Effect of Grain Boundary Characteristics on the Impact Properties of Thermomechanically Rolled API X70 Pipeline Steels
Semih Engün Servet Turan Orhan Uzun Oğuz Gündüz
AbstractA quantitative grain boundary analysis and impact properties of thermomechanically rolled X70 pipeline steels were conducted. Three different X70 samples that were coiled at different temperatures were characterized by SEM-EBSD technique. Number of low angle and coincidence site lattice (CSL) grain boundaries were quantified. Tensile and impact properties were measured and related by low angle grain boundaries (LAGB) and CSL boundaries. The results showed that, tensile and impact properties are varying with these boundary types. While yield and tensile strength increases by increasing LAGB and Σ3 boundaries, impact properties i.e Charpy and drop weight tear (DWTT) energies are generally in a decreasing trend. Moreover, it was observed that grain size due to higher Ti/N rate is a more effective mechanism for Charpy energy than the grain boundary type.