Abstract
Electron beam welding of 4J34 Kovar alloy was conducted, and the microstructure and mechanical properties of the joints in as-welded and postweld annealing treatment (PWAT) states were investigated. The martensitic transformation occurred and led to the generation of α lath martensite due to the rapid cooling in the as-welded condition. After annealing treatment, part of the α martensite transformed to γ austenite and subsequently developed the bulk γ phase and α/γ lamellar microstructures in the fusion zone (FZ) of the postwelded joint. Grains in the heat-affected zone (HAZ) clearly developed and penetrated into the FZ, causing the disappearance of the fusion line between the FZ and the HAZ. All the joints in both the as-welded and PWAT conditions exhibited ductile fracture. The maximum tensile strength of 505 MPa was obtained in the as-welded joint with the welding speed of 150 mm/min. The linear expansion coefficients of the joint and base metal decreased with the increase in temperature. However, the decreasing rate of PWAT joints was lower than that of the as-welded joints.
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