Tensile Behavior of Ferrite-martensite Dual Phase Steels with Nano-precipitation of Vanadium Carbides

Abstract

This paper reports the effect of nano-precipitation strengthening of ferrite on the tensile behavior of ferrite-martensite dual phase (DP) steels. Samples of ferrite-martensite DP steel containing a dispersion of nano-sized vanadium carbides (VCs) in the ferrite phase were produced by interphase precipitation and quenching of a V-added low carbon steel, and the mechanical properties are compared with those of conventional ferrite-martensite DP samples without VC particles. Both the yield stress and the ultimate tensile strength are significantly increased by nano-VC precipitates. For ferrite volume fractions of 20-50% a dispersion of VCs results in only a small change in the elongation, whereas for ferrite volume fractions of above 50% both uniform and post-uniform elongations are decreased by a VC dispersion. It is suggested that dispersion of nano-precipitates in ferrite is an effective approach to simultaneously improve the strength and the strength-ductility balance of DP steels. Digital image correlation (DIC) analysis demonstrates that the ferrite phase is more deformed than the martensite phase in both VC-free and VC-dispersed DP samples, but that such strain partitioning is less pronounced in the VC dispersion-hardened samples. It is found that the stress-strain relationship of DP samples can reasonably be explained based on a law of mixtures using partitioned strain and stress values as estimated from the DIC analysis.KEY WORDS: dual phase (DP) steel; interphase precipitation; vanadium carbides (VC); mechanical property; digital image correlation (DIC); strain and stress partitioning.

Randomization of Ferrite/austenite Orientation Relationship and Resultant Hardness Increment by Nitrogen Addition in Vanadium-microalloyed Low Carbon Steels Strengthened by Interphase Precipitation

“…2(f)), the amount of M(γ) is not so large to significantly influence the overall hardness. The hardness of both alloys are much higher than precipitate-free α, 21) reflecting the precipitation strengthen- ing. 4) As the temperature becomes decreased from 993 K to 848 K, the hardness increment at first in the N-free alloy was explained by the refinement in dispersion of VC formed by interphase precipitation in the GBF-dominated specimens, while the reduction later was caused by the extensive formation of softer WF/BF with near K-S OR at low temperature.…”

“…Hardness of the alloys isothermally transformed at different temperatures for 1.8 ks (almost fully transformed). Hardness of particle-free α is taken from Ref 21…”

Sulfur-free Surfactant for Carbide Nanoparticle Characterization in Steel Using Asymmetric Flow Field-Flow Fractionation Hyphenated Inductively Coupled Plasma-Mass Spectrometry

“…[1][2][3][4][5] For example, some nanocarbides have been introduced in steels for obtaining specific mechanical properties. [6][7][8] To characterize the size and chemical components of such nanoparticles in steels, direct observation and image analysis using transmission electron microscope (TEM) has been generally conducted. 7 However, using this method, a great number of view fields have to be observed and it takes a long time to obtain the size distribution of nanoparticles in steels.…”

“…[6][7][8] To characterize the size and chemical components of such nanoparticles in steels, direct observation and image analysis using transmission electron microscope (TEM) has been generally conducted. 7 However, using this method, a great number of view fields have to be observed and it takes a long time to obtain the size distribution of nanoparticles in steels. Additionally, these nanoparticles are non-uniform in steels and the one field-of-view (FOV) in TEM observation is limited to small areas to accurately observe particles in nanometer-order.…”

Metallurgical Effects of Niobium in Dual Phase Steel

“…Precipitation strengthening in the ferrite phase [27] in combination with grain refinement results in more homogeneous strain distribution within the microstructure with the potential of postponing plastic instability or necking of the material towards higher strains, i.e., an improved strength-ductility balance can be expected.…”