US1622977A - Alloy - Google Patents

Description

Patented Mar. 29, 1927.

UNITED srATEs: PATENT; OFFICE.

EZEKIEL J. SHACKELFOBD AND WILLIAM B. D. .PENNIMAN, OF BALTIMORE, MARY- LAND, AND JOHN R. CAIN, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOBS 1'0 BLDIAC METALS, LTD., OF MASTERTON, NEW ZEALAND, A CORPORATION OF NEW ZEALAND.

ALLOY.

No Drawing.

Our invention relates to methods of producing alloys of iron and chromium containing .1%' orless of carbon and 12% to 16% of chromium, known in the trade as stainless iron.

In order to secure this low carbon content in such alloys, it has been the practice heretofore to (a), make the addition of chromium by a lowcarbon ferro-chromium con taining usually 60% to 70% of chromium and 1% to .5% of carbon; or (b), to reduce into a molten low carbon iron bath chromium direct from ore, by means of reducing agents such as silicon and aluminum. Both of these methods are expensive, due partly to the hi h cost of low carbon ferro-chromium and t e ferro-silicon used for reduction purposes, and

partly to the high chromium losses incident to such processes The particular object of our invention is to make possible the'use of the carbon ferrochromium such as the 4% to 6% carbon grade known to the trade. The use of this-chea er material has heretofore been impractica le because no inexpensive method has been available for de-carbonizing the iron bath to the desired degree after the chromium has been added from such a source, or, if such a method is applied, it. results in such high chrome losses as to be impracticable.

In carrying out our invention, we employ an arc furnace of the usual Heroult type, or its equivalent. We can usethe ordinary refractory linings employed in suth furnaces for the manufacture of ordinary carbon steel, but for the bottom of the furnace, we find it highly advantageous to provide a special bottom made of ordinary commercial chrome brick cemented together with chrome cement. We are aware that it is customary to put in the bottom of such furnaces by burning in successive layers of magnesiteor dolomite,

or similar materials. These materials are usually bound with tar and duringthe burning-in operation, this tar is supposed to be completely removed. However, we find in practice, that carbonaceous material is left in such bottoms and this frequently causes carbonization of stainless iron baths molten .on such bottoms. This is particularly likely should portions of the bottom become detached, dueto violent mechanical agitation of the bath, which is liable to occur in most processes. These detached portions of the ottom, carrying carbon, rise through the Application filed April 16, 1925. serial No. 23,669.

scribed in this specification. The net result of this is that the metal being refined is subject to refining action 'both from the slag bath .and from the chrome bottom beneath, as

soon as this'bottom has'become s'ufliciently heated by conduction of heat from the arcs,

through the molten materials to the bottom below. We consider that this refining action I has much to do with the high speed of refinement and greater degree of refinement which characterize our recess, with consequent resultant elimination of chrome losses in the rdetalv bath.

We prefer to first charge our furnace with the necessary amount of limestone, then pour upon this a suitable charge of molten low carbon iron, preferably around .05%

carbon, or lower. Such iron 'may be convenientl blown be tapped off from an acid or basic openhearth furnace. molten ferro-chromium as the source of our chromium addition. Such. molten ferrochromium is conveniently obtained from an auxiliary electric furnace of the Heroult type which is usedas the means for remeltand cheaply had in the form of essemer metal, or, if desired, may

We prefer also to use mg ferro-chromium made in the usual type of ferro-chrome smeltin' electric furnace. 'As an option, if such a erro-chrome smelting furnace is available, the molten fel'rov a chromium may be tapped direct fromit. 1 vMeans must be provided for weighing the charges of molten low carbon iron and molten erro-chromium. It will be readily understood that our process can be worked with cold materials; for instance, cold scrap iron and ferro-chromium broken up into lumps 01': preferably not over 2" cube. However, mu better control and much greater eoonom can be secured by the we of molten materi x Having charged the furnace with the necessary limestone and low cerboniiron, heat is applied until the bath is somewhat superhosted then an addition of term-chromium is made such as to give about one-third. of the emount of chromium desired in the finished product. We have found in our Work that certain chromium losses take plate, so that it a certain content of chromium is aimed at in the finished product, more terrochromium' must he added than would be theoretically necessary, in order to compensate for these chromium losses which are due to oxidation reactions incidental to removing the carbon. The necessary excess to he odded depends somewhat upon the raw materiuls used and the furnace procedure, but in practice, it will he found that from 25% to more chromium must he added than one expects to obtain in the finished product. Within approximately ten minutes after the first addition 03? chromium has been made in this manner, chemical tests should he made for carbon, and the operator should convince himself by fracture tests, hardness tests, drilling tests, or other similar physical phenomenu, that the carbon-of the hath is not over 3%. When the" tests show that 6.3% carbon or less, is present, another addition of chromium approximately equal to that previously made, can be added. After" this second addition, tests are made before, and when the carbon content is at 6.3% or less, the subsequent additions can he made.

We have found this method of mat-ring the chromium addition by steps to he very silicecious end to promote the rapid removal of the carbon down to the low point desired in the finished product. It has been tained in our experiments that if the carbon uny stage is allowed to rise to .693 or .87, with. a simultaneous increase in chroiniuin from soy 16% to l i-%,-the removed of the carbon then becomes very much more dificult and high chromium losses ere hound to occur. We also found under such circumstances, that it was very ditiicult to secure the necessary regularity in working which is so essential to commercial success.

7 ll orlring in the manner we here de= scribed, it is possible to use a variety of reslags, beering in mind certain general conditions which must he 'rnainteined in order'to secure success. Thus, it is essential that the slag shell be strongly basic st all times. This can be insured by the use of cheep basic substances, such as lime, limestone or dolomite?" is necessary further, that the slag be niaintained in a high state of fluidity. This can he hr about by the use of such fluxes as tiuorsioar, rutile, ilemit'e, or, in some cases, by the addition of silicon. In still other cases, fluidity can he conferred by small additions of powdered noses?? term-silicon. Proper regulation of temperature is very important in securing and maintaining fluidity of slag.

A. very important condition which must be carefully observed, is to prevent the formation of an excess of iron oxide in the refining slag. Another important condition is to avoid the formation of too greats, volume of slug. Should the volume of the slag, or

its iron oxide content become excessive (the oxidation of chromium from the hath, as

more particularly described in Patent No. 1,527,088, to Penniman and Shaclrelford.

Having thus describedour invention, what We claim end desire to secure by Letters Patent, is l. A process of producing an alloy of iron and chromium which includes the steps of charging a furnace with basic slog producing material and molten iron having a carbon content of .05% or under, adding a charge of term-chromium, Working the bath until the carbon content is under 3%, adding a second charge of term-chromium, and repeating this step as often as necessary until the bath has the desired chromium and carhon content. i Y 2. A process of producing an alloy of iron and chromium, which includes the steps of charging a turnece with slag forming materials, and molten iron, adding a charge oi form-chromium to produce a content of chromium in the finished 'grcduct less that desired, Working the bath until the l. A. process of-producing an alloy of iron 1 and chromium, which includes the steps of charging a furnace with slag producing materials and molten iron, intermittently adding a charge of form-chromium and Workin the bath ulter each form-chromium addition until it contains a definite carbon content, and repeating the ferro-chromium'additions and working until the bath has the desired chromium and carbon content;

5. A process of preparing an alloy of iron and chromium which includes the steps of charging a furnace with slag prodncin materials and iron, intermittently a dlng charges of ferro-chromium and decarbonizing the bath after each ferro-chromi'um addition until the carbon. content is not more than a desired maximum, the ferro-chromium additions being continued with working, as necessary and until the bath contains the desired chromium and carbon content.

In testimony whereof we afiix our signatures. 2 EZEKIEL JOEL SHACKELFORD. WILLIAM B. D. PENNIMAN. J OHN R. CAIN.