Microalloyed steels

Abstract

This review considers the compositions, the main process routes, microstructure, and structural properties of microalloyed steels. The background and brief history are followed by sections dealing with aspects of precipitation which control grain size and dispersion strengthening in ferrite- pearlite steels, the approaches to modelling thermomechanical processing and the influence of multiple additions of transition metals on properties. High strength acicular ferrite/bainite steels used for linepipe are included and lead to super bainite steels. Around 12% of the world strip production is processed by the thin slab direct charging route, which is considered in some detail. The weldability of microalloyed steels now embraces joining using friction stir welding, which is discussed. Over the years, many approaches have been developed to predict the structural properties of microalloyed steels. They comprise several quantifiable microstructural features including atom clusters, relatively recently identified through atom probe tomography. A comprehensive collection of references is provided

The Effect of Tempering on the Microstructure and Mechanical Properties of a Novel 0.4C Press-Hardening Steel

“…Horn et al [31] measured PAGS of 20 µm for 4340 and 300M steels with an 870 • C austenitization temperature. Therefore, the mean prior austenite grain size (12.3 µm) can be considered to be small for austenitization temperatures of 950 to 1000 • C. This is probably attributable to the presence of the microalloying elements Ti and Nb, which have inhibited the grain growth through the formation of small finely dispersed carbides or carbonitrides [32]. Also, the relatively large amount of molybdenum (0.7 wt.%) can hinder the austenite grain growth by producing strong solute drag effect by segregating at the austenite grain boundaries and thus pinning the grain boundary movement [33].…”

A comprehensive study on the microstructure and mechanical properties of arc girth welded joints of spiral welded high strength API X70 steel pipe

“…0.1%) in various combinations. To other elements that might be present in such a steel belong molybdenum, zirconium, boron, aluminium, nitrogen and occasionally rare earth metals [3]. The microalloying elements are used to refine the grain microstructure and/or facilitate dispersion strengthening through precipitation.…”

“…They are normally regarded as having a low effect on hardenability. Controlled additions of sulphur, and occasionally tellurium, are also added to improve the machinability [3].…”

Austenite Decomposition and Precipitation Behavior of Plastically Deformed Low-Si Microalloyed Steel

“…The strengthening of advanced ferrous alloys can be achieved in many ways, including solid solution strengthening, grain refinement, cold deformation, precipitation phenomena, phase transformations, high-pressure methods, etc. [1][2][3]. One of the most interesting and evolving groups of advanced steels for the automotive industry is the multiphase transformation-induced plasticity (TRIP)-aided steels consisting of ferrite, bainite, and retained austenite [4][5][6].…”