1.4463 | GX6CrNiMo24-8-2 carbide problem

Despite a double heat treatment, this duplex steel exhibits low notch impact energy values of KV2 = 80 J instead of > 120 J. Phase precipitations in the ferrite initially indicated sigma phase. These phases are brown in color. After a Murakami etch, the sigma phase normally appears bluish. Solution annealing at 1150 °C followed by water quenching should have eliminated the sigma phase. Several quantitative EDS analyses prove that these are clearly carbides (Cr60/Fe18/Mo8/C~10). The spectrometrically determined C content is at the upper limit of 0.07 wt%. By lowering the C content and adjusting the C+Ti ratio, carbide formation could be avoided.