Speaker
Description
Abstract
The balance between strength and ductility is a key requirement in pipeline steels, where the yield-to-tensile (Y/T) ratio directly influences strain capacity and resistance to failure under complex loading conditions. In thermo-mechanical controlled processing (TMCP) of API X70 plates, maintaining a low and stable Y/T ratio while meeting strength and toughness requirements presents a critical metallurgical and process challenge.
This study presents an industrial investigation into the control of Y/T ratio in API X70 plates produced in a 4900 mm heavy plate mill. The work examines the combined effects of alloy design, deformation history, and accelerated cooling on the relationship between yield strength and tensile strength.
A coordinated optimization strategy was implemented, including reduced carbon levels, controlled microalloying, and precise Ti/N ratio management to enhance grain refinement while limiting excessive strengthening. Process parameters were refined through controlled rolling and optimized cooling conditions to promote a balanced ferritic–bainitic microstructure and suppress the formation of hard phases that elevate yield strength disproportionately.
Industrial results demonstrate that the optimized approach achieves stable Y/T ratios below 0.85 while maintaining required strength levels and toughness performance. The findings confirm that an appropriate balance between strength and ductility can be consistently achieved through integrated metallurgical and process control.
This work provides a practical framework for engineering strain capacity in TMCP plate production under real industrial conditions.