Microalloyed steel

About: Microalloyed steel is a research topic. Over the lifetime, 2183 publications have been published within this topic receiving 33586 citations.

The effects of vanadium, niobium, titanium and zirconium on the microstructure and mechanical properties of thin slab cast steels

Abstract: The evolution of precipitation and microstructure during a simulation of the thin slab direct rolling process, in six vanadium based, low carbon, steels with V, V-N, V-Ti-N, V-Nb, V-Nb-Ti and V-Zr additions was studied by optical microscopy, analytical transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX) and parallel electron energy loss spectroscopy (PEELS). Tensile properties and Charpy vee-notch toughness of the final strip were also determined. The effects of microalloying additions and processing conditions, including equalisation temperature (1 200°C, 1 100°C and 1 050°C) and end water cool temperature, on the austenite and ferrite grain sizes, as well as the type and composition of the precipitates, were determined. The relationship between the microstructure and the properties in the steels was also ascertained.

Softening and Flow Stress Behaviour of Nb Microalloyed Steels during Hot Rolling Simulation

Abstract: The roles of softening and precipitation were investigated by means of hot torsion experiments under conditions simulating either plate or sheet rolling. Six microalloyed steels containing Nb were studied. During the first few finishing passes in the sheet rolling simulations, the mean flow stress (MFS) increased as the interpass time was decreased. Due to strain accumulation, the rate of static recrystallization (SRX) increased significantly after each pass. By taking both strain accumulation and grain refinement into account, it is shown that SRX plays a marked role under sheet rolling conditions, even at temperatures below the no-recrystallization temperature for plate rolling conditions. The accumulated or retained strain reaches the critical value required to initiate dynamic recrystallization only at the lowest entry and rolling temperatures and shortest interpass times. The kinetics of the strain-induced precipitation of NbCN under continuous cooling conditions, taking partial SRX into account, indicate that precipitation begins after 2 to 5 passes when 3 s interpass times are employed, thus reducing further softening. But when 1 s interpass times are used, most of the passes take place before copious precipitation, so that static and post-dynamic (i.e. metadynamic) softening may continue to take place. As a result, the MFS level decreases as the interpass time is shortened during the final passes. The extent of grain refinement was similar in both the sheet rolling and plate rolling simulations. The ferrite grain size is shown to depend on MFS of the final pass, and is independent of the chemical composition of the microalloyed steel.

Fine-scale precipitation and mechanical properties of thin slab processed titanium–niobium bearing high strength steels

Abstract: We describe here the precipitation behavior and mechanical properties of 560 MPa Ti–Nb and 770 MPa Ti–Nb–Mo–V steels. The precipitation characteristics were analyzed in terms of chemistry and size distribution of precipitates, with particular focus on the crystallography of precipitates through an analysis of electron diffraction patterns. In addition to pure carbides (NbC, TiC, Mo 2 C, and VC), Nb containing titanium-rich carbides were also observed. These precipitates were of a size range of 4–20 nm. The mechanism of formation of these Ti-rich niobium containing carbides is postulated to involve epitaxial nucleation of NbC on previously precipitated TiC. Interface precipitation of NbC was an interesting observation in compact strip processing which is characterized by an orientation relationship of [0 0 1] NbC //[0 0 1] α-Fe , implying that the precipitation of NbC occurred during austenite–ferrite transformation.