SU1735381A1 - Process for producing cast iron for thin-walled castings - Google Patents

Abstract

The invention can be applied in a foundry industry to produce thin-walled iron castings. The essence of the method: melting of charge materials containing 0.03-0.4% of chromium, overheating and deoxidation of the melt, putting spheroidization agents and graphitizers into the ladle when the melt is released into it and pouring the molds; The silicon content in the charge is maintained at 0.4-0.6 wt.%, the pig iron is superheated to 1400-1450 ° C, after which it is aged for 0.2-0.5 h, slag loading and deoxidation 0.1-0.3 wt.% Alloy of iron-silicon-REM; spheroidizers and graphitizers are introduced into the ladle simultaneously in a mixture containing magnesium-zirconium alloy and ferrosilicobarium in a ratio of 1: (3-8) with a total consumption of a mixture of 1: 2 wt.%, and the content of chromium and silicon in the mixture is maintained at level 1 : (1-20), iron-silicon-REM alloy contains 25-30 REM; 25-30 wt.% Silicon, iron and impurities - the rest; The magnesium-zirconium alloy contains 5-15% by weight of zirconium, 0.1-3% by weight of alkaline, alkaline earth metals and magnesium halogens, magnesium is the rest, is introduced into the iron in granular form, and the indicated halogens are incorporated into these granules. in the form of their salt shell; An alloy containing 25–30 wt.% barium, 55–60 wt.% silicon, iron and impurities is used as ferrosilicobarium. 3 hp f-crystals, 1 tab. ate with

Description

The invention relates to iron metallurgy, in particular to methods for producing iron for thin-walled castings, and can be applied in a foundry.

A known method of manufacturing castings from nodular cast iron, including the selection and preparation of charge materials with a low content of phosphorus and manganese, melting of charge materials and overheating of the melt, its processing with spheroidizing and graphitizing modifiers together with the fluxes, removal of sludge and casting of metal according to the forms.

The closest in technical essence and the achieved result to the invention is a method of manufacturing castings of nodular cast iron, including the melting of charge materials containing 0.005-0.05 wt.% Phosphorus and 0.03-0.40 wt.% Chromium, overheating and melt deoxidation upon release into the ladle of 0.5-1.5% silicocalcium based on the weight of the metal, input of spheroidization agents and graphitizers into the ladle with the release of melt into it and pouring of the molds.

The disadvantage of this method is the low fluidity of the obtained chu3.

sl w

00

guna due to its insufficient acidification and metal contamination with non-metallic inclusions, as well as a high tendency to chill, which leads to a deterioration in the quality of thin-walled iron castings.

The purpose of the invention is to improve the quality of thin-walled iron castings by increasing the fluidity of the iron and reducing its tendency to chill.

The goal is achieved by the fact that in the method of producing iron for thin-walled iron castings, including melting in an induction furnace charge materials containing 0.03-0.40 wt.% Chromium, melt overheating, melt deoxidation, putting spheroidizing agents and graphitizers into the ladle with the release of the melt, the silicon content in the charge is maintained at 0.4-0.6 wt.%, the overheating of the pig iron in the crucible of the induction furnace is carried out up to 1400-1450 ° C, after which the melt is aged in the crucible for 0, 2-0.5 hours, download slag and melt deoxidize 0.1- 0.3 wt.% Of the alloy Fe - Si - REM, while spheroidizing agents and graphitizers in the ladle are introduced simultaneously into the mixture containing magnesium-zirconium alloy and ferro-silicobarium in a ratio of 1 :() with a total consumption of 1-2% Fe-Si-REM alloy contains 25-30 wt.% REM, 25-30 wt.% Si, iron and impurities - the rest, magnesium-zirconium alloy contains 5-15 wt.% Zr, 0.1-3 wt. .% alkaline, alkaline earth metal and magnesium halides, magnesium - the rest, is introduced into the cast iron in granular form, and these halides are introduced into the composition of these granules in the form of their salt shell, as ve ferrosilicoburium is used, an alloy containing 25-30 wt.% Ba, 55-60 wt.% Si, iron and impurities - the rest.

The peculiarity of the proposed method is the combination of insufficient melting of the pig iron melt at the stage of its smelting and heating due to the reduced silicon content in it when it is correlated with the content of chromium in the cast iron, which leads to the loss of the latter during this period of melting, followed by deep melting of the melt cast iron of rare-earth metals and Si, its effective simultaneous treatment with spheroidizing and graphitizing additives preventing melt deoxidation in the process of cast iron processing.

When the silicon content in the mixture is less than 0.4 wt.%, An intense carbon loss occurs in the melt, which leads to an increase in chill cast iron and lower quality

castings, and when its content is more than 0.6 wt.%, silicon has an intense deoxidizing effect, which does not allow to reduce the chromium content in the iron,

increases the tendency of thin-walled castings to chill crystallization. The ratio with the content of chromium and silicon in the charge 1: 1-20 provides the required level of melt deoxidation. If this ratio is below the lower limit, the silicon content in the melt is not enough to provide the required fluidity, hence, the quality of the castings, and when the ratio is above the upper

The limit of silicon content is unnecessary, which worsens the conditions of chromium carbon, increases the chill iron bleaching, reduces the quality of castings.

The melt aging at (1400-1450) ° C for 0.2-0.5 hours while observing the proposed ratios of silicon and chromium content in the charge ensures the flow of pig iron in the required volume of chromium, at temperatures below 1400 ° С

silicon metal waste, as well as the processes of its recovery from the furnace lining, which degrades the quality of the metal, and at a temperature of more than 1,450 ° C, an intense carbon waste occurs, resulting in

bleached in castings. A holding time of 0.2-0.5 hours ensures the necessary completeness of the reaction for the deoxidation of cast iron.

Deoxidation of cast iron 0.1-0.3% of the alloy iron-silicon-REM provides besides

with effective removal from the melt of sulfur and oxygen, input into it ready crystallization centers in the form of rare earth silicides contained in the specified alloy.

When it is introduced into cast iron in an amount of less than 0, 1 wt.%, These components are spent mainly on the deoxidation and desulfurization of cast iron, and this effect does not manifest itself, and when it is introduced into the cast iron more than 0.3 wt.%, The bleaching iron appears.

the effect of REM, the quality of castings is deteriorating

The optimum content in this alloy is 25-30 wt.% REM; 25-30 wt.% Si, Fe, and impurities — the rest provides a favorable Si: P3M ratio for forming the maximum amount of silicides. With a lower content of Si and REM, their amount is insufficient for effective deoxidizing and epigastric

action, and with more content sharply

alloy density decreases, increases

waste of its components during processing

melt and decreases its efficiency.

The simultaneous introduction of a mixture of spheridizers and graphitizers into the bucket ensures the achievement of the objective of the invention by preventing deoxidation of the melt and attenuation of the modifying effect. Entering spheroidizers and graphitizers into the molten iron in the mixture containing magnesium-zirconium alloy and ferrosilicon-barium in a ratio of 1: 3-8 with its total consumption of 1-2 wt.% Ensures the required quality of thin-walled iron castings due to the joint substrate action of silicides barium and rare-earth metals and the surface-active action of zirconium, which prevents the melt jet from oxidizing during its contact with the mold material, which increases the fluidity of the iron and the quality of thin-walled castings.

The optimum content of components in the magnesium-zirconium and ferrosilicon-barium alloy provides the maximum positive effect. With a decrease in their concentration, their indicated action does not manifest itself, and with an increase in their upper limits, the contamination of the metal with non-metallic inclusions increases, impairing the quality of thin-walled castings. When the ratio of magnesium-zirconium alloy and ferrosilicobarium in a mixture of less than 1: 3, an intense waste of magnesium-zirconium alloy occurs, as a result of which the protective effect of zirconium on the metal does not appear. With a ratio of their contents of more than 1: 8, zirconium introduced into cast iron is not enough. The optimum consumption of this mixture is 1-2 wt.% Due to the initial content of silicon and chromium in the mixture, and the more, the smaller the content of silicon in it (and, accordingly, the higher the content of chromium).

For experimental verification of the proposed method, 5 experiments were carried out.

The conditions of the experiments and their results are shown in the table.

The cast iron is melted in a commercial frequency induction furnace with an acid lining of the IChT-1 type with a capacity of 1 ton. Low silicon silicon iron of the PVC type and other wastes are used as charge. 0; Si 0.4-0.6; Cr 0.03-0.4; P 0,005-0,05; Mp 0.4-0.6; S 0.01-0.02. The standard alloy of the FSZORZMZO type is used as the alloy Fe-Si-REM, the standard granulated alloy N-2 is used as the magnesium-zirconium alloy, and the alloy FS60Ba27 is used as ferrosilicobari. The Fe-Si-REM alloy is introduced onto the metal mirror in the furnace after slag is downloaded, and the remaining components are directly to the bottom of the ladle before the iron is released into it.

The quality of castings is assessed by the magnitude of the fluidity and chilling of iron in standard samples, as well as the evaluation of defects of experimental thin-walled castings such as NPP impellers on their macrotemplates.

Claims (4)

1. Method for producing cast iron for thin-wall castings, including melting in an induction furnace charge materials containing 0.03-0.40% chromium, overheating of the melt, melt deoxidation, input of spheroidizing agents and graphitizers in the ladle, when melt is released into it, characterized in that, in order to improve the quality of thin-walled iron castings due to an increase in the fluidity of the iron and reduce its tendency to chill, the silicon content in the charge is maintained at 0.4-0.6 wt.%, overheating the cast iron in the crucible of the induction furnace is carried out up to 1400-1450 ° C, after which the melt is aged in the crucible for 0.2-0.5 h, the slag is downloaded and the melt is oxidized 0.1-0.3 wt.% alloy Fe-Si-REM, while spherodizators and graphitizers in the bucket are introduced simultaneously in the mixture containing av magnesium zirconium and ferrosilicobarium in a ratio of 1: (3–8) with a total consumption of a mixture of 1-2%. 2. A method according to claim 1, characterized in that the Fe-Si-REM alloy contains 25-30% REM, 25-30% Si, iron and impurities - the rest. 3. A method according to claim 1, characterized in that the magnesium-zirconium alloy contains 5-15% Zr, 0.1-3.0% alkali metal, alkaline earth metal and magnesium halides, magnesium - the rest is introduced into the iron in granular form, and the said halides are introduced into the composition of these granules in the form of their salt shell. 4. The method according to claim 1, characterized in that an alloy comprising 25-30% Ba, 55-60% Si, iron and impurities is used as ferrosilicobar — the rest.