US2785970A - Addition agents in manufacture of steel - Google Patents

Description

United States Patent 2,785,970 ADDITION AGENTS 1N MANUFACTURE OF STEEL Edward A. Loria, Niagara Falls, N. Y., assignor to The Carhorundum Company, Niagara Falls, N. Y., a corporation of Delaware No Drawing. Application December 3, 1953, Serial No. 396,056

5 Claims. (Cl. 75-58) This invention relates to the production of steel, and in particular to the production of deoxidized wrought steels and steel castings substantially free from pinhole porosity.

, Heretofore, in the production of deoxidized wrought steels, and steel castings many dilferent addition agents have been employed to remove oxides and oxygen from the steel and to prevent pinhole porosityin steel castings. For example, :as .a final deoxidant in steel-making such materials as aluminum, calcium-silicon, and silicon carbide have been used, whereas to prevent pinhole porosity in steel castings it has been the practice to add to the steel aluminum, either alone or in combination with another deoxidant such as calcium silicide.

While the heretofore used deoxidants are satisfactory for some types of steel, they have not been totally satisfactory under certain circumstances. If only aluminum is added to steel of low carbon content in sufli-cient quantity to prevent pinhole porosity in steel castings the resulting productsmay possess an undesirable inclusion structure. On the other hand, if aluminum is added in conjunction with another deoxidant the grain structure of the castings is not completely satisfactory for all uses.

Similarly, in the production of low carbon killed steel ingots, the use of either silicon carbide or calcium-silicon alone does not always give the required sound ingots. On the other hand, the use of aluminum alone results in sound ingots, but the initial wrought products made from such ingots usually contain inclusion segregates or stringers that undesirably efiect tensile properties and ofte interfere with further fabrication processes.

Because of this inability to obtain completely satisfactory non-metallic inclusion type and distribution when using a single deoxidant, it has become common practice to use a combination of several chemical elements for deoxidizin-g low carbon killed steel. While some of these deoxidant combinations give a product satisfactory for many uses, none of the commonly used deoxi-dants or combination of deoxidants give a product with inclusion and grain structures which are completely satisfactory for i all uses.

it is therefore an object of the present invention to pro vide a process for producing deoxidized steels. Another object is to provide a process for making steel castings which are substantially free from pinhole porosity. A

further object is to provide a method for producing deoxidized steels and steel castings having superior inclusion and grain structures.

Other objects and advantages accruing from the practice of the present invention will become apparent as the description proceeds. g

It has been found that the above and other objects may 2,785,970 Patented Mar. 19, 1957 "ice ' principles of this process, as applied to the making of steel castings, are substantially applicable to the production of deoxidized ingot steel.

In the making of sound steel castings it is necessary to add to the molten steel a substance which will prevent '-the formation of numerous small voids in the castings,

which voids are commonly referred to collectively as pin hole porosity. In the past, to prevent pinhole porosity, it has been the practice to add aluminum to molten steel which is tobe used for castings, either alone or in conjunction with calcium-silicon. There have been numerous attempts to prevent pinhole porosity by using deoxidants such as calcium-silicon and silicon carbide without also using aluminum, but these attempts have met with very little success. Prior to the present invention, to prevent pinhole porosity it has always been thought to be necessary to employ aluminum as an addition agent, despite the fact that the resulting castings can and usually do contain inclusion formations deleterious to tensile andductility properties.

lt has now been discovered that by using aluminum carbide as the addition agent to prevent pinhole porosity in steel castings, perfectly sound castings can be produced, \which castings have certain superior mechanical properties. It has also been found that by using, as an addition agent to molten steel, aluminum carbide in conjunction be accomplished by using aluminum carbide, either alone or. in conjunction with one or more other deoxidants, as an addition agent in the production of steel. When introduced' into the molten steel thealuminum carbide decomposes into aluminum and carbon in the nascentstates,

with at least one material selected from the group con sisting of. aluminum, silicon carbide, and calcium-silicon, steel castings can be made from this steel which have no trace of pinhole porosity and which have highly desirable grain and inclusion structures.

The following examples show some of the applications of the processes of the present invention.

' EXAMPLE I To prevent pinhole porosity in steel castings made from low carbon steel, additions of impure aluminum carbide in combustible containers amounting to 6 pounds per ton of molten steel were added to the shank ladle before the molten undeoxidizedmetal was drawn from the bull or receiving ladle into the shank ladle. Immediately after the molten steel hadbeen drawn into the shank ladle onto the aluminum-carbide, steel castings were poured, which castings were specifically designed to .reveal and accentuate pinhole porosity formation. Examination of the resulting castings showed them to be sound, there being no traces of pinhole-porosity.- The impure aluminum, carbide used in this operation was made in an electric-- resistance furnace, chemical analysis:

Percent f Total aluminum} including that presentas aluminum rb d Thefaddition rs pounds of this g radealumimnmcar f bide was sufficient to completely prevent pinhole porosity inthesecg stinss.

It had the following composition by 7 of mix sufliciently,

3 EXAMPLE 11 Procedure similar to that in Example I was followed,

but with only 4 pounds per ton of the same grade of aluminum carbide being added to the molten.steel. The.

resulting castingsrshowed no trace of pinhole porosity. The addition of only 4 pounds of this grade aluminum carbide was sufficient to completely prevent pinhole porosity in these castings.

EXAMPLE III Procedure similar to that in the above examples was followed, making 4 and 6 pounds per ton additions of electric resistance furnace aluminum carbide having the following composition by chemical analysis:

Total aluminum including that present as aluminum carbide.

An examination of the resulting castings showed that those made from the steel which had been treated with the 6 pounds per ton additions were completely free from pinhole porosity. The castings made from steel to which was added only 4 pounds per ton aluminum carbide were slightly porous, but were suliiciently sound for many uses. The addition of 6 pounds of this grade aluminum carbide was sufiicient to completely prevent pinhole porosity in these castings, and the addition of 4 pounds of this grade aluminum carbide was sufiicient to prevent pinhole porosity to such an extent to produce castings satisfactory for use under less drastic conditions.

EXAMPLE IV Procedure similar to that in the above examples was followed, but adding 2 pounds of aluminum carbide of the grade used in Example I plus 2 pounds of calciumsilicon. The resulting castings were perfectly sound, there being no trace of pinhole porosity.

EXAMPLE V Procedure similar to that in the above examples was followed, but adding 2 pounds of aluminum carbide of the grade used in Example III plus 2 pounds of aluminum shot. The resulting castings were perfectly sound, there being no trace of pinhole porosity.

By following a procedure similar to that in the above examples, pinhole porosity can be prevented in steel castings by adding aluminum carbide plus silicon carbide.

Aluminum carbide of varying purity can be" made in electric resistance furnaces by passing an electric current through a carbon core to heat a surrounding mixture of pure aluminum or some other source of aluminum such as alumina and a source of carbon such as graphite in the stoichiometric proportions for forming aluminum carbide. The furnace product can be used directly in most instances, no further purification being required. The resulting material adjacent the carbon core is of higher purity than that in the outer layers, and is the most desirable as an addition agent. If the furnacing operation is not continued. for a long enough time to heat the outermost layers the reaction in these layers will not progress to any great extent, in which case it may be undesirable. to use this outermost material asan addition agent. If so, this. material can be used as part of the raw mix for subsequent. furnace runs.

Instead of adding the aluminum carbide, with or without other substances, to the shank ladle, as was done in the-above-examples, the addition can-be made to'the' steel while it is stillv in the bull ladle. Also the addition can be made to the bull ladle prior to or during tapping of the '6 pounds per ton for the best results.

steel into the bull ladle. This procedure gives thorough mixing of the aluminum carbide with the molten steel whereby the aluminum carbide is decomposed, resulting in satisfactory deoxidation of the steel. To prevent pinhole porosity in the resulting castings, aluminum carbide such as that used in the above examples, when used without other deoxidants, should be added in amounts from 4 to If less pure aluminum carbide is used, as much as 8' pounds per ton may be required to produce satisfactory castings. In certain casting designs which are not prone to pinhole formationand in steel compositions which do not require strong deoxidation, less than 4 pounds of aluminum carbide per ton of steel may besufiicientf To determine whatetfect the present invention of using aluminum carbide, either alone orin conjunction with another substance, as a final deoxidant has on the tensile properties of the low carbon casting steel, test bars were cast from steel which had been treated with 4 pounds per ton and 6 pounds of aluminum carbide per ton, 2 pounds of aluminum carbide plus 2 pounds of metallic aluminum per ton, and 2' pounds of aluminum carbide and 2 pounds calcium silicide per ton. The aluminum carbide used was the less pure grade such as used in Example III. These test bars were normalized at 1800 F. for three hours at temperature and then tempered at 0 F. for three hours at temperature. Table I shows the tensile properties of the test bars made from these steels and also the average tensile properties of bars cast from the same steel deoxidized in the customary manner, namely with 3 pounds of calcium-silicon and 2 pounds of aluminum, and heat treated as above-described.

' The minimum value specifications for this type of cast alone or in conjunction with another deoxidant, have an averageyield point approximately 14% higher than that of thost'eeltreated with 3 pounds of calcium-silicon plus 2 pounds of aluminum.

To study the effect of the practice of the present invention on the grain size of the steel castings, picral etched photomicrographs were taken of the grain structures of test coupons cast from steels treated with various amounts of aluminum carbide, both alone and in conjunction with: other substances. A study of these photomicrographs showed the steel castings made in accordance with the presentinventionto have Well refined grain struc tures. A comparison of these photomicrographs with photomicrographs of the grain structures-of castings made from. steel. treated: in accordance with the commonly followed prior art methods showed that aluminum carbide is just as potent, if not more so, on a pound for pound basis as metallic aluminum in grain-refining power.

To determine the nature of the inclusion structures of unetcliedphotomicrographs were taken of test coupons cast from steels treated with various amounts of aluminum carbide, both alone and in conjunction with other deoxidants. These photomicrographs showed that steel castings made in accordance with the present invention have a most desirable inclusion structure. Those castings to which the larger additions of aluminum carbide were made contained substantially none of the undesirable types of inclusions which are usually present in castings deoxidized with aluminum.

While the present invention has been described as it pertains to making steel castings, as aforementioned, aluminum carbide, either alone or in combination with other deoaidants, is a highly satisfactory final deoXider for ingot steels. The additions can be made in the ladle prior to filling it with molten steel, or the additions can be made as the ladle is filled. The aluminum carbide may be shoveled into the ladle in loose granular form or it may be introduced into the ladle in combustible or metal containers, or in the form of bonded briquettes. For satisfactory deoxidation of killed-ingot steels about 2-6 pounds per ton of aluminum carbide of the purity of those in the examples, when used alone, should be used. The larger amounts are required for lower carbon steels (below 0.30% C.) and the smaller amounts are required for higher carbon steel (above 0.30% C.). If other deoxidants are used in combination with the aluminum carbide, proportionately lesser amounts of aluminum carbide are required so that only about one pound per ton may be required. Also, as the purity of the aluminum carbide is lowered the amounts required will be proportionately increased so that up to about 8 pounds per ton may be required in killing steel with a high oxidation level. Aluminum carbide is also highly satisfactory as a final deoxidant ladle addition for semi-killed and rimmed steels, with lesser amounts usually being required to deoxidize these types of steel to the desired level.

Where the term-deoxidized steel is used in the specification and claims it is intended to include not only ingot steel which has been deoxidized by an addition agent, but also cast steel which has been treated with an addition agent to reduce or eliminate pinhole porosity in the resulting casting, since it is believed that addition agents reduce or eliminate pinhole porosity by means of a strong deoxidizing eifect on the steel.

Having described the invention, it is desired to claim:

1. In the process of producing deoxidized steel the step of introducing aluminum carbide into the molten steel in proportion of from about 1 to 8 pounds of aluminum carbide per ton of steel whereby the aluminum carbide is decomposed and the steel is deoxidized.

2. In the process of producing deoxidized steel the step of introducing aluminum carbide into molten steel in a ladle in proportion of from about 2 to 6 pounds of aluminum carbide per ton of steel whereby the aluminum carbide is decomposed and the steel is deoxidized.

3. In the process of producing steel castings substantially free from pinhole porosity the step of introducing into molten steel in a ladle aluminum carbide in proportion of from about 2 to 6 pounds of aluminum carbide per ton of steel.

4. In the process of producing steel castings substantially free from pinhole porosity the step of introducing into molten steel in a ladle in proportion of from about 4 to 8 pounds per ton of steel a mixture comprising aluminum carbide and at least one material selected from the group consisting of aluminum, silicon carbide, and calcium-silicon.

5. In the process of producing deoxidized steel the step of introducing into the molten steel in proportion of from about 4 to 8 pounds per ton of steel a mixture comprising aluminum carbide and at least one material selected from the group consisting of aluminum, silicon carbide, and calcium-silicon.

References Cited in the file of this patent UNITED STATES PATENTS 1,732,915 Saklatwalla Oct. 22, 1929 FOREIGN PATENTS 499,647 Great Britain Jan. 23, 1939

Claims (1)

1. IN THE PROCESS OF PRODUCING DEOXIDIZED STEEL THE STEP OF INTRODUCING ALUMINUM CARBIDE INTO THE MOLTEN STEEL IN PROPORTION OF FROM ABOUT 1 TO 8 POUNDS OF ALUMINUM CARBIDE PER TON OF STEEL WHEREBY THE ALUMINUM CARBIDE IS DECOMPOSED AND THE STEEL IS DEOXIDIZED.