Investigation of cooling capacity of an aqueous solution of bischofite during quenching
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The use of oils as quenching medium is explained by their lower cooling capacity in the range of the martensite transformation in comparison with other liquids. The main shortcoming during use of oil as quenching medium is their fire hazard, their complexity of subsequent washing of parts, contamination of work areas. In developing a process for heat treatment of fastenings and other blanks, for nuclear power plant equipment the effect of cooling capacity of an aqueous solution of bischofite on the mechanical properties and microstructure during quenching was investigated. The studies were conducted on steel 38KhN3MFA (GOST [All-Union State Standard] 23304-78) from an industrial melting intended for manufacture of studs for the main casing joint of a VVER-1000 reactor. Temperature measurements along the cross section of the blanks during heating, holding and cooling were carried out with thermoelectric converters (TEC) caulked in along the cross section of the blanks with calibration KhA with a wire diameter of 0.5 mm, which ensured the necessary accuracy of temperature measurement.