In this work, changes in mechanical properties in dual phase steel containing 20% martensite volume fractions were observed at various ageing temperatures. For example, Delta Y (increase in yield strength due to strain ageing), YS and UTS exhibit maximum values at ageing temperature of 100 degrees C for the pre-strains of 2 and 4%. This is due to the formation of solute atom atmospheres around dislocation. When the ageing temperature increased to 200 degrees C, yield strength decreased due to overageing resulted from tempering that starts in martensite phase. (C) 2008 Elsevier Ltd. All rights reserved.