L51939 Weldability of High-Strength Enhanced Hardenability Steels

Since the 1970s, the development of high-strength pipeline steels has followed the route of progressively reduced harden ability through lower carbon and alloying element contents. Micro-alloying, controlled rolling (CR), and thermo-mechanical controlled processing (TMCP) have been used extensively to achieve the high-strength and other material property requirements despite the trend towards lower carbon content. The primary driving force behind the evolution of these alloying and processing strategies stems from the concerns over the weld ability, particularly the hydrogen induced cracking (HIC), at ever-increasing strength levels. Accompanying the extensive reliance on micro-alloying, CR, and TMCP, there has been a movement to tighter restrictions on micro-alloy variability, the increased use of heavy reduction at low inter-critical temperatures and, in some instances, the reliance on cold expansion.

The objective of this project was to evaluate alternate steels with enhanced harden ability and identify those that would have a potential to (1) meet the high strength/high toughness requirement but without the adverse effects of the early trial heats of micro-alloyed TMCP X80 and X100 line pipe steels, and (2) exhibit sufficient resistance to hydrogen induced cracking (HIC) when welded with processes and consumables representative of state-of-the-art, low-hydrogen field girth welding practices. The focus of the project was on the weld ability and properties of the base metal and the heat-affected zone (HAZ). The selection and development of suitable weld consumables were not part of this project.