Microalloyed steel

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

Hot Ductility of Nb- and Ti-Bearing Microalloyed Steels and the Influence of Thermal History

Abstract: The hot ductility of Nb, Ti, and Nb-Ti containing steels has been studied under direct-cast conditions. A Gleeble 3500 thermomechanical simulator was used to determine hot ductility over the temperature range 1100 °C to 700 °C at a low strain rate of 7.5 × 10−4 s−1. Tensile samples were cooled at two different cooling rates, 100 °C/min and 200 °C/min, simulating, respectively, thick and thin slab casting processes. Complex thermal patterns designed to simulate the cooling conditions experienced near the surface of a slab during continuous casting were carried out for the Nb-Ti steel. The Nb-Ti steel had lower ductility than both the Nb and Ti steels. Increasing the cooling rate generally deteriorated ductility. The low recovery of ductility at higher temperatures is explained in terms of a low strain rate and fine precipitation delaying the onset of dynamic recrystallization. This can promote intergranular cracking as a result of grain boundary sliding in the austenite. At lower temperatures, ductility was further reduced due to the formation of thin ferrite films at the prior austenite grain boundaries. Simulating the thermal history experienced near the surface of thin (90 mm) cast slab improved ductility of the Nb-Ti steel by promoting coarser NbTi(C,N). This exposes a potential flaw in a simplified hot-ductility test: a failure to accurately represent the influence of the thermomechanical schedule on precipitation and, hence, hot ductility.

Development of fracture splitting connecting rod

Abstract: The fracture splitting method used with connecting rod (C/rod) is attracting attention as a mechanical method that can reduce production cost by decreasing the manufacturing process. In this method, powder metals and forged steel (C70S6) are generally used. These materials are superior in fracture splitting properties, but inferior in fatigue strength and machinability. Therefore, the authors developed microalloyed steel for C/rod which has high fatigue strength and machinability, and started the mass production of fracture splitting C/rod using the steel.

Effect of Welding Heat Input on Simulated HAZ Microstructure and Toughness of a V-N Microalloyed Steel

Abstract: This study investigates the correlation among the welding heat input, microstructure and impact toughness of the simulated coarse grain heat-affected zone (CGHAZ) of a V-N microalloyed steel which contained 140 ppm of nitrogen using Gleeble simulation technique, light microscope, electron microscope and Charpy-V-Notch (CVN) testing. CVN toughness estimated at −20°C supported that a relatively low energy input is recommended for welding of low carbon V-N microalloyed steel, according to a fact that an impact energy as high as of more than 180j attained in the CGHAZ with heat input less than 25Kj-cm−1, while a CGHAZ with impact energy less than 80j was obtained at a heat input more than 40 Kj-cm−1. Quantitative metallography of samples showed that CVN toughness decreased with the increase of the amount of grain boundary ferrite (GBF). Quantitative metallography of two-stage electrolytically etched samples showed that the averaged size and ratio of lath martensite-austenite (M-A) constituent increased with increasing heat input, while the linear density and amount of M-A decreased. It is indicated that the toughness of CGHAZ was severely dependent on the characteristic parameters of M-A and the amount of GBF. Microhardness of M-A constituents estimated by nanoindentation technique were much higher than that of the neighboring matrix. Severer brittle cracking susceptibility can occur in the CGHAZ with higher heat input based on Chen et al's suggestion that the stress concentration and triaxiality of the neighboring matrix are increased by the hard phase particles such as M-A constituents.