Cold-rolled and heat-treated steel sheet, having a composition comprising, by weight percent: 0.10% ≤ C ≤ 0.40% 3.5% ≤ Mn ≤ 8.0% 0.5% ≤ Si ≤ 2.5% 0.003% ≤ Al ≤ 3.0% with Si+AI ≥ 0.8% 0.001% ≤ Mo ≤ 0.5% such that C eq = C % + Mn % 6 + Si % 6 + Cr % + Mo % + V % 5 ≤ 1.30 % and optionally one or more elements selected from amongst Cr, Ti, Nb, V and B, such that: 0.01% ≤ Cr ≤ 2.0% 0.010% ≤ Ti ≤ 0.080% 0.010% ≤ Nb ≤ 0.080% 0.010% ≤ V ≤ 0.30% 0.0005% ≤ B ≤ 0.003%, the remainder of the composition being iron and unavoidable impurities resulting from the smelting, including less than 0.010% S, less than 0.020% P, less than 0.008% N, less than 0.05% Ni and less than 0.03% Cu, said cold-rolled steel sheet having a microstructure consisting of, in surface fraction, between 10% and 50% of retained austenite, at most 8% of fresh martensite, and tempered martensite, said retained austenite comprising: - Mn-enriched austenite, having a Mn content higher than 1.3*Mn%, Mn% designating the Mn content of the steel sheet, and - Mn-poor austenite, having an Mn content comprised between 0.5*Mn% and 1.3*Mn%, the surface fraction of said Mn-enriched austenite with respect to the whole microstructure being comprised between 2% and 12%, the Mn-poor austenite and Mn-enriched austenite have an average C content comprised between 0.4% and 1.0%, the cold-rolled and heat-treated steel sheet having a yield strength YS comprised between 1100 MPa and 1700 MPa, a tensile strength TS comprised between 1300 MPa and 2000 MPa, a uniform elongation UE of at least 10%, a total elongation TE, measured according to ISO standard ISO 6892-1, of at least 13%, a product tensile strength x total elongation (TS x TE) of at least 19000 MPa%, a product yield strength x uniform elongation (YS x UE) of at least 13000 MPa% and a hole expansion ratio HER, measured according to the ISO standard 16630:2009, of at least 20%. 0.10% ≤ C ≤ 0.40% 3.5% ≤ Mn ≤ 8.0% 0.5% ≤ Si ≤ 2.5% 0.003% ≤ Al ≤ 3.0% with Si+AI ≥ 0.8% 0.001% ≤ Mo ≤ 0.5% such that C eq = C % + Mn % 6 + Si % 6 + Cr % + Mo % + V % 5 ≤ 1.30 % and optionally one or more elements selected from amongst Cr, Ti, Nb, V and B, such that: such that C eq = C % + Mn % 6 + Si % 6 + Cr % + Mo % + V % 5 ≤ 1.30 % and optionally one or more elements selected from amongst Cr, Ti, Nb, V and B, such that: 0.01% ≤ Cr ≤ 2.0% 0.010% ≤ Ti ≤ 0.080% 0.010% ≤ Nb ≤ 0.080% 0.010% ≤ V ≤ 0.30% 0.0005% ≤ B ≤ 0.003%, the remainder of the composition being iron and unavoidable impurities resulting from the smelting, including less than 0.010% S, less than 0.020% P, less than 0.008% N, less than 0.05% Ni and less than 0.03% Cu, said cold-rolled steel sheet having a microstructure consisting of, in surface fraction, between 10% and 50% of retained austenite, at most 8% of fresh martensite, and tempered martensite, said retained austenite comprising: - Mn-enriched austenite, having a Mn content higher than 1.3*Mn%, Mn% designating the Mn content of the steel sheet, and - Mn-poor austenite, having an Mn content comprised between 0.5*Mn% and 1.3*Mn%, the surface fraction of said Mn-enriched austenite with respect to the whole microstructure being comprised between 2% and 12%, the Mn-poor austenite and Mn-enriched austenite have an average C content comprised between 0.4% and 1.0%, the cold-rolled and heat-treated steel sheet having a yield strength YS comprised between 1100 MPa and 1700 MPa, a tensile strength TS comprised between 1300 MPa and 2000 MPa, a uniform elongation UE of at least 10%, a total elongation TE, measured according to ISO standard ISO 6892-1, of at least 13%, a product tensile strength x total elongation (TS x TE) of at least 19000 MPa%, a product yield strength x uniform elongation (YS x UE) of at least 13000 MPa% and a hole expansion ratio HER, measured according to the ISO standard 16630:2009, of at least 20%. the remainder of the composition being iron and unavoidable impurities resulting from the smelting, including less than 0.010% S, less than 0.020% P, less than 0.008% N, less than 0.05% Ni and less than 0.03% Cu, said cold-rolled steel sheet having a microstructure consisting of, in surface fraction, between 10% and 50% of retained austenite, at most 8% of fresh martensite, and tempered martensite, said retained austenite comprising: - Mn-enriched austenite, having a Mn content higher than 1.3*Mn%, Mn% designating the Mn content of the steel sheet, and - Mn-poor austenite, having an Mn content comprised between 0.5*Mn% and 1.3*Mn%, - Mn-enriched austenite, having a Mn content higher than 1.3*Mn%, Mn% designating the Mn content of the steel sheet, and - Mn-poor austenite, having an Mn content comprised between 0.5*Mn% and 1.3*Mn%, the surface fraction of said Mn-enriched austenite with respect to the whole microstructure being comprised between 2% and 12%, the Mn-poor austenite and Mn-enriched austenite have an average C content comprised between 0.4% and 1.0%, the cold-rolled and heat-treated steel sheet having a yield strength YS comprised between 1100 MPa and 1700 MPa, a tensile strength TS comprised between 1300 MPa and 2000 MPa, a uniform elongation UE of at least 10%, a total elongation TE, measured according to ISO standard ISO 6892-1, of at least 13%, a product tensile strength x total elongation (TS x TE) of at least 19000 MPa%, a product yield strength x uniform elongation (YS x UE) of at least 13000 MPa% and a hole expansion ratio HER, measured according to the ISO standard 16630:2009, of at least 20%.