| Popis: |
The new low-chromium steel grades T/P23 and T/P24 are candidate materials for components of ultra-supercritical power plants, and as potential replacement materials of conventional low alloy ferritic steels such as T/P22 in older plants. Higher creep strengths relative to that of T22 were obtained by additions of tungsten, vanadium and niobium in steel T23, and titanium and vanadium in steel T24. In addition, the new grades have the advantage that they do not require PWHT due to the lower carbon content of these steels. Long-term creep performance, microstructural evolution, welding characteristics and other properties are however not fully understood. For example, recent experience on the use of T23/T24 materials showed that stress corrosion cracking (SCC) and stress relief cracking can be major service concerns for such steels. In this chapter, welding and weldability data, including weld repairs, and the types of cracking that can occur in low alloy steel weldments, have been examined in some detail. |
