US 2786265 A
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March 26; 1957, 1.. K. KEAY, JR 2,786,265
PROCESS OF PRODUCING COMPOSITE METAL PRODUCTS Filed Feb. 5. 195a INVENT OR [at/A's fl /eeay, Tr.
BY lhgji ATTORNEY Unite PROCESS OF PRODUCING COMPOSITE NIETAL PRODUCTS Application February 3, 1953, Serial No. 334,827
8 Claims. (Cl. 2-470.9)
The present invention relates to the production of composite metal products and, more particularly, to novel improvements in the cladding of metals, such as plain carbon steel, with titanium metal as such, or in alloy form.
Metals such as steel clad with titanium are highly desirable for many uses; e. g., structural and fabricating purposes. However, in contrast to metals ordinarily clad to steel, titanium possesses certain unique properties which make it difiicult, if not impossible, to satisfactorily bond to steel using conventional pack rolling procedures. This difficulty is particularly apparent when the clad product is exposed to a subsequent heating operation, as for example, when the same must be welded to another article. The properties which make titanium diflicult to clad are: the great affinity of titanium for oxygen, nitrogen, hydrogen, water vapor, carbonaceous gases, and the like, at temperatures above about 1300" F., the high rate of inter-diffusion between titanium and most other metals having melting points compatible with steel fabricating and end-use temperatures such as copper, iron, nickel, molybdenum, and silver and the existence of brittle inter-metallic compounds in the alloy systems of titanium with the above-mentioned metals.
The reactivity of the titanium with most gases except those which are normally considered inert, such as helium and argon, is not the sole source of ditficulty in cladding titanium despite the fact that solution of these gases in titanium results in embrittlement, and surface films form. Another source of difficulty in cladding titanium to steel is the fact that diffusion is very rapid between titanium and other metals when the latter are brought into contact at elevated temperatures (e. g.,
emperatures around 1300" F. and higher). This results in a formation of inherently weak and brittle intermetallics of the titanium and steel or other metal. cordingly, if an attempt is made to clad steel with titanium by rolling a pack of these metals in the usual manner, a weak alloy will form somewhere in the diifusion zone between the titanium and steel during the rolling or preliminary heating of the pack. Hence, no bond whatsoever, or at best, an unsatisfactory bond especially when the product is reheated, is obtained.
It has now been found that the undesired diffusion referred to above and the other characteristics of titanium which have limited use of this metal for cladding purposes can be satisfactorily overcome by making certain critical modifications in conventional pack rolling procedures.
Accordingly, the principal object of the present invention is the provision of novel improvements in the cladding of a metal with titanium.
A further object of the invention is the provision of novel procedures for cladding metals with titanium, said procedures being free from the disadvantages noted above.
A more specific object of the invention is the provision .of improved pack rolling procedures for satisfactorily cladding steel and other metals with titanium.
rates atent Other objects and advantages of the invention will become apparent from the following detailed description thereof, taken in conjunction with the accompanying drawings, wherein:
Figure 1 represents a sectional view of a multiple pack, and
Figure 2 represents a sectional view of another pack, according to the invention.
Broadly stated, the foregoing objects are realized by a process involving the steps of forming a pack including a base layer of steel, or other metal, and a titanium cladding layer separated by an intermediate or barrier layer of the type described below, and thereafter subjecting the pack to two successive heating and pressure, e. g. rolling, treatments.
The barrier layer utilized in forming the pack should be an iron-chromium alloy, and any such alloy which man be hot rolled at the necessary temperatures may be utilized for this purpose. Thus, for example, ironchromium alloys containing from 11 to 30% chromium are suitable, although other iron-chromium alloys having a chromium content outside the above-mentioned range may also be used. Specific illustrations of suitable barrier layers are the 405 and 4 l0 types of stainless steels. These barrier layers, aswell as the titanium and base metal layers, need be of no particular dimensions; e. g., thickness to obtain the desired results.
Referring to the accompanying drawings, the pack formed according to the present disclosure may be of multiple ply, as indicated in Figures 1 and 2, respectively. To form the pack, the surface of the plate of steel which is to become the backing or base layer 2 is first cleaned mechanically or chemically, e. g. grit blasted, hydride descaled or pickled. Thereafter, a sheet 4 of workable iron-chromium alloy is placed on the cleaned surface of the base 2. The alloy may be nickel plated on the side placed in contact with the backing steel. Preferably, however, a sheet 4 of carbon steel clad with the desired alloy is used, said sheet having been carefully cleaned by conventional chemical or mechanical means and being so positioned on the base layer 2 that steel contacts steel.
Thereafter, an appropriate titanium cladding layer 6, also carefully cleaned, is placed on the iron-chromium alloy surface. As shown in Figure 2, a suitable parting composition 3 should be applied to the titanium surface to be separated. As the parting composition, any desirable separating medium may be utilized provided it does not react detrimentally with the titanium. A typically suitable parting composition consists of a suspension of graphite in water.
With the pack of Figure 2,.a second cladding layer 6', barrier 4 and base layer 2' respectively, are superimposed on the titanium layer 6. The assembly shown in Figure 1 is completed with a metal cover plate 9 which is secured to the base layer 2 by suitable metal intermediate spacer members 10, generally of the same material as the base layer, the same being welded as at 12 to the cover plate 9 and base layer 2 for the purpose of sealing the pack. Similar spacer members 10 are welded to the base layers 2 and 2' of the arrangement in Figure 2. The members it in either arrangement, are provided with conventional means 14 for circulating an inert gas through the pack to minimize undesirable gases, fumes, and other contaminants which react with titanium. v
After the pack is completely assembled, it is exposed, as indicated above, to two successive heating and pressure treatments, The pack is initially heated at 1350-} 1700 F. using a minimum heating period, which should not exceed the time necessary to obtain uniform heating. It is preferred to limit the initial heating timevto about an hour per inch of pack thickness, but satisfactoryresults can be obtained using other heating times; e. g., from /2 to 1 hours per inch of pack thickness.
A flow of argon or helium gas is maintained through the assembly during this heating period. This gas may be ordinary welding grade purity and serves to minimize gaseous .reactions on the titanium surfaces within the pack. The pack is then reduced by rolling, forging, or pressing. The amount of, reduction taken can be widely varied but should be less than 50% of the total scheduled reduction for the pack but greater than 10%. This pressure treatment is important to the attainment of a satis factorybond between the titanium and iron-chromium layer. The bond excludes gases, and thus further surface reactions and alloying with gases is eliminated.
The partially reduced, pack is then reheated in the temperature range of 1350 F. to 1700 F. and prefera 1y within the range of 1550-1650 F. This second heating operation is critical to the success of the invention, the purpose thereof being to dissolve impurities on the titanium and iron-chromium alloy surface. If this is not done, or if the reheating time or temperature is inadequate, no bonding or only very weak bonding will occur. On the other hand, if the reheating temperature and/ or time is too great, excessive alloying will take place, and the resulting bond again will be weak. In this connection, it is to be noted that the most suitable reheating temperature has been found to be about 1600 5.; although suitable results are obtained using any temperature within the range stated above. The heating period should be between /2 hour and 1 /2 hour per inch of pack thickness, with about 1 hour per inch of pack thickness being the preferred time. Due to bonding from initial heating, no inert gas is required during the second heating operation.
After the pack has been reheated, it is again subjected to rolling, forging, or pressing, to complete reduction of th e pack to the desired dimensions and effect the bonding.
As the backing layer, there may be used any metal or alloy which normally can be bonded to plain carbon steel in the temperature range employed (1350-1700 F.).
Hence, while the invention is most readily applied to plain carbon and low alloy steels, such metals and alloys as nickel, Monel, inconel, stainless steel, and copper can besatisfactorily bonded to titanium.
It will be appreciated that the cladding layer utilized in the present invention may be pure or substantially pure titanium or an alloy of titanium. As typically suitable titanium alloys, there may be mentioned the commercially available alloys containing iron, nickel, molybdenum, tungsten, chromium, manganese, aluminum. and vanadiuni.
The invention described above is further illustrated by "the following example:
Example A2 01 st el anes (dimensions of about .5 x 70 2 so i'n'ch'e's) were cleaned on one side by pickling. Two tita 'iuriifsheejts '(iilmensions of about x 62 x 72 inches) "'nd two 10% by thickness or the Cr-Fe alloy plain carbon steel) tyne 405 stainlessclad barrier sheets (having dimensions of about ,46 x 62 x 72 inches) we're also cleaned on both sides by pickling.
One 'of the barrier sheets was then placed on the clean steel surface with alloy side up. Thereafter, one of the titanium sheets or inserts was placed on the T405 barrier shelet'. gra hite suspension in water was then applied to the titanium surface by painting.
The second titanium insert or sheet was then placed on the graphite surface and the second T405 barrier sheet positioned thereover with the chromium-iron alloy layer of the barrier sheet contactin the titanium. Appropriate spacer bars or plates were then positioned on the steel layer about the titanium and T405 clad sheets, these plates n inlet outlet for gaseous flushla fe s' steel sheets welded to- '11 pack "st 1 /2 rashes.
The pack was thereafter placed in a furnacp at a tem; perature of 1500 F., kept therein for about 1 hour, and flushed with argon continuously during this time. Thereafter, the pack was rolled to 1 inch gauge (1.5 to 1 inches). The pack was then reheated at 1600 F. for 1 hour, rolled to (2.50 inch gauge, and the ends of the pack thereafter sheared to give a titanium clad steel sheet possessipg a bond shear strength in the neighborhood of 20,000-- 30,000 p. s. i. even when again heated.
It will be appreciated from theforegoing that the success of the present invention resides, at least to a substantial extent, in two features; namely, the use of an iron-chromium alloy as a barrierlayer between the cladding metal and the backing metal and the application of two separate heat and pressure treatments to the pack. The combination of these features has been found to satisfactorily avoid the undesired diffusion which has previously occurred in titanium cladding procedures and to avoid the formation of brittle inter-metallic compounds. The results obtained using the above-mentioned features are indeed surprising, as evidenced by the fact that when iron or chromium, and even such metals as nickel, is utilized as the barrier layer, or the designated dual heat and pressure treatments are not effected, satisfactory bonds, e. g.; bonds which will stand up in usage and maintain their physical characteristics upon reheating, cannot be obtained. For instance, if iron is used as the diffusion barrier in making titanium clad steel, the bond shear strength ofthe resulting product deteriorates severely when heated to a temperature of about 1500 F. and in the case of nickel, the product will substantially fall apart. This is in complete contrast to the results of the present invention wherein bonds demonstrating shear strengths of about -20',000-30,000 p. 's. i., even after again reheating to 1500" F., are obtained.
Referring to the barrier layer, it was mentioned that iron or chromium alone do not give completely satisfae tor y results. This is primarily so due to, in the case of iron, the rapid formation of brittle alloys at elevated temperatures and, in the case of chromium, its lack of ductility. Incidentally, iron-chromium alloys containing from 1-1 to 30% chromium are preferred, for one reason, due to the commercial availability of alloys of this chromium content. As to bonds which will stand up in usage referred to above, it is meant bonds which will maintain their strength in uses involving heating, such as for hot-forming.
It is to be understood that various modifications may be made in the invention as described herein without deviating from the scope and spirit thereof as defined in the appended claims.
1. A process for producing a composite metal product including a metal base layer and a titanium cladding layer which comprises forming a pack of said layers separated by a barrier layer having an iron-chromium alloy abutting the cladding layer and preferably of a chromium content within the range of '11 to 30 percent, heating said pack in an inert gas protective atmosphere at a temperature between 1350 F. and 1700" F, subjecting said heated pack to pressure to effect partial reduction thereof, thereafter again heating said pack at a temperature between 1350 F. and 1700 F. and subjecting said reheated 'ii'a'ck to pressure to complete reduction thereof and ease: bonding between the cladding layer and base layer.
2. The process of claim l, wherein the second heating of the pack is carried out at a temperature between 1550 F. and 1650 for a period of between /2 and 1 hour per inch of pack thickness.
3. The process of claim 1, wherein the base layer-coinprises steel.
The process bf than 1, ein the titanium use ding layer is substantially ure titanium.
5. The process of claim 1, wherein the titanium cladding layer is a titanium alloy.
6. A process for producing a composite metal product including a metal base layer and a titanium cladding layer which comprises forming a pack of said layers separated by a barrier layer having an iron-chromium alloy abutting the cladding layer and preferably of a chromium content within the range of 11 to 30 percent, and thereafter subjecting said pack to two distinct and successive heat and pressure treatments, the first such treatment comprising heating said pack at a temperature between 1350 F. and 1700 F. in an inert gas protective atmos phere for a period Within the range of one-half to one and one-half hours per inch of pack thickness and subjecting said heated pack to pressure sufficient to effect partial reduction thereof, said second treatment comprising heating said pack at a temperature between 135 0 F. and 1650 F. for a period within the range of one-half to one and one-half hours per inch of pack thickness and subjecting said reheated pack to pressure sufficient to complete References Cited in the file of this patent UNITED STATES PATENTS 625,117 Martin May 16, 1899 1,190,412 Hudson July 11, 1916 1,228,194 Fahrenwald May 29, 1917 1,886,615 Johnson Nov. 8, 1932 2,416,400 Mehl Feb. 25, 1947 2,619,715 Barr et a1. Dec. 2, 1952 2,707,323 Watson May 3, 1955