| 30Cr2Ni4MoV steel after systematic heat treatment was analyzed by the aid of optical microscopy (OM), grain size test, X-ray diffraction (XRD), residual austenite contents test and electronic microscope crystallographic analysis. The results show that:Grain size scale of the steel after 710℃×4 h +830℃×6 h is 6.8, which is superior to that of steel after adjusting refinement and isothermal annealing treatment whose grain size scale are in the range of 3 and 4. Although the grain size scale of steel after tri-normalizing is between 7~8, consider its being maleficent to energy conservation and pollution reduction, tri-normalizing is not as suitable as 710℃×4 h +830℃×6 h for the heat treatment of heavy forge.Different cooling structure can be obtained when 30Cr2Ni4MoV steel cooled from 850℃which is the austenitized temperature to room temperature, and in 0.05℃/s ~ 1℃/s cooling rate pearlite can be got.TEM analysis reveals that membrane of residual austenite surroundsαplate with a orientation relationship of {111}_γ// {110}_α, which is in accordance with K-S relationship. The content of residual austenite in the studied steel is reduced to 0.9% to annihilate microstructure heredity, benefiting microstructure refinement.
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