US2096318A - Method of making chromium steel from chromium steel scrap - Google Patents

Description

Patented 0a. 19, 1937 METHOD OF MAKING CHROMIUM STEEL FROM CHROMIUM STEEL SCRAP Vere B. Browne, Brackenridge, Pa., assignor to Allegheny Steel Com Pennsylvania pany, a corporation of No Drawing. -Application January 31, 1936, Serial No. 61,805

7 Claims.

My present invention relates to the manufacture of chromium steels and more particularly to the manufacture of chromium steels and/or chromium-containing steels from steel scrap containing chromium.

The uses of chromium and chromium-containing steels, e. g., stainless steels, oxidation resistant steels, etc., have been rapidly increasing the past few years and bid fair to find application to an even greater extent in thefuture. Many articles have been and are being fabricated from these chromium steels with the result that large I quantities of chromium steel scrap have accumulated due to the fact that the fabricating operations produce from about 40 to 50% of scrap.

This not only makes chromium steel and articles fabricated from chromum steel more expensive than they need be, but this scrap represents a serious economic loss.

Most chromium steels, at least those containing the higher amounts of chromium, are made in an electric arc furnace using carbon arcs. As a result, it is dimcult to make these chromium steels low in carbon because chromium and carbon have a great aflinity for each other. The fact that the carbon specification in these chromium steels must be low makes it necessary at the present time to use relatively expensive low carbon alloying materials such as low carbon .ierro-chrome to obtain the desired chromium content in the steel or to go to the expense of using chromite ore and directly reducing it into the steel.

Despite the relatively large demand for chromium steels and articles fabricated therefrom no simple, economical and sure way has been developed to make them inexpensively or to utilize chromium steel scrap in making low carbon chromium steels and articles fabricated therefrom. The accumulations of scrap, therefore, have relatively little use. If these scrap materials could be utilized to make first-quality, highgrade chromium steels such as are made by present methods, it would be possible not only to make these steels at materially lower cost, but their uses would be more widely distributed and certain applications could be taken advantage of at these 3 lower costs wherein chromium steels have not so far been able to be used. Moreover, the economic loss of the chromium steel scrap could be substantially entirely eliminated.

The method of my present invention enables 3 me to make first-quality, high-grade chromium While in general my new process relates to all chromium steels and/or chromium-containing steels, I have found that in particular three types of chromium steel can be readily and economically produced inaccordance with my present method. I refer in this connection especially to chromium alloy steels containing about 18% chromium, about 13% chromium, and about 4-6% chromium. These particular chromium steels are today widely used and manufactured by various processes but by my present method I can produce them equally well and at materially decreased cost by utilizing chromium steel scrap of proper composition, due regard being given to the particular steel being made.

It is, therefore, one of the objects of my present invention to provide a method of making first-quality, high-grade chromium steels by utilizing considerable percentages of scrap steel containing chromium.

Another object resides in making low carbon chromium steels in which up to or more of chromium steel scrap can be used in a given furnace charge.

An additional and more specific object resides in first producing a molten bath of steel containing no chromium, adjusting the carbon content thereof to a low figure and then incrementally adding chromium steel scrap and low-carbon ferro-chrome, where necessary, sufiicient to adjust the chromium content of the whole to the desired figure.

Those skilled in this art will appreciate the further objects and advantages which are suggested by the present description or which will be understood therefrom.

In carrying out 'my present process, I first melt down a predetermined percentage of mild carbon test or analysis shows that the carbon content is.

approximately .03%, I remove the oxidizing slag from the molten bath of iron and I deoxidize and degasify it in accordance with the process set forth in my Patent No. 1,658,879. When this process is completed, the-low carbon iron is covered and protected by a thin but voluminous calcium aluminate slag which not only protects the iron from carbon absorption and oxidation, but at the same time forms a reception slag for the chromium .steel scrap which is thereafter incrementally added.

I now add incrementally to the low-carbon molten iron bath with the protective and reception slag thereon-and the operations may be carried out successfully in an electric arc furnace-chromium and/or chromium-containing steel scrap which has a carbon content insuificient to increase the total carbon content of the final bath above the required carbon specification. Each incremental addition of chromium steel scrap is made in such manner that at first it floats partly submerged in the slag and thus burns off any carbonaceous matter with which the scrap might be contaminated before each such incremental addition becomes completely submerged in the protective slag. Such submergence is allowed to take place before power is applied. During these operations, the volume and viscosity of theslag is maintained by suitable additions of fiuxing reagents such' as alumina,- fluorspar, etc. Upon the completion of these operations, I may thereafter add in the same manner, enough low-carbon ferro-chrome to adjust the total chromium content and any other alloying elements which are desired to be incorporated in the ultimate steel and -made in the same manner as the chromium steel scrap additions.

I may, for example, make suitable'alloyingadditions such as tungsten, molybdenum, and any other desired element. In each case the additional alloying element is added in such form that it introduces no undesirable ingredients into the steel and also in such form that it does not result in increasing the carbon content beyond the permissible amount.

While I have made it possible to carry out these operations in an electric arc furna'ceand I prefer to use suchit will be understood by those skilled in this art that my initial charge of lowcarbon iron may be secured by transferring hot metal of the proper composition either from a Bessemer converter or from an open hearth furnace and that thereafter the process is carried out as explained above.

While I prefer to use a calcium aluminate slag I and to reduce the iron with aluminum, I may, however, use any suitable slag forming materials such aslime and flourspar, or lime and sand, and I may also make use of any suitable or desired reducing agent such as silicon or carbon to deoxidize the bath and to form the reception slag for 1 the scrap additions.

While my process is particularly applicable and valuable in the production of chromium steels containing in the neighborhood of .10.% carbon, or less, my process can, however, be also applied with advantage to the production of chromium steels in which a more liberal carbonspecification is permissible. As already noted, chromium steels containing in the neighborhood of .ll0% carbon'are perhaps the most valuable and atthe sametime the mostdifiicult to make so that my process is of peculiar importance and value in connection with such steels; I

I do not specifically claim, in this application, the manufacture of chromium nickel steels of the 18% chromium, 8% nickel type; such have been claimed in my copending application Serial No. 624,348 filed July 23, 1932.

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

1. In a method of the kind described, melting down a predetermined percentage of steel scrap, refining the same under an oxidizing slag until the carbon content thereof is reduced to about 0.03%, removing the slag, deoxidizing and degasifying the molten metal, adding a calcium aluminate slag, incrementally adding chromium-con- "taining steel scrap in predetermined amount, and,

bringing the alloying elements of the whole up to the desired content. I

2. Ina method of the kind described, melting down a predetermined percentage of steel scrap in an electric furnace of the arc type, refining the same until its carbon content is about 0.03%, de-

oxidizing and degasifying the molten metal, covering the molten metal with suitable slag forming materials, incrementally adding a, predetermined amount of chromium-containing alloy steel scrap,

and finally adjusting the alloy content of the whole by appropriate additions of alloying elements.

3. In a method of the kind described, melting down a predetermined percentage of steel scrap, refining the same until its carbon content is about 0.03%, deoxidizing and degasifying the molten metal, covering the molten metal with suitable slag forming materials, incrementally adding a predetermined amount of chromium-containing alloy steel scrap, and finally adjusting the alloy content of the whole by appropriate additions of alloying elements, 'said slagforming materials being calcium aluminate.

4. In a method of the kind described, melting down a predetermined percentage of steel scrap .in an electric furnace of the arc type, refining the same until its carbon content is about 0.03%, deoxidizing and degasifying themolten metal, covering the molten metal with suitable slag forming materials, incrementally adding a predetermined amount of chromium-containing alloy steel scrap, and finally adjusting the alloycontent of the whole by appropriate additions of alloying elements, said slag forming materials being lime and fluorspar.

5. In a'method of the kind described, melting down a predetermined percentage of steel scrap in an electric furnace ofthe arc type, refining the same until its carbon content is about 0.03%,

deoxidizing and degasifying the molten metal,-

covering the molten metal with suitable slag forming materials,'incrementally adding a predetermined amount of chromium-containing al-- loy steel scrap, and finally adjusting the alloy content of thewhole by appropriate additions of alloying elements, said slag forming materials being lime and ,sand.

6. In a method of the kind described, forming I a bath of molten SteeLrefining the same until the carbon content is lowered to approximately 0.03% removing the slag formed by the foregoing, so treating the low carbon molten iron thus produced as to, deoxidize and degasify the same and to form a calcium aluminate reception slag thereon, incrementally charging portions of chromium-containing steel scrap onto such reception slag, while suitably maintaining the volume and chromium alloy steel scrap of approximately the ultimate analysis desired and adjusting the composition of the bath by appropriate low carbon ferro-chrome additions.

' VERE B. BROWNE.