Effect On Corrosion Behavior Mechanism Of Pure Nickel And NiCrMoV Steel Weld Joint In Deep Sea Environment

The effect of hydrostatic pressure on the corrosion behavior of nickel in NaCl solution was investigated by electrochemical measurements and OM/SEM observation in this thesis.The increasing hydrostatic pressure deteriorated the pitting corrosion resistance of nickel,distinguished by the decrease of critical pitting potential(Ecirt)with increasing passive current density.The results also demonstrated that hydrostatic pressure had three effects on the corrosion behavior of nickel:The increasing hydrostatic pressure hindered the passive film formation;The increasing hydrostatic pressure retarded the B1 process(parallel birth and death stochastic model)and accelerated the A3 process(parallel birth stochastic model);The pitting growth probability increased.Metal nickel as a kind of important alloy element is added to the new type of low alloy steel 10Ni5CrMoV steel to improve the corrosion resistance.As a new generation steel of deep sea engineering,10Ni5CrMoV steel is widely used in construction of deep sea engineer and deep submergence vehicle.The construction of deep sea engineering and deep submergence vehicle is dependent on the welding technical.The comprehensive performance of 10Ni5CrMoV steel welded joint directly affects the service safety of deep sea engineering and deep submergence vehicle.Therefore,to investigated the influence of welded joint deep-sea corrosion in the welding process become very urgent.This paper using MSC.Marc finite element method numerical simulated the welding process based on a 1.85 KJ/mm,2.34 KJ/mm,3.17 KJ/mm three kinds of welding line energy preparation 10Ni5CrMoV steel welding joint.The research results showed that when increasing the line energy,the weld metal area showed a higher temperature and longer duration,the stress field and strain field value decreased gradually.The results show that the greater the formation of the region of heat affected zone width was greater by metallographic analysis when welding line energy heighten.The greater the welding line energy is,the lower the cooling rate is.It occur that the higher possibility from martensite phase transformation to bainite phase transformation,and the welding residual thermal stress level of welding joints is higher.Corrosion test results show that welding joint under condition of 1.85KJ.mm-1 and 3.17KJ.mm-1 line energy has serious local corrosion and pitting corrosion phenomenon in deep sea environment.10Ni5CrMoV steel welded joint under condition of 2.34KJ.mm-1 line energy has the high corrosion resistance in deep sea environment.The welded joint of 10Ni5CrMoV steel appear local corrosion and pitting in deep sea environment has two aspects:on the one hand,the welding thermal cycle lead to the welded material increased the corrosion sensitivity in deep sea environment with residual thermal stress in the surface of welded joint because of mechanical and chemical inhomogeneity;On the other hand,the characteristics of welded joint metal between the metallic materials in deep-sea environment appear larger potential difference lead to galvanic corrosion,accelerated the corrosion rate of welded metal and heat affected zone in a deep-sea environment.Using finite element method simulated the electrochemical corrosion of welded joints in complex multi-factor coupling deep sea environment.The results showed that the welded metal and heat affected zone has strong corrosion sensitivity.The local corrosion is easy to appear on surface of weld joints in deep sea environment.It is endanger the safety of welded joints service in deep sea corrosion.It provided guidance of corrosion evaluation for welded joint of 10Ni5CrMoV steel in deep sea through buildied the mathematical model in corrosion prediction with different of environmental parameters in sea water environment,and combining with the finite element analysis methods researched the corrosion electrochemical of weldied joint in shallow sea and deep sea environment.