A quantitative analysis was carried out in the present study to determine the effects of titanium (Ti) addition on microstructures and strength of Nb-Ti microalloyed steel. The obtained results revealed that strength was significantly improved with an increase in Ti content from 0.041 to 0.079 wt pct. The difference in the yield strength between the two steel samples occurred due to the different strengthening effects of grain refinement, precipitation, and dislocation strengthening, among which the grain refinement and precipitation strengthening contributions were dominating. With a further increase in the Ti content, ferrite grains became refined. Consequently, a homogeneous ferrite microstructure was attained for high Ti contents. Moreover, large-sized (Ti, Nb)C particles manifested the Kurdjumov–Sachs (KS) relationship, whereas fine (Ti, Nb)C particles held the Baker–Nutting (BN) relationship; thus, abundant fine nanoscale (Ti, Nb)C particles formed after coiling. Furthermore, the high dislocation density facilitated the precipitation of (Ti, Nb)C particles along dislocation lines.

Quantitative Analysis of Microstructures and Strength of Nb-Ti Microalloyed Steel with Different Ti Additions

Investigating the Properties of Coil Tail in Ti–Nb–Mo Microalloyed Hot‐Rolled Strip

Grain refinement of Fe--Ti alloys fabricated by laser powder bed fusion

The microstructural evolution, nanosized precipitation behaviors and mechanical properties of a Ti-bearing micro-alloyed steel at different coiling temperatures were studied using optical microstructure (OM), scanning electron micrograph (SEM), transmission electron microscopy (TEM), Vickers hardness and tensile tests. When the coiling temperature was 500 °C, the specimen showed mainly bainitic structure, whereas polygonal ferrite was visible as the coiling temperature increased to 650 °C and 700 °C. The Vickers hardness of tested steel reached the maximum, which can be attributed to the largest number of nanosized precipitates in ferrite at the coiling temperature of 650 °C. A coiling temperature of 650 °C was optimal for the formation of TiC because of the high diffusion rate of alloying elements and kinetics of precipitation. In the laboratory rolling experiment, when the coiling temperature was 630 °C, the steel with yield strength of 682 ± 2.1 MPa and tensile strength of 742 ± 4.9 MPa was produced. The fine-grain strengthening and precipitation strengthening were 262 MPa and 268 MPa, respectively.

https://www.mdpi.com/2075-4701/10/9/1173/pdf

Influence of Coiling Temperature on Microstructure, Precipitation Behaviors and Mechanical Properties of a Low Carbon Ti Micro-Alloyed Steel

The precipitation behavior of TiN particles under homogeneous and heterogeneous nucleation conditions in a low-carbon high-strength steel with 0.11 wt% Ti was investigated by thermodynamics and dynamics equations combining with the microstructural observations on the surface and at the core of the casting slabs. The effect of cooling rate on the morphology and dimension of TiN particles was also analyzed in the present study. In addition, the three-dimensional and the spatial tridimensional morphology of compound TiN–Al2O3 was innovatively characterized by a focused ion beam scanning electron microscope. It was found that TiN particles possessed inerratic facet morphology (such as squares and clusters), and the square morphology was predominant. The preferential plane for TiN precipitates in the tested steel was {100}. Moreover, TiN particles precipitated both in solid and liquid phases from the solid–liquid phase region during the solidification process, and preferential precipitation was observed in the solid phase. Furthermore, the size of TiN particles decreased with the increasing cooling rate during the casting process. Al2O3 particles provided nucleation sites for the heterogeneous nucleation of TiN particles.

Investigation on Precipitation Behavior and Morphology of TiN Particles in High-Ti Low-Carbon High-Strength Steel

Four Nb-Ti microalloyed steels were refined and rolled to study the composition optimization of Nb-Ti microalloyed steels. The effects of Nb and Ti on the microstructures, precipitates and properties of Nb-Ti microalloyed steel were investigated. The results showed that an increase in Ti content resulted in the appearance of many fine precipitates leading to a strong precipitation strengthening effect. Hence, the yield strength increased. Besides, the increased strength by the combined increase of Nb and Ti was similar to that observed for the increase in Ti content alone. This increase in strength was attributed widely to the increase in the Ti content alone rather than Nb. Moreover, the increase in Nb content beyond 0.036 wt% exerted no significant effect on the strength of Ti-Nb microalloyed steels, in which more Ti could be added to further improve the strength of steels.

Xiaolong Gan

Papers

Quantitative Analysis of Microstructures and Strength of Nb-Ti Microalloyed Steel with Different Ti Additions

Composition Optimization of Nb-Ti Microalloyed High Strength Steel