Study On The Effect Of Controlled Rolling And Controlled Cooling Process On Microstructure And Mechanical Properties Of X70 Pipeline Steel

Pipeline steel is used for transporting oil, gas, etc of the large diameter welded steel pipe used for hot rolled coil plate or lenient plate.Pipeline steel in use process, in addition to the requirement has high compression strength, also requires a high low temperature toughness and excellent welding performance.Pipeline steel has been widely used in high pressure under the condition of the long distance transportation of oil and gas,In our "west to east gas pipeline project ",X70and above levels of the pipeline steel with high strength, high toughness, good welding performance, corrosion resistance and organization for low carbon steel or low carbon acicular ferrite organizational requirements.This article through to the determination of X70pipeline steel static CCT curve,based on the determination of X70pipeline steel static CCT curve,and alloy elements to form the effects of acicular ferrite X70pipeline steel,investigate the supercooled austenite under the conditions of continuous cooling transformation rule,through the microstructure and hardness of after cooling and fracture analysis of the cooling rate and the influence of chemical composition on the structure and hardness.This not only for X70pipeline steel thermal simulation scheme design, provides a theoretical basis for X70pipeline steel provides theory basis for practical production.This paper concluded:Three experiments respectively on the basis of1#steel, added Mo element experiment on2#steel and Nb, V, Mo added on3#steel.when rolling heating temperature is1170℃±15℃,the austenitic grain group is smallest.1#and3#experiment of X70pipeline steel finishing temperature should be controlled in800±15℃,and2#experiments of steel finishing temperature should be controlled in820±15℃.Experiment1#steel crimp temperature should be controlled in540±15℃,2#and3#steel crimp temperature should be controlled in540±15℃.Add Mo elements and high Nb content of experimental steel can at lower cooling rate and larger cold speed range obtain acicular ferrite structure, and the experimental steel hardness increases with the increase of cooling rate.Temperature reasonable design of hot rolling process, meet the capacity of1450sets of production equipment for HSM in Panzhihua area.