Microstructural Evolution and Mechanical Properties of Low C-Mn Steels Subjected to Accelerated Cooling

Abstract

Microstructure consisting of ferrite and bainite in low C-Mn steels with different manganese contents (0.75-1.49 mass %) can be formed by accelerated cooling. Microstructure observation reveals that the transformation products of 0.75%Mn and 1.06%Mn steel mainly consist of equiaxed ferrite and pearlite when hot finish deformation was processed at the temperature of 800°C, while the transformed products mainly contained irregular ferrite and upper bainite when finish rolling temperature (FRT) increases to 850°C or 900°C. However, a large amount bainite can also be attained in 1.49%Mn steel when FRT decreased to 800°C. The strength increases by about 100MPa with the increase of manganese content from 0.75% to 1.49%. The 1.06%Mn steel exhibits a superior strength-elongation combination by deforming at FRT of 850°C and then accelerated cooling at the cooling rate of about 40°C/s to coiling temperature in the range of 490~510°C.

On a New Two‐Step Air Cooling Method Following Thermomechanically Controlled Rolling: Microstructural Evolution and Mechanical Properties of a High‐Strength Multiphase Medium Carbon Microalloyed Steel

“…This type of cooling results in some portion of ferrite and significant changes in morphology of the nonequilibrium phase mixtures, especially when the FRT is low and the degree of deformation is high. [11][12][13][14][15] The microstructure that contains only the nonequilibrium phase mixtures does not exhibit enough ductility and formability that are essential for structural applications, especially in the automotive industry.…”