US2075879A - Method of coating iron, steel or steel alloys - Google Patents

Description

c. A. BASORE 'ET 'AL 2,075,879

METHOD OF COATING IRON, STEEL OR STEEL ALLOYS I April 6, 1937.

Filed March 16, 1955 C/ebwwe/Z fiazaore .Fll f' Dan/e/ TJ'OHGG.

Patented Apr. 6, 1937 UNITED STATES PATENT OFFICE METHOD OF COATING IRON, STEEL OR STEEL ALLOYS tion of Delaware Application March 16, 1935, Serial No. 11,500

9 Claims.

This invention is a method for coating bodies of iron, steel or steel alloys by subjecting the body to a surface contact with a suitable molten mass whereby a coating is formed which offers a maximum resistance to impact, abrasion or corrosion.

The main object of the invention is to provide relatively thick metallic coatings on bodies of iron, steel or steel alloys by Suitably heating such bodies and subjecting same to contact with a 10 molten mixture of suitable metallic alloy and fluxing material.

Another object is to provide a method of coating with heat wherein a relatively thick coating is applied in a minimum of time.

Another object is to apply to iron or iron base alloys -a coating which offers relatively great resistance to impact, abrasion and corrosion.

A further object is to provide a method of coating with heat wherein the desired thickness of coating may be applied quickly and at a relatively,low cost of labor and materials.

Other objects will appear from the specification which follows when considered with the accompanying drawing, wherein-- Figure 1 is a view in section of certain furnaces used.

Figure 2 is a view in section of a modification,

and

Figure 3 is a view in section of a further modification.

According to the prior art and practice, the usual method of coating iron or iron base alloys contemplates the use of welding rods which are composed of such material as will produce a hard surface coating when the material is applied to the article coated. The rod material is heated and fused either by an electric are or by a gas torch employing acetylene or other gas or gases that provide very high combustion temperatures.

The initial expense of the better grades of such rods is very high and their use requires the services of skilled high paid workmen. The coating obtained by such process is not uniform and that process is impossible for use under certain conditions and for articles of particular shapes or that are to be applied to certain uses.

Various practical methods have been followed for applying relatively soft coatings to metals, which methods make use of the common molten bath of the coating material. Methods have been proposed also for case hardening iron,.steel, etc., with a thin coating of white iron or for applying thin soft coatings to such metals using a molten bath. We are not aware, however, that any method has been developed for depositing a hard, wear resistant binary or tertiary alloy steel under reducing conditions and of a definite composition, and which has a coefllcient of expansion rather closely'comparable to low carbon steel, nor of any prior art method of sufficient practical value and merit which is adapted to provide, quickly and cheaply, a relatively thick alloy coating of iron or iron base alloys. Our method is applicable in fields where resistance to impact, abrasion and corrosion is important, such as drill points,

v gear teeth, crusher jaws, dies, dipper teeth, steel plows and agricultural equipment, etc. According to the best authorities, white iron has only very limited application and is employed usually as a hard surface on the outside of gray iron castings.

According to our method, the article to be coated is given a preliminary heat treatment preferably under neutral or reducing conditions. The article is then subjected to contact with a molten mass of material of predetermined composition and in a specific manner to produce the desired coating.

The article may be subjected to either a dipping or a pouring contact and, preferably, under a neutral or reducing condition. The several component elements that form the molten mass may be varied somewhat according to the nature of the coating to be produced although the main character of the mass in all cases is broadly the same.

An important feature of the coating process to be described in detail relates to the materials employed to form the molten coating bath or compound. An essential portion of this compound comprises a fiuxing component composed of free carbon and borax with or without other slag forming materials such as water glass, soda ash, or fluorite the proportion of borax preferably being less than that of the other slag forming materials that may be added. The remainder of this compound may be varied according to the type of metallic coating to be applied. In lieu of borax, we may use boric acid or boron trioxide.

The remainder of the coating compound consists of a suitable steel alloy, either binary, tertiary or quaternary, the elements of which may be selected from the following group:

Cast iron. Ferrochrome. Ferromanganese. Cobalt.

Nickel. Tungsten. Molybdenum.

, furnace.

The particular steel alloy used will be determined from the character of the coating desired. An alloy containing manganese, nickel, tungsten or molybdenum will produce a coating that. is hard or tough. An alloy containing chromium will produce a coating resistant to common rust.

Before melting thereof, the dry ingredients of the compound are reduced to a suitable fineness by grinding to not less than a 60 mesh, although good results are obtained if the cast iron and steel alloy portions are reduced in size only to about A". The portions of steel alloy, free carbon and borax are thoroughly mixed and the water glass solution is then mixed into the other ingredients in a manner to thoroughly coat the surface of all finely divided particles. This mixture should then be melted in a manner to insure no loss of carbon content; hence, it is preferable, to melt this mass under neutral or reducing conditions which should include a contacting atmosphere of inert or reducing gases. 7

The actual application of this molten compound may be either by a clipping or a pouring step, either of which steps will require a different type of apparatus in the nature of a heating or melting As an important preliminary step, the article of iron or steel to be coated is first heated under neutral or reducing conditions to a point just below its melting point or to a deep red corresponding to about 1800 to 2200 degrees F.

In following out a dipping process, the apparatus shown conventially in Fig. 1 maybe employed wherein a preheating furnace l is shown arranged close to a melting furnace 2. An article 3 in furnace I may be passed through aligned openings 4 into furnace 2. The furnace I is shown as provided with a top door 5 and a side door i. The molten dipping compound in furnace 2 consists of the molten alloy portion 1 and a slag portion I. The furnace 2 is heated preferably by gas and the space above the slag layer 8 is filled with inert or reducing gases. In Fig. 2 is shown a modified form. of melting furnace wherein carbon electrodes 9 are used to melt the coating compound by means of alternating current passed therethrough in a. well known manner.

Prior to heating and dipping thereof, no preliminary treatment need be given to an article when a thin coat is desired, not even to the extent of removing any rust thereon. In the event that thick coatings are desired, the article is first roughened as by cutting grooves or forming holes therein. The article 3, iron or steel, is then heated to a deep red as above set forth under non-oxidizing conditions in furnace I. If desired, reducing gases from products of combustion from furnace 2 may be used in furnace I as the atmosphere.

The article 3 is then passed into melting furnace 2 and dipped slowly into the molten bath passing first through the slag layer and then into the steel alloy 1. The submerged article is moved slowly upwardly and downwardly several times so that it passes alternately through the molten slag and molten steel so as to come into contact several times with the slag. The cleaning action of the slag is applied thereby several times in a manner to facilitate a better bond between the coating and article.

The metal article is maintained in contact with the molten alloy long enough to insure a good bond and a deposit or coating of desired thickness. The time of contact should be from 30 to 90 seconds and the temperature of the bath at 2300 to 2500 degrees F.

The article is now removed upwardly through the slag in a manner to permiea smooth uniform layer of slag to adhere to the alloy steel coating. The coated article is then maintained in the cooler part of the furnace, in the reducing atmosphere, until the alloy steel coating solidifies free from bubbles to a uniform thickness or for about one minute. The final steps comprise removing the coated article from furnace 2 and cooling same in air or by quenching in water or oil. From time to time additional amounts of slag may be added and additional amounts of steel alloy charge preferably coated with water glass.

A typical charge of molten bath consists of 12 parts of steel. 12 parts of cast iron (or equivalent in steel and carbon) parts of ferromanganese, 5 parts of ferrochrome, 1 part bf carbon, 1 part of borax and 5 parts of water glass solution of 42 degrees B.

Another typical charge consists of 6 to 18 parts of cast iron (or equivalent), 6 to 18 parts of steel,

2 to 8 parts of ferromanganese, 2 to 8 parts of ferrochrome, .5 to 1.5. parts of carbon, .5 to 1.5 parts of borax and 2 to 8 parts of water glass solution.

It will be noted that the water glass solution is much larger in proportion to that of borax. If desired, small amounts of molybdenum (.5 to 5%) or cobalt (.5 to 5%) or titanium. (.2 to 2%) may be added to the typical charge noted just above. The borax may vary from to 25% by weight of the water glass-solution or its equivalent as dry water glass. Such proportion insures a relatively high melting point for the slag.

Our process of coating is equally adaptable to pouring the molten compound of alloy steel and slag onto the surface of the article to be coated and may be used,- preferably, when it is desired to coat a selected surface to a greater thickness than another. To this end, the selected surface is provided with narrow grooves, ridges, holes, or with raised boundary edges to retain coating compound. The article isfirst prepared by heating as described supra for the dipping process. A heating furnace l0 (Fig. 3) is suitable for the by gas or electrically. The article II to be coated is suported on refractory blocks 12, with the grooved surface ll facingtowards the inlet ll through which the molten coating compound is poured. A charge of alloy steel as described supra is melted separately in a suitable melting furnace from which it is conveyed by a ladle. The article I l be initially heated in position on blocks II to a temperature below its melting point or about a cherry red. The heating must be done in a neutral or reducing atmosphere. A charge of slag comprising carbon, borax and water glass is also melted in another melting furnace, from which the slag is ladled and poured directly onto surface l3 of the article and portions of this slag are retained within the grooves or holes or between the raised edges l5 according to which are provided. The molten alloy being heavier passes downward through the molten slag and into contact with surface I! of the article I l. The pouringof molten alloy is continued until same has contacted surface l3 sumciently long to insure a good bond between same and the article and to allow for refining so as to obtain an equal distribution thereof over the surface I) and to allow gas bubbles to'escape. Since the temperature of the furnace I0 is maintained below the melting point of the coating alloy, the refining process takes place before the coating alloy solidifies on the surface l3. The slag which rose to the top of the coating alloy being of a gummy constituency due to its relatively high melting point, remains on the surface of the'alloy coating when the coated article is removed from the furnace ill in a manner to prevent oxidation. This oxidation is further prevented in furnace ID by maintaining therein a neutral or reducing atmosphere or condition.

It will be noted that, in both the dipping and pouring method, the slag employed, the molten steel alloy employed and the non-oxidizing conditions are similar and common to both methods, and that these methods are generically the same, differing only in the manner of contacting the surface to be coated with the coating material.

It will be understood that variations may be made in the process herein described or in the relative proportions and nature of specific materials involved to an extent permitted by the scope of the appended claims.

What we claim is: 1 a V 1. A method of coating iron, steel or steel alloy articles with a coating of steel alloy which comprises heating the article to substantially a red heat, applying under reducing conditions to the surface of the article, a mass of molten material at about 2300 F. composed of 6 to 18 parts of iron, 6 to 18 parts of steel, ferromanganese 2 to 8 parts, ferrochrome 2 to 8 parts, carbon .5 to 1.5 parts, borax .5 to 1.5 parts and water glass solution 2 to 8 parts. a

2. In the method set forth in claim 1, wherein the article is immersed in the molten mixture for a predetermined time.

3. A method of coating articles of iron or steel comprising mixing a quantity of water'glass solution with portions of steel alloy, carbonand borax, heating said mixture to provide a molten compound, maintaining an inert atmosphere above the compound, heating the article to be coated to a point substantially below'its melting point, applying the molten compound to the surface of the heated article, then passing the coated article into the inert atmosphere whereby the steel alloy component of the compound forms a coating on the surface of the article.

5. A method of coating articles of iron, steel 2 or steel alloys comprising heating the article to substantially a red heat, subjecting the 'heated article to contact with a molten mass of slag comprising borax and water glass, subjecting the article to contact with a molten mass of alloy steel for a suflicient time to permit intimate bonding of a layer of the molten alloy steel to the surface of the heated'article, then passing the coated article into an inert atmosphere to permit the article to cool therein in a manner to emit gases from the coating and ensure a uniform coating.

6.. The method of applying a relatively thick hard and wear resisting coating of steel alloy to ferrous metallic articles which comprises heating the articles to a red heat, contacting the surface of the heated articles with molten slag material containing borax, then contacting said surface under reducing condition with a molten mass of -9. A method of coating iron, steel or steel alloy articles with a coating of steel alloy which comprises heating-the article to substantially a red heat, and applying under reducing conditions to the surface of the article a mass of molten material at about 2300 degrees F. composed of 12 parts of cast iron, 12 parts of steel, ferromanganese 5 parts, ferrochrome 5 parts, carbon 1 part, borax 1 part and water glass solution 5 parts.

CLEBURNE A. BASORE. DAN. 'r. JONES.

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