Welding new steels for power engineering

An analysis of the conventional steam turbine components and of the components of saturated steam turbines for nuclear power shows that in operation, welded structural parts are exposed to temperatures of up to 400 degC and to temperatures reaching the inlet steam temperature, i.e., 350 and 565 degC depending on the steam turbine type. For steels operating up to a temperature of 400 degC, a detailed analysis was carried out of steels CSN 11483, 13320, 15222, 15422, 15216, and 15218. The pre-heat temperature and the highest hardness in the overheated zone during the basic structure formation was calculated using a new method of weldability assessment and crackability parameter calculation. The analysis of crackability parameters and the calculation of the highest hardness achieved in the overheated zone of the basic material show that steels CSN 11455, 15218 and 15216 may be welded without pre-heating in the tested thickness of 20 mm. Although steels CSN 11483 and 15222 are within the limits of the specifications, they may only be welded at a limited thermal input, which affects the resulting structure in the temperature-affected zones of a welded joint. Steels CSN 13220 and 15422 should be pre-heated for welding. The results for weldable steels operating in the creep region show that the level of the creep properties of low-alloyed refractory steels and welding metals depends on the amount, size, morphology, stability and method of separation of the basic carbidic phase. Observing the prescribed methods of heat treatment and of welding with intermediate cooling and subsequent heat treatment, refractoriness and relaxation resistance tests were assessed of welding metals and of welded joints of the studied steels CSN 415335 and GS 17CrMoV5.11. (J.B.)