Microstructural Characterization and Mechanical Properties of Direct Quenched and Partitioned High-Aluminum and High-Silicon Steels

Abstract

A new experimental steel containing in weight percent 0.3C-2.0Mn-0.5Si-1.0Al-2.2Cr and 0.3C-1.9Mn-1.0Si-1.0Cr was hot rolled in a laboratory rolling mill and directly quenched within the martensite start and finish temperature range. It was then partitioned without reheating during slow furnace cooling to achieve tensile yield strengths over 1100 MPa with good combinations of strength, ductility and impact toughness. Gleeble thermomechanical simulations led to the selection of the partitioning at the temperatures 175 and 225 °C, which produced the desired microstructures of lath martensite with finely divided retained austenite in fractions of 6.5% and 10% respectively. The microstructures were analyzed using light and scanning electron microscopy in combination with electron backscatter diffraction and X-ray diffraction analysis. The mechanical properties were characterized extensively using hardness, tensile and Charpy V impact testing. In tensile testing a transformation induced plasticity mechanism was shown to operate with the less stable, carbon-poorer retained austenite, which transformed to martensite during straining. The auspicious results in respect to microstructures and mechanical properties indicate that there are possibilities for developing tough ductile structural steels through thermomechanical rolling followed by the direct quenching and partitioning route.

Kinetics of Carbon Partitioning during Non‐Isothermal Treatment and Mechanical Properties of the First Industrial Coils of Hot Rolled Quenched and Partitioned Steel

“…As shown in Figure a, after initial quenching, the non‐isothermal transformation occurred rapidly within tens of seconds, which consumed a large fraction of untransformed austenite. The fraction of quenched martensite was estimated from Koistinen and Marburger (KM) equation and then the fraction of non‐isothermal transformation that was illustrated in Figure b could be calculated using the ratio of dilatation between point a and c. Within 15 s, one can see that ≈73% austenite was transformed into BCC phase that was considered to be mixture of martensite and bainite, as shown in Figure c. In addition, the temperature drop was 0.75 °C within 15 s. Thus, it is reasonable to ignore the dilatation change caused by temperature drop.…”

Density functional theory study of ω phase in steel with varied alloying elements

“…The predicted results were cross‐checked via observation of the high‐magnification structure in an ultrahigh‐strength steel which had the same alloy constituents as employed in the DFT calculations. The studied material was an experimental medium‐carbon steel with the chemical composition 0.3 C/0.6 Si/2.0 Mn/1.1 Al/2.2 Cr (wt%) and was produced using a thermomechanical rolling process combined with direct‐quenching and partitioning 22 . Prior to rolling, vacuum‐cast 110 × 80 ×60 mm blocks were annealed at 1200°C for 2 hours.…”

Advanced High-Strength Steels by Quenching and Partitioning

“…This was related to higher volume fraction and the higher stability of film-like retained austenite located between martensite laths. A similar process was applied by Wu et al [4] to a Fe-0.2C-0.68Si-1.75Mn-0.06Nb (wt.%) steel. It was demonstrated that the DQ&P process refined retained austenite, promoting the TRIP effect and toughness of the grade, in comparison to the alloy without Q&P treatment.…”