A method for producing a steel sheet having a tensile strength of at least 980 MPa, a total elongation according to ISO standard 6892-1 of at least 16% and a hole expansion ratio according to ISO standard 16630:2009 HER of at least 20%, wherein the method comprises the following successive steps: - providing a cold-rolled steel sheet, the chemical composition of the steel containing in weight %: 0.15% ≤ C ≤ 0.23% 1.4 % ≤ Mn ≤ 2.6%, 0.6% ≤ Si ≤ 1.5% 0.02% ≤ Al ≤ 1.0%, with 1.0% ≤ Si+Al ≤ 2.0%, 0 ≤ Nb ≤ 0.035%, 0 ≤ Mo ≤ 0.3%, 0 ≤ Cr ≤ 0.3%, Ni < 0.05%, Cu < 0.03%, V < 0.007%, B < 0.0010%, S < 0.005%, P < 0.02%, N < 0.010%. the remainder being Fe and unavoidable impurities, - annealing the steel sheet at an annealing temperature TA comprised between Ac1 and Ac3 so as to obtain a structure comprising at least 40% of austenite and at least 40% of intercritical ferrite, - quenching the sheet from a temperature of at least 600°C at a cooling rate of at least 20°C/s down to a quenching temperature QT comprised between 180°C and 260°C, - heating the sheet up to a partitioning temperature PT between 375°C and 470°C and maintaining the sheet at this partitioning temperature PT for a partitioning time Pt comprised between 25s and 440s, the partitioning time Pt being comprised between 100s and 440s if the partitioning temperature PT is comprised between 375°C and 400°C, and comprised between 25s and 150s if the partitioning temperature PT is comprised between 450°C and 470°C, - cooling the sheet down to the room temperature, the steel sheet having a final microstructure consisting, in area fraction, of: - between 11% and 40% of tempered martensite, the tempered martensite having a C content of at most 0.45%, - between 10% and 20% of retained austenite, - between 40% and 60% of ferrite, - at most 6% of fresh martensite, - at most 18% of bainite. - providing a cold-rolled steel sheet, the chemical composition of the steel containing in weight %: 0.15% ≤ C ≤ 0.23% 1.4 % ≤ Mn ≤ 2.6%, 0.6% ≤ Si ≤ 1.5% 0.02% ≤ Al ≤ 1.0%, with 1.0% ≤ Si+Al ≤ 2.0%, 0 ≤ Nb ≤ 0.035%, 0 ≤ Mo ≤ 0.3%, 0 ≤ Cr ≤ 0.3%, Ni < 0.05%, Cu < 0.03%, V < 0.007%, B < 0.0010%, S < 0.005%, P < 0.02%, N < 0.010%. the remainder being Fe and unavoidable impurities, 0.15% ≤ C ≤ 0.23% 1.4 % ≤ Mn ≤ 2.6%, 0.6% ≤ Si ≤ 1.5% 0.02% ≤ Al ≤ 1.0%, with 1.0% ≤ Si+Al ≤ 2.0%, 0 ≤ Nb ≤ 0.035%, 0 ≤ Mo ≤ 0.3%, 0 ≤ Cr ≤ 0.3%, Ni < 0.05%, Cu < 0.03%, V < 0.007%, B < 0.0010%, S < 0.005%, P < 0.02%, N < 0.010%. - annealing the steel sheet at an annealing temperature TA comprised between Ac1 and Ac3 so as to obtain a structure comprising at least 40% of austenite and at least 40% of intercritical ferrite, - quenching the sheet from a temperature of at least 600°C at a cooling rate of at least 20°C/s down to a quenching temperature QT comprised between 180°C and 260°C, - heating the sheet up to a partitioning temperature PT between 375°C and 470°C and maintaining the sheet at this partitioning temperature PT for a partitioning time Pt comprised between 25s and 440s, the partitioning time Pt being comprised between 100s and 440s if the partitioning temperature PT is comprised between 375°C and 400°C, and comprised between 25s and 150s if the partitioning temperature PT is comprised between 450°C and 470°C, - cooling the sheet down to the room temperature, - between 11% and 40% of tempered martensite, the tempered martensite having a C content of at most 0.45%, - between 10% and 20% of retained austenite, - between 40% and 60% of ferrite, - at most 6% of fresh martensite, - at most 18% of bainite.