A metal reverse buckling sanitary rupture disc (12) is provided having a central bulged section (16) in which the convex surface of the bulged section (16) is relatively smooth and of substantially uninterrupted configuration. A small segment region (22) of the central bulged section (16) is strain hardened by plastic deformation causing the segment region (22) to have greater residual stress than the remainder of the central bulged section. When the disc (12) is subjected to an overpressure condition against the convex surface of the bulged section (16) sufficient to effect reversal of the bulged section (16), such reversal commences at the higher residual stress segment region (22) of the bulged section (16).