Current Understanding of Microstructure and Properties of Micro-Alloyed Low Carbon Steels Strengthened by Interphase Precipitation of Nano-Sized Alloy Carbides: A Review

Abstract

The current understanding of the microstructural features and mechanical properties of micro-alloyed low carbon steels strengthened by interphase precipitation of nano-sized alloy carbides are critically reviewed in this paper. The experimental results obtained via advanced quantitative characterization have revealed that interphase precipitation is promoted at the ferrite/austenite interface with a relatively lower degree of coherency caused by the deviation from the exact Kurdjumov–Sachs orientation relationship. Its dispersion becomes refined by enlarging the driving force for its precipitation, as adjusted by changing the transformation condition and chemical composition. The occurrence of interphase precipitation can significantly increase the strength of steels due to its large precipitation strengthening, and maintain good ductility as a result of enhanced work-hardening and dynamic recovery in different stages of tensile deformation. Finally, the application of interphase precipitation to ferrite/martensite dual-phase steels, together with our outlook on the challenging points in future research, are briefly explained.

Quantitative SAXS Analysis of Precipitate Characteristics Limiting Hot Ductility in HSLA Steels Containing V, Nb & NbTi

“…Thus strengthening is diminished when particle spacing is too low and the particles are sufficiently small that dislocations may cut through precipitates when driven by low or moderate shear stresses. 30) The Orowan stress model is consistent with the particle spacing and reduction-of-area trends observed for Grades 1, 2, and 4, i.e., reduction-of-area increases as particle spacing increases, lowering the required stress for Orowan bowing to occur and decreasing precipitate strengthening effects overall.…”

“…6 demonstrates increasing volume percentage of precipitation leading to increased strength, and decreased reduction-of-area values. 30) When considering volume fraction and reduction-of-area trends in Fig. 2, we observe that as temperature decreases from 1 100°C to 800°C, precipitate volume percentage increases and the corresponding reduction-of-area values decrease until ~700°C.…”

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

“…When the annealing temperature was relatively low, many dislocations remained and intertwined with the carbide particles, as shown in Figure 7 e. When the annealing temperature was high, for example, at 700 °C, most carbides were still segregated at the interfaces, as shown in Figure 7 f. The surface analysis revealed high vanadium segregation at the ferrite–austenite interface and dislocations near the interface. It can be seen from Figure 7 (f i ) that the ferrite and austenite have the following relationship: // and // , which is reported to facilitate the segregation of carbides [ 29 ].…”

Strengthening of Low Carbon Steel by Nano-sized Vanadium Carbide in Ferrite and Tempered Martensite

“…[7][8][9] The other one is the newly developed interphase precipitation, which occurs as a result of nucleation at the migrating interphase boundary during ferrite transformation. 10,11) Recently, the contributions to strength of these two types of precipitation were comparatively studied in a vanadium (V)-microalloyed low carbon steel (Fe-0.1C-0.8Mn-0.2Si-0.3V (mass%)) by some of the present authors. 12) Typical interphase precipitation of nano-sized vanadium carbide (VC) dispersed in sheets in ferritic matrix and precipitation by aging dispersed randomly in bainitic matrix were obtained by isothermal ferrite and bainite transformation at 963 K and 873 K, respectively.…”