Research On Microstructure Property And Production Technology Of Hot Rolling Of X65 Pipeline Steel

For long distance transportation used pipe steel, high ductility is the key to assure pipeline's safty and cost reduce. Appropriate chemical combination is one of the methods that can improve final properties, and technology of rolling and cooling control is another effective method to improve properties.This paper makes X65 pipeline slab made by hot slab factory as research object, through thermal simulated test and lab rolling test, effects of technologic parameters of controlled rolling and controlled cooling on microstructure and properties are studied. With methods of microstructure control and refinement, X65 pipeline steel meets the national standard of properties.This article makes analysis of the effect of different technical conditions on microstructure and properties of X65 pipeline steel by simulated test. Analysis shows that during the period of rough rolling, smaller and more homogeneous austenit grain can be gained in five-pass rolling than three-pass rolling. Starting finish-rolling temperature should be controlled under 900℃. The much lower the finishing rolling temperature is, the smaller and more homogeneous the microstructure is. When finishing rolling temperature is 750℃, the grain is very small with continuous distributing of small particle and average grain size is about 4μm. Cooling rate after rolling should be controlled between 10℃/s and 15℃/s. Batching temperature has little effect on refinement of microstructure under the condition of 15℃/s or more.X65 pipeline steel has been practically simulated rolled after technologic parameter set, based on experimental results of thermal simulation. Microstructure and properties are analyzed which offer theoretical principles to establishing production technology of X65 pipeline steel in Tangshan Steel Co.Ltd. It shows that techniques with finishing rolling temperature of 810℃, cooling rate after rolling of 14℃/s and final cooling temperature of 535℃are perfect. X65 pipeline steel with superior properties can be obtained.Production technology is adjusted and X65 pipeline steel is testing rolled in 1700 production line in Tangshan Steel Co.Ltd. on the base of experimental results. Microstructure is ferrite and a little pearlite. Types of impurity are silicate and sulfuret. Mechanical properties of X65 pipeline steel are content to the national GB/T1591-94 standard. Finally, the perfect technologic scheme of X65 pipeline steel is obtained: finish-rolling temperature of 990℃, finishing rolling temperature of 822℃, cooling rate after rolling of 12℃/s, final cooling temperature of 608℃and rolled reduction of 29.8%, 34.4%, 27.8%, 16.4%, 13.1%, 7.3%. That provides theoretical and technical support for the realization of X65 even more higher grade production in Tangshan Steel Co.Ltd.