A method for producing a steel sheet is provided. The method includes providing a cold-rolled steel sheet including 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%, and a remainder of Fe and unavoidable impurities, annealing the steel sheet at an annealing temperature between Ac1 and Ac3 to obtaining at least 40% austenite and at least 40% intercritical ferrite, quenching the sheet from at least 600° C. at a cooling rate of at least 20° C./s to a quenching temperature between 180° C. and 260° C., heating the sheet to a partitioning temperature between 375° C. and 470° C. and maintaining the sheet at this partitioning temperature for a partitioning time Pt between 25 s and 440 s, then cooling the sheet to room temperature. A steel sheet is also provided.