RU2506142C1 - Method electroslag casting of billet of casing with branch pipe - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to electrometallurgy and can be used for moulding shaped billets, in particularly, cases of fountain accessories with flanges and pipes. Remelting of consumable electrode in flux bath with smelting of vertical case and horizontal branch pipes and with increasing the electric power in smelting of branch pipes. Prior to smelting the branch pipes die is heated in their forming zone by hot water. Then, electric power fed to flux bath is increased by 11-16%. Said electric power is smoothly decreased after termination of branch pipe smelting by 28-35% to heating conditions and retained for 0.4-0.7 of total time of smelting. Thereafter, electric power is smoothly increased to working level to smelt the case remainder and kept invariable till the start of pipe discharge before terminating of smelting.

EFFECT: higher metal quality at pipe-to-case joint.

Description

The invention relates to electrometallurgy and can be used for the smelting of shaped billets, in particular, bodies of fountain fittings, with flanges and nozzles.

A known method of electroslag smelting of a body preform with a nozzle comprising remelting a consumable electrode in a slag bath to form a metal bath crystallizing into a preform, the shape of which corresponds to the mold, and when slag is filled with 0.1-0.25 volume of the crystallizer nozzle, it is overheated by 50-200 ° C, and when filling with slag over 0.25 of the volume of the nozzle, overheating is reduced by 40-60% and the temperature of the slag is kept constant until the beginning of the exit of slag from the nozzle, after which the temperature of the slag bath is tively lowered to a temperature corresponding to the temperature in the melting of the housing.

(SU 1462820, C22B 9/18, published 03/20/1997).

The closest in technical essence is the method of electroslag smelting of the workpiece body with a nozzle, including remelting the consumable electrode in a slag bath with an increase in the input power to it up to 30% in the process of smelting the nozzle, moreover, in the process of smelting the nozzle in the period of decreasing the height of the slag bath to 0.8 its height when smelting the body, the power is increased by 1-5% due to increased voltage, and during a decrease in the height of the slag bath from 0.7 to 0.5 of the above value, a further increase in power is produced due to m current is increased by 10-15% and further increase the tension in the 3.5-5% compared with the voltage value of the smelting enclosure.

(SU 1387461, C22B 9/18, published 01/27/1997).

A disadvantage of the known technical solutions is the low quality of the metal of the smelted nozzle and the interface zone of the nozzle with the housing.

The objective and technical result of the invention is to improve the quality of the metal of the smelted nozzle and the metal in the zone of connection of the nozzle with the housing.

The technical result is achieved by the fact that the method of electroslag smelting of the body blank with the nozzle includes remelting the consumable electrode in the slag bath with an increase in the power introduced into it during the melting of the nozzle, and before the start of the melting of the nozzle, the mold in the formation zone of the nozzle is additionally heated with hot water, and from the beginning smelting of the nozzle increases the input electric power by 11-16%, which, with the completion of the melting of the nozzle, gradually decreases by 28-35% to the heating mode and maintains during 0.4-0.7 total time of melting the billet of the body with the nozzle, then gradually increase to a value that ensures the remaining part of the body is melted and keep it unchanged until the beginning of the shrinkage shell withdrawal before completion of the melting process.

It is known that crystallization of an ingot during electroslag remelting is characterized by a dynamic equilibrium between the heat introduced into the metal bath and the heat removed to the solidified part of the ingot and to the walls of the mold.

The increase in power described in the known method violates the aforementioned dynamic equilibrium and is the reason for the formation of layered segregation due to a periodic change in the crystallization rate, which entails a change in the composition of metal layers that crystallize at different rates.

In addition, with sharp changes in the temperature conditions of melting, coarse crystallization bands, contaminated with sulfide chains, are usually observed in the zone of change in the crystallization rate.

In the melting zone of the nozzle, the axis of which is horizontal, there is a decrease in slag and metal baths and at the same time an additional cooling zone appears on the side of the walls of the mold forming the nozzle, while the zone of the nozzle is melted by the metal of the consumable electrode by less heated metal due to its removal from the sub electrode zone - the place of heat input into the melt.

All this leads to a difference in the rate of crystallization of the metal in the housing and the pipe, which causes off-axis segregation - spotted segregation and segregation strips in the area of the interface of the housing with the pipe.

The proposed technical solution significantly improves the quality of the metal in the lost wax pipe and the interface zone between the housing and the pipe.

The increase in power during the smelting of the axial zone of the nozzle shifts the formation of segregation zones to its axial part, where they are removed by mechanical boring of the cavity in the nozzle.

Reducing the power to the heating mode after melting the nozzle allows you to remove the shrink shell from the mating zone of the housing and the nozzle, which appears due to the different depths of the metal bath in the housing and the nozzle, in addition, heating helps to remove slag tangled in the liquid metal from the nozzle zone and eliminates the formation of bridges when shrinkage.

Heating the pipe formation zone with hot water before it begins to be filled with slag and metal melt reduces heat removal from the pipe melting zone and helps to reduce the formation of corrugations and slag inclusions on the surface of the smelted pipe.

Experimental swimming trunks were carried out at the experimental installation of ESR at NPO TsNIITMASH. Smelted the fountain body weighing 175 kg. As a consumable electrode for remelting in a slag bath, a continuously cast billet of ϕ 100 mm from 04X13H4M stainless steel was used. The workpiece of the fountain valve body was a cylinder with two flanges at the ends, equipped with two nozzles at an angle of 90 °, placed in the middle of the body on one axis.

When implementing the method, a vertically placed housing with flanges and horizontally placed nozzles were formed. The process of electroslag smelting began with the smelting of the lower flange of the casing with a working value of the input smelting capacity of 133 kW at a current of 3.5 kA and a voltage of 38.0 V from an electric energy source.

Before the start of melting of horizontally formed nozzles, the mold in the zone of nozzle formation was additionally heated with hot water with a temperature of 90-95 ° C circulating in heat exchangers placed on the mold body.

From the beginning of the smelting of the pipe, the input electric power was increased by 12.7% to 150 kW at a current of 4.0 kA and a voltage of 37.5 V.

After completion of the smelting of the nozzles, the input electric power was gradually reduced by 32.8% to a heating mode of 100.8 kW at a current of 2.8 kA and a voltage of 36.0 V, and this mode was maintained for 22 minutes, which is 0.48 the time of smelting the workpiece , then gradually increased power by up to a working value of 133 kW at a current of 3.5 kA and a voltage of 38.0 V (an increase of 30-35%), which ensures the remaining part of the body is melted, keep it unchanged until the start of the shrinkage shell before completion of the smelting process . The total melting time for the billet body with nozzles was 45 minutes.

To study the quality of the metal and the chemical composition, axial templates were cut out of the nozzle, as well as the housing in the area of its interface with the nozzle. The analysis showed the uniformity of the chemical composition of the metal in all studied areas of the workpiece housing with the pipe. The metal over the entire cross section of the templates is dense, without looseness and porosity, and there are no off-axis, spotted, and layered segregations in the interface between the housing and the pipe.

Claims (1)

Method of electroslag smelting of a workpiece of a fountain valve body with nozzles, including remelting of a consumable electrode in a slag bath with smelting of a vertical housing and horizontal nozzles and increasing the electric power introduced into it during smelting of nozzles, characterized in that prior to the smelting of nozzles the mold is additionally in the formation zone heated with hot water, and then increase the electric power introduced into the slag bath by 11-16%, which with the completion of smelting smoothly reduce by 28-35% to the heating mode and maintain for 0.4-0.7 the total melting time of the aforementioned workpiece, after which a smooth increase in the input electric power to the operating value is carried out, ensuring that the remaining part of the body is melted and keep it unchanged until the beginning withdrawal of the shrink shell before the completion of the smelting process.