Peter the Great St. Petersburg Polytechnic University (St. Petersburg, Russia):

V. V. Desnitskiy, Dr. Eng., Prof., Higher School of Physics and Materials Technology
L. V. Desnitskaya, Cand. Eng., Associate Prof., Higher School of Physics and Materials Technology
I. A. Matveev, Cand. Eng., Associate Prof., Higher School of Physics and Materials Technology
P. V. Kovalev, Cand. Eng., Associate Prof., Higher School of Physics and Materials Technology, E-mail: kovalev_pv@spbstu.ru

Cast fittings made of austenitic chrome-nickel steel has found wide application in industry, which is associated with the high corrosion resistance of these products, and resistance to elevated temperature and pressure. However, their applicability is limited by the likelihood of leakage during operation. The reason for the above is most often captured (provided that the porosity does not receive excessive development), as well as the structural features of parts of this type. So, usually a leak is found in the area of transition of the casting wall to the flange at a distance of 5–50 mm from the flange. There are a variety of methods to increase the tightness of cast fittings. As a measure to combat captivity, alloying with various elements should be used. This article analyzed the composition of steel with different contents of nickel, chromium, carbon, titanium and niobium, and casting conditions varied. Based on the implementation of the experiment with cyclic thermal load, it was determined that the most effective method of combating captivity is the replacement of titanium with niobium, as well as the implementation of pouring into dry sand forms. The fittings design itself plays an important role in increasing the tightness. In order to provide directional solidification of castings, technological overlaps are widely used. The use of overlaps is most eff ective for castings of small and medium thickness. For massive castings, in the presence of overlays, the solidification time increases signifi cantly, and they turn out to be less effective. To determine the optimum direction of solidifi cation, we used direct thermal analysis of the solidification of complex castings. Thermocouples were installed in thermal centers; on the basis of the data obtained, the solidification time of each of them was determined. It was determined that the best direction of solidifi cation is provided when the metal is fed into the flange, and the optimum pouring temperature is the interval 1530–1560 °С. The research results are the basis for the preparation of normals for cast steel fittings. The implementation of this scheme in production recorded an improvement in the integrity of the casting.

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