2019 International Conference on Petroleum Tubular Goods, Equipment & Materials (TEC 2019)

78 / 2019-04-19 17:43:05

Effect of Niobium in simulated coarse grained heat affected zone of high strength microalloyed pipeline steels

Pipeline & storage and transportation facilities materials > Pipeline & storage and transportation facilities materials

Low carbon high strength microalloyed steels provide significant economic and technical advantages in pipeline projects. Critical attention has been given to the ability of the steel to maintain mechanical properties in the weld heat affected zone (HAZ). Increased levels of niobium in a titanium microalloyed, low carbon high strength steel has been shown to mitigate the detrimental effects of austenite grain coarsening in the critical high temperature region of a weld HAZ. Improved austenite grain size control enhances the transformed microstructure with a concomitant improvement in Charpy V-notch (CVN) toughness. The present paper evaluates the CVN toughness of the CGHAZ of a modern high Nb steel and compares performance with a traditional Nb/V microalloyed steel using weld thermal simulation techniques. High Nb steel showed superior performance in control of the CGHAZ Charpy toughness. Inductively coupled plasma mass spectroscopy (ICP-MS) of the thermally simulated CGHAZ, has revealed increased levels of niobium in solid solution is associated with improved control of the prior austenite grain size. Small austenite grains reduce hardenability, avoids unfavourable microstructures and so enhance mechanical properties at the CGHAZ.