Study On Microstructure And Properties Of The Casting ZG1Cr11Ni2WMoV Martensite Heat-resistant Steels

The effects of alloying elements Si,Mn,N and tempering temperature and long-term aging on the microstructure and mechanical properties of cast ZG1Cr11Ni2WMo V martensitic heat-resistant steels were investigated by field emission scanning electron microscope and energy spectrum analyzer in field emission projection electron microscope and polycrystalline X-ray diffraction apparatus and hardness and impact test at different temperatures.The conclusions are made as follows:The remelted cast test stick addition of 0.5%Mn can reduces the precipitation ofδ-ferrite,and addition of 0.3 to 0.4%Si increasesδ-ferrite precipitation.The addition of Si and Mn in the remelted master alloy increases the tensile strength and yield strength of the heat-resistant steel.The remelting the mother alloy after quenching,its tensile properties are superior to direct tempering.After adding 0.5%Mn,0.3%Si and 0.08%N to the remelted cast test stick,the elongatedδ-ferrite was reduced,and the tensile strength and yield strength were improved.However,the impact energy value varies greatly under different heat treatments.In the as-cast microstructure,the microstructure was the same as the tempered at 550°C.The presence of elongatedδ-ferrite was distributed at the prior austenite grain boundary.After being tempered at 580°C for 2hours,it can not only be eliminated but also precipitated around it.For the M₂₃C₆type carbides,it was found that cracks were preferentially formed and expanded around theseδ-ferrites in the fractured longitudinal section of the impact specimen.The main reason,it can be seen that the existence ofδ-ferrite is low impact energy absorption of the steel under direct tempering in the as-cast condition.Casting test bars after high temperature quenching,due toδ-ferrite to reduce the change in morphology,so that a slight increase in tensile properties,but impact absorption work significantly improved.In summary,the heat treatment process has little effect on the tensile properties of the heat-resistant steel,but has a greater influence on the impact absorption work.The reason is related to the deformation rate of the two test methods,the continuous distribution ofδ-ferrite is more sensitive.Remelted master alloy cast test bars have different carbide types at different tempering temperatures after quenching.The temperature in 550～600°C,the M₆C-type carbides and M₂₃C₆type carbides were more within the martensite lath.The temperature in 650～700°C,the M₂₃C₆type carbides distributed along the prior austenite grain boundary and the martensite lath boundary.The shape of M₂₃C₆type carbides were block in 600～650℃,but the temperature at700℃,the shape of M₂₃C₆type carbides were long rod.Remelted master alloy cast test bars after quenched 1050°C for1 hour air-cooled and at550°C and 600°C long-term aging treatment.After at 550°C for 2 hour,the microstructure of the test steel was mainly fine and dispersive M₆C type carbides,and the tempered martensite laths were big.With the aging time increases,the needle-like M₆C on the original slats were disappeared and the chain-like M₂₃C₆carbides distributed along the lath boundary were appear.M₂₃C₆carbides and Laves phases were precipitated inδ-ferrite.The steel at 600°C,with the aging time increases,M₂₃C₆type carbides from the dispersion to the chain distribution,M₂₃C₆carbides and Laves phases were precipitated inδ-ferrite.