On the Microstructure Development under Cyclic Temperature Conditions during WAAM of Microalloyed Steels

Abstract

This paper shed light on the kinetics of transformation and the developed microstructure during wire arc additive manufacturing (WAAM). Three microalloyed alloys, two of them are high strength low alloyed steel (HSLA) grades and the third is a Ni-Cr-Mo steel, from which the welding wires are being produced, were investigated. Repeated cycles around varied temperatures from a reheating temperature of 1350 °C and down to a temperature 35 °C below the Ae1 are applied using dilatometer on samples from the steels. After applying the cycles, the dilatometric-samples were investigated metallographically and their macro- and microhardness values were measured. It is shown that the WAAM using HSLA steels produce softer structure than the steel of the welding wire. Combined microalloying with Ti and Nb can present a useful strategy for producing finer structure in the WAAM components due to the effect of Ti in inhibiting the prior austenite grain-growth and that of Nb in refining the final structure. Additionally, repeated heating near Ae3 refines the prior austenite grains and produced fine ferrite-pearlite structure in case of HSLA steels and a microstructure predominated by the granular bainite in case of welding wire alloy. The former microstructure was the softest one for the case of HSLA steels, whereas the softest structure in case of the welding wire alloy was the tempered martensite structure developed by reheating below Ae1. Idealized temperature curves were chosen for the heat treatment, which could be characterized in a well-defined manner. In future work such idealized curves together with temperature histories obtained in WAAM-process will be used to set up a database to train an AI-model for predicting structure and material properties.

Alloy and Process Design of Metallic Materials

“…In essence, a robust process window is the key to unlocking the full potential of medium-manganese steels in industrial praxis. Huang et al [8] highlighted the dependence of microstructure development on the alloying composition and thermal cycling parameters during wire arc additive manufacturing (WAAM). They suggested that the HSLA steels are more suitable for producing softer and consequently tougher components than that produced from the conventional welding wires.…”

Design for Material Properties of Additively Manufactured Metals Using Topology Optimization

“…The subsequent heating cycle and the corresponding peak temperature determine whether these child phases transform back to the parent austenite phase. In steels, the critical 𝐴𝑐 3 temperature is the temperature above which all child phases transform back to the parent phase completely [21,22,18]. This critical temperature is hence termed the reset temperature in the remainder and is indicated in Fig.…”