US1775339A - Manufacture of irons and steels - Google Patents

Description

Patented Sept. 9, 1930 UNITED STATES HENRY A. DE FRIES, or ALBANY, NEW YORK, ASSIGNOR 'ro LUDLUM STEEL COMPANY,

PATENT OFFICE F WATERVLIET', NEW YORK, ALEORPORATION OF NEW JERSEY MANUFACTURE OF IRONS AND STEELS No Drawing.

My invention relates to the manufacture of iron and steel and particularly to the development of improved methods of deoxidization whereby the quality of steels and irons is greatly enhanced, and to an improved procedure in the remelting of alloys contain- ,ing easily oxidizable constituents such as chromium and silicon, for example, whereby scrap steels and irons of such composition may now be advantageously utilized 1n the manufacture of ferrous alloys.

Various substances either singly or in combination have been used as deoxidizers in the process of making ferrous-alloys. Among those often used is aluminum which is generally added to the molten metal in the ladle or in the ingot mold, and in very rare in-, stances, in the furnace. Aluminum is light, melts at a comparatively low temperature go and is readily oxidized. Therefore, when added in the usual way to a molten metal of higher specific gravity and having a much higher melting point, it melts quickly on the surface of the molten metal and, because of its great affinity for oxygen, very quickly picks up oxygen from the air instead of from the molten metal to which it has been added. Because it is readily oxidizable its action in molten steel or iron proceeds very quickly, so and if complete deoxidization does not take place almost instantaneously there is great danger that it does not take place at all. Again, Where the aluminum is added in the ladle, for example, oxide inclusions are very as likely to be present in the final product, due first, to the fact that sufficient time does not elapse for these alumina inclusions to rise to the surface of the molten metal, and second, to the fact that any free aluminum in 40 the steel will be oxidized during the pouring as the molten stream of metal passes through the air. The oxide thus formed is churned into the ingot and appears as' crystalline alumina in the finished product. Then too, the aluminum forms a dross which is an ir- Application filed April 27, 1928. Serial No. 273,433." V

reducible compound of aluminum and alumina. Sometimes this dross gets into the steel and forms inclusions of the worst pos'- sible character. The use of aluminum as a deoxidizer is, therefore, always attended with great uncertainty of operation, and the result sometimes is the opposite of that which it was desired to attain.

I find that by using the intormetallic compound FeAl or an alloy very closely approaching thiscompound, instead of ahnniin the furnace, thereby insuring complete (1e oxidization and complete removal of the alumina and other inclusions into the slag before the melt is poured. As a deoxidizer its action takes place throughout the entire bath instead of at the surface thereof as in the case of aluminum. Generally speaking, it is immaterial at what stage of the manufacturing process the FeAl is added because its beneficial action is continued throughout the melting, pouring and casting, and where a slight excess over and above that necessary to deoxidize the steel is provided, itprevents 4 the metal from going wild in the mold. In addition to functioning as a highly eflicient deoxidizcr it will be found extremely useful in the general manufacture of ferrous-alloys as hereinafter outlined,

In the manufacture of carbon steel in which carbon is the principal element (aside from iron), it acts as a true deoxidizer when added to the bath in the furnace before pouring.

In the general manufacture of alloy steels the ferro-aluminum may be added to the bath as a deoxidizer before making the alloy addition. In this case the residual aluminum in liquid solution from the ferro-aluminum prevents the alloy addition from oxidizing while being melted in.

In the remelting of easily oxidized metals and scrap, such as chromium, high chromium or silicon steel and iron, any alumina which may form from the oxidation of the aluminum will have time to rise to the surface of the bath and combine with the slag, thus leaving the final product practically free from oxide inclusions.

In the manufacture of chromium-silicon irons or steels, high nickel chromium steels and irons, high nickel, high chromium-silicon steels and irons, or in fact all those various ferrous-alloys which are today classified as heat resisting, stainless steels or irons, the necessary amount of Fe'Al added to the cold remelting charge or scrap charge will pre vent oxidation and will, therefore, keep the carbon content reasonably close to the carbon content of the initial charge. If a building up of alloys is necessary, some additional ferro-aluminum maybe added to the bath before the alloys.

In the manufacture of gray iron, FeAl added in the ladle not only fully deoxidizes the iron, thereby making a denser structure,

but also efi'ects therein a finer dissemination and a more uniform distribution of graphitic carbon than has heretofore been attainable.

In using ferro-aluminum it is always preferable to add it in as large masses as possible, preferably preheated to about 1000-1500 degrees F. I find that such large masses will melt more uniformly into the bath and be more thoroughly distributed therein. After .the ferro-aluminum is melted in, the bath should be stirred vigorously to obtain a thorough mixing.

While many modifications of the procedure herein outlined may be made, I find that the following will give very satisfactory results.

In the manufacture of carbon steel having the following composition, for example I Per cent Carbon 1. 05-1. 15 Manganese 0. 20-0. 30 Silicon 020-0. 30 Phosphorus 0.015 I Sulphur 0.015 Balance iron,

the scrap charge is melted and a sample taken.

The steel is then deoxidized by standard debefore pouring. The resulting stecl'will be free. from aluminum oxide because any reair during pouring.

In the manufacture of chromium steel conforming to the following specification, for

examplea Per cent Carbon 095-1. 05' Manganese 0. 25-0. 35 Silicon 0. 20-0. 30

Chromium 1111.04.50

Balance iron,

the scrap charge is melted down and the regular deoxidizing slag is put on. SuflEicient ferro-aluminum is then added not only to deoxidize the steel but to provide a slight excess so that there will be some aluminum in liquid solution in the bath. The chromium is then added andmelted in. Where the proper amount of ferro-aluminum is used there will be no change in color or composition of the slag, establishing the fact that m; oxidation of the chromium has taken place.

In the making of chromium rustless iron, after making a low carbon melt down to say 0.04%, it has heretofore been found extreme- 1y difficult to prevent a considerable carbon increase when melting in the chromium. This is due to the facility with which chromium takes up carbon from the furnace electrodes. Where it is desired, to make a 10,000 pound heat of rustless iron conforming to the following specification, for example- Per cent Carbon (maximum) 0. 09 Manganese 0. 5O Silicon 0.75-1.00 Chromium 16. 50-18. 50

the procedure may be as follows:

Common scrap plus 250 pounds of silico manganese manganese, 20% sllicon, 1% carbon) is melted down. 400 pounds of iron ore is added to bring the carbon down to 0.04% and the slag is then pulled. A new its slag of lime mixed with fine silicon or fe'rrosilicon is added for primary deoxidization, then 85 pounds of ferro-aluminum, preferably preheated, is melted in and thoroughly stirred into the bath. The required amount of low carbon ferro-chromium, properly preupon an additional 15 pounds offerro-aluminum is added. The final product will be found to contain about 0.08%-0.10% aluminum, but will be practically free from alumina and other oxide inclusions and will show no alligator skin. Furthermore, there will be no appreciable increase in the carbon content which is probably due to the fact that the deoxidizing action of the aluminum in the bath prevents, to a great extent, the absorption of carbon by the chromium While being melted in.

heated, is then added and melted 1n, where- In making a heat of silicon chromium steel conforming to the following specification, for example Per cent Balance iron,

it has been found very diflicult to remelt scrap steel of this analysis without excessive losses in chromium and silicon due to oxidation comes so thoroughly entrappe during the melting down. Furthermore, the chromium and silicon oxide roduced bein the steel that it has heretofore been practically impossible to remove them with known deoxidizers. I find that the addition of FeAl to the initial charge overcomes this difficulty, and sound steel may be produced using silicon chromium steel scrap only.

For a 10,000 pound heat the procedure is i as follows: 75 pounds of FeAl is added to charge is melted down and the slag removed.

A new lime slag mixed with fine ferro-silicon is then put on and a small amount of FeAl is melted in. Following this, the necessary alloy additions are made to make up for the amount lost during the melting down, and

r the heat is poured.

I am aware that others have heretofore suggested the method of alloying aluminum with steel or iron by pre-alloying the aluminum with iron to form a so-called ferro-aluminum and, then incorporating this'in the melt, For example, Hadfield, in U. S. Pat ent No. 461,333,- suggests the use of a ferroaluminum containing a 10% of aluminum; Cooper in U. S. Patent No. 1,550,509 suggests the use of a ferro-aluminum containing equal percentages of iron and aluminum to'produce an alloy containing between 10% and 16% of aluminum. It has also been suggestedby VVittenstrom that castings of wrought iron and steel are improved by the addition of from 0.1% to 0.2% of metallic aluminum.

While my present invention concerns the roduction'of ferrous alloys of superior quality by the use of aferro-aluminum, it must 'be borne in mind that the advantageous results herein pointed out cannot beexpected unless the ferro-aluminum employed .is approximately a true intermetallic compound.

conforming to the formula FeAl or about 40%,iron and 60% aluminum.

In claiming m invention I have used the general term errous alloys as defining those compositions of matter which are principally iron or which contain a substantial amount of iron combined with one or more other elements.

What I claim isa 1. In the manufacture of iron and steel, the method of deoxidizing the bath which comprises incorporating therewith an alloy of iron and aluminum conforming approximately in composition to the iritermetallic compound FeAl and thereafter holding the heat for an appreciable interval before pours ing to insure deoxidization.

2. The method of manufacturing a ferrous alloy containing an easily oxidizabl'e ele ment which comprises incorporating in ,the bath a sufficient quantity of an alloy of iron and aluminum conforming approximately in composition to the intermetallic compound FeAl to effect deoxidization, and thereafter adding the oxidizable element.

3. The method of manufacturing a ferrous alloy containing an easily oxidizable element which comprises creating a liquid solution of aluminum in the bath by incorporating there in an alloy of iron and aluminum conforming approximately in composition to the intermetallic compound FeAl and in a quantity slightly in excess of that required to effect deoxidization, and thereafter adding the oxidizable element.

4. In the manufacture of ferrous alloys fromv scrap containing chromium, the method of preventing excessive oxidation of the chromium and the entrappingof chromium oxides in the steel which comprises melting 105 with the scrap charge up to about 1% of an alloy of iron and aluminum approximating in composition .the intermetallic compound FeAl 5. In the manufacture of ironor steel, the 1 method of forming a liquid solution of aluminum in the bath which comprises incorporating therein an alloy of iron and aluminumapproximating in composition the intermetallio compound FeAl and in a'quantity slightly in excess of that required for deox'idization.

6. These steps in. the manufacture of ferrous alloys containing easily oxidizable elements which comprise effecting a primary deoxidization of the bath, and thereafter completely deoxidizing by the addition of an alloy iron and aluminum approximating in composition the intermetallic compound FeAl making the necessary alloy additions, and thereafter adding an additional quantit of FeAl the total quantity of FeAl a ded being slightly in excess of that required to efiect deoxidization.

' HENRY A. DE FRIES.