US1578254A

US1578254A - Protection of metals against corrosion

Info

Publication number: US1578254A
Application number: US722462A
Authority: US
Inventors: Irving T Bennett
Original assignee: Individual
Current assignee: Individual
Priority date: 1924-06-26
Filing date: 1924-06-26
Publication date: 1926-03-30
Anticipated expiration: 1943-03-30

Description

March 30 1926.

l. T. BENNETT PROTECTION 0F METALS AGAINST CORROSIN Filed J 26 1924 i Snom/ttor /rU/ng 7156/7/76# 3g) fbi@ w 47 LW Passata M". 3o,` 192e.

'UNITED STATES PATENT'oFFlca.

IR'VING T. BENNETT, 0l' BROOKLYN, NEW YORK, ASSIGNO TO THOHAS E. IUR'RAY',-

Ol' BROOKLYN', NEW YORK.

PROTECTION OF KETALS AGAINST COBBOSION.

Application Medlime 26, 1924. Serial lo. 788,462. j

To all whom it may concern.' v

Be it known that I, IRVINe T. BENNETT, acitizen of the United States, and a resident of Brooklyn, county of Kings, "and State of New York, have invented certain new and useful Improvements in the Protection of Metals Against Corrosion, of which the following is a specification.

When steel and other metals are subjected to high temperatures the tend to oxidize more rapidly than at or inary atmosheric temperatures. Various methods have geen devised for treating steel to increase its durabilit under such conditions. The most successfu of such methods have involved the formation upon the surface of the steel of a continuous, adherent film of oxide, which is non-porousand of low ox gen solubility. 'This film thus protects t e underlying metal from further oxidation.

In practice I have found that the best of the known methods is effective only at moderately high temperatures, and that at exceedingly high temperatures the surface protection isl not durable. My present invention aims to provide a surface rwhich shall be durable at vexceedingly high temperatures and which can be economically ap lied to steel, or iron, or similar metals; suc as, for examine, low carbon steel. I have demonstrate' its success particularly with boiler tubes made of steel containing 0.15 to 0.20 per cent carbon. The invention is of particular Ivalue in connection with tubes provided with fins, as described in application No. 715,369, andY other applications, of Thomas E. Murra These tubes have longitudinal fins wel ed on to them and are inv some cases located in the boiler furnace and exposed to the radiant heat of the burning fuel, so that they maybe heatf ed to an exceedingly high temperature, appreaching 2500 degrees By treating such ns in accordance with the present invention, their durability under such conditions is eatly.- increased.

he articles of steel protected by the process are adapted also to various other uses, havin a surface which is practically non-corrodl le under ordinary conditions. The treatment ma in fact, be so ap lied as to make the articls practically inso uble in all acids, exce t forvv'e slow solubility in aqua regia an hydroch orio acid. The acof chromium 2. The rod thus produced is then electroplated to provide a second coating 3 of nickel.

The article with these coatings deposited thereon, is then heated for two hours or' more to a temperature in the range 1800 de! grecs F. to 2500 degrees F. in an oxidizing atmosphere. In this heating operation there are formed apparently alloys as indicated in Fig. 2. The outer surface is covered by a very thin continuous film ofextremely adherent oxide indicated by the heav line 3, which has practically the same coe cient of expansion as steel, and which is very dense or non-porous. This isy probably a mixture of nickel oxide and chromium oxide intimately dispersed and of low oxygen solubility.v I mmediatel coating 4, in all proba ility an alloy composed chiefly of nickel and chromium, in solid solution, which adheres closely to an inner coating' probably composed chiefly of iron and chromium in solid solution; which in turn adheres closely to the steel 1. After heating it will be noted that there are two different layers. But these are not of the same composition as before heating. The' outer layer 4 has a hi h resistance to acids and to extensive oxidation; whence, and from its appearance, I conclude that it is an alloy of nickel and chromium in solid solution similar to known alloys of these two metals. f

The inner coating 5 merges `into the steel in an ill-defined line. In someplaces the microsco indicates the formation of pearlite litween this inner coatin steel `foundation. The coating 5 1s apparently an valloy composed chiefly of iron and chromium in solid solution, bein hard to etch and resistant to' corrosion. hromium below` this is theprotected in accordance with the of carbon, is electroplated to form a coating and the e Yiis iron into each other.

in this inner coating is also indicated-byk the ,formation of pearlite referred to, it being known that chromium lowers the eutectoid composition and permits the formation of more pearlite than in the case of ordinary carbon steels of a similar carbon content. Y

Chromium and iron alloy in th solid state when heated together under pro r conditions of contact and atmosphere. ut unless the conditions are reducing, the clito-- mium oxidizes and union with iron does not take. place. In my process the outer layer of nickelprotects -the chromium fr omcxidation during the .heatingi operation and gives it a chance"topenetrate the steel and alloy with it.n At the same time the chromium alloys with the nickel toform a heatresistant alloy which together with the thin 'lm ofadherent oxide aforementioned further protects the chromium -iron alloy, which directly' protects the steel. It is probable that migration of the chromium and nickel into each other is more rapid than the migration of the chromium andV Thus the chromium coating is .promplgr vprotected and time iS givenfoi'` the for ation of the iron chromium alloy.

The steel. with the chromium and the nickel coating deposited thereon may be considered lthe finished product, ready to beput into use where it will be subjected to high temperature. In that case` the conditions of use: will lix the coatings bythe oxidizing and lalloying eiects which have vbeen referred to.

Or the article coated withchromium and nickel ma be heated to fix the coatings as described fore itis put into use; In eati ing the coated articles it is Iireferable to luse an oxidizing atmosphere for, as previously mentioned, the success of the process depends on the 'formation of a pro r oxidev coatin together with alloying e ects produced y the heating.

Chromium is preferred because -it is highlly resistant to heat and because it combines readily with iron to-'formuhigbl non-corrosive alloys, some common y own.- as stainless steel. Nickel is preferred for the outer. coating because it readily combines with chromium to form highly resistant ale 4invention may be applied,l however,- with other materials than chromium land nickel. Also, though I have foundv electroplating a' convenient method of applying the metals, yet the .may be applied in other known or-suitab el ways.

The process is not confined to a single coating of each metal.' There' ma be several. coats of each metal, the two ing-deposited alternately; and indeed other metalsmay be added. As an example of the method of depositving the chromium, a bath the followingcomp'osition:

Chromic acid, 200-250 grams; chromium sulphate, *4 grams; water, 1000 cc.; anode wof chromium; cathode'of steel; cathodecur-` rent density per sq. ft. 100 amps.' solution E. M. volta f I have found that two hoursA bath willl give a satisfactory deposit, and

that agitation will aid this deposition.

in such a4 used may be of Y .An example of the 'method of depositing 1it)heh:nckel involves the use ofthe following Boric acid, l5 gm.; nickel-ammonium sul phate, gm.; ammonium chloride, 15 gin.; water, 1000 cc.; anode of nickel; cathode.

Lof chromium deposited on steel; cathode current density (amps. per sq. ft), 2-3; so-

lutioii E. M. F., 1.5,volts.

Two hours in this bath givesa satisfactorydeposit.

In usinga greater number of coatings I propose, afterthe first compoundcoating of chromium and nickel, to coat in succession with chromium, iron, chromium and nickel, repeating thisseries a'sdesired;the`

purpose of the iron being to alloy with the chromium on either side of it so that the heated article will consist of several layers i of the two different alloys.4 Though the above order of deposition of the various metals is preferred,'any other order which gives satisfactory results maybe used; that is, the nickel may be deposited on the iron and the chromium on the nickel, with` but sli ht dierence in properties.

have subjected test pieces made as above with asingle coating of the chromium and nickel to temperatures of 1800 and 2200 degrees F. vfor two hours in an oxidizing-atmosphere and found the article to maintain a good looking surface withh oxidation to a depth of only about one ten-thousandth of an inch; whereas the same steel, untreated, subjected to the s'ame testwas oxidized to a depth of from three hundredths to seven hundredths .of an inchv and badly scaled. With a temperature of about 2500 degrees F.

for half an hour ordinary steel was badly derlying steel. I have'subjected test pieces madeas above with a sing e coating of the chromium 'and nickel to -ter'nperatures of,

1800 to 2300 degrees F.' for 576 hours in an f oxidizing atmosphere land found the article to maintain a' d looking surfa with 'ox-- idation to a depth of only one ten-thousandth of an inch; whereas the same steel untreated subjected to the same test was entirely destroyed rby oxidation2 burning u completely. Articles coated with chromiui y isc corrosion-resisting and acid-resisting ro crties of the coated steel to be very high Taking a lsample which had been electroplated as above described and then. heated in an oxidizing atmosphere to cause the oxidizing and alloying action, I immersed it in various acids and compared the results with those obtained by similar tests on coininercial acid-resisting metals, chromium,

nickel and alloys of nickel and chromiumy and ofl chromium and iron. Steel treated in accordance with the invention and heated to 1832 degrees F. for two hours showed a resistance to corrosion equal to that of chromium in -all acids except concentrated hydrochloric acid in which it far surpassed chromium, being practically insoluble while the chromium rapidly dissolved. In fact, the protective coating on the steel treated according to` this. invention may be made to approach platinum in resistin acids. .This resistance is due, in all robabi ity, chiefly to insolubility of the oxi efilm'and, secondly,

to the two alloys underlying this film which are in themselves very similar to commercial resistant alloys.

l The' corrosion resisting pro rties of the treated vsteel make it .valuab e in laboratories and workshops where strong acids are y practicall or `substantiallyl its entire employed or where, because ofthe corrosive fumes presentfit would be impossible to use untreated steel.

The invention may be applied also to jthe protection of a. piece of lmetalmadeup1 vk t ic ' ness by t is process; that is, starting with vthickness of the a small core and building up with successive coatings to the desired size. For example,

the fins 8 of Fig. 3 might be madeup".-

throughout all or the greater partof their successive coatings -diescribed above. 1

I have stated above my theory as towhattakesplace in theV application of my process'. And it seems clear that the process is de-v pendent on the didusion of metals in the solid state, resulting in the formation of alloys or series of alloys which are extremelv ture applied and the length of time of its application, and the product may vary in this respect within a considerable range.

for,

Such a variation is'to be expected-,also where the metals used are of different compositions. For example, I have referred to steel or iron or similar metals, which I may include in the term ferrous metals, and Ihav'e got-ten satisfactory protective results with both cast iron and wrought iron.- But I should expect the direct results of the treatment1 to be different for each of these base` meta s.

The invention contemplates not only the use of nickel but also the use in the sameA way 'i'or of equivalent metals; that is, metals closely allied in their chemical and physical properties, belonging to the same chemical grouD and occupying similar places in Mendele jcis periodic table.

Though I have described with great particula-rity of detail certain embodiments of my invention, it is not to be understood therefrom, that the invention is restricted to the embodiments illustrated. Various moditications thereof maybe made by those. skilled in the art without departing from the invention as defined in the following v claims.

What I claim is: l. The method of protecting the surface of ferrous metal, which consists in applying chromium thereto and applying a protective i layer over the chromium.

2. In the protecting of the surface of fertous metal, the method which consists `in ap'- plying chromium thereto and applying nickel over thechromium.

3. The method of protecting the surface of ferrous metal, which consists in applying chromium thereto and applying to the surface an adherent oxidecoating.

4. The method of protecting thesurface of ferrous metal, which consists in applying chromium thereto' and applying a protective layer over. the chromium, and heating the article to` cause 'thealloying of the iron andr chromium, and to` form on the outside an' adherent oxide coating; l

j 5 The vmethod of protecting the surface of ferrous metal, which consists in applying chromium thereto and .ap 'lying nickel over tlie'chromium, and heating the article to cause the alloying of the iron and chromium and of the chromium and nickel, and to form on the outside an adherent oxide coating.

f A,6. The method of protecting the surface l of ferrous metal, which consists in applying thereto electrolytically .a coating of chroinium, protecting the latter by an outer coating, and heating Athe article to cause the chromium to alloy'with the iron, and to c form on4 the outsid resistant to oxidation and yto. acids. .But

such diffusion is dependent on the tempera# e anl adherent oxide coating;

7. T e method of protecting the surface of ferrous metal', which consists in applying thereto electrolytically a coating of chromiuin, applying an outer coating of nickel to 'thachfomiummdvhming the miele u cause the chromium-to alloy with the iron and the nickel to alloy with thel chromium,

` :fand4 to form on the 'outsidef'an adherent plying a' coating of chromium to ferrous metal and 'a coating of nickel to the chrog 9.' The method of producing; composite.

piece of metal which consists in applymn coating of chromium to ferrous an navega'.

coating of nickel to the chromiu'm'and heat ing the same to cause an alloying of the iron la and chromium `und of .the y chromium and A nickel and to cause the formation of anou`t sidevcoeting of adherentl oxide.

10. The method of rotecting the of ferrous metal whic "consists'in applying 2 thereto rotective la .one of chromium and anotlher of nickel.

In witness whereof, I have hereunto signed 'IRVING pr;-lim'nifr'r.r