Abstract
The microstructure evolution process of X100 pipeline steel is analysed, and the influence of different alloy composition and accelerated cooling process on microstructure evolution is studied in this article. It is obtained that acicular ferrite microstructure can make the yield strength of steel reach 650 MPa through micro alloying and thermo-mechanical control process(TMCP) with the comprehensive reinforcement effect of grain refinement, micro-alloying element precipitates and dislocation substructure. Acicular ferrite has the characteristics of fine grain, cross distribution, large angle grain boundary and presence of sub structure and high density movable dislocation. Test results of product quality also show that X100 pipeline steel which adopts Mn-Nb-Ti component system with a small amount of Ni (V), Mo alloy addition and TMCP process has obvious characteristics of fine grain. The Matrix is consisted of granular bainite and appropriate amount of MA as dispersion phase, which makes the tensile strength reach more than 800 Mpa. At the same time, the X100 pipeline steel has the characteristics of high toughness and good weldability, which is beneficial to ensure the safe operation of high pressure natural gas pipeline.
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