V. 326, №5 , 2015

Role of structural factors in improving corrosion resistance of pipe steel under cyclic heat treatment Bulletin of the Tomsk Polytechnic University Vol. 326, № 5

The paper discusses the possibility of using multiple structural recrystallization to improve the performance of the 20 steel used for manufacturing heating surface tubes. Relevance of the work is caused by the continuous increase in number of corrosion damage elements of boilers. The authors have evaluated the influence of microstructure parameters (inequigranular) on the corrosion resistance and proposed the method of heat treatment which increases the operational reliability of the pipes. The essential dependence of corrosion characteristics of dimensional parameters of the grains was determined. The most effective mode that reduces inequigranular microstructure is double normalization mode at 920 °С and a single mode at 940 °С. The maximum value of 0,49 the inequigranular factor reaches at double normalization at 920 °С. In this mode the value of the average area of ferrite grains decreases by 42 %, the value of the inequigranular factor increases in 3,3 times in comparison with the baseline. This heat treating mode ensures minimal corrosion rate, while the mechanical properties are within the requirements of the relevant regulations. There is a decrease in depth of intergranular cracks in 1,5 times (from 31,7 to 21,1 microns) in comparison with the cracks formed on the samples held on the recommended ТU 14-3r" 55-2001 heat treatment. Application of the double normalization mode at 920 °С for heat treatment of carbon steel 20 used in heat power engineering for manufacturing heating surface tubes, will increase the life of heat exchanger elements of a boiler due to significant decrease in the rate of external corrosion.

Keywords:

inequigranular of microstructure, external corrosion, intercrystalline corrosion, resource of boiler tubes

Authors:

Pomazova Anna

Panova Tatyana

Gering Gennadiy

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