Selection of Alloy Design for Low-temperature Toughness Plates Used for Line Pipes

The low toughness and poor weldability of the higher carbon steel grades restricted their acceptability for line pipe steel,and therefore,created good demand of low carbon micro-alloyed steels for line pipe steel for both onshore and offshore applications.In low carbon micro-alloyed steels,alloy design plays an important role to achieve the desired mechanical properties with minimum processing and alloy cost.During the alloy design process,though primary focus is given to the hot rolling process starting from slab re-heating to final rolling,but steelmaking and continuous casting cannot be overlooked for cleanliness of the steel.This paper presents a detailed study of alloy design and hot rolling parameters to achieve the optimum mechanical properties including higher toughness measured by drop weight tear test at -25℃.These experiments were carried out with API 5L X70M PSL2 grade slabs,which were rolled into plates of size 25 mm x 3 830 mm.The test results were co-related with microstructure analysis and hot rolling parameters.