Correlation of rolling conditions, microstructure, and low-temperature toughness of X70 pipeline steels was investigated in this study through statistical analysis. High strength API X70 steel grade with excellent DWTT toughness can be designed by the developed statistical equation. The predicted equation is as follows; ‘Pct Shear area of DWTT (−10°C) = 954 − 0.3*SRT + 0.5*TBT − 0.4*FRT + 0.04*CT − 306*C −60*(Mn+Ni+Cu) + 38*(Mo+Cr) − 791*(Ti+Nb+V) − 4*MA’ and the predicted equation showed very good relationship. M/A constituent showed high relationship with DWTT toughness. By inserting this effect into the equation, the reliability of the equation has been improved. By using the prediction equation, new chemical composition and relevant processing variables could be optimized and newly designed steel shows proper tensile properties with the excellent DWTT toughness at −10°C.

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