Comparing the Hot Ductility Behaviour of Low‐Carbon Microalloyed Nb‐V‐Ti Steels During Two Thermal Cycling Routes: Solutionizing and Precipitation Treatments

Abstract

The hot ductility behavior of commercial low-carbon microalloyed Nb-V-Ti-steel was studied in both wrought and cast conditions by means of hot tensile tests over a wide range of temperature (750-1200 8C) and at three strain rates (0.01, 0.002 and, 0.0005 s À1 ). To replicate the straightening operation undergone by the two materials during hot drawing of plates and continuous casting process, respectively, two kinds of thermal cycles, namely solutionizing and precipitation treatments, were adopted to compare their respective influence on the formation of surface cracking. After deformation, the lowest ductility values were found at 900 8C in the single g-domain for the as rolled material in the former treatment, and at 800 8C in the two-phase domain for the as cast product in the second one. By contrast, the largest values were observed at 750 8C and above 1000 8C for the two examined materials in both types of treatment. On the whole, surface cracking was found as a result of grain boundary sliding which was acknowledged as the main fracture mechanism. An attempt was also made to determine a relationship between the synergistic effect of the various intervening micromechanisms and the resulting embrittlement.

Optimisation of the Technology of Smelting and Refining of Steel Into Hot Rolled Sections on an Innovative Production Line

“…In order to ensure the required high strength properties and impact strength in the S355J2 steel sections at -20°C, a vanadium microadditive was added to its composition, forming V(CN) precipitates limiting the austenite grain growth during heating for rolling, and increasing the strength properties as a result of precipitation strengthening [2][3][4]. The effective action of vanadium in steel ensures the presence of dissolved aluminium, affecting grain refinement.…”

“…Secondary oxidation of steel streams takes place during the continuous casting of steel intended for sections, from the tundish to the moulds without shielding the streams with inert gas. The oxidised surface of the liquid steel, as a result of turbulence in the mould, flows out in the form of 1) Content of metallic aluminium in liquid steel and/or section's material 2) Content of metallic aluminium in the section's material 3) Values proposed on the basis of the analysis of 'peritectic sensitivity' of steel [1] with simultaneous fulfilment of the required carbon equivalent calculated per the following formula: C E = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15 a slag film to the surface, mainly due to the precipitation and outflow of gas bubbles. The bubbles leave a slag film on the surface of the metal, which is crushed in the process of rolling into individual inclusions, containing FeO, MnO, SiO 2 , Al 2 O 3 and AlN, resulting from the treatment of steel with the Al wire in the mould.…”

“…Since the beginning of the 1990s, austenite grain refinement was used in order to obtain the required high impact properties in steels without aluminium, by creating acicular ferrite nucleating on small complex oxide inclusions with precipitates on them during solidification in an MnS crystalliser [1][2][3][4]. The effect of acicular ferrite formation is increased by introducing micro-additions of elements such as: Ti, V, Nb, Ce, Zr into the steel, forming very fine oxides or nitrides with lattice constants similar to the lattice constant of MnS precipitating on them [5][6][7][8][9][10][11][12].…”

Effect of Vanadium and Strain Rate on Hot Ductility of Low-Carbon Microalloyed Steels

“…On the other hand, the carbide precipitates could also provoke a loss of the hot ductility of steels by themselves, as reported by many published works [21][22][23][24][25][26]. The precipitates at grain boundaries reduce the binding force of grain boundaries, retard the onset of dynamic recrystallization and cause stress concentration, thus promoting intergranular failure and reducing hot ductility.…”