Effect of V Addition on Microstructure and Mechanical Properties in C–Mn–Si Steels after Quenching and Partitioning Processes

Abstract

Three C-Si-Mn Q&P steels with different V addition after one-step and two-step quenching and partitioning (Q&P) processes were investigated by means of optical microstructure observation, X-ray diffraction (XRD) measurement, transmission electron microscopy (TEM) characterization and particle size distribution (PSD) analysis. The effect of V addition on strength and ductility of the steels was elucidated by comparative analysis on the microstructure and mechanical properties as functions of partitioning time and temperature. For one-step Q&P treatment, the mechanical properties were mainly controlled by the tempering behavior of martensite during partitioning. V addition was helpful to mitigate the deterioration of mechanical properties by precipitation strengthening and grain refinement strengthening. For two-step Q&P treatment, the satisfying plasticity was attributed to the transformation-induced plasticity (TRIP) effect of retained austenite maintaining the high work hardening rate at high strain regime. The higher volume fraction of retained austenite with high stability resulted from the refined microstructure and the promoted carbon partitioning for the steel with 0.16 wt% V addition. However, the carbon consumption due to the formation of VC carbides led to the strength reduction of tempered martensite.

Isothermal decomposition of austenite in presence of martensite in advanced high strength steels: A review

“…These elements are known to form carbides that may refine the PAGS on the event the precipitate dissolution temperature is not reached [110] and therefore both the martensite and bainite structure will be refined. In addition, austenite could be strengthened through grain boundary strengthening and precipitation hardening leading to increased volume fraction of retained austenite [111,112]. However, the carbon content of the retained austenite may decrease because of the carbide precipitates [111,112], in turn increasing the driving force for bainite formation.…”

“…In addition, austenite could be strengthened through grain boundary strengthening and precipitation hardening leading to increased volume fraction of retained austenite [111,112]. However, the carbon content of the retained austenite may decrease because of the carbide precipitates [111,112], in turn increasing the driving force for bainite formation. The alloy carbides themselves may act as potential nucleation sites, thereby potentially increasing the kinetics of subsequent transformations.…”

“…The overall rate of bainite formation will therefore depend on the dominating factor of the above discussed points. Although the effect of microalloying elements on the Q&P process has been studied by a number of researchers [111][112][113][114][115][116], their effect on the bainite formation in presence of martensite is largely understudied and therefore more investigations are necessary.…”

Effects of Vanadium Microalloying and Intercritical Annealing on Yield Strength–Ductility Trade-Offs of Medium-Manganese Steels

“…They found that the steel exhibited increased strength but decreased total elongation relative to the base metal. However, Zhang et al found that microalloying improved the plasticity of the steel through an effective “phase transformation induced plasticity” (TRIP) effect from stable austenite [ 18 ]. Other researchers have found that microalloying elements can significantly increase strength but have a weak effect on plasticity [ 19 , 20 ].…”

Strain-Induced Phase Transformation Modeling of QP980 Steel and Its Application to Complex Loading Paths

“…Overcoming the difficulties in the application of QP steel can effectively promote the lightweight process of automobiles, realize energy saving and emission reduction, and improve the safety of automobiles [4,5]. The excellent mechanical performance of QP steels is owing to the transformation of the internal carbon-rich residual austenite (RA) into martensite (RA→M) during deformation, which induces plasticity by phase transformation and effectively enhances the plasticity of the steel [6][7][8]. In multiphase steels, the hard and soft phases may benefit the overall strength and plasticity, respectively, through an effective partitioning of stress/flow strain among the constituent phases during deformation [9,10].…”