Effect of rolling temperature on microstructure and mechanical properties of medium manganese steel

The effect of rolling temperature on the incomplete recrystallization behavior and the relationship to mechanical properties in 0.06C-4Mn-1.2Cr (wt.%) steel was investigated. Three plates of experimental steel were produced by hot rolling at different temperatures and intercritical annealing processes in this study. The microstructure of experimental steels was examined by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM). The mechanical properties of test steel were examined by impact test and tensile test. Austenite reversion and cementite precipitation-dissolution was numerically simulated under the assumption of local equilibrium. With the decrease of hot rolling temperature from 1000 degrees C to 800 degrees C, the uniform equiaxed prior austenite grains microstructures changed to heterogeneous microstructures of laminated and ultrafine prior austenite grains arranged alternatively. The tensile and impact tests revealed that the medium manganese steels rolling at 800 degrees C had an excellent combination of mechanical properties. Elongation had a great relationship with retained austenite fraction and stability. The fractography of impact specimens was examined to explore the toughening mechanism of the micro-laminated steels. The steel with uniform equiaxed grain structure exhibited a relatively low tensile strength of 750 MPa and low elongation of-20% and an extremely poor low-temperature toughness of-40 J at-40 degrees C. An enhanced low-temperature toughness (-233 J at-40 degrees C), as well as an improved tensile strength (823 MPa) and higher elongation of-40%, was obtained in the steel with heterogeneous microstruc-tures. The content of austenite in heterogeneous microstructure is twice that in uniform equiaxed grain structure. And cementite dissolved more thoroughly in the heterogeneous microstructure. The high austenite content of heterogeneous microstructures enabled the steel to be significantly stronger and ductile, which contributed to the high tensile strength and elongation to some extent. It is concluded that the effect of interface decohesion resulted in the occurrence of delamination. And the high austenite content and delamination greatly improved the low-temperature toughness of experimental steel.

Automated summary

The effect of rolling temperature on the incomplete recrystallization behavior and mechanical properties was investigated in the experimental steel. The microstructure analysis revealed that decreasing the hot rolling temperature led to a change in grain structure from uniform equiaxed grains to heterogeneous microstructures. The mechanical tests showed that the steel rolled at 800°C exhibited excellent mechanical properties, attributed to the high austenite content and thorough cementite dissolution in the heterogeneous microstructure. The enhanced low-temperature toughness and improved tensile strength and elongation were observed in the steel with the heterogeneous microstructure.