Special features and causes for operational damage in welded components of high-temperature diaphragms are considered. Comparative testing was performed of welding-technological properties of some commercially available coated electrode grades for welding heat-resistant steels of Cr-Mo and Cr-Mo-V compositions. Implant procedure and welding of Tekken technological samples were used to assess the delayed fracture susceptibility of 15Kh12VNMF + 15Kh1M1FL steel welded joints at application of selected electrodes. It is established that to ensure a high cold cracking resistance of these steel welded joints, it is necessary to apply preheating at 200-250 °C. Proceeding from the data of measurement of metal hardness in welds and HAZ of welded joints and weld metal impact toughness, an optimum mode of heat treatment of 15Kh12VNMF + 15Kh1M1FL steel welded joints was determined. It is shown that a softening zone of lower hardness forms in the HAZ metal structure of 15Kh12VNMF steel, in which the samples fail at testing for static tension at working temperature of 570 °C.

One of the problems in producing the welded joints of complexly-alloyed heat-resistant steels is the providing of the required level of weld metal impact toughness. The improvement of its ductility and toughness is attained by a postweld high-temperature tempering using the modes regulated by the developer of welding electrodes. In case of welding of an experimental high-chromium martensite steel by electrodes Thermanit MTS616 (10Kh9V2MFB type) with account for conditions of its fulfillment, the heat treatment was required by 30-40 o C lower than that usually applied for welds of the mentioned type. The effect of modes of the manual arc welding and duration of tempering at 730-720 o C on hardness and impact toughness of weld metals was determined. Intervals of holdings were found in tempering, during which the secondary hardening was observed. The modes were selected, providing the required level of impact toughness of welds (impact energy KV ≥ 41 J). It is shown that alongside with the selected duration of temperature the important factor, providing the increase in toughness of the deposited metal, is the application of multi-pass welding at the reduced energy input. 11 Ref., 4 Figures. K e y w o r d s : heat-resistant martensite steel, manual arc welding with covered electrodes, weld metal, high-temperature heat treatment, tempering mode, hardness, impact toughness Received 29.02.2016Figure 4. Temperature versus holding at high tempering to provide the required impact toughness of metal of welds in manual arc welding: 1 -recommendations of electrode manufacturer; 2 -results of experiments

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* Metallographic examinations were carried out with the participation of T.A. Alekseenko. ** Testing at 600 °C/20 min showed larger spread of ψ values. Lower value was considered in carried analysis as the possible worth variant of ductility.

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