Microalloyed steel

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

The determination of optimum forging conditions for the production of high strength-high impact toughness automotive parts

Abstract: The influences of various reheating and forging temperatures as well as cooling rates on the microstructure and mechanical properties, particularly impact energy, during the forging of a Nb-V microalloyed steel to be used for automotive safety parts were investigated. Increasing the prior austenite grain size increased the volume percent of acicular ferrite and reduced pearlite content in the microstructure even for very low post-forging cooling rates, resulting in improved toughness and tensile strength values. Increasing the cooling rate enhanced the acicular ferrite content, thereby increasing the impact energy properties. At lower reheating temperatures the yield strength and impact energy levels are determined by the percentage of pearlite present in the microstructure; while as the cooling rate is increased the amount of acicular ferrite and retained austenite are increased, improving the toughness and tensile strength of the forged part. This effect is more pronounced for the parts solutio...

Effect of Annealing Temperature on Recrystallization Behavior of Cold Rolled Ti-Microalloyed Steel

Abstract: In order to develop cold rolled Ti-microalloyed steel strips, the effects of annealing temperature on recrystallization behavior of experimental steel were researched by optical microscopy (OM), transmission electron microscopy (TEM) and Vickers hardness test. The annealing treatment could be divided into three distinct stages: recovery, recrystallization and grain growth. Recrystallization took place from 933 to 1033 K, during which a large number of recrystallized grains appear and hardness drops sharply. The morphology and size of TiN particles nearly remained unchanged at different stages of processing. With increasing annealing temperature, nanometer precipitates coarsened and the dislocation density was significantly reduced. In comparison with annealing time, annealing temperature was more crucial for recrystallization of cold rolled Ti-microalloyed steel. It could be concluded that the pinning force of nanometer particles on dislocations increased the recrystallization temperature. At higher annealing temperature, recrystallization took place because of precipitates coarsening caused by Ostwald ripening.

The Effect of Processing History on a Cold Rolled and Annealed Mo-Nb Microalloyed TRIP Steel

Abstract: In this paper, a Mo-Nb microalloyed TRIP Steel was subjected to several heat treatments designed to generate different microstructures. These microstructures were then cold rolled and TRIP-annealed, and the resulting tensile properties and retained austenite characteristics were determined. The results reveal that prior heat treatment has a significant effect on the cold rolled and annealed behavior. Generally, an increasing volume fraction of proeutectoid ferrite prior to cold rolling and TRIP annealing leads to improved tensile ductility. This is due to increased work-hardening rates, which, in turn, correlate to increased carbon enrichment in the retained austenite. These results can clearly be used to optimize the hot rolling process to produce hot strip for the subsequent production of cold rolled Mo-Nb TRIP Steel.

Mobility Analysis of the Austenite to Ferrite Transformation in Nb Microalloyed Steel by Phase Field Modelling

Abstract: It is well-known that the solute drag effect due to dissolved Nb and the pinning effect due to NbC in Nb microalloyed steel cause retardation of the grain growth during austenitisation and of the transformation during cooling. These effects strongly depend on the austenitisation-temperature. But there is little numerical research on both effects simultaneously so far. In this study the mobility behaviour during austenite (γ) to ferrite (α) transformation was investigated by phase field modelling, showing that the α/γ boundary velocity during cooling increases with increasing austenitisation-temperature. These phenomena are caused by both pinning and solute drag effects. The effect of pinning decreases as the austenitisation-temperature increases because NbC dissolves with austenitisation treatment at high temperature. On the other hand, the strength of the solute drag effect is the highest for intermediate austenitisation-temperature, where the α/γ boundary velocity during cooling is in the intermediate range, and the strength is determined by the effects of both the concentration of dissolved Nb atoms and the α/γ boundary velocity. These features are quantitatively discussed from the simulation results.

Atmospheric Corrosion Performance of Quenched-and-Tempered, High-Strength Weathering Steel

Abstract: Eight-year atmospheric corrosion tests of A 588B (UNS K12040) weathering steel were conducted in industrial, marine, and rural environments. The material was tested following two types of heat treatment: quenched-and-tempered to produce a tempered martensite microstructure and normalized to produce a microstructure comprised of ferrite and pearlite. Results of these tests indicated that these heat treatments had no effect on the corrosion resistance and that the performance of weathering steels can be estimated solely on the basis of composition.