US2914432A - Process for facilitating the plastic deformation of metals - Google Patents

Description

United States Patent C) Fritz Singer, Starnberg, Germany Application November 19, 1957 Serial No. 697,335

11 Claims. (Cl. 148-624) No Drawing.

This invention relates to a process for facilitating the plastic deformation of metals, and particularly to a process for producing a coating on metals of the ferrous group, which coating serves to facilitate such deformation.

This application is a continuation in part of my co pending patent application, Serial No. 548,267, filed November 21, 1955, now abandoned, which is a continuation in part of my patent application, Serial No. 256,134. filed November 13, 1951, now abandoned.

In my United States Patent No. 2,105,015, I have described a process for facilitating the plastic deformation of iron or steel by forming a phosphate or other crystalline coating on the article to be deformed. This process is now extensively used for facilitatnig the cold drawing of wire and tubes and the cold extrusion of hollow steel casings.

Subsequent to my above patent it was discovered that sulfide coatings furnish advantages over phosphate coatings in their capacity for facilitating plastic deformation While the phosphate coatings are of the coated metal. of crystalline and brittle nature and serve primarily as a means for preventing contact between the surfaces of work pieces and tools, and as carriers for lubricants, the sulfide coatings are amorphous, soft and plastic, and are capable of acting not only as a separating layer, but also they themselves serve as a very eflicient lubricant.

Various methods have previously been proposed for producing sulfide coatings, particularly on ferrous surfaces. According to one of these methods, the ferrous articles are immersed in water through which hydrogen sulfide is bubbled, or they are first wetted with water and then subjected to hydrogen sulfide gas. The thus produced sulfide coating is dark and is not firmly bonded to the surface. Another drawback of this process consists in the formation of aqueous solutions of poisonous hydrogen sulfide, requiring measures for protecting the workers from poisonous gases when the articles are introduced in and taken out of the bath.

While the sulfide coating which is not firmly bonded facilitates cold working to some degree, it is far less effective than my herein described sulfide coating which is firmly bonded to the surface.

Referring again to the prior art, it has been proposed to produce a sulfide coating in the cold working operation itself by using so-called sulfidizing lubricants of water-soluble sulfides such as ammonium sulfide or ammonium polysulfide added to oil-in-water emulsions. Such sulfidizing lubricants may be effective but the r use is limited to the cold working of low-carbon steels or non-ferrous metals. Another drawback of sulfidizing lubricants of this kind is their offensive odor.

With the foregoing in mind, it is an object. of the present invention to provide a new and improved process for facilitating the plastic deformation of a metal, which does not suffer the prior disadvantages.

Another object is to provide a new and improved process for facilitating the plastic deformation of a metal "ice wherein a tightly adherent metal sulfide coating is pro duced on the metal.

A further object is to provide a process for facilitating the plastic deformation or working of ferrous metals which is simple and reliable in use and productive of improved coatings.

An additional object is to provide an economical and practical process which may be used on high carbon, alloy and other types of hard ferrous metal. These and other objects and advantages of the invention will become apparent upon reading the following specification.

In accordance with my invention, the plastic deformation of metals of the ferrous group is facilitated by producing a tightly adherent sulfide coating thereon. The plastic deformation is carried out shortly after coating the metal, or the operation may take place subsequently if the coating is protected against oxidation in the meantime. The process is especially useful in cold working metals of the ferrous group such as iron, nickel and cobalt.

According to a preferred embodiment of my invention, the metal in the dry state is exposed to the action of a hydrogen sulfide and oxygen in effective amounts throughout the formation of the coating. The hydrogen sulfide and the oxygen are preferably supplied in stoichiometric amounts during the formation of the coating to carry out the reaction according to the equation,

where R is iron, nickel or cobalt. Excesses, to drive the reaction and to provide for losses due to oxidation-reduction side reactions, are tolerable to a small degree but should be reduced as much as possible.

When a hydrogen sulfide is referred to herein, it is intended to include both hydrogen sulfide and hydrogen polysulfides. The hydrogen sulfide may be supplied as free or chemically uncombined hydrogen sulfide, or it may be supplied by a hydrogen sulfide-producing substance. It may be employed in the gaseous state, as free H S, or as a product of the dissociation or decomposition of a substance to H 8. The hydrogen sulfide may also be produced or liberated directly on the surface of the metal, as by decomposition of a hydrogen sulfide-producing chemical composition.

Reference to oxygen contemplates free or chemically uncombined oxygen. Air is the preferred oxygen-containing gas for the reaction. Air of normal humidity will serve to supply the oxygen and the small water vapor requirements. The gaseous source of hydrogen sulfide may contain water vapor, as is usually the case when H 5 is produced by wet methods. Moisture present on the surface of the metal may also contribute to the reaction. The humidity of the atmosphere surrounding the metal being treated Will vary under different conditions. It is ordinarily preferred that the atmosphere have a relative humidity of about 30-70% for ease and rapidity of reaction. Higher humidities are preferably avoided to avoid oxidation of the sulfide coatings and to avoid the loose formation of the sulfide coatings. Water vapor is a product of the reaction and is not consumed but performs a function catalytic in nature, so that the exact quantity of water vapor present is not of great importance.

In referring to the dry state of the metal I mean that the metal surface need only, be visibly dryor visibly free of water or other liquid, although it may contain dispersed, adsorbed or occluded moisture. .Water or. other liquid must preferably not be present on the metal surface in the continuous state 'or phase, that is, as, a flowable liquid or a liquid film. This condition is mandatory for producing a tightly adherent protective coating according to the invention. Thus, 'oxygenrnust' 3 be presentin effective amounts or concentrations at the reacting metal surface throughout the production of the coating, and this condition is only achieved when the metalis in the dry state and free from layers of liquid on the surface.

When proceeding according to my invention, the metal surface is exposed to the simultaneous presence and reaetionof hydrogen sulfide and oxygen supplied in stoichiometric quantities. The reaction and formation of the coating on ferrous surfaces takes place in the presence of water vapor according to the simplified equation:

While the invention is not limited to theoretical considerations, a postulated course of the reaction is as follows. Hydrogen sulfide in the presence of oxygen and water vapor is gradually oxidized to sulfur. The reaction is not simple but takes a complicated course with the formation of unstable intermediate products. It is further postulatedthat the formation of the metal sulfide coating is not caused by the direct action of the hydrogen sulfide, but by the intermediate products of the oxidation of the hydrogen sulfide. For this reaction to take place and produce a tightly adherent iron sulfide coating, it is necessary that the metal surface be free of liquid water.

Where liquid water is present on the metal surface as in prior art processes, it is an aqueous solution of hydrogen sulfide which reacts. Although hydrogen sultide is a very weak acid, an aqeous solution thereof reacts with ferrous surfaces very rapidly. This reaction proceeds according to the following equation:

The hydrogen liberated in the rapid reaction with the aqueous solution seemingly separates the iron sulfide produced from the metal surface and thus produces a loosely adherent coating. Even the presence of air does not alter the course of the reaction. Hyrogen sulfide is readily soluble in water (1 volume part of water dissolves 2.61 volume parts of H 8 at 20 C.), while the solubility of oxygen is low (1 part of water dissolves 0.031 part of oxygen at 20 C.). Thus, any oxygen dissolved in the aqueous solution of hydrogen sulfide does not reach the reaction zone, namely, the ferrous surface, as it is rapidly consumed in an oxidation-reduction reaction with the hydrogen sulfide. The result of the prior art treatment of the metal surface with hydrogen sulfide in the presence of liquid water appears to be a rapid reaction, requiring perhaps only seconds, which produces a loosely .bound coating.

In my invention, involving a different type of reaction, a firmly bonded sulfide coating may be produced in about to 60 minutes. The difference in magnitude of the reaction time may be caused in part by the relatively low concentration of hydrogen sulfide in the reaction zone and its gradual supply to the reaction surface and consumption thereon. The slow formation of the sulfide coating contributes, however, to the firm bonding of the coating. The process can be controlled so that the hydrogen sulfide is completely consumed and there are no difiiculties caused by noxious gases when the coated articles are removed from the reaction chamber. This is accomplished by supplying approximately stoichiometric quantities of hydrogen sulfide and oxygen during the reaction.

According to one method of carrying out my invention, the metal is contacted With hydrogen sulfide in the gaseous state. According to this embodiment, it will be necessary first to remove any scale from the metal. The metal de-scaled and in a visibly dry state may be placed in a closed chamber, which can be a wooden box, into which hydrogen sulfide is introduced. Instead 93 8 a i dies? alfi erodu ss substance may e disli ed a hu o nlfide .t rHS),

which volatilizes at normal temperatures and dissociates into ammonia and hydrogen sulfide. The metal to be coated will often come directly from a pickling operation where scale has been removed, and it need not be absolutely dry but may be placed in the reaction chamber as soon as any visible water has disappeared. The moisture adsorbed or occluded on the metal surface and which is not visible is useful in initiating the process.

Where the total surface area of the metal in the chamber is not too great, the air originally present properly diluted with hydrogen sulfide may supply enough oxygen for the formation of the coating. Otherwise, the supply of hydrogen sulfide can be supplemented by the introduction of air or other oxygen-containing gas from time to time or continuously, to replace the oxygen consumed in the formation of the coating and by oxidation of hydrogen sulfide, so that approximately stoichiometric proportions are present throughout the coating operation. It is normally unnecessary to introduce water vapor specifically, as noted above, since the average relative humidity of air is sutficient and water vapor is formed in the reaction. There may also be water vapor present in the hydrogen sulfide.

To conserve hydrogen sulfide and to avoid giving off noxious gas, it is advisable to compute approximately the linear surface of the charge to be coated. This latter computation helps to determine the stoichiometric quantities. The amount of hydrogen sulfide supplied will depend upon the thickness of the coating which is desired. The coating will generally be formed in about 20 to 60 minutes, depending upon the desired thickness of the coating. When combined hydrogen sulfide is used, the resulting coating has a bright irridescent appearance, and its color varies between silver and brass. When ammonium hydrosulfide is volatilized, the coating is generally black with no metallic luster.

In carrying out the coating operation, approximately stoichiometric proportions of hydrogen sulfide and oxygen are supplied in the presence of water vapor to effect the desired coating. However it should be understood that there may occur some deviation in the stoichiometric proportions without endangering the formation of the coating. The sulfide coating produced is resistant to the action of a surplus of oxygen and in case of a surplus of hydrogen sulfide the reaction would merely stop. In practice the operator will preferably interrupt the supply of humid air upon a change in the color of the coating from black to brown. To this extent, the proportions of the reacting ingredients are critical to prevent oxidation of the sulfide coating.

Another very efficient and simple method of treating the articles with hydrogen sulfide according to my invention consists in dipping or spraying the articles with an aqueous solution of ammonium sulfide or ammonium polysulfide, allowing them to drain and dry and then subjecting them to air until a black coating is formed. The formation of the tightly adherent sulfide coating is effected by the combined action of the dissociating ammonium hydrosulfide or the polysulfide and the oxygen of the air after the ammonium sulfide solution has dried. In order to retain the necessary quantities of ammonium sulfide on the iron surface, it may be necessary to increase the very low viscosity of the ammonium sulfide solutions by adding thickening agents such as methylcellulose or cellulose glycolate. To produce a sulfide coating on ordinary steel, the articles may be dipped into a 20% aqueous solution of ammonium hydrosulfide into which .5 to 1% methyl-cellulose or cellulose glycolate has been stirred. The articles are allowed to drain and dry and are then subjected to air of normal humidity at normal or slightly elevated temperatures, for example 30 to 50 Centigrade. When using yellow ammonium poly sulfide or ammonium sulfide. containing ammonium polysulfide, t e s l t n. upon be gme paq e .d e to t e s n rati s of olloida su fur.

Because the sulfide coatings are liable to be oxidized in the humid atmosphere, the ferrous articles after being coated are preferably either immediately cold worked or are stored in a dry atmosphere.

Important fields of application of the invention are cold drawing and cold extrusion of ferrous metals, especially in wire, profile and tube drawing. The new process is especially useful in facilitating the deformation of ferrous and nickelous metals, such as iron, steel, nickel, nickel alloys and the like. In such cases, a tightly adherent or firmly bonded coat of metal sulfide, iron sulfide or nickel sulfide as the case may be, is formed on the surface of the metal by reaction of the metal with the hydrogen sulfide and oxygen. Iron, mild and low alloyed steels react with hydrogen sulfide easily and extensively in the presence of oxygen and water vapor at normal temperatures, i.e., atmospheric or room temperatures. Some metals such as stainless steels may preferably require the use of a moderately elevated or superatmospheric temperature, for example, 50-80 C. A temperature within the range of about 80 C. will serve ordinarily for economic operation with these and other ferrous metals such as high alloyed steels.

When proceeding according to my invention, by contacting a metal of the ferrous group in the dry state with a hydrogen sulfide, oxygen and water vapor, a tightly adherent coating is formed which is very advantageous in the plastic deformation of the metal. The process is very simple and reliable, and it is economically carried out with but very small material and equipment requirements.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above process and in the article set forth without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What I claim is:

1. A process for facilitating the plastic deformation of a metal article of the ferrous group comprising the steps of producing a tightly adherent sulfide coating on said article by contacting it, in the absence of visible water on said article and in the presence of water vapor with stoichiometric amounts of hydrogen sulfide and oxygen according to the equation where R is a material selected from the group consisting of iron, nickel and cobalt, until a black coating of metal sulfide has been formed thereon and thereafter plastically deforming said coated metal article.

2. The process of claim 1 further defined in that said metal of the ferrous group is an iron alloy.

3. The process of claim 1 further defined in that said hydrogen sulfide is free hydrogen sulfide.

4. The process of claim 1 further defined in that said hydrogen sulfide is provided by the volatilization of ammonium hydrosulfide.

5. A process for facilitating the plastic deformation of a metal article of the ferrous group comprising the steps of producing a tightly adherent sulfide coating on said article by coating it with an aqueous solution of ammonium sulfide, drying said solution coating on' said article in the open air, continuing to contact the resulting coated article in air for about 20 to about minutes in the absence of visible water on said article until a black coating has formed according to the equation where R is a material selected from the group consisting of iron, nickel and cobalt, and plastically deforming the sulfide coated article.

6. The process of claim 5 further defined in that said ammonium sulfide is ammonium sulfide of the formula Q2 7. The process of claim 5 further defined in that said ammonium sulfide is ammonium hydrosulfide.

8. The process of claim 5 further defined in that said ammonium sulfide is ammonium polysulfide.

9. The process of claim 5. further defined in that said ammonium sulfide solution contains a thickening agent to increase its viscosity.

10. A ferrous metal article treated for plastic deformation, said article being provided with a tightly adherent sulfide coating by contacting it, in the absence of visible water on said article and in the presence of water vapor with approximately stoichiometric amounts of hydrogen sulfide and oxygen according to the equation R+H S+V2O RS+H O, where R is a material selected from the group consisting of iron, nickel, and cobalt.

11. A ferrous metal article of the class described having formed thereon a tightly adherent sulfide coating by contacting it, in the absence of visible Water on said article and in the presence of water vapor with approximately stoichiometric amounts of hydrogen sulfide and oxygen according to the equation R+H S+ /zO- RS+H O where R is a material selected from the group consisting of iron, nickel and cobalt.

References Cited in the file of this patent UNITED STATES PATENTS 2,054,737 Brunner Sept. 15, 1936 2,245,561 Nelson et al June 17, 1941 2,350,491 Butler et al. June 6, 1944 2,445,962 Mell July 27, 1948 FOREIGN PATENTS 510,780 Belgium May 15, 1952

Claims (1)

1. A PROCESS FOR FACILITING THE PLASTIC DEFORMATION OF A METAL ARTICLE OF THE FERROUS GROUP COMPRISING THE STEPS OF PRODUCING A TIGHTLY ADHERENT SULFIDE COATING ON SAID ARTICLE BY CONTACTING IT, IN THE ABSENCE OF VISIBLE WATER ON SAID ARTICLE AND IN THE PRESENT OF WATER VAPOR WITH STOICHIOMETIC AMOUNTS OF HYDROGEN SULFIDE AND OXYGEN ACCORDING TO THE EQUATION