GB2113577A

GB2113577A - Method of overlaying stainless steel material with a precious metal alloy

Info

Publication number: GB2113577A
Application number: GB08201523A
Authority: GB
Inventors: Akira Shibata
Original assignee: Chugai Electric Industrial Co Ltd
Current assignee: Chugai Electric Industrial Co Ltd
Priority date: 1982-01-20
Filing date: 1982-01-20
Publication date: 1983-08-10
Also published as: GB2113577B

Abstract

In order to overlay a stainless steel material for decorative articles and ornaments with a precious metal alloy, a comparatively thin layer of the alloy or a plurality of constituent thin layers of the alloy are overlaid on a selected surface of the stainless steel and heated to a temperature higher than 800 DEG C for the diffusion bonding of the layer or layers to the stainless steel body and for annealing of the body, and thereafter another thicker layer or constituent layers of a precious metal alloy are overlaid on the stainless steel material with or without heating the second mentioned layer or layers.

Description

SPECIFICATION Method of overlaying stainless steel material with a precious metal alloy This invention relates to a method of overlaying a stainless steel material with a precious metal alloy, in particular overlaying a stainless steel material for decorative articles and ornaments with an Au, Pt and/or Pd based alloy.

U.S Patent Application Serial No. 1 50 1 90 of May 15, 1 980 describes a method of overlaying an austenite stainless steel material for decorative articles and ornaments with an Au, Pt, and/or Pb based alloy, which comprises plating selected surfaces of the stainless steel material with the constituents of the alloy in any desired order, one at a time in a plurality of successive layers, the respective layers being of a thickness and volume which correspond to the constituent ratios of an alloy of desired purity and dimension, and heating the layers to a temperature sufficient to cause them to alloy in the liquid phase.

We have now found that the Au, Pt and/or Pb based alloy which is overlaid on an ingot of stainless steel material by the aforementioned method for fabricating decorative articles and ornaments, such as spectacle frames, watch casings and watch bracelets, does not sometimes present the originally required colour when the stainless steel material overlaid with the alloy is subjected to a temperature which causes it to alloy in the liquid phase, viz. a temperature higher than 800'C. This is because when an alloy of the aforementioned kind is heated to a temperature higher than 800on, its diffusion into the stainless steel occurs, while constituents of stainless steel such as Fe, Cr, Ni and others which are activated by Au, Pd and/or Pt at an elevated temperature diffuse into the alloy also.Such diffusion is advantageous for firm diffusion bonding between the stainless steel matrix and the overlaid precious metal alloy, but is disadvantageously discolours the alloy.

Annealing is often required for a stainless steel material either of austenite or ferrite in order to reduce or avoid its working hardening, i.e. increase its workability. Unless annealing is effected in the case of stainless steel matrices overlaid by precious metal alloys, the alloy will come off from the matrix when it is subjected to a bending test, because of the hardness of the matrix. If mild stainless steel materials which do not require annealing are employed, they are very suceptible against sweat from the wearer of such a decorative article.

Annealing which is carried out at a temperature higher than 800"C in case of austenite, ferrite or martensite stainless steel for increasing their workability is, however, accompanied also by the diffusion of Fe, Cr, Ni and other contents of stainless steel material into an Au, Pt and/or Pd based alloy, which diffusion discolours the alloy.

The present invention provides a method of overlaying a stainless steel material for decorative articles and ornaments with an Au, Pt and/or Pd based alloy, which comprises bonding at least one selected surface of a stainless steel material with a thin layer of a said alloy or with the constituents of a said alloy and heating to a temperature higher than 800"C to effect diffusion bonding and/or annealing, and overlaying the alloyed surface with a thicker layer of the said alloy or with the constituents of the said alloy without heating or with heating at a temperature lower than 800"C.

In order to overlay a stainless steel material for decorative articles and ornaments with a precious metal alloy by the method according to the invention, a comparatively thin layer of the alloy or a plurality of constituent thin layers of the alloy are overlaid on a selected surface of the stainless steel and heated to a temperature higher than 800"C for the diffusion bonding of the layer or layers to the stainless steel body and for annealing of the body, and thereafter another thicker layer or constituent layers of a precious metal alloy are overlaid on the stainless steel material with or without heating the second mentioned layer or layers.

Thus there is provided a method of overlaying a stainless steel material for decorative articles and ornaments with an Au, Pt and/or Pd based alloy, in which the top layer of alloy will not be discoloured, firm diffusion bonding of the alloy to the stainless steel matrix is obtained, and the overlaid stainless steel matrix has good workability for being rolled or pressed.

In the method of the invention, a base or barrier thin layer or layers of an Au, Pt and/or Pd based alloy are bonded upon a stainless steel matrix body and heated to a temperature higher than 800"C, and thereafter a thicker top layer or layers of an Au, Pt and/or Pd based alloy are overlaid upon the base or barrier layer, whereby the discolouring of the top layer is prevented, and the base or barrier layer is firmly diffusion bonded to the stainless steel material while the stainless steel is annealed so as to have a good workability.

The invention will be further described with reference to the following illustrative Examples.

EXAMPLE 1 A wire having a rectangular cross section of 4mm in height and 4mm in width of austenite stainless steel (SUS 316-L) was plated with layers of Au, Ag and Cu over its upper half surfaces, while its lower half surfaces were masked. The total thickness of these layers was 2 microns and their total constituent amounts corresponded to a 2N-18 gold alloy, viz. 75 weight per cent of Au, 1 5 weight per cent of Ag, and 10 weight per cent of Cu.

This wire was placed in a furnace under a hydrogen atmosphere at a temperature of 950"C for 5 minutes. The layers which were solidified upon the stainless steel wire had a milky gold colour. The wire was annealed. A microscopic examination and EDM analysis showed that about 5 to 10 per cent of the constituent elements of the stainless steel material had diffused into the alloy overlayer.

The wire was semi-immersed in synthetic sweat at a temperature of 50"C for 7 days; no rust was produced.

The thus intermediately processed wire was cold-pressed by tandem rollers so that its height was reduced to 3mm, while the hardness of the stainless steel was increased from Hv. 1 70 to Hv. 280.

Au, Ag and Cu layers having a total thickness of 9 microns, the total constituent amounts of which corresponded to a 2N-18 gold alloy, were plated over the wire. The wire was kept under vacuum 10-4 at 750"C for one hour. The stainless steel has a hardness of Hv. 250, and its outer layer had a brilliant golden colour. The wire was rolled so as to have a height of 2 mm. The wire was annealed at 750"C for 3 minutes, and its hardness was reduced to Hv. 220.

This wire was subjected to tests of (1) twisting through 180 four times, (2) bending through 90 with the plated surface up and (3) immersing into synthetic sweat for 7 days at room temperature. The results of the tests (1) and (2) showed no physical change of the wire, and after the test (3) no rust was observed.

EXAMPLE 2 The intermediately processed wire of Example 1 was press-bonded with a tape of 40 microns of a 2N-18 yold alloy over its plated layer by passing it through a hydrogen atmosphere kept at 750"C. The wire was rolled so that its height was reduced to 1 mm of which the alloy layer comprised 10 microns, and was thereafter annealed at 750"C.

This wire was subjected to the same tests as in Example 1. The results obtained were as good as in Example 1.

Claims

1. A method of overlaying a stainless steel material for decorative articles and ornaments with an Au, Pt and/or Pd based alloy, which comprises bonding at least one selected surface of a stainless steel material with a thin layer of a said alloy or with the constituents of a said alloy and heating to a temperature higher than 800"C to effect diffusion bonding and/or annealing, and overlaying the alloyed surface with a thicker layer of the said alloy or with the constituents of the said alloy without heating or with heating at a temperature lower than 800"C.

2. A method as claimed in Claim 1, further comprising annealing the said surface overlaid with the said thicker alloy layer at a temperature lower than 800"C.

3. A method according to Claim 1 of overlaying a stainless steel material, substantially as herein described in either of the foregoing Examples.

4. A method of overlaying a stainless steel material for decorative articles and ornaments with a alloy of Au, Pt and/or Pd bases, which comprises bonding selected surfaces of the steel material with a thin layer of said alloy or with the constituents of said alloy and heating them to a temperature higher than 800on for their diffusion bonding and/or annealing, overlaying them with a thicker layer of said alloy or with the constituents of said alloy without heating or with heating at a temperature lower than 800"C, and annealing them, if desired, at a temperature lower than 800on.