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Effect of Niobium on Weld Metal Microstructure and Properties in Submerged Arc Welded X70 Steel

Oil and gas pipelines transport a wide range of products and are subjected to extreme environmental conditions. Modern micro-alloyed steels used in the oil & gas industry are thermo-mechanically control processed (TMCP) to obtain desired microstructures and mechanical properties. Line pipe is produced from the TMCP coil or plate (called skelp) by helically winding or longitudinally forming and welded using submerged arc welding (SAW).

Currently, X70 is produced using several different compositions and rolling recipes. Niobium (Nb) is widely used due to its low cost and other advantages, but questions have been raised about the effect of Nb on microstructure and properties when introduced into the weld metal via dilution. The specific concern is that poor and/or inconsistent weld metal toughness is obtained with high-Nb base metals.


Industry Sponsor: Arcelor Mittal

Faculty Mentor: John Lippold (OSU)

Graduate Student: Tate Patterson

Industry Contact: Murali Manohar