Wire-arc additive manufacturing of a duplex stainless steel: thermal cycle analysis and microstructure characterization

Abstract

The evolution of microstructures with thermal cycles was studied for wire-arc additive manufacturing of duplex stainless steel blocks. To produce samples, arc energy of 0.5 kJ/mm and interlayer temperature of 150 °C were used as low heat input–low interlayer temperature (LHLT) and arc energy of 0.8 kJ/mm and interlayer temperature of 250 °C as high heat input–high interlayer temperature (HHHT). Thermal cycles were recorded with different thermocouples attached to the substrate as well as the built layers. The microstructure was analyzed using optical and scanning electron microscopy. The results showed that a similar geometry was produced with 14 layers—4 beads in each layer—for LHLT and 15 layers—3 beads in each layer—for HHHT. Although the number of reheating cycles was higher for LHLT, each layer was reheated for a shorter time at temperatures above 600 °C, compared with HHHT. A higher austenite fraction (+ 8%) was achieved for as-deposited LHLT beads, which experienced faster cooling between 1200 and 800 °C. The austenite fraction of the bulk of additively manufactured samples, reheated several times, was quite similar for LHLT and HHHT samples. A higher fraction of secondary phases was found in the HHHT sample due to longer reheating at a high temperature. In conclusion, an acceptable austenite fraction with a low fraction of secondary phases was obtained in the bulk of wire-arc additively manufactured duplex stainless steel samples (35–60%), where higher austenite fractions formed with a larger number of reheating cycles as well as longer reheating at high peak temperatures (800–1200 °C).