The effect of molybdenum on interphase precipitation and microstructures in microalloyed steels containing titanium and vanadium

Effects of using (Ti,Mo)C particles to reduce the three-body abrasive wear of a low alloy steel

Evolution of microstructures and mechanical properties during solution treatment of a Ti–V–Mo-containing high‑manganese cryogenic steel

Here, we investigated the effects of adding a micro-alloying element to medium-Mn steel and explored why a resulting sample containing precipitates exhibited higher strength than one without precipitates, without sacrificing ductility. The model alloys comprised steels of Fe–8Mn-0.2C–3Al-(0, 0.2)V (wt.%); they were cold-rolled and intercritically annealed at identical temperatures between 670 and 730 °C for 30 min. These annealed steels exhibited two-phase microstructures consisting of ferrite (α) and retained austenite (γR), with a nanoscale globular morphology. Smaller grain sizes and lower volume fractions of γR were observed in the V-containing specimen, relative to the V-free specimen, owing to the formation of VC precipitates. The latter were mostly formed in the α phase, rather than in the γR phase. These VC precipitates meant that the V-containing steel showed a lower C concentration in γR and a higher C concentration in α than the V-free steel. We propose that such phase compositions enhanced the strain hardening rate during the later stage of mechanical loading due to more active twinning-induced plasticity and dynamic strain aging. These effects resulted in the observed higher tensile strength in the V-containing steel, without sacrificing ductility.

Improved strength of a medium-Mn steel by V addition without sacrificing ductility

The possibility of enhanced hydrogen embrittlement resistance of medium-Mn steels by addition of micro-alloying elements

A new Ti–V–Mo complex microalloyed hot-rolled high-strength steel sheet was developed by controlling a thermo-mechanical controlled processing (TMCP) schedule, in particular with variants in coiling temperature. The effects of coiling temperature (CT) on various hardening mechanisms and mechanical properties of Ti–V–Mo complex microalloyed high-strength low-alloy steels were investigated. The results revealed that the steels are mainly strengthened by a combined effect of ferrite grain refinement hardening and precipitation hardening. The variation in simulated coiling temperature causes a significant difference in strength, which is mainly attributed to different precipitation hardening increment contributions. When the CT is 600 °C, the experimental steel has the best mechanical properties: ultimate tensile strength (UTS) 1000 MPa, yield strength (YS) 955 MPa and elongation (EL) 17%. Moreover, about 82 wt% of the total precipitates are nano-sized carbide particles with diameter of 1–10 nm, which is randomly dispersed in the ferrite matrix. The nano-sized carbide particles led to a strong precipitation hardening increment up to 310 MPa.

Development of Ti-V-Mo Complex Microalloyed Hot-Rolled 900-MPa-Grade High-Strength Steel

Precipitation behavior of (Ti, V, Mo)C and microstructural evolution of the ferritic Ti–V–Mo complex microalloyed steel were investigated through changing coiling temperature (CT). It is demonstrated that the strength of the Ti–V–Mo microalloyed steel can be ascribed to the combination of grain refinement hardening and precipitation hardening. The variation of hardness (from 318 to 415 HV, then to 327 HV) with CT (from 500 to 600–625 °C, then to 700 °C) was attributed to the changes of volume fraction and particle size of (Ti, V, Mo)C precipitates. The optimum CT was considered as 600–625 °C, at which the maximum hardness value (415 HV) can be obtained. It was found that the atomic ratios of Ti, V and Mo in (Ti, V, Mo)C carbides were changed as the CT increased. The precipitates with the size of < 10 nm were the V-rich particles at higher CT of 600 and 650 °C, while the Ti-rich particles were observed at lower CT of 500 and 550 °C. Theoretical calculations indicated that the maximum nucleation rate of (Ti, V, Mo)C in ferrite matrix occurred around 630 °C, which was consistent with the 625 °C obtained from experiment results.

Xin-Jun Sun

Papers

Development of Ti-V-Mo Complex Microalloyed Hot-Rolled 900-MPa-Grade High-Strength Steel

Precipitation Behavior and Microstructural Evolution of Ferritic Ti–V–Mo Complex Microalloyed Steel