US2105888A - Process of treating metal - Google Patents

Description

aiented Jan. 18 1938 UNITED STATES PATENT OFFICE PROCESS OF TREATING METAL No Drawing. Original application April 22, 1932,

Serial No. 606,907.

tion March '7, 1936,, Serial No. 67,702

4 Claims.

This invention relates to the process of treating metal and particularly to a process which involves the treatment of a body of metal to form upon it or introduce within its mass another element which combines and alloys with the metal of the original mass.

It has for one object, therefore, to form upon a mass of metal a layer of an alloy in which the metal of the original mass and the added element are alloyed together.

It has for another object to introduce into the body of the original metal, to a greater or a less depth, another element which alloys with the original metal so that the original metal is alloyed throughout a part of or all of its mass.

The process involves the step of carrying one element into a mass of metal to become alloyed with it. It has been found that the halogen gases, such as bromine, chlorine, iodine and fluorine, will act as carriers for certain elements by combining at high temperatures with them to form gaseous compounds of them, and when such a gaseous compound of an element and a halogen gas is brought into contact with a body of metal at suitable temperatures and for suitable times, the gaseous compound will be carried into the metallic body and will produce an alloy in which the metal combines with the element which was introduced in the gaseous form.

One example of this process involves the use of silicon and chlorine with a ferrous metal to form an iron silicon alloy in the ferrous metal; or an iron silicon coating on the surface of the-ferrous metal, or both. At suffiiciently high temperatures silicon combines with chlorine to form a siliconehlorine gas. In general, in the specification and the claims, where the expression silicon-chlorine gaseous compound is used, we mean any gaseous compound of silicon and chlorine. Iron or steel when subjected to this silicon-chlorine gas will take up the silicon and an iron-silicon alloy is formed, first at the surface of the mass of iron or steel, and upon continued subjection, the silicon penetrates increasingly into the iron or steel and thus the depth of the layer of the alloy is increased. If the process is continued sufliciently, the entire mass of metal may be alloyed with silicon.

In practice, for the sake of economy, it is usually advisable to use the most common and the I most cheaply produced of the halogens; this is chlorine and it is readily produced from common salt. One practical application of our process involves the following steps: Iron castings are packed in ferro-sillcon or silicon and salt and are Divided and this applica- Hard iron castings may be packed, as above 5 described, and put through the normal annealin treatment which in usual practice, without the special packing, would malleableize them and it is found that after the usual annealing cycle, due

to the ferro-silicon or silicon and salt packing,

the resulting castings have a silicon alloy surface layer, and the usual soft malleable core. Thus the malleableizing of the hard iron castings has been effected during the same process in which the silicon alloy layer is produced. In either case.

whether the process includes the malleableizing step or not, it is believed that the silicon was transferred to the iron by the silicon-chloride gas which is formed during the heating. Experiments in which a silicon-chloride gas was passed over pieces of iron which were otherwise not in contact with the silicon, have shown that the silicon is carried over by the gas and alloyed with the iron by this method.

For certain purposes, and particularly for greater cheapness, any other suitable source of silicon may be used in a packing of common salt and sand. This packing, in addition to furnishing the silicon necessary, is arranged to take care of the oxygen which may be present from any source. This effect is accomplished by the breakdown of the sodium-chloride or common salt into chlorine which furnishes the gaseous halogen with which the silicon combines to make a siliconchloride gas, and furnishes also the sodium which acts as a reducing agent.

Frequently it is desirable to carryout the alloying or coating above described as a part of an annealing or malleableizing treatment. A typical example of this is given below, in which the steps for making a silicon alloy in an annealing cycle are discussed.

If hard iron castings are submitted to the usual malleableizing cycle or treatment, in the presence of a packing including ferro-silicon or silicon or some other source of silicon and salt or some other source of a halogen gas, the usual malleableizing effect will be accomplished and at the same time and during the same process the sill- The usual malleableizing cycle involves heating 5 conizing will take place and as before, in the simo the iron to approximately 1600 I". to 2000' 1". The casting is held at that temperature suflicisntly to permit throwing of the carbon out of combination with the iron. While this will not take place completely, the major part of the iron' carbide is thus removed. The casting is then cooled to a point somewhat above its critical tempera-, ture in the neighborhood of 1350 F. and during this cooling a further quantity of the carbon is thrown out of combination. In the usual method the carbon that still remains in combination is thrown out by controlling the final cooling, so that it occurs very slowly through the critical temperature range, the cooling being as slow as 1 per hour and the final cooling alone frequently requiring 48 hours. Where the malleableizing is thus carried out and the formation of the silicon alloy is to occur at the same time, the packing above indicated is used, in place of the usual packing for malieableizing, and the temperature may be as high as 1600' I". to 2000 F. to cause the formation of the silicon-chloride gas and to permit its penetrationinto the iron to the desired degree. Many modifications of this malleableizing cycle are used and generally in most of them the step of alloying may be included, provided only that the proper ingredients are introduced to produce the gaseous compound of silicon and a halogen and that the proper temperatures are attained for its production.

While we have mentioned a number of sources of silicon, we do not limit ourselves to these but they are mentioned only as being the most commonly present and commercially and economically available. Any source of the alloying metal which is desirable may be used and the above examples are given merely as possible sources.

While we have spoken of sodium chloride or common salt as a source of the halogen, we do not limit ourselves to 'this particular source. It is a convenient and economical one but other sources of halogen are available and the use of any source of halogen is within the contemplation of the invention. Sodium chloride has the advantage that it acts as a source both of the halogen and of sodium which is a reducing agent.

The effect of the salt and its use in our process may be summarized as follows:

(1) When a ferrous metal is heated in an uncontrolled atmosphere it probably forms an oxide at temperatures below 1475 F. and this oxide forming reaction may occur with increasing rapidity at the higher temperatures.

(2) The sodium chloride is heated to a temperature higher than 1475 F. and breaks down into chlorine and sodium in the presence of the other packing ingredients. This heating ordinarily occurs in the presence of the coating metal which is thus correspondingly heated.

(3) The sodium released, as mentioned in (2) above, being a stronger reducing agent, combines with the oxygen of the iron oxide, reducing it to iron and forming a sodium oxide. It also combines with the oxygen of the atmosphere of the container to make that a neutral atmosphere and to prevent further oxidation of the iron.

As a result, therefore, of the break down of the salt in the presence of the coating metal, the iron oxide is reduced to prepare the iron to receive the coating metal and the gaseous compoundof the chlorine with the coating metal is formed directly and its penetration into and deposition upon the iron occurs.

Where a source of the coating metal is used which providu an excess of oxygen, it may be desirable to add a reducing agent in addition to that which is formed by the breakdown of the sodium chloride and our process therefore contemplates the addition of appropriate quantities of a further reducing agent should that be necessary. For many sources of the coating metal it is not necessary. Where such added reducing agent is necessary any one may be used. Carbon. because of its cheapness, is frequently satisfactory, but others may be used.

While in the specific examples above mentioned we have referred generally to the treatment of iron, it is to be understood that steel can equally well be treated and the processes described above can be applied to steel. Where steel is treated with the silicon the packing will again consist of a source of silicon and salt and may include sand. Depending upon the analysis of the steel used, the heating temperature may be as low as 1300 F. and from that up to 2000 F.

In general, where steel is to be treated according to the process above outlined, the material is heated to the treating temperature, preferably for upwards of three hours, and is allowed to cool. No efiort is ordinarily made to control the rate of cooling.

This application is a division of our previously filed application Serial Number 606,907, filed April 22, 1932.

Where in the specification and claims we have referred to the ore of silicon, this expression may be understood as meaning the ore in the sense in which that word is generally defined, for example, in Webster's Dictionary the definition of an ore is metal in its unreduced state. As an example of an ore of silicon in this sense, silica may be considered such an ore since it is silicon x x x x in its unreduced state.

We claim:

1. The method of coating and alloying a ferrous metal, of the group consisting of iron and steel, with silicon, which includes the steps of placing the ferrous metal, together with common salt and an ore of silicon, in a container, heating said container and contents to a point sufficient to break down the salt to chlorine and sodium and cause direct combination of the chlorine and silicon and free the sodium for action as a reducing agent on the ferrous metal, whereby the surface of the ferrous metal is alloyed and coated with silicon.

2. The method of coating and alloying a ferrous metal, of the group consisting of iron and steel, with silicon, which includes the steps of placing the ferrous metal, together with common salt and silicon, in a container, heating said container and contents to a point sufficient to break down the salt to chlorine and sodium and cause direct combination of the chlorine and silicon and free the sodium for action as a reducing agent on the ferrous metal, whereby the surface of the ferrous metal is alloyed and coated with silicon.

3. The method of coating and alloying a ferrous metal, of the group consisting of iron and steel, with silicon, which includes the steps of placing the ferrous metal, together with common salt and ferro-silicon, in a container, heating said container and contents to a point sufiicient to break down the salt to chlorine and sodium and cause direct combination of the chlorine and silicon and free the sodium for action as a reducing agent on the ferrous metal, whereby the surface of the ferrous metal is alloyed and coated with silicon.

4. The method of coating and alloying a ferrous metal, or the group consisting of iron and steel, with silicon, which includes the steps of placing the ferrous metal, together with common salt and a source of silicon selected from the group of materials consisting oi ferro-silicon,

silicon and an ore of silicon, in a container, heating said container and contents to a point sumcient to break down thesaltto chlorine and sodium and cause direct combination of the chlorine and silicon and tree the sodium for action as a reducing agent on the ferrous metal, whereby the surface of the ferrous metal is alloyed and coated with silicon.

CARL F. LAUENS'I'EIN. PAUL F. ULMER.