SU551371A1 - Modification method of gray iron - Google Patents

Description

one

The invention relates to metallurgy and can be used in the production of responsible iron casting.

There is a method of improving the mechanical properties of cast iron, in which the hardening is reached by blowing molten iron with ammonia, with different duration of ammonia blowing through liquid iron, resulting in various mechanical properties of the latter.

There is also known a method for modifying pig iron with boron.

However, the introduction of boron into the liquid melt stabilizes the superstructure of the cement due to the occurrence of carboborides B C in the melt, which dramatically increases the tendency of the pig iron to chill.

Increasing the boron content in the entire casting volume is not always desirable. For example, in the manufacture of differential castings, the introduction of boron in cast iron has a positive effect on the properties of castings in large sections, but at the same time, chills out and degrades the workability of thin 25

walls and edges. Similarly, boron behaves itself and nitrogen.

The purpose of the invention is to improve the quality of the cast.

This is achieved by the combined treatment of liquid iron with boron and nitrogen, and the residual content of boron and nitrogen must correspond to the stoichiometric ratio ensuring the formation of boron nitride.

Experiments have shown that, while boron and nitrogen separately increase chill, while their introduction together, the tendency of pig iron to chill is sharply reduced. Moreover, the greater the amount of boron and nitrogen together introduced into the iron, the higher the effect.

Claims (1)

Example. Billets of synthetic cast iron of the following composition, weight. %: C 3.5; H 1.63; Si 0.15; NJ Oh, 15; Cl O, 013; A1 0.012 is melted in an induction furnace at the bottom of the crucible, which is pre-packaged with a calculated amount of amorphous boron powder (92.5% B). The melt is overheated to 155 ° C, kept at this temperature for 5 minutes, and then equal portions of metal are cast into the ladle, and the calculated amount of nitrogen is introduced into it. To enter nitrogen, mixtures of electrolytic Mie and nitrated electrolytic Mp (4.6% N) are used to apply their ratio so as to maintain a constant Mn content (1%) at different concentrations of az. 100x50x20 mm, one of the ends of which is cooled by a massive steel refrigerator. By chemical analysis it was determined that the boron content is 0.037%, and the nitrogen content of C is left, wt.%: 0.004; 0.0057; 0,0173; 0,0035. Thus, when the content in the iron is 20 0.037% of boron and O, O035% of nitrogen (fourth break), the bleached zone is almost absent. This stoichiometric ratio corresponds to boron nitride BN, the particles of which, obviously, are the centers of graphite formation. The use of the proposed method allows to improve the quality, reduce the tendency to chill and improve the workability of pig iron intended for critical difference and thin-walled parts. Claims simultaneously with boron, nitrogen is introduced into the melt in a stoichiometric ratio to produce boron nitride.