Quasi-Situ Characterization of Retained Austenite Orientation in Quenching and Partitioning Steel via Uniaxial Tensile Tests

Abstract

As a representative of the third generation of advanced high strength steel, the quenching and partitioning steel has excellent potential in automobile manufacturing. The characterization and analysis of the mechanical properties and microstructure of the quenching and partitioning steel during deformation is an effective way to explore the microstructure evolution and transformation-induced plasticity effects of complex phase steels. The relationship between the microstructure morphology and mechanical properties of a 1180 MPa-grade quenching and partitioning steel was investigated through interrupted uniaxial tensile tests plus quasi-situ electron backscatter diffraction measurements. A mixture of ferrite, martensite, and retained austenite was observed in the microstructure. It was found that the volume fraction of global retained austenite decreased linearly with the increase of displacement (0 mm–1.05 mm). The evolution of the retained austenite with typical crystal direction ranges with deformation was characterized. Results show that the orientation (111) and (311) account for the highest proportion of retained austenite grains in the undeformed sample and the mechanical stability of the (311) retained austenite grains is the best. Moreover, the retained austenite grains rotated significantly in the early stage of the specimen deformation process (around yielding), and the work hardening of the specimen was weak at this stage, simultaneously.

Microstructure Evolution and Mechanical Properties of X6CrNiMoVNb11-2 Stainless Steel after Heat Treatment

“…It is should be noted that Ni 3 Mo is rod-shaped, where the length direction of the rod and matrix is in the <111> direction [ 2 ]. The close-packed surface and direction of δ-Ni 3 Mo and η-Ni 3 Nb phases are parallel to the matrix, with the existence of the coherent or semicoherent relation between δ-Ni 3 Mo/η-Ni 3 Nb and matrix, thus the strength is remarkably improved [ 1 , 2 , 51 , 52 , 53 , 54 ].…”

“…Meanwhile, when the quenching temperature is too high, the austenite grains will be coarsened, resulting in coarser martensite [ 51 ]. Therefore, a quenching temperature should be selected within an appropriate range, neither too low nor too high, or the expected requirements will not be met [ 41 , 52 ]. Then, the effect of quenching cooling rate on the mechanical properties during quenching at 1040 °C and tempering at 650 °C is investigated through the analysis of the measured data.…”

Effect of Cold Rolling Reduction Rate on the Microstructure and Properties of Q&P Steel with a Ferrite-Pearlite Initial Structure

“…Cold rolling with a reduction rate (ratio of the reduction in plate thickness to the initial thickness of the plate) of 60–70% is necessary [ 15 ], as the typical required thickness for Q&P steel in service is considerably thinner (0.7~1.2 mm) than that of conventional hot-rolled plates (2~3 mm). Meanwhile, in order to reduce the cold rolling force, the hot rolling-coiling temperature must be controlled to adjust the microstructure of the hot-rolled plate to a softer ferrite-pearlite structure [ 16 ]. To address the global focus on carbon reduction, especially in steel industry, the thin slab casting and rolling (TSCR) technology is being widely promoted due to its environmentally friendly and energy-saving characteristics [ 17 ].…”