The effects of thermomechanical processing on the precipitation in an industrial dual-phase steel microalloyed with titanium

Abstract

Analytical transmission electron microscopy was employed to characterize the precipitation at each step of the fabrication process and thermomechanical treatment of an industrial dual-phase steel microalloyed with titanium. Theoretical thermodynamic calculations as well as experimental analysis showed that more than half of the titanium carbosulfide (Ti 4 C 2 S 2 ) precipitates would dissolve during reheating at 1240 ЊC. Despite this dissolution at 1240 ЊC, the remaining titanium carbonitrides and carbosulfides were effective in pinning austenitic grain boundaries, keeping the austenitic grain size at around 40 m (at 1240 ЊC). It is also shown that, during hot rolling, there exist three regions of titanium carbide precipitation. The first is defined by an increase of titanium carbide precipitation due to deformation. The second region is marked by the insignificant change in precipitation. The third region is indicated by another increase in precipitation due to the austenite-to-ferrite transformation. The experimental and theoretical results on the contribution of TiC precipitation to hardening of ferrite (Orowan mechanism) were in excellent agreement, showing that TiC precipitates have the most important effect on increasing the yield strength, overshadowing the austenitic grain-boundary pinning contributions by Ti(C,N) and Ti 4 C 2 S 2 precipitates.

Evolution of precipitates, in particular cruciform and cuboid particles, during simulated direct charging of thin slab cast vanadium microalloyed steels

“…While the larger size of the cruciforms suggests that they nucleate earlier in the process and are less restricted in their growth, they do not appear to have a core of a particle nucleated at a much higher temperature, such as an oxide, sulphide or titanium nitride, as was found in earlier work. 1,20,22 . This is supported by the data given in The size of the cuboids in Steel V-Ti decreased with equalisation temperature from 10-50 nm after 1100°C to 7-20nm after 1200°C.…”

“…However, this effect was found in steels having higher Ti and C levels than in the present steels. 20 One of the concerns in this work is its relevance to commercial practice. It is not clear whether or not the cruciforms are just an artefact due to the simulation process and would therefore not be observed in a commercial process.…”

Novel ultrafine Fe(C) precipitates strengthen transformation-induced-plasticity steel

“…At temperatures between 1400 and 1200°C, precipitation of smaller TiN and Ti 2 CS precipitates takes place in supersaturated austenite [5]. Since annealing of steels takes place at about 900-950°C and given that both TiN and Ti 2 CS have higher dissolution temperatures, they are expected to pin the grain boundaries, thereby limiting the recrystallization and grain growth process during hot rolling, leading to refinement of the final ferritic grain size [12].…”

Effect of initial microstructures on the properties of Ferrite-Martensite Dual-Phase pipeline steels with Strain-Based design

“…This kind of combination makes them possess continuous yielding, low yield strength, high tensile strength, high initial work-hardening rates, superior uniform and total elongation compared to other high-strength low alloy (HSLA) steels at a given strength level [7][8][9][10] . At present, the usual methods to produce dual-phase steels are either intercritical annealing 3,4,7,8 or thermomechanical control process (TMCP) 5,11,12 .…”