A ferritic-austenitic steel alloy, the elementary composition of which comprises, in percentages by weight: C up to 0.05; Si 0 - 0.8; Mn 0 - 4.0; Cr more than 29 - 35; Ni 3.0 - 10; Mo 0 - 4.0; N 0.30 - 0.55; Cu 0 - 0.8; W 0 - 3.0; S 0 - 0.03; Ce 0 - 0.2; the balance being Fe and unavoidable impurities; wherein the austenite spacing, as determined on a sample by DNV-RP-F112, Section 7, using the sample preparation according to ASTM E 3- 01, is smaller than 20 μm; and wherein the largest average austenite phase length/width ratio selected from the average austenite phase length/width ratio determined in three cross-sections of a sample as needed, the cross-sections taken at three perpendicular planes of a sample is smaller than 5; the average austenite phase length/width ratio being determined by the following procedure: i. preparing the cross-cuts surfaces of the sample; ii. polishing the surfaces using diamond paste on a rotating disc with a particle size of first 6 μm and subsequently 3 μm to create a polished surface; iii. etching the surfaces using Murakami's agent for up to 30 seconds at 20°C thereby coloring the ferrite phase, the agent being provided by preparing a saturated solution by mixing 30 g potassium hydroxide and 30 g K 3 Fe 6 in 100 ml H 2 O, and allowing the solution to cool down to room temperature before use; iv. observing the cross-cut surfaces in etched condition under an optical microscope with a magnification selected such that phase boundaries are distinguishable; v. projecting a cross-grid over the image, wherein the grid has a grid distance adapted to observe the austenite-ferrite phase boundaries; vi. randomly selecting at least ten grid crossings on the grid such that the grid crossings can be identified as being in the austenite phase; vii. determining, at each of the ten grid crossings, the austenite phase length/width ratio by measuring the length and the width of the austenite phase, wherein the length is the longest uninterrupted distance when drawing a straight line between two points at the phase boundary, the phase boundary being the transition from an austenitic phase to the ferrite phase; and wherein the width is defined as the longest uninterrupted distance measured perpendicular to the length in the same phase; calculating the average austenite phase length/width ratio as the numerical average of the austenite phase length/width ratios of the ten measured austenite phase length/width ratios. i. preparing the cross-cuts surfaces of the sample; ii. polishing the surfaces using diamond paste on a rotating disc with a particle size of first 6 μm and subsequently 3 μm to create a polished surface; iii. etching the surfaces using Murakami's agent for up to 30 seconds at 20°C thereby coloring the ferrite phase, the agent being provided by preparing a saturated solution by mixing 30 g potassium hydroxide and 30 g K 3 Fe 6 in 100 ml H 2 O, and allowing the solution to cool down to room temperature before use; iv. observing the cross-cut surfaces in etched condition under an optical microscope with a magnification selected such that phase boundaries are distinguishable; v. projecting a cross-grid over the image, wherein the grid has a grid distance adapted to observe the austenite-ferrite phase boundaries; vi. randomly selecting at least ten grid crossings on the grid such that the grid crossings can be identified as being in the austenite phase; vii. determining, at each of the ten grid crossings, the austenite phase length/width ratio by measuring the length and the width of the austenite phase, wherein the length is the longest uninterrupted distance when drawing a straight line between two points at the phase boundary, the phase boundary being the transition from an austenitic phase to the ferrite phase; and wherein the width is defined as the longest uninterrupted distance measured perpendicular to the length in the same phase;