US2269407A - Addition agent and its use in the treatment of iron and steel - Google Patents

Description

Patented-Jan. 6. 1942,

I summon AGENT-AND us use m was uni-moor mos an arm June a. crime. Dourluton. and Walter Falls, N. Y... salmon to Elec- Cratts. Niagara tro Metallurgical Company, a'corporation of No Drawing.

Original application lepru 14.1w, Serial No. 201,031. Divided and um app ication December 1,1938. Serial No. 243,825

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. The invention relates to the treatment 01 molten iron and steel to promote a line grain structure and freedom fromdeleterious impurities. application is a division of our application Serial No. 201,931, filed April 14, 1938.

During manufacture, steels become contaminoted with certalnoxides and occluded gases, which, ii not substantially removed or rendered innocuous, detrimentally affect the soundness and physical properties oi the finished steel. To overcome the deleterious efiects of such impurities, an addition of ferrosillcon or ten-omensanese, or both, as deoxidizers, is usually made to the steel shortly before casting into ingots or other shapes. For further deoxidatlon, 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 pur oees, and in the manner described above, tend to produce a steel containing deleterious types and quantities oi 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 suificient to produce the desired results. and titanium as heretofore used tends to produce a steel containing numerous objectionable nonmetallic impurities.

, According to the present invention, a steel that ssubstantially free from deleterious, gaseous or solid non-metallic impurities and that has improved'mechanicai 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 50% to 55% of silicon. remainder iron and at least two elements selected from the following two groups: (1) titanium, zirconium, cerium,

hafnium, and thorium; (2) vanadium, columbium, and tantalum, at least one element being present from each group, each in an amount at leest 3%. Iron is present as an impurity or diluent unavoidably introduced in producing an economical and commercially practicable material. The total amount of the elements selected irom the groups herein described is preferably at least 10% of the composition of the addition agent. If the number of elementsdn said mixture is only two, said total amount should preferably not exceed 25% of the composition of the addition agent, and if such number is more then This two, said total amount preferably exceeds 25% by not more than 5% for each of said elements above' two. A preferred addition agent compositlon contains 50% to silicon, 5% to 15% gconium, 5% to 15% vanadium, the remainder n. r The constituents of the addition agent are preferably presllcyed in the form of a master alloy; but they may be unalloyed or only partielly alloyed, and used in the form of a briquet of comminuted material. Also, some of the constituents thereof may suitably be in the form 01' easily reducible or decomposable compounds such m nitrides, nitrates or mixtures thereof. It is essential, however, that the constituents be closely associated, because successive additions of the several constituents separately to the steel do not yield the improved results of the invention.

in general, the more complex the addition agent, that is, the greater the number of deciddizing ingredients, selected from the above groups, the better the results.

ln'practicins the processor the invention, we

prefer to add to the molten steel being treatedv a sumcient amount of the addition agent of the invention that the silicon content of the steel is increased by about 6.25%. The deoxidizing or groin refining power may be controlled and varied by adding more or less than enough material to increase the silicon content of the steels by about 0.25%, or alternatively, the concentra-' tion of silicon relative to the other constituents of the addition agent may be varied. If less grain refinement is required, part oi 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 composition may be added to the steel in any well known manner, for example, in the furnace, in the ladle, or in the molten stream during pouring. If the agent is added to the steel in the furnace, the iron content of the agent may be greater than 50%.

By proper selection of elements, a grain size of No. 6 or No. '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 Elli-33. 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, o that the total amount of agent to be addedto the steel for best results mustbe 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 theinvention is 7 added in an amount which is'sumcient to de oxidize the metal, yet is rnsumcaem to' develop harmful inclusions.

. Steels treated according to the invention are sound, substantially free from excessive nonmetallic'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: i. A composition of matter for use as an addition agent for treating molten ferrous metal. composed of between 50% and'85% silicon; at least one element of the group consisting of titanium, zirconium, cerium, hafnium, and tbor-r ium, in an aggregate percentage between 5% and 20%; at least one element of the group consisting. of vanadium, columbium, and tantalum, in an aggregate percentage between 5% and 20%;

=the sum of the percentages of all elements of both of such groups being not over 25%; and iron .as the remainder.

2. A method of treating molten steel which 7 comprises adding thereto a grain-refining pro- JAMES H. CRITCHE'I'I'. WALTER CRAFTS.