| The effects of precipitates and alloying elements on impact toughness have been investigated for 30Cr super-ferritic stainless steel welds, in which the total content of carbon and nitrogen was controlled below 250 ppm. The toughness of weld metals was evaluated by sub-size Charpy v-notch impact tests. V-notch tensile test was also undertaken to study crack initiation site and propagation. In order to identify the precipitate phases, its precipitation sites, and morphologies, thin foil, extraction replica and chemical extraction specimens were prepared for TEM analysis. Addition of tungsten in super-ferritic stainless steel weld metals reduced toughness significantly by increasing amount of coarse and angular shaped precipitates such as titanium carbonitride, and successive precipitation along the grain boundary, which provided crack initiation sites and easy propagation. The addition of nickel in the weld metal, however, gave a beneficial effect on the toughness by reducing amount of precipitate and by enhancing formation of fine precipitates. |
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