Microalloyed steel

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

Constitutive model for vanadium microalloyed steel under hot working conditions

Abstract: Hot compression tests were carried out in the temperature range $850-1150^oC$ at $0.1-60 s^-1$ strain rates. The hyperbolic sine equation and neural networks were used to model the constitutive behaviour. Evaluating constitutive parameters n, Q and A using the usual log – log plots does not yield constant values. The n, Q and A values were determined simultaneously using a non-linear optimisation procedure and were fitted as functions of strain. These relations, in conjunction with the hyperbolic sine equation, describe the constitutive behaviour of the steel. A 3 : 4 : 1 neural network is trained using 75% of the stress – strain data. The network predicts flow stresses and peak strains with good accuracy. Vanadium increases the peak strain, peak stress, and mean flow stress of austenite significantly.

Influence of Thermal Simulated and Real Tandem Submerged Arc Welding Process on the Microstructure and Mechanical Properties of the Coarse-Grained Heat-Affected Zone

Abstract: The X80 high-strength low-alloy microalloyed steel was procured as a hot rolled plate with accelerated cooling. The thermal simulated process involved heating the X80 steel specimens to the peak temperature of 1400°C, with different cooling rates. The four-wire tandem submerged arc welding process, with different heat input, was used to generate a welded microstructure. The martensite/austenite constituent appeared in the microstructure of the heat-affected zone region for all the specimens along the prior-austenite grain boundaries and between bainitic ferrite laths. The blocky-like and stringer martensite/austenite morphology were observed in the heat-affected zone region. The Charpy absorbed energy of specimens was assessed using Charpy impact testing at −50°C. Brittle particles, such as martensite/austenite constituent along the grain boundaries, can make an easy path for crack propagation. Similar crack initiation sites and growth mechanism were investigated for specimens welded with different heat i...

Influence of Accumulated Stress in Austenite on Transformed Ferrite Grain Size by Hot Rolling for a V-microalloyed Steel

Abstract: Torsion test rolling simulations have been performed in different conditions (pass strain, interpass time) for a V-microalloyed steel (C=0.165; V=0.170 wt%). The accumulated stress (Δσ) in austenite at temperatures below the no-recrystallisation temperature (Tnr) has been measured. The accumulated stress is directly related to the dislocation density. The ferrite grain size (Dα) obtained after hot rolling simulations for different conditions and a cooling rate of 3.5 K/s has been measured. Dα is found to be dependent on Δσ and on the austenite grain size prior to the austenite–ferrite transformation during cooling. On the other hand, a higher strain accelerates recrystallisation between passes, lowers the Tnr value, and consequently leads to a smaller accumulated stress. It is seen that a minimum value of 15 MPa must be reached in order for Dα refinement to begin.

Static and dynamic fracture toughness of a medium carbon microalloyed steel of three different microstructures

Abstract: A multiphase ferrite-bainite-martensite (F-B-M) microstructure was developed in an automotive grade V-bearing medium carbon microalloyed steel, 38MnSiVS5. It was characterized using optical, scanning, and transmission electron microscopy. The tensile, Charpy impact, and static and dynamic fracture toughness behaviors were evaluated. The results are compared with those of ferrite-pearlite (F-P) and tempered martensite (T-M) microstructures of the same steel. Although the tensile properties of the multiphase microstructures were superior, the Charpy impact and static and dynamic fracture toughness properties were inferior compared with those of the other two microstructures. The F-P condition displayed the highest plane strain fracture toughness value (KIC), while the T-M condition was characterized by the highest dynamic fracture toughness (conditional) value (KIDQ). The Charpy impact energy of the T-M condition was greater than that for the other two conditions. An examination of the surfaces of fractured samples revealed predominant ductile crack growth in the F-P microstructure and a mixed mode (ductile and brittle) crack growth in the T-M and the F-B-M microstructures. Although the Charpy impact energy, plane fracture toughness (KIC), and conditional dynamic fracture toughness (KIDQ) of the multiphase microstructure were inferior to those of the T-M and the F-P microstructures, the toughness properties were comparable to those of medium carbon low alloy steels having bainite-martensite (AISI 4340) or tempered martensite microstructures.