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Coal-fired power plants will remain an essential major part of energy supply in the world for the next decades. However, the need to reduce carbon dioxide emissions of new fossil plants by improved net efficiency by increased steam temperature is one of the biggest challenges of mankind in the near future. The goal to realize a steam power plant with a net efficiency of 50% and more can only be achieved by the use of Nickel-base Alloys, because of the needed steam temperatures of 700 °C. One of the most promising candidate alloys for rotor forgings subjected to 700 °C is Alloy 617, which was already intensively investigated and producibility for large parts was proven (in Blaes, Proceedings 6th international conference on advances in materials technology for fossil power plants, 2010, pp 436–449). In 1998, in Europe, the development of a 700 °C Power Plant started with the project AD700. Saarschmiede was always involved in most of the important 700 °C technology RD Proceedings 19th international forgemaster meeting, 2017, pp 335–344). The development, manufacturing process and test results of production for very large prototype nickel-base alloy rotor forgings for A-USC power plants are reported.

The present research is dealing with the comparative study of inelastic/elastic behavior of reference ∼12%Cr steel ZL3 and three new trial steels ZU1, ZU2, ZU3, with different ratio of alloying elements and equal content of Cr, using internal friction measurements. The samples were examined in “as-received” condition and after additional electric current tempering at 700˚C under different fixed external mechanical tensions. The values of deformation critical amplitudes for dislocation breakaway (e1) and for microplastic deformation beginning (e2) were determined in addition to the activation energies of relaxation processes in the investigated steels. It is shown that all the three trial steel samples in “as-received” condition exhibit considerably higher values of e2 in comparison to those of reference ZL3 steel. Among them the ZU3 steel has the highest values of e1 and e2, and demonstrates the visible (∼40%) increase in strength characteristics at elevated temperatures (600÷750˚C), achieved by the addit...

The European COST programme has a long standing interest in the development of creep resistant 10%Cr steels for rotor forgings designed to operate at ≥600°C. The steel COST E is now widely used for steam turbine shafts, seeing a strongly rising market share, in addition to its applications in gas turbines. The fail–safe manufacturing procedure developed for COST E rotors at Saarschmiede is described; this procedure is backed up with an increasing amount of mechanical properties and long term data. More recently, the production of COST F steel rotor forgings for high/intermediate pressure turbines has commenced, with delivered weights up to 44 t. In an attempt to increase the permitted service temperature, the effect of boron additions has been investigated in a COST activity. Saarschmiede has produced full size trial rotors to develop a production procedure. These prototype components are now under testing and the production of boron containing 10%Cr steels has begun.

In part I, the autofrettage of a smooth thick-walled tube of the austenitic stainless steel AISI 304 L was studied by finite-element (FE) modelling. It was shown that low- temperature autofrettage is more efficient than autofrettage at room temperature, since it produces a larger beneficial compressive residual tangential (hoop) stress at the inner bore of the tube and hence permits a more significant enhancement of the fatigue resistance against pulsating internal pressure. The objective of the present study (part II) was to investigate the technically more relevant case of a thick-walled tube with a cross-bore made of the same steel. For this purpose, three-dimensional FE calculations were performed in order to characterize the influences of the autofrettage pressure and temperature on the stress and strain changes, in particular at the site of the cross-bore, also taking into account the effects of work hardening and reverse yielding. The results indicate that low-temperature autofrettage can also be applied advantageously in the case of thick-walled tubes with a cross-bore by virtue of the significantly larger residual compressive stresses, compared to room temperature autofrettage. From the quantitative FE calculations, the optimal combination of autofrettage temperature and pressure were concluded to lie in the range of to , respectively. The calculated results were found to be in fair agreement with the measured values.

The stresses and strains introduced by low-temperature autofrettage of smooth thick-walled tubes made of the austenitic stainless steel AISI 304 L were modelled by the finite-element (FE) method. The objective was to show that low-temperature autofrettage is much more efficient than autofrettage at room temperature in enhancing the fatigue resistance by introducing a higher beneficial tangential (hoop) residual compressive stress at the inner part of the tube. Attention was paid to the influences of the autofrettage temperature and pressure, the work hardening and the reverse yielding on the residual stress components and on the total strain components of the tube. The FE calculations confirmed that more beneficial residual stress patterns can be attained by autofrettage at low rather than at room temperature. From the quantitative calculations, the optimal autofrettage temperature and pressure of the tube were concluded to be about and 4000 bar, respectively. The results of the calculations were shown to be in good agreement with recently measured data.

Austenitic stainless steels are widely used mainly because of their excellent corrosion resistance. For applications where high strength is required, metastable variants of these materials may be used as the strength of these metastable steels can be increased via the formation of martensite. The martensitic transformation can occur spontaneously by quenching the steel below the martensite start temperature (M[sub 3]). Above M[sub 3] the phase transformation can be assisted either by elastic stresses or plastic deformation. Cyclic deformation at low temperatures can strongly enhance the strength of metastable steel with acceptable decrease in ductility and toughness. Investigations based on fatigue tests have shown that the fatigue life depends strongly on the kinetics of the martensite formation. The temperature dependence of the kinetics of the martensitic transformation with and without superimposed external stresses below the yield point and during plastic deformation have been intensely investigated. In this paper, the kinetics of the martensitic transformation are investigated during low-temperature cyclic deformation.

Kickel base alloq 706 has estensi~e application historq for rotating parts in land based gas turbines combining high strength and toughness o\ er the \\hole range of the sen ice temperatures. Thls material is tqpicallj finish forged in a closed die press. The size of parts needed for the land-based gas turbines is Lrerq large requiring the use of the largest forging presses in the norld. Finish forging of alloq 706 and other nickel-based alloj s for rotating parts in gas turbines require homogenous structure and properties throughout the forging. Manj evperts considered that open die forging process u ould not be able to achieve such uniformlt>. ,411 experiment mas done to determine if a \\ell-controlled open die forging process could achie\ e the necessarj uniformit! in microstructure and properties for a large gas turbine part made of allo~ 706 I'his paper mill describe the details of the forging and heat treatment process. Results of mechanical tests and metallographic examination \+ill be also discussed. Issues with process control and repeatability for open die forging are also discussed.