Study On Service Properties Of 500MPa LPG Marine Cryogenic Steel

Liquefied Petroleum Gas(LPG)is a new fuel and basic chemical raw material.Liquefied production,storage,and transportation are used.Related storage and transportation equipment also work at a low temperature.Steel must have sufficient low temperature toughness,strength,plasticity,weldability,fatigue and corrosion resistance and other comprehensive properties.In this thesis,500 MPa LPG Marine low-temperature steel is taken as the research object,and the low-temperature mechanical properties of base metal and welded joints are studied by gas shielded welding and submerged arc welding methods.Series lowtemperature tensile test,Charpy impact test,CTOD test and fatigue test of LPG steel and welded joints are carried out.The abrasion and erosion properties and characterization methods of LPG steel are studied,and the main conclusions are as follows:(1)The yield and tensile strength of 500 MPa low-temperature steel for ship use increase with the decrease of temperature.It can be predicted that the plastic deformation can still be maintained at-70℃,and the low-temperature tensile resistance is good.The low temperature impact performance of 500 MPa LPG steel is better.The average transverse impact performance of LPG steel surface is still greater than 100 J at-70℃,which fully meets the requirements of standard F-class Marine steel.The low temperature CTOD value of 500 MPa LPG steel base metal meets the traditional Boltzmann distribution,and its CTOD value can still meet the requirements of the specification when it is at-40℃.The fatigue limit of the material at-20℃ is about320 MPa.In comparison,the ultimate strength of the material at low temperature is better than that at normal temperature and high temperature.(2)The strength of the welded joint is higher than that of the base metal,but the impact toughness is not as good as that of the base metal.The strength of the submerged arc welding wire is low,but the impact toughness is greatly improved at low temperature.The characteristic values of weld center and heat-affected zone CTOD of two kinds of welded joints of 500 MPa LPG steel were analyzed.The results showed that compared with base material and weld,the toughness of materials in heat-affected zone deteriorated more rapidly and decreased more rapidly with temperature.If the CTOD value of the affected zone was taken as the evaluation standard,At-40℃,the CTOD value of LPG steel welded joint can barely meet the requirements of the specification.Compared with the impact test,the ductile-brittle transition temperature was higher and the brittle tendency was more obvious in the CTOD test.(3)The difference in wear value of 500 MPa LPG steel under normal temperature dry friction condition is not large,and the data of other polar ship steel is similar.Generally speaking,the material has good anti-abrasion performance,which is not much different from that of imported materials.If the material performance is evaluated at low temperature,the low-temperature anti-abrasion ability still has room for improvement.The corrosion resistance and erosion performance of 500 MPa LPG steel need to be improved,and the erosion performance of the material needs to be further studied.