The microstructure and mechanical properties of 12Kh1MF boiler tubes
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The microstructure of 12Kh1MF boiler tubing is substantially affected by the original microstructure of the hot rolled tubing. The prevalence of thin sections in intermediate components impairs the microstructure of the finished tubing. The microstructure with dense pearlite is less resistant in final heat treatment and is responsible for the unsatisfactory structure resulting from tempering at 730–740°C.
The microstructure is satisfactory after normalization at 980–1000°C with holding for 10 min and tempering at 700–720°C for 1 h. Heat treatment of the finished tubing should be conducted in a continuous furnace, which ensures high accuracy of the temperature and even heating.
To obtain the required microstructure and mechanical properties, boiler tubing should be manufactured by cold rolling. The tensile stresses predominating in drawn tubing inhibit recrystallization, as the result of which the ultimate strength of drawn tubing is almost 10 kg/mm2 higher than that of cold rolled tubing. Tubing can be manufactured by drawing if the upper limit of the strength is disregarded.
KeywordsMicrostructure Heat Treatment Recrystallization Tensile Stress Thin Section
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