Thermodynamic Study on the Precipitation Behavior of Carbonide and Nitride in X80 Pipeline Steel

In order to clarify the precipitation rule of precipitated particles in the solidification process of X80 pipeline steel,the Thermo-calc software was used to analyze the austenite and ferrite phase transition temperature,the type of precipitates,the precipitation temperature of the precipitates and the maximum mass fraction of the precipitated phase during the solidification of X80 pipeline steel.The calculation results show that the precipitation phase of X80 pipeline steel solidification process mainly includes MnS phase,AlN phase,ferrite phase and austenite phase,titanium-rich phase carbonitride precipitation phase,cerium-rich phase carbonitride precipitation phase and vanadium carbide precipitation phase.The precipitation temperature of the titanium-rich phase carbonitride precipitation phase is 1 390 ℃,the mass fraction is 1.2×10^-4,and the precipitation phase is inhibited by the increase of the content of C element and Nb element.The increase of N and Ti content promotes the formation of carbonitride precipitation phase in the titanium-rich phase,and the V element mass fraction increment has no obvious effect on the precipitation of titanium-rich phase carbonitride.The carbon-nitrogen precipitation phase of the yttrium-rich phase precipitated at 1 110 ℃,and the mass fraction was 1.3×10^-3.With the increase of the content of C and Nb,the precipitation of carbon and nitrogen in the eutectic phase was promoted.Increasing the content of N element and Ti element inhibits the precipitation of carbon-nitrogen precipitation phase in the enthalpy-rich phase,and V element has no obvious influence on the cerium-rich carbonitride.The precipitation temperature of vanadium carbide precipitation phase is 596 ℃,and the mass fraction of precipitated phase is 4.59×10^-5.Increasing the content of C and V element is beneficial to the precipitation of vanadium carbide phase.The increase of Nb content can inhibit the vanadium carbide phase.