Some aspects of physical metallurgy of microalloyed steels

Abstract

Some aspects of deformation, precipitation, and recrystallization behavior in medium carbon V-microalloyed and low carbon Nb/Ti-microalloyed steels are presented in the paper. Changes in microstructure are explained together with methods of quantification. The temperature of No-recrystallization (Tnr) is defined as a milestone to show the onset of retardation of recrystallization while the apparent activation energy for hot working shows the extent of this retardation. In the case of high cooling rates, this method is not sufficiently sensitive and Trl (recrystallization limit temperature) and Trs (recrystallization stop temperature) must be evaluated from softening data. Paper presented the possibility to estimate Tnr temperature on six stands finishing train at Hot Strip Mill in HBIS Iron and Steel Serbia, Smederevo as well as the activation energy for static recrystallization, QSRX, derived from Tnr temperatures.

Revealing Precipitate Development During Hot Rolling and Cooling of a Ti–Nb Micro‐Alloyed High Strength Low‐Alloy Steel through X‐Ray Scattering

“…600 and 650 °C are typical coiling temperatures after hot rolling and a comparison of the measured particle size and volume fraction for those samples is shown in Figure a. The increase in strength due to precipitates is usually described by the Orowan–Ashby model [ 19 ] where D is the particle diameter, in μm, and f v is the volume fraction of the precipitates. The strengthening contribution from the precipitates for the different cases is shown in Figure 7b, where it is seen that the strength contribution is highest for the slowly cooled sample.…”

Hot Deformation Behavior of C-Mn Steel with Incomplete Recrystallization during Roughing Phase with and without Nb Addition

“…The relatively high Nb content in 240 Nb allows a sufficient phase fraction of Nb(C,N) needed for the Zener pressure for MFS comparison. An equation for ferrite-pearlite steels provided by Pickering was taken from [5,29,32] and used for strength estimation. Similar compositions are found for flat structural products as they are common for so-called commodity grades as presented in [33]; if needed, they are modified by introducing V for controlled post-rolling precipitation for additional strength increase.…”

“…The latter is more probable for thin plate, wire, or sheet rolling where lower temperatures with sufficient cumulative strain are common [9][10][11]. Additionally, based on [5], the needed strain for dynamic recrystallization (DRX) should be above 14% reduction in thickness, and in our case, the whole roughing stage was conducted using a close-to-linear trend beginning from 9 to 15% of reduction (R1, 8.63-8.76%; R2, 11.53-11.78; R3, 13.16-13.22%; R4, 15.02-15.15%; R5, 15.03-15.12%; R6, 14.98-15.07%, R7, 15.05-15.09%). Based on Gleeble hot-compression tests, the minimum for the chemical composition in this study for DRX should be above 12.2-16.49% for 1 s −1 and 3 s −1 determined at rouging temperature 1150 • C with ε = 0.8 to observe DRX phenomena.…”

“…Useful tools for predicting whether the Nb is in austenite solution or in form of precipitates are solubility products calculated for Nb, C, and N in austenite. There have been numerous equations posted by different researchers in the past [4,5]. In addition, the Calculation of Phase Diagrams (CALPHAD) approach can be used for multicomponent systems for equilibrium and homogeneous precipitation of non-deformed austenite for estimation of free [Nb] in austenite before the roughing phase is conducted, for example by using commercial software such as Thermo-Calc (Thermo-Calc 2022a software AB, TCFE 11.0, Stockholm, Sweden) [6].…”

Hot Working Tool Steel with Bainitic Microstructure—The Mechanical Properties at Elevated Temperature

“…7) Other elements like V and Nb may be added mainly for suppressing extensive grain coarsening and also suppress the formation of ferrite and perlite. [ 8–10 ]…”