| According to the national future development plan,the market demand for marine engineering steel will be increasing.The development of Arctic waterway and the navy's ocean cruise require high strength ship plate steel with better lowtemperature-toughness and corrosion resistance.EH47 ship plate steel,as a new generation of developed products,has become an indispensable material for large ships and polar ice breakers serving in harsh natural environment.In this paper,EH47 ship plate steel is taken as the research object,the effect of hot deformation parameters such as reduction,cooling rate after deformation and final cooling temperature on the microstructure of EH47 ship plate steel was studied by thermal simulation experiments.The effects of different quenching temperature and tempering temperature on the microstructure of EH47 steel plate were studied by means of modulation heat treatment experiment.Combining optical microscope(OM),scanning electron microscope(SEM)and transmission electron microscope(TEM),the evolution of EH47 high strength ship plate steel with parameters of different deformation and heat treatment process was studied.Thermal simulation compression experiments were carried out by adjusting the reduction of intermediate passes and final passes.The results show that when the reduction of intermediate passes is 35% and the reduction of final passes is 40%,a large number of acicular ferrite and upper bainite in the microstructure of EH47 steel are uniformly distributed,and the microhardness of the experimental steel is also greater than that of the experimental steel under other conditions.The distribution of acicular ferrite and upper bainite in the microstructure is uniformly when the cooling rate after rolling is 50?/s and the final cooling temperature is 650?.When the final cooling temperature after rolling is increased to 700?,the percentage content of bainite in the material microstructure can be increased,and the microhardness of the experimental steel also increases.By adjusting the process parameters such as quenching temperature and tempering temperature,it is concluded that the strip defects in EH47 ship plate steel after hot rolling can be eliminated by quenching at 960? for 30 minutes and then tempering at 640? for 30 minutes.There are more lath bainites in TEM microstructure,the grain size is more refined,the ferrite and bainite are interlaced and uniformly distributed,there is obvious second phase precipitation between ferrite grain boundaries and bainite laths,and the microhardness of the experimental steel is higher.The microstructures of EH47 ship plate steel are observed at different cooling rates,it can be found that when the cooling rate is 0.5?/s,there are many slender lath bainites in the microstructure and the second phase precipitates in the lath bainite.When the cooling rate is 10?/s,there are obvious M/A islands in the microstructures and crystal twins can be observed in the M/A islands. |
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