Microalloyed steel

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

Influence of the microstructure on the fracture toughness and fracture mechanisms of forging steels microalloyed with titanium with ferrite-pearlite structures

Abstract: Titanium addition to vanadium microalloyed forging steels is one of the ways proposed to improve fracture toughness Fine TiN particles inhibit austenite grain growth after recrystallization at the high temperatures used to forge these steels TiN particles, however, can be formed in the liquid, and as their sizes exceed one micron, they could act as cleavage nucleation sites, impairing the fracture toughness The present work reports fracture toughness results obtained in Ti treated microalloyed forging steels, showing that in coarse microstructures cleavage is nucleated in coarse TiN particles, but that after refining the microstructure, voids originate at the same particles, resulting in ductile rupture

Effect of composition and thermo-mechanical processing schedule on the microstructure, precipitation and strengthening of Nb-microalloyed steel

Abstract: In order to study the influence of composition and thermo-mechanical processing schedule on the kinetics of austenite recrystallization, strain induced precipitation and final microstructural evolution in Nb-microalloyed steels, thermo-mechanical processing simulations have been carried out inside Gleeble® by varying the number of deformation passes (2-pass vs. 6-pass), deformation temperatures (1000–800 °C) and inter-pass times. Low-C high-Mn steel (LCHMn) has been found to offer finer ferrite grain size and finer Nb-precipitation which contributed to superior hardness to that steel, compared to high-C low-Mn steel (HCLMn). Among the deformation schedules applied, 6-pass schedule has been found to be superior over 2-pass schedule in terms of precipitation strengthening and hardness. This study also proposes a mathematical framework to explain the effect of composition and processing schedule in Nb-microalloyed steels following Dutta and Sellars approach on precipitation-recrystallization interaction.

Precipitation in V bearing microalloyed steel containing low concentrations of Ti and Nb

Abstract: The paper describes the precipitation behaviour in a thermomechanically processed V bearing microalloyed steel containing small additions of Ti and Nb (0·007–0·008 wt-%) using analytical transmission electron microscopy. An intriguing aspect is the significant precipitation of titanium and niobium at these low concentrations, contributing to strength. A high density of multimicroalloyed precipitates of (V, Nb, Ti)(C, N) are observed instead of simple TiN, TiC, and NbC precipitates. They are characterised as cuboidal (45–70 nm), spherical (20–45 nm), irregular (20–45 nm), and fine (10–20 nm). Estimation of solubility products of carbides and nitrides of V, Nb, and Ti implies that the precipitation of titanium occurs primarily in austenite. Interphase precipitation of niobium occurs during austenite to ferrite transformation, while complete precipitation of vanadium takes place in the austenite–ferrite region close to completion of transformation. Substoichiometric concentrations of Ti and Nb, the p...

Microstructure and mechanical properties of a novel 1000 MPa grade TMCP low carbon microalloyed steel with combination of high strength and excellent toughness

Abstract: A novel low carbon Nb–V–Ti–Cr microalloyed bainitic steel with yield strength of 1000 MPa and excellent low temperature toughness was successfully processed. Two cooling procedures were adopted to optimize the mechanical properties. The microstructural evolution, precipitation behavior, and strengthening mechanisms were systematically studied, and the fracture mechanisms were analyzed via combination of fractographs and deflection–load curves. The experimental results indicated that the steel subjected to cooling rate of 65 °C/s and coiling temperature of ~380–400 °C resulted in superior mechanical properties. The yield strength, tensile strength, yield ratio, and elongation-to-fracture were 1058 MPa, 1192 MPa, 0.88, and 10.6%, respectively. The impact energy of the 1/4-size Charpy specimen and tested at −20 °C was 24 J. The ultra-high yield strength is primarily attributed to transformation strengthening from lower bainite and precipitation hardening from nano-scale (Nb,Ti)C precipitates. The excellent toughness is associated with lower bainite and acicular ferrite together with high fraction of large misorientation grain boundaries by controlling the coiling temperature.