Coarsening Behavior of Nanometer-Sized Carbides in Hot-Rolled High Strength Sheet Steel

Abstract

This study deals with a relationship between strength and coiling temperature of high strength hot-rolled sheet steels consisting of ferrite and nanometer-sized carbides in order to evaluate the stability of the strength against the variation of the coiling temperature. Ti-Mo-bearing and Ti-bearing steels were prepared to form (Ti,Mo)C and TiC in ferrite matrix, respectively. Ti-Mo-bearing steel exhibited the high strength even under the high temperature coiling while the strength of Ti-bearing steel decreased significantly. Ti-bearing steel just after transforming at 923K had the same hardness as that at 898K. In addition, hardness of Ti-bearing steel coiled at 898K decreased significantly by holding at 923K for 8.64ks while Ti-Mo-bearing steel did not represent a large change in hardness. These results confirm that (Ti,Mo)C is not coarsened easily by Ostwald ripening at the high coiling temperature unlike TiC. Consequently the retardation of Ostwald ripening of (Ti,Mo)C is attributed to the small amount of titanium in solution in Ti-Mo-bearing steel.

Investigating nano-precipitation in a V-containing HSLA steel using small angle neutron scattering

“…Vanadium carbide has a relatively high coarsening rate and consequently, significant attention has also been given to the investigation of Ti and Ti-Mo-containing steels. Both systems exhibit IPP but it has been found that the coarsening of carbide precipitates is significantly retarded in Ti-Mo alloys [14,[21][22][23][24][25].…”

“…Previous studies of IPP have included topics such as the effect of transformation temperature [11,15,26], time [27], cooling rate [16,[28][29][30], orientation relationship [15,[31][32][33][34][35], hot deformation [17,36] as well as the addition of Mo [10,14,[21][22][23][24][25] on precipitate composition, size, morphology and number density. The majority of these prior studies have used transmission electron microscopy (TEM) to characterise the precipitates [14,18,19,22,37,38].…”

Titanium microalloyed steels

“…decelerated diffusion of Ti atoms into particles due to solute drag effect of Mo atoms at the particle/ matrix interface [196], . reduced concentration of Ti due to partial substitution by Mo [197], and…”

“…In a series of well-executed investigations, Wang et al [194] have considered in detail the evolution of precipitation of (Ti, Mo)C particles. They have summarised the mechanisms considered responsible for this phenomenon of type II precipitates, described by Lui and Jonas [119], including weakened diffusivity of Ti atoms in the matrix due to Mo atoms [195], decelerated diffusion of Ti atoms into particles due to solute drag effect of Mo atoms at the particle/ matrix interface [196], reduced concentration of Ti due to partial substitution by Mo [197], and decreased misfit strain at the particle /matrix interface due to Mo incorporation [198]. …”

Application of nanoengineering to research and development and production of high strength steel sheets

“…Concretely, X-Y-C ternary carbide system was studied with various combinations of X and Y, revealing that extremely fine precipitates can be obtained in a system where proper amounts of Ti and Mo are coadded to a 0?04C-1?3Mn base steel, and these precipitates show extremely high thermal stability. 12,13 Figure 8 shows an SEM image of the microstructure and a TEM (dark field) image of precipitates in the developed steel. The microstructure consists of ferrite single phase with a large number of ,3 nm precipitates arranged in rows.…”