Research On The Heat Treatment Online Process And The First-principles Characterization Of X90 Pipeline Steel

In this paper,by heat-treatment on-line process to the traditional TMCP of single-phase X90 pipeline steel,received B + M/A group of bipolar.To adopt the material microscopic analysis,mechanical property test,such as technology,studied the microstructure and mechanical properties of B + M/A X90 pipeline steel,established the relations between organization and performance which applied to the large deformation of pipeline steel process under complex geological conditions.And to discuss alloying elements on the influence of the austenitic stability use the first principle.The results show that:by changing the stop-cooling temperature of heat treatment on-line process,we can get the different proportions of B +M/A group of bipolar.With the increase of stop-cooling temperature,test the strength of the steel,hardness than a downward trend; Break elongation and uniform elongation showed increasing trend. When the stop-cooling temperature is 350 ℃,test the uniform elongation of steel not less than 8%,showed less than 0.80,the deformation reinforcement index were greater than 0.10,conform to the requirements of the large deformation of pipeline steel.At this point,the bipolar tissues thin beams of lath bainite, lath exist certain number of M/A group,and slat distribution between the small dispersion carbide alloy,thus has the high strong plasticity.As partitioning temperature of HOP rising,steel yield strength,tensile strength and hardness is trend to decrease,uniform elongation and break elongation showed a trend of increase.Showed and deformation strengthening index is relatively stable,show a good level of plastic and large deformation capacity.This is due to bainite matrix carbon in the degree of supersaturation and crystal lattice distortion decreases with the increase of temperature,the dislocation density of lower bainite and lath width,the number of precipitation of carbide bainite matrix and morphological changes,and results made the decrease of strength and plastic.As extension the partitioning time,the test of steel yield strength,tensile strength,break elongation ratio,uniform elongation increase.It is mainly due to the grain of bainite, lath beam width,bainitic lath between thin layers of massive M/A group and grain boundary group changes from small to big,which resulted is reduced the strength of the steel,increase plastic of the steel.The total energies and binding energies of a niobium atom or a carbon atom of interstitial solid solution and substitutional solid solution in γ-Fe and α-Fe were calculated.Based on the total energies and binding energies we determine the form of solid solution of niobium and carbon.The calculation results indicate that in γ-Fe,niobium exists in the form of substitution solid solution and carbon could be in the form of substitution solid solution or interstitial solid solution,the carbon atom is more likely to exist in the form of interstitial solid solution.But in α-Fe,neither niobium nor carbon exists in the form of solid solution.In containing niobium atomic displacement solution austenitic crystal cell,the diffusion of carbon atoms can make the total energy of the system in the austenite appear larger fluctuation.Join niobium in steel elements,can improve the transfer of carbon atoms activated,reduces the austenite to ferrite transformation temperature,delayed the austenite to ferrite transformation,makes the stability of austenite increases.