Microstructure and properties of intercritically reheated coarse-grained heat affected zone in pipeline steel after secondary thermal cycle

As a kind of high strength microalloyed steel, pipeline steel has high strength and toughness. However, the formation of the intercritically reheated coarse-grained heat affected zone (ICCGHAZ) during the welding process is an important limitation affecting its performance. Herein, microstructural transformation in the ICCGHAZ of X100 pipeline steel after a secondary thermal cycle and hydrogen sulfide stress corrosion cracking (SSCC) resistance of the transformed microstructure are investigated. The microstructure of X100 pipeline steel after the secondary thermal cycle is similar to that after the primary thermal cycle, comprising lath bainite and granular bainite. With an increase in t(8/5) (time required for the material to cool from 800 degrees C to 500 degrees C), the M-A constituents that continuously precipitate along the prior austenite grain boundaries in the second thermal cycle are coarsened and form a necklace-type structure. A variation in t(8/5) does not significantly affect the crystallographic characteristics of the ICCGHAZ. The stress corrosion test shows that the resistance to SSCC decreases and cleavage fracture characteristics become more noticeable with an increase in t(8/5). (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.