Method of production of a cold rolled and heat treated steel sheet and use of such steel to produce vehicle parts

A method of production of a cold rolled and heat treated steel sheet having the following steps: providing a cold rolled steel sheet with a composition with the following elements, expressed in percent by weight: 0.10%≤carbon≤0.6%; 4%≤manganese≤20%; 5%≤aluminum≤15%; 0≤silicon≤2% aluminium+silicon+nickel≥6.5%; and optionally at least one of certain optional elements; a remainder being composed of iron and unavoidable impurities caused by processing; heating the cold rolled steel sheet up to a soaking temperature between 750 and 950° C. during less than 600 seconds, then cooling the sheet down to room temperature; and reheating the steel sheet to a soaking temperature of 150° C. to 600° C. during 10 s to 1000 h, then further cooling the sheet.