A method of heat treating a cold rolled steel strip, which method comprises the steps of: a) soaking a cold rolled steel strip above (Ac3 - 60) for a soaking time t2 of 1 - 150 seconds, thereby obtaining a cold rolled steel strip having an at least partially austenitic microstructure; b) cooling the soaked steel strip resulting from step a) to a temperature T4 in the range of Bn - Ms; c) heat treating the cooled strip obtained in step b) in a temperature range of Bs - T4 for a period of time t5 of 30 - 300 seconds; d) cooling the heat treated steel strip to ambient temperature; such that the steel strip has a microstructure (in vol. %) comprising polygonal ferrite + acicular ferrite + higher bainitic ferrite: 20 - 55; wherein polygonal ferrite: 0 - 45; lower bainitic ferrite: 20 - 65; retained austenite: 5 - 20; martensite: 0 - 20; wherein the steel strip has a composition (in mass %) comprising C: 0.15 - 0.35; Mn: 1.50 - 3.00; Si: 0.50 - 2.00; Al: 0.01 - 1.50; P: less than 0.050; S: less than 0.020; N: less than 0.0080; wherein the sum (Si + Al) is ≥ 0.60; and optionally one or more elements selected from 0 < Cr ≤ 0.35; 0 < Cu ≤ 0.20; 0 < Ni ≤ 0.50; 0 < Mo ≤ 5 0.30; 0 < Nb ≤ 0.10; 0 < V ≤ 0.10; 0 < Ti ≤ 0.10; 0 < B ≤ 0.0030; 0 < Ca ≤ 0.0050; 0 < REM ≤ 0.0100, wherein REM is one or more rare earth metals; and the remainder being iron and inevitable impurities. a) soaking a cold rolled steel strip above (Ac3 - 60) for a soaking time t2 of 1 - 150 seconds, thereby obtaining a cold rolled steel strip having an at least partially austenitic microstructure; b) cooling the soaked steel strip resulting from step a) to a temperature T4 in the range of Bn - Ms; c) heat treating the cooled strip obtained in step b) in a temperature range of Bs - T4 for a period of time t5 of 30 - 300 seconds; d) cooling the heat treated steel strip to ambient temperature; such that the steel strip has a microstructure (in vol. %) comprising polygonal ferrite + acicular ferrite + higher bainitic ferrite: 20 - 55; wherein polygonal ferrite: 0 - 45; lower bainitic ferrite: 20 - 65; retained austenite: 5 - 20; martensite: 0 - 20; wherein the steel strip has a composition (in mass %) comprising C: 0.15 - 0.35; Mn: 1.50 - 3.00; Si: 0.50 - 2.00; Al: 0.01 - 1.50; P: less than 0.050; S: less than 0.020; N: less than 0.0080; wherein the sum (Si + Al) is ≥ 0.60; and optionally one or more elements selected from 0 < Cr ≤ 0.35; 0 < Cu ≤ 0.20; 0 < Ni ≤ 0.50; 0 < Mo ≤ 5 0.30; 0 < Nb ≤ 0.10; 0 < V ≤ 0.10; 0 < Ti ≤ 0.10; 0 < B ≤ 0.0030; 0 < Ca ≤ 0.0050; 0 < REM ≤ 0.0100, wherein REM is one or more rare earth metals; and the remainder being iron and inevitable impurities. such that the steel strip has a microstructure (in vol. %) comprising polygonal ferrite + acicular ferrite + higher bainitic ferrite: 20 - 55; wherein polygonal ferrite: 0 - 45; lower bainitic ferrite: 20 - 65; retained austenite: 5 - 20; martensite: 0 - 20; wherein the steel strip has a composition (in mass %) comprising C: 0.15 - 0.35; Mn: 1.50 - 3.00; Si: 0.50 - 2.00; Al: 0.01 - 1.50; P: less than 0.050; S: less than 0.020; N: less than 0.0080; wherein the sum (Si + Al) is ≥ 0.60; and optionally one or more elements selected from 0 < Cr ≤ 0.35; 0 < Cu ≤ 0.20; 0 < Ni ≤ 0.50; 0 < Mo ≤ 5 0.30; 0 < Nb ≤ 0.10; 0 < V ≤ 0.10; 0 < Ti ≤ 0.10; 0 < B ≤ 0.0030; 0 < Ca ≤ 0.0050; 0 < REM ≤ 0.0100, wherein REM is one or more rare earth metals; 0 < Cr ≤ 0.35; 0 < Cu ≤ 0.20; 0 < Ni ≤ 0.50; 0 < Mo ≤ 5 0.30; 0 < Nb ≤ 0.10; 0 < V ≤ 0.10; 0 < Ti ≤ 0.10; 0 < B ≤ 0.0030; 0 < Ca ≤ 0.0050; 0 < REM ≤ 0.0100, wherein REM is one or more rare earth metals; and the remainder being iron and inevitable impurities.