US1949529A - Refining of steel - Google Patents

Description

Patented Mar. 6, i934 1 I nsrmmc OF STEEL Vere B.- Browne, Brackenridge, Pa., assignor to Allegheny Steel Company, Brackenridge, Pa., a corporation of Pennsylvania No Drawing. Application April 26, 1930 Serial No. 447,770

' 9 Claims.

This invention relates to the refining of steel and especially to a new and'novel method of effecting such refining by invoking and utilizing the principles of physical chemistry.

It has been generally considered that the reactions taking place in a furnace are purely chemical and that in order to remove impurities from the steel it has been assumed that a chemical union must take place so that theimpurities are 10 either oxidized or reduced and thus put in a condition in which they can be isolated or collected and removed. 7 While this is true as far as it goes, I have discovered that certain impurities can be removed without depending solely on a chemicalunion, but rather by changing the solution pressures of the two liquids (steel and slag) so that the utilized tendency or effect is a physical rather than a chemical onel is the refining of steel by a change of solution pressure, thus utilizing the principles of physical chemistry.

Another object of my invention is to refine steel of any type having a supernatant slag by causing the oxids dissolved in the steel to migrate to the slag.

A further object of my invention is the conversion of oxids to silicates in the Slag by adding in effect the SiOz radical to the slag in excess.

Other and further objects will be understood by those skilled in this particular art.

I have discovered. that steel can be produced free from oxids, such as FeO and MnO and the like, even under a slag extremely high in oxids provided that the solution pressure can be changed so that the oxids migrate or tend to ,migrate from the-metal to the slag and provided that there is an acid radical present' to combine 40 with the oxids. This is, I believe, a logical explanation-ofthe difference between acid and basic steel; e

Forexample, in the making of silicon steel in an electric or open hearth furnace, it isdesired to have the carbon content as low as possible, but when the carbon content has been reduced to say about 102% the slag will contain, many times, as much as about 35% FeO and the metal fwill be practically saturated with oxids. When silicon is added to such steel the silicon reduces, the FeO and is itself oxidized to silica (SiOz) which 'is entrapped in the metal in the form of an emulsion. Even the removal of the slag does not help materially under such con- 5 ditions as the metal still contains dissolved oxids.

One of the objects of my invention, therefore,

I have discovered further that these oxids can be removed by changing the composition of the slag and so changing the solution pressures of the two'liquids, thus causing the oxids to migrate to the slag instead of remaining in the metal. This phenomenon may be termed mass action equilibrium. For example, a slag consisting of CaO MnSiOa xFeO FeSiOa' will have a relation to the metal which will cause the FeO to migrate to the slag, where it chemically unites with the SiOz.

I have discovered, therefore, that it is possible to remove oxids completely from low carbon steels such as are used, for example, in the manufacture of transformer sheets by adding sand to the slag at the end of the operation in an amount sufficient to more than combine with all the MnO and FeO present. This will effect a change in the solution pressure and the dissolved oxids will be liberated from the metal to combine with the excess silica. It is known that metallic silicates dissolve in each otherwhen melted and also that they dissolve oxids of metals, but they do not dissolve metals or reduced substances.

In case one prefers to remove the slag entirely the same result can be obtained by replacing the original slag with a slag composed of CaO and SiOz butwith a liberal excess of SiO2 over and above that amount calculated to combine with the amount of dissolved oxids estimated to be present.

Experimentation has proved not only the accuracy of the above considerations, but that valuable results are secured economically and eniciently.

In general, when acid .radical is present in suflicient quantities all the basic substances in the slag are satisfied and hence the slag has a further capacity for attracting to itself additional oxids, which are likewise satisfied, and the migration continues.- If the slag has an excess of cid radical it is understood that all the oxids wil be removed from the steel.

(vSiOz The process is applicable to any kind of steel and may be used, for example, in connection with silicon steel or chrome alloys, but it is not limited thereto.

What I claim as new and desire to secure by Letters Patent is:

1. In the process of refining steel containing dissolved basic oxids and having a surface slag thereon, adding in eiTect the SiOz radical in excess of that theoretically necessary to convert all said dissolved oxids into silicates, bringing about a change in the relative solution pressures of steel and slag so as to set up a migratory tendency of the dissolved oxids from the steel to the slag, said oxids being converted in said slag into corresponding silicates, said excess SiOz radical in said slag maintaining said slag free from uncombined oxids other than SiOz and hence preventing a premature equilibrium or a reversal of the migration. I

2. In the process of refining steel containing dissolved basic oxids and having a slag thereon, causing the dissolved oxids to migrate from said steel to said slag by adding in effect to said slag an amount of acid radical over and above the combining equivalent of the oxids, said oxids there combining with the chemical equivalent of acid radical and maintaining said slag free from uncombined oxids other than those of the acid radical itself.

3. In the process of refining steel containing dissolved basic oxids and having a slag thereon, causing all the dissolved oxids to migrate from said steel to said slag by adding to said slag in effect the S102 radical in excess of the combining equivalent of said oxids, said oxids there combining with an equivalent amount of said S102 radical.

4. In the process of refining steel containing dissolved basic oxids and having a slag thereon, causing all the dissolved oxids to migrate from said steel to said slag by adding to said slag in effect the SiOz radical in excess of the combining equivalent of said oxids, said oxids there combining with an equivalent amount of said Si02 radical producing corresponding silicates and maintaining said slag free from uncombined oxids other than those of the acid radical itself.

5. A process of removing dissolved basic oxids from low carbon steels containing the same and having a supernatant slag, comprising adding sand to the slag at the end of the steel-making operations in an amount more than sufiicient to combine with said dissolved oxids.

6. A process of removing basic oxids entrapped in molten steel containing the same and having a supernatant slag, comprising liberating said oxids from said steel and causing them to migrate to said slag where they are chemically combined by adding in efiect to said slag the SiOz radical in excess of the combining equivalent of said oxids.

7. In the manufacture of steel containing dissolved iron and manganese oxids and having a supernatant slag, the steps of adding acid radical S102 in effect in excess of the combining equivalent of said oxids to said slag, causing said iron and manganese oxids to migrate to said slag and to combine with a portion of said acid radical SiO2 to form iron and manganese silicates which remain in and become a part of said slag.

8. A physico-chemical method of treating steel containing dissolved or entrapped oxids and having a supernatant slag involving causing said oxids to physically pass from said steel to said slag by an adjustment of solution pressures of steel and slag to bring about such transference by adding SiO2 in excess of the combining equivalents of the oxids and causing said so-transferred oxids to chemically unite with a portion of said slag specially added for such purposes.

9. A physico-chemical process of refining molten steel which has a supernatant molten slag thereon, both steel and slag containing dissolved and entrapped oxids, comprising adding available SiOz to the slag in an amount more than sufiicient to combine with all such oxids, thus converting oxids in the slag to corresponding silicates, setting up a physical migration of oxids from steel to slag, converting to corresponding silicates such migrated oxids, and preventing premature equilibrium or reversal of the aforesaid action.

VERE B. BROWNE.