Influence of Heat Treatment on Microstructure Stability and Mechanical Properties of a Carbide‐Free Bainitic Steel

Abstract

Carbide-free bainitic steels represent attractive candidates for the automotive industry to meet the conflicting requirements of increasing safety and decreasing vehicle weight. Their fine-grained multiphase microstructure enables a well-balanced combination of high strength and ductility. To identify and characterize all phases in dependence of the isothermal transformation temperature, metallographic and high-resolution techniques are applied. The stability of the individual phases is evaluated based on their C concentration determined by atom probe tomography and, subsequently, linked to the mechanical properties.

Influence of Transformation Temperature on the High‐Cycle Fatigue Performance of Carbide‐Bearing and Carbide‐Free Bainite

“…This may lead to better deformability as well as higher tensile strength and hardness. [10,46] Moreover, solid solution strengthening due to silicon alloying is another factor that improved the mechanical properties of CFB alloys. [19,41,47] Decreased phase transformation temperature enhanced the mechanical properties of CBB alloys.…”

“…[4] Depending on the stability of austenite that varies with local carbon concentration, size, and morphology, some part of it may transform to martensite during cooling and form a complex structure called martensite-austenite (MA) islands. [8][9][10] The RA may transform to martensite through transformation-induced plasticity (TRIP) effect during deformation, leading to enhanced performance of the steel under static, [10,11] and cyclic loading [12,13] conditions. According to the incomplete-reaction phenomenon (T 0 concept), the reduction in transformation temperature results in more diffusionless bainite transformation until a critical carbon concentration is reached, in which the free energy of BF is no longer less than that of austenite.…”

A generic high-throughput microstructure classification and quantification method for regular SEM images of complex steel microstructures combining EBSD labeling and deep learning

“…Electropolishing was conducted at 25 °C and 20 V for 20 s. In order to avoid the mechanically-induced martensite transformation of meta-austenite in Q&P steel during sample preparation, the grinding and polishing were carefully performed with very little force. As reported by Hofer et al [41] , a final manual polishing step should perform after electropolishing in order to prevent the transformation of the metastable retained austenite during preparation. However, this step is not available in present work because the surface morphology after electropolishing should be retained well for observing the SEM morphology to maintain the same morphology as in the EBSD experiment.…”

Improved Toughness of a High‐Strength Low‐Alloy Steel for Arctic Ship by Ni and Mo Addition

“…[19] Hofer et al suggested that the M-A constituent is enriched with C atom, and the decreasing C content reduces the content of martensite in steel. [20] It was suggested that the segregation of C, Mn, Ni, and Cr atoms in the M-A constituent/matrix interface decreases the mean free path for the crack initiation and propagation, leading to a decreasing toughness in HSLA steels. [3] Schwarz et al studied the crack propagation in dual-phase steel, and suggested that the crack preferentially propagates at the ferrite/austenite interface.…”