US1331888A - Coated strain-hardened metal - Google Patents

Description

UNITED STATES PATENT oEEicE.

WILLIS R. WHITNEY, 0E msxarnm, NEW Yonx, nssrenon. '10 GENERAL ELECTRIC comm, A conrona'rron on NEW Yonx.

COATED STBAiN-HAB-DENED METAL.

No Drawing.

To all whom it may concern:

Be it known that I, WILLIS R. Wnrrnnr, a citizen of the United States, residing at Niskayuna in the county of Schenectady,

State of New York, have invented certain likewise greatly reduced the tensile strength.

Experiments which have been made indicate that the deleterious effect is connected in some way with the generation of'hydrogen at the surface of the ferrous metal.

I have discovered that this deleterious effect may be obviated by providing metal under strain before being subjected to a hydrogen-generating bath, with a coating of material which is substantially impervious to nascent hydrogen, for example, metallic tin. The metal thus coated may subsequently be electro-plated without any deleterious effects upon its mechanical proper ties.

In carrying out my invention which includes both a process and a new article resultin therefrom, the metal to be coated is pre erably first cleaned mechanically, for example, by sand blasting, and is then dipped, in the presence of a suitable flux, into a coating metal. When thus treating a metal such as spring steel which has been given a temper or set under strain, it is necessary that a plating material should'be chosen which has a melting point below the temperature at which the metal has been tem ered. In case of sprin steel the tempermg tem rature is somew ere about 300 0. As tin as a melting point of 232" and as it can readily adhere to a clean surface of ferrous metal, it is particularly well suited for the purpose of my invention. The

' cleaned steel springs or other strain-hardened articles to be coated, may be d pped Specification of Letters Patent.

sequent c Patented Feb. 24, 1920.

Application filed June 15, 1918. Serial No. 240,177.

into the tin bath in the resence of rosin or other suitable flux. ubsequent to the tinning operation the steel articles may be electroplated in the usual way, for example, with copper, without impairing their mechanical properties.

The followin specific figures will illustrate the bene ts of my invention. Two steel springs were selected from a lot of springs, samples of which upon test had broken on the testing machine with a ull varying between 310 and 439 pounds. he selected test springs were made cathode for one-half hour a copper cyanid solution and when tested were found to break at 69 and 137 pounds pull respectively. 'The electrolytic treatment had reduced the breaking strength to about 22% and 31% respectively, of the average value of strength of similar untreated sp Furthermore, the copper plated samp es stretched very little before they broke, while the untreated stretched one or two times their original length. Two more test springs were pickled respectively for three minutes and one hour in a 20% sulfuricacid solution. The sample pickled for three minutes broke at 198 pounds showing a reduction of strength to 50% of the untreated value and the second sample pickled for one hour, broke at 29 pounds with a reduction in strength to 7% ofthe untreated value. The latter sample had been reduced by but one-thousandth of an inch in diameter by the action of the acid, which clearly shows that diminution of size does not account for the weakening of the metal.

Additional samples of steel springs were first sand blasted, dipped into molten resin and then into molten tin heated to a temperature of about 260 to 300 C. After having been tinned the samples were copper plated in the same solution used for copper plating the test samples above described. These tin plated samp es showed a breaking strength ranging from 318 to 417' pounds, all

strength values obtained for the untreated springs, In other words, the mechanical properties of the samples had not been appreciablyaffected by the tin treatment and these properties were retained during a subectrolytic treatment.

. Although I have described the benefits of my'invention with particular reference to strained spring steel, I desire it to be under stood that my invention is also a plicable with beneficial result to other f drms of strain-hardened, steel, for example, steel articles of various sorts which have been formed by cold ressi or otherwise strained beyond their elastic limit.

What I claim as new and desire to secure 4 by Letters Patent of the-United States, is

1. The process of reventing ferrous metal while under strain rom becoming brittle by .the action of a hydrogen-generating agent.

which consists in providing said metal with a coating of material which is substantially impermeable to hydrogen, and then subjecting the metal to said agent. 4

I 2. he process of electroplating strainhardened ferrous metal which consists in v first providing said metahwith .a coating of conductive material such as tin impermeable to nascent hydrogen whilepreventing electrolytic action, andthen subjecting to a desired electro-plating treatment.

3. The process of preventing strain-hardened steel from becomin brittle by the action of an electrolytic bat which consists in roviding said steel with a coating of tin while preventing the generation of hydrogen at the surface of said steel, and then subjecting the coated steel to the desired electrolytic treatment.

' 4. The process of plating strain-hardened steel by. electrolysis which consists in applying to said steel a coating of tin in the absence of an agent generatlng'hydrogen, and then applying a desired metal by electroly- SIS.

5 The process of coating steel springs which consistsin mechanically cleaning said springs, applying a ,coating of tin in the presence of a reslnous flux and then applying a desired coating of metal by electroly- SIS. K

' 6. An article of manufacture comprising ferrous spring metal, a coating of tin thereon and a coating of electro-deposited metal upon said tin, said metal having substantially the same mechanical .roperties as unplated metal of the same 0 aracter.

7. An article of manufacture, comprising a steel spring, a coating of tin thereon, and a coating of electro-deposited copper upon said tin, said spring having substantially the same mechanical PI'QPQIQIGS as unplated steel of the same character.

8. An article of manufacture, comprising a strain-hardened ferrous metal, a coating of conductive material substayally imper- "meable to hydrogen upon sai