Microalloyed steel

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

EFFECT OF CONTROLLED ROLLING PROCESSING ON NANOMETER–SIZED CARBONITRIDE OF Ti–Mo FERRITE MATRIX MICROALLOYED STEEL

Abstract: Single nanometer-sized particles, which are smaller than 10 nm, can significantly en- hance the precipitation strengthening in microalloyed steels, thus causing their strength to be promoted greatly. In order to improve the strength of the steel, it is quite necessary to get a large amount of single nanometer-sized particles through optimizing rolling technology. In this work, the effects of two different kinds of controlled rolling technologies on the size and distribution of precipitated particles in the Ti-Mo ferritie matrix microalloyed steel have been researched using SEM, TEM and small-angle X-ray scattering. The results show that with the same total rolling reduction, the steel rolled only in phase crystallization zone can obtain a higher portion of single nanometer-sized particles than that rolled respectively in phase recrystallization and nonrecrystallization zones, in which those single nanometer-sized particles account for about 75% (mass fraction) of whole precipitated particles. In order to study the effect of deformation potency in phase zone on the amount of precipitates in phase and the micro-crystal size, nucleation rate and incubation time of following precipitates in ! � transformation and ferritie matrix after ! � transformation, some thermodynamics and kinetics calculations and analysis on precipitation are also conducted.

The Hot Ductility of V, Nb/V and Nb Containing Steels

Abstract: The hot ductility behaviour of a series of V, Nb/V and Nb containing steels having a base composition of 0.1 %C, 1.4%Mn, 0.3 %Si have been examined. Two levels of V, (0.05 and 0.1%), N (0.005 and 0.01%), and Nb, (0.015 and 0.03%Nb) were selected. Tensile samples were heated to 1330°C and cooled at 50°C/min to test temperatures in the range 700 to 1000°C and tested to failure using a strain rate of 3x10 -3 s -1 . Heat treatment was chosen to closely follow the commercial continuous casting conditions and the strain rate used was that applied during the straightening operation. In addition, to make the tests more relevant to continuous casting, tensiles from selected steels were melted, re-solidified and cooled to the test temperature as for the samples solution treated at 1330°C. In all cases a ductility trough was obtained in the temperature range 750 to 950°C. The 0.030%Nb containing steel gave the worst hot ductility of all the steels examined. For samples heated to 1330°C, increasing the V and N levels in the V containing steels caused the ductility to deteriorate but the product of the total V and N concentrations had to be as high as 1.2 x 10 -3 , i.e. 0.1%V and 0.012%N, before approaching the low values of reduction of area exhibited by the Nb containing steel. The hot ductility curves for all the Nb/V containing steels at the 0.005% N level were very similar. Adding V at this low N level to the 0.03%Nb containing steel was found to improve ductility in the temperature range 800 to 900°C. For the as-cast samples, again the V containing steels were found to give better ductility than the 0.03%Nb containing steel. The hot ductility behaviour was found to be mainly related to the size of the precipitates, the coarser the precipitation the better being the ductility.

Effects of Cu addition on the synergistic effects of Ti-B in thermomechanically processed low carbon steels

Abstract: The present study concerns the influence of Cu addition on the synergistic effects of Ti–B in low carbon thermomechanically processed steels. Effective retardation of the γ → α transformation due to the combined addition of Ti and B is known to enhance the hardenability of a wide range of low carbon microalloyed steel. On the other hand, addition of Cu in low carbon age hardenable steel suppresses the pearlitic transformation resulting into a microstructure constituted by interspersed islands of martensite in ferritic matrix. Therefore, it may be of interest to examine the role of Cu on the synergistic contribution of Ti and B in respect of increasing hardenability of austenite. In the present study, effects due to the addition of Ti, B and Cu in different steels are interpreted in respect of microstructure–property correlation. It is demonstrated that the addition of 1.5 wt% Cu perceptibly enhances the synergistic effect as manifested by lowering the transformation temperature of austenite. Addition of 0.8 wt% Ni in Cu–Ti–B steel does not alter the transformation temperature of austenite to any appreciable extent. However, Cu–Ni–Ti–B steel has resulted into the enhancement of strength–ductility combination.

A study on the influence of cutting parameters on forces during machining the multiphase V-microalloyed steel

Abstract: The ferrite-bainite-martensite (FBM) multiphase V-microalloyed steel with a yield strength of 1384 MPa was subjected to turning test in order to study the effect of cutting parameters such as cutting speed, feed, and depth of cut on cutting force, feed force, and radial force. The cutting forces are found to decrease with increase in the cutting speed for various feed with constant depth of cut. The analysis of variance (ANOVA) for all the three forces shows that feed rate and depth of cut are the significant parameters at 95 % confidence level, and also, the interaction between cutting parameters is insignificant. The optimum parameter for machining multiphase (FBM) microalloyed steel is found to be cutting velocity 80 m/min, feed rate 0.05 mm/rev, depth of cut 0.1 mm. The multiphase microalloyed steel requires less force as compared to quenched and tempered, microalloyed, and other existing high strength low alloy (HSLA) steels like AISI 4340. The easy machinability of multiphase microalloyed steel is promoted by soft polygonal ferrite (PF) and bainite phases present in the microstructure of the steel.

Improving mechanical properties in high-carbon pearlitic steels by replacing partial V with Nb

Abstract: The effects of combined addition of niobium (Nb) and vanadium (V) on the transformation, microstructure and mechanical properties of high-carbon pearlitic steels were investigated. In-situ observations on a high-temperature laser scanning confocal microscope (LSCM) were conducted to study the pearlitic transformation, the results from which indicate that single V or combined Nb and V addition led to higher transformation temperature and more pearlitic nucleation sites. But the growth rate of pearlite was significantly impeded due to the smaller diffusion coefficient of carbon, resulting in the refinement of the interlamellar spacing and nodule size of pearlite. In addition, compared to the base steel, single V addition in high carbon pearlitic steels was beneficial to the increase of strength, but it deteriorated the toughness, whereas the composited addition of Nb and V resulted in the increase of strength without the expense of the toughness. It is concluded that replacing part V with similar content of Nb is very promising since the impact toughness of the Nb + V steel is increased by 21% without the expense of the strength compared to the V-microalloyed steel. Nb and V strengthened pearlitic steels primarily due to the precipitation of M(C,N), thinner pearlite interlamellar spacing and smaller pearlite nodule size. Compared to the V steel, the improvement of toughness in Nb + V steel was mainly attributed to the smaller nodule size and more uniform grain size distribution. In summary, under the premise of similar microalloying element amount in high-carbon (∼0.77 wt%) pearlitic steels, replacing part V with Nb is beneficial to obtain the finest microstructure and the best comprehensive mechanical properties.