelling machine.FIG. 2.