The Research And Development Of Hot Rolled High Toughness Pipeline Steel Strip S450

The hot rolled pipeline steel S450 with a high strength, a good toughness and weldablility, Resistance of HIC&SCC, corrosion resistance was researched and developed on ASP line in Jinan Steel. The chemical composition of the steel was involved in decreased C,Si, increased Mn, lowered S and P, and microalloy element Ni,V,Ti. With the application of the technology of controlled rolling and cooling,Various thick gauge steel strips for diverse technical requirement was practiced.The key production process and technology of steel S450 was investigated. The technical parameters such as heating temperature, finishing temperature and coiling temperature To be intensively studied and established. the steel with fine homogeneous microstructure and high performance integrated mechanical properties was obtained. the adoption of the technology of dead pass on the F2 mill stand, then the finishing rolling pass was from 6 decreased to 5. The inadequate of intermediate slab thickness, the small amount deformation of non-recrystallization region was disposed. For no deformation in austenite partially recrystallization, the rate of mixed crystals was reduced. Two phase cooling measure was adopted for disposing the problem of higher yield ratio in thin gauge steel strip. The measure is turning off the first three part cooling phase, then prolonging the steel strip in high temperature time, decreasing the cooling rate during the first cooling phase, and combined the water flow rate of the first and second cooling phase optimized the process of laminar cooling. And adoption the "hot tail" technology, obtained the equal properties of the steel coil in its middle and tail.The paper also deeply Discussed the mechanism of strengthening and toughening and systematically researched the microstructure of the steel strip, the effect of the grain refining, solution strengthening, phase transformation, precipitation strengthening, dislocation strengthening to the steel. It points out The most important element to the steel is grain refining and nano size precipitation strengthening. It settled a base for increasing properties of steel through controlling structure and developing the high grade pipeline steel.