US2025425A - Steel making process - Google Patents

Description

Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE:

lic Steel Corporation, Youngstown, Ohio, a corporation of New Jersey No Drawing. ApplicationApril 18,1935, Serial No. 17,138

4 Claims.

This invention relates tothe manufacture of steel, and particularly to a method of controlling the abrasiveness of non-metallic substances in steel.

Highly abrasive non-metallic substances are usually present in steels produced by present day methods. When a steel containing such substances is machined, these substances quickly dull and wear the cutting tools so that the life of such tools is short.

I have found that the degree of ab asiveness of such substances can be greatly redu ed with coincident prolongation of cutting tool life. The reduction I have accomplished has increased the cutting tool life by 100% or more without any attendant disadvantages.

The present invention is predicated on the discovery that the abrasiveness of non-metallic substances normally formed by chemical reactions in the molten steel during its manufacture, is traceable largely to the amount and form of manganese and associated non-metallic manganese compounds present in the steel; and on the discovery that alteration of the form of such manganese and manganese compounds will result in a change in the degree of abrasiveness of the non-metallic substances in the steel.

Briefly described, the present invention includes the steps of making molten steel in any suitable manner, determining the approximate composition of the steel and substances there'- in, and the nature and amounts of non-metallic forming ingredients, particularly manganese and. associated metallic compounds in the steel, and treating the steel in a manner to give the desired properties to the non-metallic substances in the steel.

The present invention will be better understood by those skilled in the art by the following examples in which it may be practiced.

Steel to be machined was made by the usual Bessemer practice. It contained the usual amounts of impurities including sulphur, phosphorus, as well as non-metallic substances such as silicates, the approximate amounts of which were known, and about .05% of manganese in metallic and non-metallic form. About 1.25% of manganese, in the form of ferromanganese, was added in solid form to the steel during pouring and when the ladle was about one-quarter filled with steel. after the manganese had been added, about 4 pounds of siderite (FeCOz) per ton of steel was thrown into the ladle, the pouring being continued until the ladle was filled. The siderite During pouring, and preferably just evidently decomposed, liberating oxygen or an oxygen containing gas. The metal in the ladle was violently agitated and gas was evolved, and

, the resulting steel was relatively free from abrasive, non-metallic substances as measured by 5 cutting tool life which was more than double the life obtained on similar steel made in the same way except for the addition of the siderite.

The content of. manganese in metallic and nonmetallic forms, in-the steel of the foregoing example before the addition of the ferromanganese was, as stated, about .05%, and after treatment with the siderite was about .90%. If no siderite or equivalent material had been added the manganese content would have been about 1.00%. Thus the present process tends to remove some of the manganese which would otherwise remain in the steel. This tendency is important, for if it be disregarded difiiculty in finishing a steel within the limits of manganese specified may be encountered, particularly in open hearth steels high in manganese.

The amount of siderite or its equivalent which should be used in my method will vary somewhat with the manganese desired inthe finished steel. For example, the variation per ton of steel is on about the order of 4 pounds of siderite for .80% of manganese, '7 pounds for 1.00% of manganese and 10 pounds for 1.50% of manganese.

It is important to determine the amount of 3 manganese in the steel in metallic and nonmetallic forms as a preliminary to determination of the amount of siderite or its equivalent to use. If toosmall an amount of siderite is used, 35 the degree of abrasiveness of the non-metallic substances will not be greatly decreased, while if too large an amount is used the manganese content in the finished steel may be lower than is desired. Also the cost may be unduly increased be-' 40 cause of undue loss of manganese and waste of siderite or its equivalent. I believe that there is a fairly well defined balance between the amounts of manganese present in metal form, and in nonmetallic substances in steel and that when this balance is disturbed there is a tendency for reestablishment of the balance. Consequently, it is important to known the manganese content before determining how much siderite or its equivalents to use. Knowledge of the amounts of ingredients used to make a given steel and the manner in which the given steel was made are usually sufiicient for this purpose and the making of a chemical analysis is not necessary.

Substances, other than siderite, which possess the property of reducing the abrasiveness oi the non-metallic substances in steel include iron oxide ores such as limonite, phosphate ores such as viviam'te, and slow acting non-ferrous carbonates such as cerussite, rhodochrosite malachite and azurite. In general, any substance which will liberate oxygen or an oxygen containing gas in the molten steel rapidly, but not so rapidly as to result in an explosion, may be used. Combinations of two or more of these substances may be used. Although ores are mentioned because of their relatively low cost, substances which contain the oxygen compounds of these ores may be used satisfactorily. Sodium carbonate decomposes too rapidly for safe use, for it tends to explode and throw molten metal out of the ladle.

Ibelieve that the treatment of steel with substances which decompose rapidly, but not too rapidly, in the steel, and liberate oxygen or an oxygen containing gas, bring about an oxidation of manganese and iron with resultant fluxing of the MnO with ,FeO and lowering of the fusing temperature; and that substances such as iron silicates, manganese silicates, iron manganese silicates, MnO, corresponding aluminates and other substances which are ordinarily relatively iniusible, and therefore highly abrasive, are converted by such oxidizing or fluxing actions into more readily fusible substances, even into substances which melt at temperatures below the melting point of steel, with coincident decrease in abrasiveness. Moreover, I believe that the decrease in melting points of such substances with the agitation due to evolution of gas in the steel results in movement of considerable quantities ofsuch substances into the slag, thus reducing the amount of such substances remaining in the steel when cold.

This invention is applicable to open hearth steels such as killed and rimming steels, steels having above about .80% of Mn, and steels in which the Mn is high to counteract high sulphur. This method may be carried out on open hearth steel with good results as follows: Tap the molten'steel into a ladle, adding the predetermined amount of ferromanganese when the ladle is about one-fourth filled and then add the calculated amount of siderite or other equivalent substances before slag covers the metal in the ladle. Alternatively, some of the manganese may be added in the furnace, if desired.

The invention is also of advantage with electric furnace steels. The metal is tapped while hot andthe siderite or other equivalent is added in predetermined amount to the ladle during flow of the steel into the ladle.

Having thus described my invention so that those skilled in the art may understand and be able to practice the same, what I desire to secure by Letters Patent is defined in what is claimed.

What is claimed is:

1. The process of making steel which includes the steps of making Bessemer steel containing about .05% of manganese, adding about 1.25% of manganese to such steel while it is being poured into a ladle, and adding between about four and seven pounds of siderite per ton of steel to the steel during pouring into the ladle.

2. The process of making steel which includes the steps of making steel containing between about .80% and about 1.5% of manganese and non-metallic substances, and mixing with such steel, while molten, between about four pounds and about ten pounds of siderite per ton of steel.

3. The process of making steel which includes the steps of making, by the open hearth process, steel containing manganese and other nonmetallic substance-forming ingredients, adding manganese to such molten steel to bring the total manganese content of the steel to between about .80% and about 1.50%, and treating the molten about .80% and about 1.50% of manganese and 40' from the group consisting of siderite and llmonite H per ton of steel.

EARL C. SMITH.