Microstructure evolution and mechanical properties during industrial intercritical quenching and partitioning (IQ&P) processing of a low alloy steel

Abstract

The evolution of the microstructure, texture and mechanical properties of a low alloy steel containing 0.09C-2Mn-0.4Si (wt.%) was investigated during the industrial intercritical quenching & partitioning (IQ&P) process. The steel sheet was thermally treated and characterized by scanning electron microscopy, electron backscatter diffraction, x-ray diffraction, etc. Low alloy steel treated with different processes can reach a tensile strength above 900 MPa. A multiphase structure composed of lath martensite, fine ferrite and retained austenite was obtained after annealing at 770–870 °C, and the retained austenite produced a discontinuous transformation induced plasticity (TRIP) effect and coordinated deformation in the tensile strain. The fractions of the textures {111} 〈112〉 and {111} 〈110〉 were found to gradually abate as the annealing temperature increased, while the textures {100} 〈001〉 and {001} 〈110〉 continuously expanded. The recrystallized texture gradually disappears with decreasing quenching temperature, although the fraction of the texture caused by the martensite transformation increases, and the texture gradually changes from {113} 〈110〉 to {111} 〈110〉. The effect of texture and microstructure evolution on mechanical properties was discussed in terms of character and morphology.