Peculiarities of qualitative indicators of metal of the forged boiler tuber
DOI:
https://doi.org/10.15407/mom2019.03.047Keywords:
forged boiler tubes, chemical composition, short-term mechanical properties, microstructure, long-term strengthAbstract
Qualitative indicators (chemical composition, microstructure, short-term mechanical properties at room and elevated temperatures, as well as long-term strength) of metal of forged and machined 377 to 920 mm diameter 15Cr1Mo1V steel boiler tubes manufactured by Novokramatorsk Machine-Building Plant JSC, Kramatorsk, according to TU3-923-75 Specification using billets of home production. Actual value of long-term metal strength (100 thousand hours at temperatures of up to 560 °С) standardized by above Specification was determined for the first time for 15Cr1Mo1V steel forged tubes produced by Novokramatorsk Machine-Building Plant JSC. It was shown that the technology existing at the plant does not guarantee obtaining of 15Cr1Mo1V steel forged boiler tubes in various size ranges with high service reliability. It has been established that metal of forged and machined 15Cr1Mo1V steel boiler tubes of all sizes under study features an unfavorable ratio of concentrations of carbide-forming vanadium and carbon. This fact can adversely affect performance characteristics of metal of these tubes. Metallographic examinations have established that the heat treatment conditions applied at Novokramatorsk Machine-Building Plant JSC to the 15Cr1Mo1V steel tubes do not make it possible to obtain a stable and homogeneous metal microstructure in forged boiler tubes that would provide required level of long-term strength required by normative documents. It was shown that absence in TU3-923-75 Specification of requirements to the metal microstructure in 15Cr1Mo1V steel forged boiler tubes and conditions of their heat treatment does not allow Novokramatorsk Machine Building Plant JSC to produce tubes of high service reliability. A need to develop an up-to-date national Specification for 15Cr1Mo1V steel large-diameter forged boiler tubes with inclusion of requirements, foremost requirements to microstructure and heat treatment conditions ensuring high service reliability of the tubes which will be operated without failures in power generating equipment at high temperatures and pressures during the design period (at least 100 thousand hours) instead of TU3-923-75 Specification being of no effect currently in Ukraine was shown.
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Copyright (c) 2019 L.V. Opryshko, T.V. Golovnyak
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