Effect of Silicon and Oxygen Content on the Toughness of Ferritec Weld Metal in 9%Ni Steel

Abstract

The effects of silicon and oxygen content on the toughness of 9%Ni steel weld metal were investigated using ferritic welding wires. (1) The toughness behavior against heat treatment temperatures is similar to that of 9%Ni steel plate, showing a peak value by tempering at 590°C regardless of the content of the two elements. (2) Reducing oxygen content improves the peak value when the silicon is low (0.10wt%), but it works adversely when the silicon is high (0.45%). At a medium silicon (0.27%), the toughness reaches a peak when the oxygen content is about 230ppm. The absolute value of vE-196, however, tends to decrease with an increase in silicon content. To use a low silicon wire in a pure argon shield is the best measure for furnishing sufficient toughness to the weld metal. (3) The temper-softening is retarded by increasing silicon content, and non-metallic inclusions are multiplied by increasing oxygen content. The toughness behavior against oxygen contents is determined by the balance between the content of silicon in solid solution and the amount of non-metallic inclusions. (4) At the optimum tempreing temperature of 590°C, the amount of retained austenite shows a peak value as well. However, the retained austenite alone is not considered the major factor influencing the toughness of ferritic weld metal.