Development And Research Of Pressure Vessel Steel Q345R(HIC)

In order to adapt to the increasing depletion of oil and gas resources in recent years,oil and gas fields offen containing corrosive medium H2S,Cl-and other harsh environments are successively extracted,It leads to the increasing of the service environment of the pressure vessel steel.The shell and the welded joint are directly subjected to the physical and chemical action of the corrosion medium,Extremely prone to corrosion reactions lead to failure.Q345R as the most widely used and the largest amount of special steel in pressure vessel steel,It is difficult to adapt to the requirement of more and more severe service environment.It is urgent to develop a pressure vessel steel Q345R(HIC),which has both mechanical properties,corrosion resistance and welding properties.Cl-and H2S has strong corrosive,it Easy to cause corrosion of base metal and welded joint,Therefore,it is necessary to research the corrosion behavior of Q345R(HIC)steel.It can provide technical parameters for industrial production to obtain the comprehensive performance of the Q345R(HIC)steel.This part has studied microstructure,mechanical properties and corrosion behavior in different corrosion environment of pressure vessel steel Q345R(HIC).The main research contents of this paper are as follows:(1)Using low C,Mn elements,low S,P content,C-Mn system alloy composition design.The critical phase transformation point,the static CCT curve and the dynamic CCT curve of the experimental steel are measured by Formastor-F II dilatometer and DIL805 dilatometer.The results show that:The critical phase transformation point Ac1 and Ac3 of the experimental steel are 699? and 837? respectively.in the continuous cooling process,researched the transformation regular pattern of the microstructure of the over cold austenite at different cooling rates,By comparing the dynamic and static CCT curves,the deformation makes the dynamic CCT curves move to the Upper left of each phase and the time required for the phase transformation is also shortened.Deformation significantly expanded ferrite and pearlite complex phase transformation region,reduced bainite,martensite transformation region.The result of rolling and heat treat experiment research of pressure vessel steel Q345R(HIC)shows that:hot rolled samples have excellent comprehensive mechanical properties,After rolling choice of normalizing temperature is 900?,the normalizing time is 10min,the best comprehensive mechanical properties can be obtained in the experimental steel,and the transverse impact energy of 0? is 270J.(2)Research on the corrosion behavior of hydrogen induced cracking and the influence factors,The results show that:Although there is no hydrogen bubbling on the Q345R surface of the steel plant,there are a lot of long cracks in the sample,and And does not meet the requirements of NACE TM 0284-2011 for anti hydrogen induced cracking performance.There is a small amount of hydrogen bubbling on the surface and no crack in the ferrite pearlite microstructure samples and ferrite bainite microstructure samples for the laboratory rolling,and no crack in the samples,and meet the requirement of NACE TM 0284-2011 for the hydrogen induced cracking resistance.Banded structure is a good transport channel for hydrogen,and hydrogen induced cracking is generally extended along the banded,and the higher the band structure,the greater the hydrogen cracking susceptibility.The interface between inclusion and matrix is a strong trap of hydrogen,and it is the source of hydrogen induced cracking,and the higher the inclusion level,the greater the hydrogen cracking susceptibility.The smaller the grain size is,the larger the effective grain boundary area is,Could make the hydrogen trap more evenly dispersed into the steel matrix,Thus it can improve the performance of anti hydrogen induced cracking.(3)Through electrochemical polarization curves measurement experiment and electrochemical impedance spectroscopy,The polarization curves and Nyquist diagram and Bode diagram of electrochemical impedance spectroscopy were plotted.The research shows that:Cl-as a solution of strong corrosive ions,can erosion the passivation film on metal surface,with the Cl-concentration increased,the corrosion resistance decreased.The more uniform the microstructure is,the better the surface passivation film is formed,the impedance value is increased,the phase is close to 90°,and the corrosion resistance is improved.The smaller the grain size,the more conducive to the free transfer of erosion ions,the worse the corrosion resistance.(4)By using submerged arc welding to Q345R(HIC),Testing Tensile,impact,bending,hardness and HIC of welding joint.The results show that:The tensile specimen is broken at the position of the base material,The impact toughness of the heat affected zone is poor,but it also reached 152J,far exceeding the standard of 41J,There is no crack after bending,the hardness of the heat affected zone is highest,up to 221HV,which is far from reaching the 350HV of the International Welding Engineers Association.After the HIC experiment,there is no hydrogen bubbling on the surface of the welding joint and no crack in the sample,which had excellent anti hydrogen induced cracking performance.