Abstract: The effect of normalizing process on evolution of microstructures and tensile properties of cold-rolled low-alloy cryogenic steel plate was investigated by tensile test, microhardness test, OM, SEM and TEM. The results showed that the cold-rolled samples were in recovery when the heat treatment temperature was 700 ℃,and the dislocations in ferrite matrix featured severe tangles configuration or grid structure. As the normalizing temperature increased to 750 ℃ and 800 ℃, recrystallization and phase transformation processes occurred simultaneously, and formed granular structure characterized by M/A islands. The microstructure of 860 ℃ normalized sample was composed of equiaxed ferrite and dispersed pearlite, and dislocations were sparse dislocation wall configuration. The ferrite grain size of cold-rolled sample with 23% reduction rate after 860 ℃ normalizing was refined to 10.2 μm, while that of cold-rolled sample with 10% reduction rate was 12.0 μm. The optimal combination of strength and ductility was obtained at the normalizing temperature of 860 ℃, and the product of strength and ductility were 20 007 MPa% and 17 850 MPa% for the cold-rolled samples with 10% and 23% reduction rate, respectively. Compared with that of 700 ℃ normalized sample, the number of microvoids near tensile fracture and necking zone in 860 ℃ normalized sample reduced significantly, indicating the improvement of tensile deformation ability.
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2017, Vol. 31 
