Effect of Carbon Partitioning and Residual Compressive Stresses on the Lattice Strains of Retained Austenite During Quenching and Isothermal Bainitic Holding in a High‐Silicon Medium‐Carbon Steel

Abstract

The residual compressive stresses and dimensional changes related to the lattice strains of retained austenite (RA) phase in a high‐Si, medium‐carbon steel (Fe‐0.53C‐1.67Si‐0.72Mn‐0.12Cr) are investigated for samples austenitized and quenched for isothermal bainitic transformation (Q&B) in the range 5 s to 1 h at 350 °C. Also, samples are directly quenched in water (DWQ) from the austenitization temperature for comparison with Q&B samples. Field emission scanning electron microscopy (FE‐SEM) combined with electron backscatter diffraction (EBSD) analyses, and X‐ray diffraction are used to investigate the microstructural evolution, phase distribution, and lattice parameters of RA phase. While the Q&B samples showed formation of bainite and high‐carbon fresh martensite in conjunction with stabilization of various fractions of RA, the DWQ samples displayed nearly complete martensitic microstructure. For short holding durations (≪200 s), there was limited formation of bainite and the inadequate carbon partitioning to the adjacent untransformed austenite areas resulted in significant martensite formation and the associated c/a ratio of martensite resulted in high compressive residual stresses within the RA phase. While, at long isothermal holding times (≫ 200 s), there was a significant formation of bainite. The DWQ samples displayed maximum lattice strain in a small fraction of untransformed RA phase.

Multiscale simulation and experimental measurements of the elastic response for constructional steel

“…Comparison with experimental measurements. As an advanced high-strength steel, the residual stress of constituents affects not only the mechanical properties 44 but also the dimensional stability 45 of 35CrMo steel. In this study, the 35CrMo steel is quenched for 40 min at 750 °C and tempered for 120 min at 300 °C to obtain the fine strengthened martensitic phase 46 .…”

Decomposition Mechanism of Prior Austenite in Low‐Temperature Zone and Its Relationship to Fracture Behavior of High‐Strength Medium‐Mn Steel

“…Strength can be achieved by obtaining the multiphase composite structure of high-strength martensite or bainite matrix due to the lath-like structure and high-density lattice defects. [7][8][9] Bhadeshia and Caballero [10][11][12] et al carried out the low-temperature isothermal treatment (above bainite start temperature) for C-Si-Mn steels and found that the slender plates of bainitic ferrite of just 20-40 nm thick were generated, that is, nanostructured bainite or very strong bainite. The excellent mechanical properties with a combination of strength levels exceeding 2000 MPa, hardness at 600-670 HV, and toughness exceeding 30 MPa m 1/2 were achieved.…”