This article covers the vexing problem of properly cooling forged microalloyed steels. This first of two parts will discuss the technical and business benefits of forged microalloyed steels. The process of forging these steels is traced from billet to trimmed part, zeroing in on the challenge facing forgers: controlled cooling. This article will cover material modeling, critical cooling rates and chemistries. Part II will appear in the February 2020 issue with details on heat-transfer coefficients, experimentation, production simulation and final results enabling more extensive use of this class of steels.
Microalloyed steels are plain-carbon or low-alloy steels with small additions (hence the name microalloyed) of additional elements, primarily vanadium. This class of steels was developed in the 1960s for steel plate and pipeline applications, with niobium playing a major role despite its “bit part.” In the 1980s, forgers began to hammer and press significant quantities of microalloyed steel components for demanding applications requiring assured, higher properties.