US1923471A - Manufacture of steel - Google Patents

Description

Patented Aug. 22, 1933 UNITED STATES PATENT- OFFICE.

No Drawing. Application February 11, 1930, Serial No. 427,642, and in Germany January 15,

3 Claims.

This invention relates to the manufacture of steel in an electric furnace containing one or more of the metals tungsten, molybdenum and vanadium.

It is known, in the manufacture of alloys or special steels in an electric furnace, to produce a preliminary slag consisting chiefly of lime and fluorspar on the liquid metal bath for the purpose of removing phosphorus and sulphur, which 10 slag preferably before the addition of the alloying metals is replaced by a final slag similarly composed, apart from an addition of carbon-containing substance and silica.

In the manufacture of tungsten and like steel, however, the use of a final slag containing fluorides has been found uneconomical since considerable losses occur in the alloying ingredients, and particularly in tungsten, but also in chromium, molybdenum and vanadium.

According to the present invention this objection is avoided in the manufacture of tungsten and like steel in the electric furnace by replacing the fluorine containing slag serving for the removal of phosphorus and sulphur before the addition of the alloying metals, by a slag covering which is free from fluorine and consists of alkali or alkaline earth silicates or mixtures of both.

First an oxidizing lime and fiuorspar containing slag is inserted in the bath for removal of phosphorus, and then the slag is taken off and the deoxidizing lime and fluorspar containing slag is put into the bath for removal of sulphur. The slag is then removed and replaced by the final slag, which is free of fluorine and consists of alkali or alkaline earth meta-silicates or mixtures of both. But the desulphurizing, the deoxidation and the alloying of the bath may be also at the same time in the manner, that after having removed the oxidizing slag, the ferro-alloys are added and the desired content of carbon, and the final slag of the meta-silicates of alkali or alkaline earths or mixtures of both, is put into the bath.

It has been found that the cause of the loss in the steel making processes hitherto used is due to the fact that the alloying metals tungsten, molybdenum and vanadium combine at the high temperatures used with the fluorine from the fluorspar to form volatile fluorides or form slag with alkalies or alkaline earths and finally disappear with thefumace gases and vapors owing to the high vapor pressures of the compounds formed. These undesirable by-reactions do not t ke place with the final slag according to the fresent invention, because at the temperature of the electric furnace and as silicic acid is a nesium meta silicate or both is laid on the pracstronger acid than the acids of the said metals, a reduction of the silicic salts cannot take place. According to the invention a final slag consisting of a mixture of calcium silicate, magnesium silicate, and sodium and potassium water glasses is advantageously used in the form of the commercial meta silicates.-

The final slag is formed on the .bath as follows. i

After removal of the desulphurizing slag, a covering of 1 to 3% of the weight of the bath of a mixture which consists of one tenth to one third of sodium or potassium water glass and two thirds to nine tenths of calcium or magtically pure iron high melting point bath. Instead of the calcium or magnesium meta-silicate an intimate mixture of finely ground quicklime (CaO) and/or magnesia (MgO) and silicic acid corresponding to the saturation proportions of the meta-silicates, can be used with water glass in the above stated proportions. Further, the exclusion of air from the bath can be effected by laying a covering on the bath after removal of the desulphurizing slag, consisting only of calcium meta-silicate, magnesium meta-silicate or an intimate mixture of both or of lime and/or magnesia and silicic acid in saturation proportions, the covering being maintained in a thinly liquid condition after the addition of carbon and the ferro-alloys the solution of which lowers the melting temperature of the bath by about 300 C., by the gradual addition of sodium or potassium water glass.

Having now particularly described and ascertained the nature of my said invention and in what manner the'same is to be performed, I declare that what I claim is: a

1. The process for production of high speed steel alloys containing substantial amounts of tungsten, which comprises treating a molten ferrous bath in an electric furnace with limefiuorine-containing slag to remove phosphorus and sulphur, removing said purifying, slagging material and thereby leaving a relatively pure ferrous bath, and then making a final slag on this bath consisting of calcium silicate, magnesium silicate and water-glass in the propor- .tion of about 1 to 3%, and alloying in the presence of this final slag with tungsten and at least one of the following elements from the group comprising chromium, molybdenum and vanadium to produce the aforesaid high speed steel.

2. The process for production of high speed steel alloys containing substantial amounts of duce the aforesaid high speed steel; the alloy elements being added after the final slag.

3. The process inaccordance with claim 1, in which the final slag is composed of from onetenth to one-third of elements selected from a group consisting of sodium-water-glass and potassiumwater-glass, mixed with from twothirds to nine-tenths of elements selected from .a group consisting of calcium meta-silicate and magnesium meta-silicate.

CHRISTIAN ARNOLD.