RU2163933C1 - Method of steel alloying with bismuth - Google Patents

Abstract

FIELD: ferrous metallurgy, particularly, production of bismuth-containing steel. SUBSTANCE: method includes uphill casting of metal into ingot mold, introduction of bismuth in the form of shot or globules into gating system during casting. Linear pouring rate of steel up to filling the ingot mold to height of 300-400 mm is maintained within 10-15 mm/s. Then it is reduced to 5-7 mm/s and introduction of bismuth is started. Upon completion of bismuth introduction, linear pouring rate of steel is increased to 10-15 mm/s for 2-5 s. Pouring is finished at rate of 1.5-3 mm/s. Difference between time of ingot casting and time of bismuth introduction shall not exceed 250 s. EFFECT: higher assimilation and uniform distribution of bismuth in volume of ingot, improved quality of blooms produced after hot deformation of ingots. 1 dwg, 4 tbl, 1 ex

Description

 The invention relates to ferrous metallurgy, in particular, to the production of bismuth-containing steel and can be used for alloying steel with bismuth during casting by siphon.

 A known method of producing steel alloyed with fusible metal, in particular lead or bismuth, comprising casting steel into a chill mold and introducing lead or bismuth into a stream of steel in the form of fractions and globules (see US patent N 4247326 from 01/27/1981, IPC C 22 C 38/60).

 The absence of regulated parameters for casting steel and introducing fusible metal leads to its large losses in the form of sublimates, uneven distribution in castings and unsatisfactory surface quality after hot deformation of castings.

 The closest analogue of the invention is a method of introducing alloying additives in the form of a fraction into steel, in which bismuth can be introduced into the gating system as an additive when casting metal by siphon into the ingot casting mold (EP 0092764 A1, C 21 C 7/00, C 22 C 33/00, 02.11.83).

In the known method of alloying steel with bismuth, the time parameters of steel casting and input of bismuth are not described bismuth has a high vapor pressure (bismuth boiling point 1560 ^o C), the absence of regulated parameters of steel casting and input of bismuth leads to large losses of bismuth in the volume of the ingot and the unsatisfactory surface of the blooms obtained by hot deformation of the ingot.

 The objective of the invention is to provide a method for the production of bismuth-containing steel with a low loss of bismuth, its uniform distribution in the volume of the ingot and the good quality of the blooms obtained after hot deformation of the ingots.

 The problem is solved by casting metal with a siphon into the mold, bismuth in the form of fractions and globules is introduced into the gating system during casting, and the linear speed of casting of steel until the mold is filled with metal to a height of 300-400 mm is maintained within 10-15 mm / s , then it is reduced to 5-7 mm / s and bismuth input begins, while after the bismuth input is completed for 2-5 s, the linear casting speed is increased to 10-15 mm / s, and the difference between the ingot casting time and the bismuth input time is not must exceed 250 s, and the end of the casting pro odyat at a rate of 1.5-3 mm / s.

Bismuth has a high vapor pressure, the boiling point of bismuth is 1560 ^o C, which is comparable to the temperature of the cast steel (1540-1620 ^o C).

 For this reason, during the introduction of bismuth into steel, both its intense evaporation from the open surface of the steel and boiling in the bulk of the steel are observed. In addition, during the movement of steel with bismuth along the gate system, cavitation phenomena are observed in the form of the formation of bubbles filled with bismuth vapor. Particularly intense formation of bismuth bubbles occurs on the rough surface of the gate system in places where there is a sharp increase in the speed of steel flow or a change in the direction of its movement. Cavitation bismuth bubbles in steel can exist for as long as desired, as long as the external pressure on the bubbles is less than or equal to the pressure of elasticity of the bismuth vapor.

 When bismuth bubbles fall in a region where the external pressure is greater than the elastic pressure of bismuth vapor, the bubbles collapse, and a strong shock wave is created, which can produce certain damage. If the collapse of the bubble did not occur in the volume of steel, then it can be carried by metal flows to the steel-air interface and removed into the external environment.

 If the collapse of the bismuth bubble occurs on the hardening surface of the ingot, the latter collapses, which leads to the formation of surface defects on the ingot.

 However, cavitation phenomena have a positive meaning, as during bubble formation and subsequent collapse, a pressure of up to 1000 atmospheres develops, due to which the dissolution of bismuth in steel is accelerated, and in the volumes of steel, where the bismuth content is greater than its solubility limit, the elementary bismuth particles forming are several orders of magnitude smaller than the initial bismuth particle from which the bubble formed. Thus, in order to obtain a high-quality ingot and reduce bismuth losses, the parameters of ingot casting and doping with bismuth should be determined by optimal cavitation phenomena.

 In view of the foregoing, a method has been developed for alloying steel with bismuth when casting it with a siphon. The supply of bismuth began after filling the mold with metal to a height of 300-400 mm. When the height of the steel in the mold is less than 300 mm, strong borehole is observed in the latter and, for this reason, in the case of bismuth supply, its bubbles are carried out to the surface from which bismuth is removed into the atmosphere, and the bubbles that fall on the crystallized surface of the ingot collapse and destroy it . With a steel height of more than 300 mm, drilling sharply decreases, and at 400 mm it disappears. Steel casting without bismuth smoothes out irregularities on the surface of the gating system, thereby reducing the intensity of cavitation phenomena on the surface of the gating system.

 Steel casting with a linear speed of 10-15 mm / s to a pouring height in the mold of 300-400 mm allows to obtain a high-quality surface of the ingot in the bottom section. When the casting speed is less than 10 mm / s, steel splashes are formed on the surface of the lower part of the ingot, which are not welded to the ingot. At a speed of more than 15 mm / s, the crystallized crust of steel formed on the surface of the mold is very thin, and, with the subsequent supply of bismuth, it is easily destroyed.

 The supply of bismuth at a casting speed of steel 5-7 mm / s allows for controlled cavitation of bismuth, while achieving low bismuth burnout, its good dissolution in steel. With a decrease in the steel casting speed of less than 5 mm / s, a crust forms on the surface of the steel, which tucks during the casting, which leads to a decrease in the quality of the surface of the ingot. When the casting speed of steel is more than 7 mm / s, bismuth burn increases.

 An increase in the casting speed after the end of bismuth supply to 10-15 mm / s for a period of 2-5 s allows one to average the bismuth content over the entire volume of the ingot. At a time of less than 2 s, the averaging is weak; at more than 5 s, transverse cracks on the surface can form in the ingot.

 The end of the casting at a speed of 1.5-3 mm / s reduces shrinkage in the upper part of the ingot, in the discontinuities of which accumulation of bismuth occurs, the size of individual particles of which reaches more than 1 mm.

 With an increase in the difference between the time spent on casting the ingot and the time spent on introducing bismuth for more than 250 s, the absorption of bismuth by steel decreases.

 OJSC Zlatoust Metallurgical Plant carried out work on the development of the production of structural steels alloyed with bismuth. Experimentally-theoretically established the optimal parameters of steel casting with alloying with bismuth during casting.

 Smelting of steel grade AB9HGN was carried out in a 10-ton arc electric furnace. After finishing the steel by chemical composition, it was poured into a steel pouring ladle. Steel casting was carried out by siphon, simultaneously in 4 molds. The section of the molds is a square of 570 mm, the weight of the ingot is 2875 kg. Bismuth in the form of fractions and globules with a diameter of 1-4 mm was fed from the hopper - dispenser into the receiving funnel of the gating system during the casting of steel. The casting of steel was carried out with a coating of the metal mirror in the molds with an ash-graphite mixture. The ingots underwent hot deformation on bars with a section of a square of 220 mm. On these rods, surface quality, bismuth distribution along the length and cross section were evaluated, and bismuth assimilation by steel was analyzed. In the optimal mode in the mold, the linear speed of steel casting to a height of 300-400 mm was maintained in the range of 10-15 mm / s, after which the speed was reduced to 5-7 mm / s and bismuth was introduced. After the introduction of bismuth was completed for 2-5 s, the linear casting speed was increased to 10-15 mm / s. The end of the casting was carried out at a speed of 1.5-3 mm / s. The difference between the ingot casting time and the bismuth injection time was maintained to a value of less than 250 s. On a number of melts, casting and alloying of steel with bismuth was carried out with a deviation from the optimal parameters.

 The quality of the steel met the requirements of regulatory and technical documentation. The relationship between the quality characteristics of steel and the technological parameters of casting and alloying are given in tables 1-4 and in the drawing. As can be seen from them, when casting steel and alloying it with bismuth, the claimed parameters achieve the maximum effect on the quality and assimilation of bismuth.

Claims (1)

 A method of alloying steel with bismuth, including the introduction of bismuth in the form of fractions and globules into the gating system during the casting of metal by siphon into the ingot mold, characterized in that until the mold is filled with metal to a height of 300 to 400 mm, the linear speed of casting of steel is maintained within 10 - 15 mm / s, then it is reduced to 5 - 7 mm / s and bismuth input begins, while after the bismuth input is completed for 2 - 5 s, the linear casting speed is increased to 10 - 15 mm / s, and the end of the casting is carried out at a speed of 1 , 5 - 3 mm / s, and the difference between the time ingot casting it and bismuth input time should not exceed 250 seconds.

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