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| Stránský K., Šenberger J., Levíček P., Dobrovská J., Dobrovský L. |
| OXIDATION RE-MELTING OF THE CR13NI1 CAST STEEL BY MEANS OF OXYGEN-BLOWING |
Abstract
Corrosion-resistant 13% Cr and 1% Ni cast steels are used to produce castings for the Kaplan, Pelton and Francis turbines. These cast steels also have a satisfactory cavitation resistance. The oxidation re-melting process, where oxygen is blown into the bath, was elaborated with the aim of reducing the gas content (hydrogen and nitrogen) in re-melted Cr13Ni1 steel scrap. This technology was tested on and described for twenty-five melts, with special regard to oxygen-blowing conditions, mechanical properties (verified by the impact test) of the cast steel, and suppressing the formation of gas holes in the castings. A basic electric-arc furnace was used in the oxidation re-melting process of steel scrap. The measuring of bath temperature and oxygen activity in the bath, and the parallel sampling for chemical analysis of the bath were realized in the following melt periods: (1) after melt-down and heating before oxygen blowing; (2) immediately after the end of oxygen blowing; (3) at the start of the reduction period, after preliminary deoxidation with Al, slag reduction and modification of chemical composition; (4) in the bath at the end of the reduction period; and (5) in the ladle, after tapping and after SiCa deoxidation. Results of this measuring are given in Table I and the corresponding mechanical properties of and impact test results for re-melted steels are in Table II. The heat treatment of cast samples of re-melted corrosion-resistant steels was as follows: homogenisation annealing at 1150?C / (6?20 h – as a function of the wall thickness of castings) / (air cooling) plus hardening at 940?C / (4?6 h) / (air cooling) and tempering at 720?C / (4?6 h) / (air cooling). The castings from re-melted steel of this type were without bubbles.
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| Keywords: corrosion-resistant steel|castings|water turbines|oxidation re-melting|oxygen-blowing condition|oxygen activity|mechanical properties| |
| No 3 (2003), p. 182-190 |
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| Kristofory F., Mohyla M., Mikuláš D., Vítek J. |
| HARDNESS OF NICKEL ELECTRODEPOSITS |
| Keywords: cathodic deposition|nickel|sulphosalicylate|hardness|heat treatment|wear resistance| |
| No 3 (2003), p. 203-209 |
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| Zegzulka J. |
| LOGISTICS OF BULK MATERIALS |
| Keywords: logistics of bulk material|mechanical and physical properties|optimum consumption energy| |
| No 3 (2003), p. 240-244 |
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