US2221783A - Addition agent and its use - Google Patents

Description

Patented Nov. 19, 1940 James H. Critchett, Douglaston, and Walter Crafts, Niagara Falls, N. Y., assignors to Electro Metallurgical Company, a corporation of West Virginia No Drawing. Original application April 14,1938, Serial No, 201,931. Divided and this application December 1, 1938, Serial No. 243,324.

May 9,1940

Renewed 8 Claims. (01. 75-58) Theinvention relates to the treatment of molten iron and steel to promote a fine grain structure and freedom from deleterious impurities. This application is a division of our application Serial No. 201,931, filed April 14, 1938.

During manufacture, steels become contaminated with certain oxides and occluded gases, which, if not substantially removed or rendered innocuous, detrimentally affect the soundness and physical properties of the finished steel. To overcome the deleterious eflects of such impurities, an addition of ferrosilicon or ferromanganese, or both, as deoxidizers, is usually made to the steel shortly before casting into ingots orv other shapes. For further deoxidation, and to provide an inherently fine-grained steel having inhibited, grain growth tendencies at elevated temperatures, a later addition of aluminum is often made to the molten steel.

Aluminum additions,"in the amounts, for the purposes, and in the manner described above, tend to produce a steel containing deleterious types and qualities of non-metallic inclusions. It has been proposed to substitute for the aluminum other agents, such as vanadium, or titanium, but none of these elements is entirely satisfactory. Vanadium is usually too expensive to add in an amount suflicient to produce the desired.

. results, and titanium asyheretofore used tends to produce a steel containing numerous objectionable non-metallic impurities.

According to.the present invention, a steel that is substantially free from deleterious, gaseous or solid non-metallic impurities and that has improved mechanical properties (including improved impact strength) and excellent fine grain characteristics is produced-by adding to the steel while it is molten in the ladle or otherwise shortly before casting, an addition agent containing 25% to 85% (preferably 35% to of silicon, remainder iron and at least two elements selected from the following two groups: (1) beryllium, magnesium, calcium, barium, strontium, boron, and aluminum; (2) vanadium, columbium,

and tantalum, at least one element being present from each group, each in an amount at least 3%. Iron is present as an impurity or diluent unavoidably introduced in producing an economical and commercially practicable material, and should'not exceed about 65%.

- described is preferably atleast 10% but not over of the composition of the addition agent. If the number of elements in said mixture is only two.

The total amount of the elements selected from the groups herein agent, and if such number is more than two, said total amount preferably exceeds 25% by not more than 5% for each of said elements above A preferred addition agent composition exceed 25% of the-composition of the addition contains 45% to silicon, 5% to l5%'aluminum, and 5% to 15% columbium, the remainder...

iron.

The constituents of the addition agent are preferably prealloyed in'the form of a master alloy; but they may be unalloyed or only partiallyalloyed, and used in the form of a briquet of comminuted material. Also, some of the constituents thereof may suitably be in the form of easily reducible or decomposable compounds such as nitrides, nitrates or mixtures thereof. It is essential, however, that the constituents be closely associated, because successive additions do not yield the tion.

In general, the more complex the addition improved results of the inven- V agent, that is, the greater the number of deoxiof the addition agent may be varied. If lessgrain refinement is required, part of the silicon required for deoxidizing may be added as' the agent of the invention and part as ordinary'ferrosilicon, and if more grain-refinement is-required, the action of the addition agent may be supplemented by an addition of aluminum or other grain refiner.

The desired compositio n may be added to the steel in any well known manner, for example, in the furnace, in the ladle, or in the molten of the several constituents separately to the steel stream during pouring. When adding the addition agent to the steel either in the ladle or in i the molten stream, an agent containing less than No. 6 or Nu. '7 may readily be procured in steels treated according to a method of the invention. Throughout the present specification, grain size refers to austenitic or inherent grain size determined by the McQuaid-Ehn carburizing test conducted at a temperature of 925 C. for 8 hours, as defined by the A. S. T. M. specification E 1933. The degree of grain refinement or deoxidation of the steel per unit of addition agent added will vary, not only with the combination of elements selected, but also with the type of steel being treated, so that the total amount of agent to be added to the steel for best results must be determined by trial. Ordinarily, this total amount of agent will be less than 5%, and most frequently less than 1%.

While the addition agents of this invention are especially useful in the treatment of steels which are to be hot worked, the invention is also applicable to the treatment of steels which are to be employed as castings. Used for the latter purpose, it has been found that, in many instances, the characteristics of the casting may be improved if the material of the invention is added in an amount which is sufficient to deoxidize the metal, yet is insuflicient to develop harmful inclusions.

Steels treated according to the invention are sound, substantially free from excessive non-metallic inclusions, and possess improved ductility and shock resistance. Further, the few inclusions distributed throughout such steels are more uniform than diverse, that is, the majority of the inclusions which usually accompany any deoxidizing treatment'that produces small grain size are not noticeable in the steels deoxidized in accordance with the invention until a higher degree of grain refinement is attained than that attainable by the addition of aluminum alone.

We claim:

1. A method of treating molten ferrous metal which comprises adding to the molten ferrous metal a grain refining amount less than 1% of an addition agent consisting of 25% to 85% sili con, iron, and at least one element selected from each of the following groups: (1) beryllium, magnesium, calcium, barium, strontium, boron, and aluminum; (2) vanadium, columbium, and tantalum; the total percentage of elements from each group being between 3% and 20%.

2. A method of treating molten ferrous metal which comprises adding to the molten ferrous metal a grain refining amount less than 1% of an addition agent consisting of 25% to silicon, iron, and at least one element selected from each of the following groups: (1) beryllium, magnesium, calcium, barium, strontium, boron, and aluminum; (2) vanadium, columbium, and tantalum; the total percentage of elements from each group being between 3% and 20%, and the sum of the elements of both of said groups being at least 10% and not exceeding 25% by more than 5% for each of said elements above two.

3. A method of treating molten ferrous metal which comprises adding to the molten ferrous metal a grain refining amount less than 1% of an addition agent containing 35% to 55% silicon; 3% to 20% of at least one element selected from the group beryllium, magnesium, calcium, barium, strontium, boron, and aluminum; 3% to 20% of at least one element selected from the group vanadium, columbium, and tantalum;rand the remainder iron.

4. A method of deoxidizing molten iron or steel which comprises adding to the molten iron or steel a grain refining amount less than 1% of an addition agent containing 35% to 55% silicon, 3% to 20% aluminum, 3% to 20% columbium; and the remainder iron.

5. A composition of matter, suitable for use as an addition agent for treating molten ferrous metal, consisting substantially of 25% to silicon, iron, and at least one element selected from each of the following groups: (1) beryllium, magnesium, calcium, barium, strontium, boron, and aluminum; (2) vanadium, columbium, and tantalum; the total percentage of elements from each group being between 3% and 6. A composition of matter for use as an addition agent for treating molten ferrous metal, containing 25% to 65% silicon, iron, and at least one element selected from each of the following groups: (1) beryllium, magnesium, calcium, barium, strontium, boron, and aluminum; (2) vanadium, columbium, and tantalum; the total percentage of elements from each group being in an amount between 3% and 20%, and the sum of the elements of both of said groups being at least 10% and not exceeding 25% by more than 5% for each of said elements above two.

'7. A composition of matter for use as an addition agent for treating molten ferrous metal, containing 35% to 55% silicon; 3% -to 20% of at least one element selected from the group beryllium, magnesium, calcium, barium, strontium, boron, and aluminum; 3% to 20% of at least one element selected from the group vanadium, columbium, and tantalum; and the remainder iron.

8. An addition agent for deoxidizing molten iron or steel, containing 35% to 55% silicon; 3% to 20% aluminum, 3% to 20% columbium; the remainder iron.

' JAMES H. CRITCHETT.

WALTER CRAFIS.