Moscow, Russia
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International Heat Treatment and Surface Engineering | Year: 2011

The creep resistance of 9% chromium high temperature steels is determined by the alloy content and structure resulting from heat treatment. This paper describes the analysis of the phase composition using CALPHAD numerical modelling methods, of known modifications of 9% high temperature chromium steel: 9Cr-0?1C, 0?9Mo, 0?21V, 0?1Nb, 0?04N (P91) and 9Cr-0?1C, 2W, 0?5Mo, 0?21V, 005Nb, 0?05N, 0?005B (P92). The effect of alloying elements on the phase composition of the steel and the mutual effect of the composition on the nature and quantity of the phases Me23C6 and Me(CN) in the temperature range 570-620°C is described. On the basis of calculated data and experimental results, a composition for new high temperature steels with additional Co alloying (up to 3%) and varying carbon contents in the range 0?02-0?10% is proposed. Results are shown for investigations on high temperature chromium steels containing cobalt, including: effect of complex alloying with tungsten, molybdenum, and cobalt on the service properties and structural composition of steels; heat treatment processes for alloy variants and kinetics of structural change during creep and prolonged thermal aging. Data have been obtained comparing calculated and experimental data for the phase composition in chromium steel, also the effect of the phase composition on creep characteristics. On the basis of a complex laboratory investigation and industrial pilot heats, optimal composition variants for the alloy content of high temperature Cr-Mo-V-Co steels have been determined for practical applications. CNIITMASH has developed a chromonitriding technology for improving the corrosion, wear and scratch behaviour, as well as for protection against self-welding and other service characteristics of austenitic steel components and nickel alloys. Chromonitriding technology includes saturation of the component surface with chromium and nitrogen. The technology is intended for strengthening valves and bushings, water pump components, and components operating in liquid metal, burnt fuel residue, and other aggressive environments. The conditions governing the formation of the strengthening layers, consisting of an austenitic matrix (c solid solution) and containing Cr 2N with a depth of up to 250 mm and a hardness of 750-950 HV have been determined. Thermodynamic analysis of phase formation conditions during the chromising and subsequent nitriding process over a wide range of temperatures and saturating media has been carried out. The technology has been optimised for process and media composition leading to a structure with maximum surface properties. © 2011 IHTSE Partnership.

Skorobogatkh V.N.,PJSC RPA CNIITMASH | Tsikh S.G.,PJSC RPA CNIITMASH | Stepin V.S.,PJSC RPA CNIITMASH | Grachev O.E.,TSPC LTd | Muhametova S.S.,TSPC LTd
Proceedings - European Conference on Heat Treatment and 21st IFHTSE Congress | Year: 2014

In this paper the technology of laser cladding of valves for thermal power plants is considered. We used a robotic setup of laser cladding on the basis of a diode laser with a wavelength of 0.9 ... 1.03 μm, which allows generating a continuous radiation output power up to 6 kW. Using the setup cladding of materials of S-6, C-6, C-12 on the basis of pearlitic (14MoV6-3) and austenitic (X12CrNiTi18-9, X6CrNiMoTi17-12-2) steels was carried out. Assessment of repair possibility of parts was performed in laboratory studies and tests. As a result of metallographic investigations was found that laser cladding forms cast metal structure of the cladded layer, characterized by a grain size of 1.5 ... 2 times lower than PTA process. Laser cladded metal hardness is 5...15 HRC higher than one, obtained by PTA process. Studies of the deposited layer by EDS analysis showed that the desired chemical composition is achieved at a distance of 80 μm from the boundary coating-base. Resistance to thermal cycling was assessed by testing samples of plates wedge gate valves imitators with circular cladding layer performed by the laser method. Test results indicate that the laser cladding method does not impair the stability of the material under thermal cycles in spite of higher hardness comparing with PTA process. Galling of cladding layer at temperatures 570 ± 15 °C was studied in the air at a pressure up to 100 MPa. All materials showed resistance to galling no worse than similar metal, cladded by PTA process. On the base of these studies and tests was shown that coatings obtained by laser cladding method have good performance in many parameters superior to those of the coatings applied by PTA process.

Bogachev V.A.,All Russia Thermal Engineering Institute | Zmienko D.S.,PJSC RPA CNIITMASH | Korneev A.E.,PJSC RPA CNIITMASH | Pshechenkova T.P.,All Russia Thermal Engineering Institute | Shkol'nikova B.E.,All Russia Thermal Engineering Institute
Thermal Engineering (English translation of Teploenergetika) | Year: 2012

The elemental and phase compositions of the altered layer, as well as the conditions under which this layer emerges and grows in coils made of chromium-nickel (Grade 12Cr18Ni12Ti) and chromium-manganese 10Cr13Mn12Si2Ni2Cu2Nb (Grade DI59) austenitic steels are investigated. The dependence of layer thickness on the operating temperature and time of operation is revealed. It is proposed to use magnetic ferritometry for examining thermal nonuniformity in the steam superheaters of boilers at thermal power stations. © Pleiades Publishing, Inc., 2012.

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