Microalloyed Steels through History until 2018: Review of Chemical Composition, Processing and Hydrogen Service

TLDR

Microalloyed steels have evolved in composition, processing, and metallurgical characteristics since the early 20th century to meet the cost and mechanical property demands of gas and hydrocarbon transport, achieving high strength and ductility through microalloying, thermomechanical processing, and controlled cooling, though hydrogen diffusion during corrosion can severely affect these microstructures and cause failures, prompting the adoption of martensite–bainite with acicular ferrite for hydrogen‑prone environments. The aim of this review is to summarize the main changes in chemical composition, processing techniques, and the evolution of mechanical properties of high‑strength low‑alloy steels, as well as the effects of hydrogen in newly created pipelines. The review examines the mechanisms of hydrogen embrittlement in these steels.

Abstract

Microalloyed steels have evolved in terms of their chemical composition, processing, and metallurgical characteristics since the beginning of the 20th century in the function of fabrication costs and mechanical properties required to obtain high-performance materials needed to accommodate for the growing demands of gas and hydrocarbons transport. As a result of this, microalloyed steels present a good combination of high strength and ductility obtained through the addition of microalloying elements, thermomechanical processing, and controlled cooling, processes capable of producing complex microstructures that improve the mechanical properties of steels. These controlled microstructures can be severely affected and result in catastrophic failures, due to the atomic hydrogen diffusion that occurs during the corrosion process of pipeline steel. Recently, a martensite–bainite microstructure with acicular ferrite has been chosen as a viable candidate to be used in environments with the presence of hydrogen. The aim of this review is to summarize the main changes of chemical composition, processing techniques, and the evolution of the mechanical properties throughout recent history on the use of microalloying in high strength low alloy steels, as well as the effects of hydrogen in newly created pipelines, examining the causes behind the mechanisms of hydrogen embrittlement in these steels.