DEVELOPMENT OF 690MPa HIGH STRENGTH STEEL WITH LOW YIELD RATIO AND GOOD WELDABILITY FOR BUILDING STRUCTURES IN WISCO

摘要

690MPa high strength steel with low yield ratio for building structure has been developed successfully by micro-alloying design and thermal-mechanical controlled processing in WISCO. The mechanical properties, weldabilities and microstructure of the based steel were studied by means of mechanical property test and microstructural analysis with optical microscope and transmission electron microscope. The results show that the mechanical properties meet the requirement of specification for developed steel, the microstructure of the based steel primarily comprised of fine lath and granular bainite, small fraction of ferrite and martensite-austenite constituent. During the thermal cycle, the austenite grain growth, microstructure coarsening, increasing of volume fraction and grain size of M-A constituent, and blocky M-A constituent in HAZs are the main reasons for deteriorating low temperature toughness. The plates of developed steel have high strength, high toughness, lower yield ratio and good weldability, and the plates will be the suitable high strength materials for fabricating high-rise, super high-rise building structures and large span projects.