Study On The Microstructure And Mechanical Properties Of Marine Steel After Thermal Deformation

In this paper,two kinds of ship steel with different nickel content are studied.Through heat treatment,simulated controlled rolling cooling and controlled rolling cooling experiments,the effects of different experimental conditions such as holding time,cooling mode,deformation,final rolling temperature and different nickel content on the microstructure and properties of ship steel are systematically studied.The main elements are as follows:After different heat treatment processes,the effects of different holding time and different cooling methods on the structure and properties of ship steel were studied.The results showed that the holding time increased at the same temperature,and the hardness increased because of the precipitation strengthening effect.At the same temperature,that is,with the increase of cooling rate,the hard phase,including bainite and martensite,is gradually formed in the structure,which improves the hardness and performance of the test steel.At different temperatures,the increase of cooling temperature will make the material produce hard phase and increase the hardness.The effect of different deformation and final rolling temperature on the microstructure and properties of the test steel was studied.At the same open rolling temperature and final rolling temperature,the dislocation and precipitation phases in the microstructure of ship steel samples with different deformation increased.At the same time,with the increase of deformation,the size of ferrite grain becomes smaller,which increases the hardness and performance of the test steel.With the decrease of final rolling temperature,the grain size of ferrite in the test steel becomes finer,and the amount of hard produced increases,resulting in the increase of hardness and better performance.However,the hardness increases with the decrease of temperature and the overall hardness of the sample is higher than that of the sample without water cooling under the same deformation,which indicates that the hardness of the test steel can be improved by water cooling after rolling.Make the performance better.The structure of granular bainite,upper bainite,needle ferrite,polygon ferrite and a small amount of pearlite were obtained by controlled rolling and cooling.The tensile strength,yield strength,elongation and hardness of the two steels are very high,while the properties of B steels are better than those of A steels.both steels achieved good performance through fine-grained strengthening,martensitic strengthening,precipitation strengthening and controlled dislocation strengthening caused by rolling cooling.Alloy element nickel effectively improves the low temperature impact toughness of experimental steel.both steels have excellent impact work due to the high texture strength of RD specimens.