Lawrence Cho

The present contribution examines the effect of V microalloying on the microstructural evolution in 1080 wire rod steel. Previous research has shown that V improves the hardness and tensile strength of hypereutectoid steels. Industrial 1080 wire rod compositions, with and without 0.035 wt pct V, were analyzed using dilatometry and detailed microstructural characterization. Prior results showed that V slows the pearlite transformation and refines the pearlite interlamellar spacing. Furthermore, proeutectoid grain boundary cementite formation is observed to be reduced with V alloying. Atom probe tomography was conducted to analyze V partitioning and VC precipitation. Partitioning of V into pearlitic cementite was shown to occur at transformation temperatures of 600 °C and above while little to no partitioning of V and other alloying elements occurs at 550 °C. Furthermore, Cr and Mn were quantitatively shown to enrich in cementite. In contrast, Si and Cu are rejected from cementite.

Toughness and fatigue resistance of welds and associated heat-affected zones (HAZs) in high-strength steels are important design parameters in structural applications. Acicular ferrite microstructures, which can be achieved through control of weld process and nucleant (inclusions or precipitates) characteristics, are often regarded as key to enhancing weld metal and HAZ properties of welded steels. This paper addresses the transformation characteristics of acicular ferrite related to alloying and weld processing as well as the specific role of acicular ferrite in weld performance, along with future research needs to identify weld processes suitable to specific alloying strategies.

Recent research efforts to develop advanced–/ultrahigh–strength medium-Mn steels have led to the development of a variety of alloying concepts, thermo-mechanical processing routes, and microstructural variants for these steel grades. However, certain grades of advanced–/ultrahigh–strength steels (A/UHSS) are known to be highly susceptible to hydrogen embrittlement, due to their high strength levels. Hydrogen embrittlement characteristics of medium–Mn steels are less understood compared to other classes of A/UHSS, such as high Mn twinning–induced plasticity steel, because of the relatively short history of the development of this steel class and the complex nature of multiphase, fine-grained microstructures that are present in medium–Mn steels. The motivation of this paper is to review the current understanding of the hydrogen embrittlement characteristics of medium or intermediate Mn (4 to 15 wt pct) multiphase steels and to address various alloying and processing strategies that are available to enhance the hydrogen-resistance of these steel grades.