Study On The Influence Of Microalloyed Elements On Microstructure And Properties Of 0.5%Ni Steel

Low temperature steel has experienced a history of more than 100 years.Its emergence is a milestone in the history of industrial revolution and has laid the foundation of the world energy industry.The boiling point of liquefied natural gas is very low.Its storage and transportation equipment must be made of materials with high low temperature toughness.The development of low-temperature steel is a national key technology and equipment project.In this paper,0.5ni% low temperature storage tank steel was designed and prepared.The effects of Microalloying Elements Nb and V on the microstructure and properties of different normalized 0.5ni% steel were studied by means of metallographic microscope,scanning electron microscope,tensile testing machine and low temperature impact testing machine.The following results were obtained.In terms of microstructure,the microstructure of low-temperature steel after normalizing at 890 ℃ with different microalloying elements grows along the rolling direction.With the increase of normalizing temperature,the microstructure becomes more and more uniform,but the grain size also increases.After adding Nb and V to the material,Nb plays the role of fine grain strengthening,and V plays the role of fine ferrite and precipitation strengthening.In terms of mechanical properties,the yield strength of the low-temperature steel without Nb and V after normalizing at 890 ℃ is 4MPa lower than the standard,while the tensile strength and elongation after fracture meet the service requirements;However,the low-temperature toughness after different normalizing temperatures did not meet the use standard.After normalizing at 890 ℃,910 ℃ and 930 ℃,the yield strength,tensile strength and elongation after fracture of the low-temperature steel added with Nb meet the service requirements,and the tensile property is the best after normalizing at 930 ℃;The low-temperature toughness is not up to the standard.After normalizing at 890 ℃,910 ℃ and 930 ℃,the yield strength,tensile strength and elongation after fracture of the low-temperature steel added with V reached the service requirements,and the tensile property was the best after normalizing at890 ℃;The low temperature toughness is the best after normalizing at 890 ℃,and all the data are higher than the use standard.After normalizing at 910 ℃ and 930 ℃,all the data do not meet the use standard.The mechanical properties of low temperature steel normalized at 890 ℃ are relatively optimal.After normalizing at 890 ℃,910 ℃ and 930 ℃,the yield strength,tensile strength and elongation after fracture of the low-temperature steel added with Nb and V meet the service requirements,and the tensile property is the best after normalizing at 890 ℃ and much higher than that of the low-temperature steel only added with V;The low temperature toughness is the best after normalizing at 890 ℃,and the impact toughness decreases after normalizing at 910 ℃ and 930 ℃.The mechanical properties of low temperature steel normalized at 890 ℃ are relatively optimal.Considering comprehensively,the performance of low temperature steel with Nb and V addition after normalizing at 890 ℃ is the best.