Effect of Heat Input and Annealing Temperature on the Microstructure, Impact Properties and Microhardness of Electron Beam Welded Duplex Stainless Steel Joints

In this paper, defect-free joints were achieved through electron beam welding (EBW) with varying heat inputs. The effects of heat input and annealing temperature on the microstructure, impact toughness (at −40 °C) and microhardness of the EBW joints were investigated. The results indicated that post-welding heat treatment (PWHT) could enhance both the impact toughness and microhardness of the EBW joints. As the annealing temperature increased, the impact toughness reached its maximum value at 1080 °C. The impact toughness was not only determined by the content of austenite, but also by the presence of spherical austenite. Most of the spherical austenite and ferrite formed non-coherent random phase boundaries. The proportion of random phase boundaries in the annealed joints at 1080 °C (43.4%) was greater than that at 1020 °C (39.3%) and 1050 °C (36.0%). Additionally, the proportion of CSL boundaries (Σ≤ 29) was 29.5%, exceeding the values observed at 1020 °C (27.6%) and 1050 °C (25.1%). Thus, the non-coherent phase boundaries between spheroidal austenite and ferrite, along with the specific CSL boundaries (Σ≤ 29) in the spheroidal austenite, were identified as key factors contributing to the enhancement of impact toughness.