GB1598827A - Alloys - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO ALLOYS (71) We, UNITED KINGDOM ATO MIC ENERGY AUTHORITY, London, a British Authority do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to alloys of iron, chromium, aluminium and yttrium in the form of wire.

The present invention provides, in a first aspect, an alloy of iron, chromium, aluminium and yttrium in the form of wire, which alloy comprises from 20 to 25 weight per cent of chromium, from 4 to 5.5 weight per cent of aluminium, from 0.1 to 0.5 weight per cent of yttrium and the balance of iron.

We have found that the alloys used in the present invention have good oxidation resistance as evidenced by tests we have carried out on representative alloys and which are described in the examples of this specification. Such alloys in the form of wire may therefore have particular application in the form of resistance heating elements.

The alloys used in the present invention may be made by methods known in the art for making alloys of iron, chromium, aluminium and yttrium and may be fabricated into the form of wire, for example by means of conventional techniques such as reduction of ingots by forging, extrusion, rolling and then drawing. Thus, the invention comprises, in a second aspect, a method making an alloy of iron, chromium, aluminium and yttrium in the form of wire, which comprises drawing into wire an alloy comprising from 20 to 25 weight per cent of chromium, from 4 to 5.5 weight per cent of aluminium, from 0.1 to 0.5 weight per cent of yttrium and the balance of iron.

The alloys of our invention may also contain unspecified incidental ingredients such as may be introduced in or accompanying the process of alloy manufacture, for example in accordance with common steelmaking processes, and do not materially affect the characteristics of the alloys.

The invention will now be particularly described, by way of example only, with reference to the examples below. All proportions in the examples are by weight.

Example 1 Fe - 23.7 Cr - 5.1 Al - 0.43 Y Pure samples of Fe, Cr, Al and Y were taken in proportions corresponding to the above, with a little excess Y to account for losses thereof, and arc-melted together to give an Fe - Cr - Al - Y alloy with the above composition and in the form of a button weighing several hundred grams. This was then rolled to a sheet of 20 thousandths of an inch thickness. The loss of Y is caused by it forming a slag on the surface of the alloy.

A sample of the sheet was tested for oxidation resistance by heating in wet air.

At 1300"C, the life of the sheet was in excess of 2,500 hours, and at 12500C the life of the sheet was in excess of 5,000 hours.

The 'life' of the sample was assessed by following the weight of the sample. The life is the time taken for a marked increase in weight to occur (usually termed 'breakaway') as a result of very severe local oxidation, which can, in fact, be observed visually. The life of the sample of the subsequent example of this specification was assessed in a similar way.

Example 2 Fe 24.1 Cr - 4.5 Al - 0.5 Y The procedure and tests described in Example 1 were carried out using proportions of metals to give the above alloy composition.

At 1300"C, the life of the sheet was in excess of 2000 hours, and at 12500C was 4300 hours.

WHAT WE CLAIM IS: 1. An alloy of iron, chromium, aluminium and yttrium in the form of wire, which alloy comprises from 20 to 25 weight per cent of chromium, from 4 to 5.5 weight per cent of aluminium, from 0.1 to 0.5 weight per cent of yttrium and the balance iron.

2. An alloy as claimed in claim 1 in the form of a resistance heating element.

3. A method of making an alloy of iron, chromium, aluminium and yttrium in the form of wire which comprises drawing into wire an alloy comprising from 20 to 25 weight per cent of chromium, from 4 to 5.5 weight per cent of aluminium, from 0.1 to 0.5 weight per cent of yttrium and the balance of iron.

4. Wire made by a method as claimed in

Claims (1)

1. claim 3.