A method for the ultrasonic inspection of metal components by a synthetic aperture focusing technique, comprising the steps of: alternatively emitting ultrasonic inspection signals (S I) towards the inside of a metal component and receiving return signals (S R) in each of a plurality of detection positions (θ I, θ I+J) defining a scanning path of the metal component; sampling the return signals (S R), to form first vectors (A-SCAN I, A-SCAN I+J) comprising respective series of temporally sorted elements (A-SCAN I+J); defining a synthetic array (SA I) including a plurality of first vectors (A-SCAN I, A-SCAN I+J) corresponding to respective adjacent detection positions (θ I, θ I+J); and focusing the first vectors (A-SCAN I, A-SCAN I+J) of the synthetic array (SA I), wherein the step of focusing comprises applying phase translations (K') to the elements (A-SCAN I+J) of the first vectors (A-SCAN I, A-SCAN I+J) of the synthetic array (SA I); wherein the phase translation (K') respectively applied to each element (A-SCAN I+J) is correlated to a position of said element (A-SCAN I+J) in the series of elements forming the respective first vector (A-SCAN I, A-SCAN I+J) of the synthetic array (SA I); characterised in that applying phase translations comprises: defining a plurality of focusing depths (R L) for a first central vector (A-SCAN I) of the synthetic array (SA I), corresponding to a central detection position (θ I); defining a plurality of sections (S 1, S 2,..., S L) of the first central vector (A-SCAN I), associated to respective focusing depths (R L); calculating a detection delay (τ I+J,L) for each side detection position (θ I+J) other than the central detection position (θ I) and for each focusing depth (R L); associating a respective delay (τ I+J,L) to each element (A-SCAN I+J) of first side vectors (A-SCAN I+J) in order to generate second vectors (A-SCANR I, A-SCANR I+J). alternatively emitting ultrasonic inspection signals (S I) towards the inside of a metal component and receiving return signals (S R) in each of a plurality of detection positions (θ I, θ I+J) defining a scanning path of the metal component; sampling the return signals (S R), to form first vectors (A-SCAN I, A-SCAN I+J) comprising respective series of temporally sorted elements (A-SCAN I+J); defining a synthetic array (SA I) including a plurality of first vectors (A-SCAN I, A-SCAN I+J) corresponding to respective adjacent detection positions (θ I, θ I+J); and focusing the first vectors (A-SCAN I, A-SCAN I+J) of the synthetic array (SA I), wherein the step of focusing comprises applying phase translations (K') to the elements (A-SCAN I+J) of the first vectors (A-SCAN I, A-SCAN I+J) of the synthetic array (SA I); wherein the phase translation (K') respectively applied to each element (A-SCAN I+J) is correlated to a position of said element (A-SCAN I+J) in the series of elements forming the respective first vector (A-SCAN I, A-SCAN I+J) of the synthetic array (SA I); characterised in that applying phase translations comprises: defining a plurality of focusing depths (R L) for a first central vector (A-SCAN I) of the synthetic array (SA I), corresponding to a central detection position (θ I); defining a plurality of sections (S 1, S 2,..., S L) of the first central vector (A-SCAN I), associated to respective focusing depths (R L); calculating a detection delay (τ I+J,L) for each side detection position (θ I+J) other than the central detection position (θ I) and for each focusing depth (R L); associating a respective delay (τ I+J,L) to each element (A-SCAN I+J) of first side vectors (A-SCAN I+J) in order to generate second vectors (A-SCANR I, A-SCANR I+J). defining a plurality of focusing depths (R L) for a first central vector (A-SCAN I) of the synthetic array (SA I), corresponding to a central detection position (θ I); defining a plurality of sections (S 1, S 2,..., S L) of the first central vector (A-SCAN I), associated to respective focusing depths (R L); calculating a detection delay (τ I+J,L) for each side detection position (θ I+J) other than the central detection position (θ I) and for each focusing depth (R L); associating a respective delay (τ I+J,L) to each element (A-SCAN I+J) of first side vectors (A-SCAN I+J) in order to generate second vectors (A-SCANR I, A-SCANR I+J).