Microalloyed steel

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

Cu-bearing high-strength low-alloy steels: The influence of microstructure on the initiation and growth of small fatigue cracks

Abstract: The fatigue characteristics of a Cu-bearing high-strength low-alloy (HSLA) steel were investigated in air, relative humidity ≈50 pct, as a function of microstructure, which was altered by heat treatments and welding. Small fatigue cracks (≈30-Μm long) were naturally initiated from smooth specimens and grown past the transition length (≈200 Μm), where they exhibited the characteristics of large fatigue cracks. The number of cycles to crack initiation depended on stress magnitude but not on microstructure, although the site of initiation was microstructurally dependent. Small cracks in all microstructures grew at δK values below the large crack threshold. The as-received (polygonal ferrite) microstructure and one of the lath microstructures that resulted from heat treatment exhibited the same growth rate correlation as large cracks in the linear (Paris) region, and could be considered as an extension of the large crack growth region down to the point of initiation. Small cracks grew at rates faster than expected through one of the heat-treated and the weld microstructures; therefore, the number of cycles required for growth from initiation to the transition to large crack growth decreased about threefold, which is a potentially important factor in predicting lifetimes of structures made from this steel.

Hot-rolled microalloyed steel and its use in variable-thickness sections

Abstract: A vanadium-nitrogen microalloyed steel is continuously hot rolled to C-shaped sections that meet property requirements for side rails of truck frames with no heat treatment. Sections with different thicknesses of the web and flange regions can also be prepared by the same processing. The composition of the steel is from about 0,16 to about 0.20 percent carbon, from about 1.2 to about 2.0 percent manganese, from about 0.45 to about 0.55 percent silicon, from about 0.10 to about 0.30 percent vanadium, from about 0.001 to about 0.030 percent aluminum, from about 0.010 to about 0.027 percent nitrogen, less than about 0.080 percent phosphorus, less than about 0.030 percent sulfur, balance iron totalling 100 percent, with all percentages by weight. Variations of this steel containing either from about 0.01 to about 0.02 percent titanium or 0.04 to about 0.07 percent aluminum are also permissible.

Study of austenite grain size of microalloyed steel by simulating initial solidification during continuous casting

Abstract: The austenite grain growth behaviour of microalloyed steel during continuous casting was simulated by confocal laser scanning microscope, and the effect of the cooling rate during the solidification, T γ (the starting temperature for austenite grain growth) and steel composition on the behaviour of austenite grain growth were analysed. Next, the model for predicting the austenite grain size, which is put forward by the Bernhard model, was revised. The results show that by the lab simulation of continuous casting initial solidification process at the cooling rate between 1·5 and 2·5°C s−1, the austenite grain size lying within the size range on the slab surface was obtained; T γ was calculated using equivalent carbon content CP and showed the exponential function relation to the latter; the revision factor K, describing the effect of microalloyed elements on austenite grain sizes, showed exponential function relation with PTi (precipitation amount of titanium); both T γ and K were used to revise th...

Kinetics of Precipitation Behavior of Second Phase Particles in Ferritic Ti-Mo Microalloyed Steel

Abstract: Two types of stress relaxation tests were carried out to investigate the incubation time for incipient precipitation of Ti(C,N) in deformed austenite and (Ti, Mo)C in ferrite of ferritic Ti-Mo microalloyed steel. The size distribution, amount and chemical composition of precipitates were obtained by using physicochemical phase analysis, and calculated according to thermodynamics and kinetics. The experimental results demonstrated that the incubation time was reduced with increasing Ti content, and prolonged with the addition of Mo. After 30% deformation at 850 °C, the nucleation of strain-induced Ti(C,N) was a relatively slow process. On the other hand, the temperature where the nucleation rate of (Ti, Mo)C in ferrite was the highest descended first and then ascended with increasing Ti content, and so did the temperature where the incubation time was the shortest. The key point is that the temperature of steel containing about 0. 09% Ti is the lowest. The mass fraction of MC-type particles with size smaller than 10 nm in steel containing 0. 09% Ti and 0. 2% Mo reached 73. 7%. The size distributions of precipitates in steel containing 0. 09% Ti were relatively concentrated compared with that in steel containing 0. 07% Ti.