Microalloyed steel

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

STUDY ON THE PRECIPITATION BEHAVIOR OF TiN IN THE MICROALLOYED STEELS

Abstract: The precipitated behavior of TiN in liquid steels and during solidification of the microalloyed steels containing Ti has been studied by experiment and thermodynamic calculation The results show that precipitation occasion and condition of TiN in the microalloyed steels can be controlled by adjusting the content of N and Ti, that may reduce its detriment to the steel properties The probability of utilizing the fine and disperse TiN in liquid steel as the nuclei for crystallization of the casting structure, which could obtain fine and equiaxial grains, was also discussed

Fatigue properties of a 4340 steel coated with a Colmonoy 88 deposit applied by high-velocity oxygen fuel

Abstract: The fatigue behavior of a quenched and tempered AISI 4340 steel has been evaluated in three different conditions: (a) uncoated; (b) grit-blasted with alumina; (c) grit-blasted and coated with a thermal-sprayed Colmonoy 88 deposit 220 μm thick, employing a high-velocity oxygen fuel (HVOF) gun. The results indicate that grit blasting the base steel can lead to a significant reduction in the fatigue properties of the material. The microscopic observation of the fracture surfaces of the blasted samples indicates that the fatigue processes are initiated at the alumina particles that were retained within the matrix near to the surface of the specimens, giving rise to the presence of stress concentrators that act as nucleation sites of the fatigue cracks. Coating the blasted substrate with this kind of deposit leads to a further reduction of the fatigue properties of the base steel. Such a reduction has been associated with the fracture and partial detachment of the coating from the substrate along the substrate-deposit interface and the reduction in the area of the load-carrying segments of the composite material during fatigue testing. SEM observations of the fracture surfaces of coated samples tested at low alternating stresses, that support this view, have been presented. Under some alternating stresses, the HVOF deposits are believed to contribute to endure the stress applied to the material and therefore the evaluation of the fatigue properties of this kind of coated materials must take into account the thickness of the deposit sprayed unto the substrate. The analysis of the fracture surfaces of the coated specimens revealed that, in this case, the crack nucleation sites are also associated with the presence of Al 2 O 3 particles at the substrate-deposit interface. The fatigue performance of the material under the different conditions analyzed has been quantified by determining the Basquin parameters from the fatigue life curves obtained.

Effect of TMCP Parameters on the Microstructure and Properties of an Nb-Ti Microalloyed Steel

Abstract: Thermal mechanical control processing (TMCP), which includes combination of controlled rolling and controlled cooling, provides a powerful means of developing high-strength low alloy (HSLA) steels by intensive microstructural control. In the present investigation, the effects of TMCP parameters, consisting of the finish cooling temperature and the start rolling temperature in non-recrystallization region, on the final microstructure and mechanical properties of an Nb-Ti microalloyed steel has been studied by tensile, Charpy impact tests, optical microscopy and scanning electron microscopy. The TMCP parameters for Q460 grade steel have been optimized by laboratory experiments. The microstructure and properties of industrial product were coincident with the results of laboratory experiments.

Kinetics of austenite grain growth in medium-carbon niobium-bearing steel

Abstract: In order to locate a reasonable heating system, the austenite grain growth behavior of Nb microalloyed medium carbon steel has been experimentally studied at various austenitizing temperatures and for different holding times. It is indicated that austenite grain growth increases with increasing austenitizing temperatures and holding times. Particularly when the austenitizing temperature was above 1100 °C, austenite grains grew rapidly, and an abnormal austenite grain growth was observed. When the austenitizing temperature was lower than 1100 °C, austenite grain size and growth rate were small. The activation energy of grain growth in the tested steel is 397 679.5 J/mol. To ensure an absence of coarse grains in microstructures, the heating technology of the tested steel should be controlled for 1 h at 1100 °C. The relationships of austenite average grain size with soaking temperature and time of tested steel were obtained by mathematical calculation, and austenite average grain size was found to be in agreement with the measured size for different holding times.

Inhibition of abnormal grain growth during isothermal holding after heavy deformation in Nb steel

Abstract: The microstructural evolution during isothermal holding at 590-750°C after heavy deformation was examined in Nb steel. The strain induced ferrite transformation of Nb steel was significantly retarded compared with that of plain C-Mn steel, when Nb was mostly dissolved. When the grain boundary ferrite was present before deformation and strain free ferrite was formed during the following isothermal holding, abnormal grain growth occurred at the regions near the deformed ferrite by strain-induced boundary migration (SIBM). The SIBM was caused by the energy unbalance at the boundaries between deformed and strain free ferrite grains transformed from the deformed austenite. This rapid growth was not inhibited by the strain-induced NbC precipitates, which means the driving force for the abnormal growth was greater than the pinning force by the precipitates. However, the abnormal grain growth could be prevented by isothermal heat treatment in either fully transformed or untransformed structure. The ultrafine and polygonal ferrite grains were obtained by the recrystallization of ferrite and the grain growth was inhibited by strain-induced NbC precipitates during isothermal annealing at 650°C after deformation.