Method for improving an iron-nickel-chromium-manganese alloy for timepiece applications

Abstract

A method for improving an iron-nickel-chromium-manganese alloy for timepiece applications, particularly for producing a balance spring, is described. The base alloy contains, by mass, from 9.0% to 13.0% of nickel, from 4.0% to 12.0% of chromium, from 21.0% to 25.0% of manganese, from 0 to 5.0% of molybdenum, and/or from 0 to 5.0% of copper in addition to iron. The alloy is hardened while its anti-ferromagnetic properties are maintained by introducing 0.10% to 1.20% of carbon and 0.10% to 1.20% of nitrogen interstitially, based on the mass of the base alloy.

Claims

1. A method for hardening an iron-nickel-chromium-manganese base alloy, the method comprising: introducing, based on the base alloy, 0.10% to 1.20% by mass of carbon and 0.10% to 1.20% by mass of nitrogen interstitially into the base alloy with a mass ratio of carbon to nitrogen ranging from 1.0 to 2.0 so as to harden the base alloy and maintain anti-ferromagnetic properties of the base alloy, wherein the base alloy comprises, by mass: from 4.0% to 13.0% of nickel, from 4.0% to 12.0% of chromium, from 21.0% to 25.0% of manganese, from 0 to 5.0% of molybdenum and/or from 0 to 5.0% of copper, and iron.

2. The method according to claim 1, wherein a sum of the introduced carbon and nitrogen ranges between 0.60% and 0.95%.

3. The method according to claim 2, wherein the sum of the introduced carbon and nitrogen ranges between 0.75% and 0.95%.

4. The method according to claim 3, wherein the sum of the introduced carbon and nitrogen ranges between 0.80% and 0.85%.

5. The method according to claim 1, wherein said base alloy comprises at least 8.0% of chromium.

6. The method according to claim 1, wherein said base alloy comprises, by mass: from 0.5% to 5.0% of molybdenum and/or copper.

7. The method according to claim 1, wherein ferrochromium is added to nitrogen.

8. The method according to claim 1, wherein ferromanganese is added to carbon.

9. The method according to claim 1, wherein ferrochromium is added to nitrogen, and ferromanganese is added to carbon.

10. A timepiece balance spring, comprising: an alloy produced by the method according to claim 1.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) The invention relates to a method for improving an iron-nickel-chromium-manganese alloy for timepiece applications.

(2) According to the invention, a base alloy is chosen and produced, comprising by mass: from 4.0% to 13.0% of nickel, from 4.0% to 12.0% of chromium, from 21.0% to 25.0% of manganese, from 0 to 5.0% of molybdenum and/or from 0 to 5.0% of copper, the complement in iron,
and hardening of this alloy is effected whilst maintaining its anti-ferromagnetic properties, by introduction of carbon and of nitrogen interstitially with, by proportion of mass of the base alloy: from 0.10% to 1.20% of carbon, and/or from 0.10% to 1.20% of nitrogen.

(3) The proportion of chromium is therefore very much less than that of document EP2924514 cited earlier.

(4) More particularly, this introduction of carbon and nitrogen is adjusted, such that the sum of the proportions, by mass of the base alloy, of the carbon and of the nitrogen, is between 0.60% and 0.95%.

(5) More particularly, this introduction of carbon and nitrogen is adjusted, such that the sum of the proportions, by mass of the base alloy, of the carbon and of the nitrogen, is between 0.75% and 0.95%.

(6) More particularly, this introduction of carbon and nitrogen is adjusted, such that the sum of the proportions, by mass of the base alloy, of the carbon and of the nitrogen, is between 0.80% and 0.85%.

(7) More particularly, this introduction of carbon and nitrogen is adjusted, such that the ratio of the percentages of carbon and of nitrogen, by total mass of the base alloy, is between 0.5 and 2.0.

(8) More particularly, this introduction of carbon and nitrogen is adjusted, such that the ratio of the percentages of carbon and of nitrogen, by total mass of the base alloy, is between 1.0 and 1.5.

(9) More particularly, this base alloy is chosen comprising, by mass, at least 8.0% of chromium.

(10) More particularly, there is incorporated in the base alloy, as a proportion of the mass of the base alloy, between 0.5% and 5.0% of molybdenum and/or of copper in order to improve its resistance to corrosion.

(11) More particularly the base alloy is chosen and produced, comprising by mass: from 4.0% to 13.0% of nickel, from 4.0% to 12.0% of chromium, from 21.0% to 25.0% of manganese, from 0 to 5.0% of molybdenum and/or from 0 to 5.0% of copper, the complement in iron.

(12) More particularly, ferrochromium is added to the nitrogen in order to arrive at the correct chemical composition.

(13) More particularly, ferromanganese is added to the carbon in order to arrive at the correct chemical composition.

(14) More particularly, ferrochromium is added to the nitrogen, and ferromanganese to the carbon in order to arrive at the correct chemical composition.

(15) More particularly, production of this alloy includes a casting process, comprising the following steps: preparing, in adequate proportions, on the one hand, pure metals, nickel, chromium, iron and, on the other hand, pre-alloys of the type:
low carbon ferrochromium, termed Nitrided Low Carbon Ferro Chromium, with 65% of chromium, 3% of nitrogen, the remainder in iron,
high carbon ferromanganese, termed High Carbon Ferro Manganese, with 75% of manganese, 7% of carbon, the remainder in iron,
low carbon ferromanganese, termed Low Carbon Ferro Manganese, with 95% of manganese, the remainder in iron, in a vacuum induction furnace, melting, under nitrogen partial pressure, iron, nickel and chromium, adding the low carbon ferromanganese and the high carbon ferromanganese, controlling the temperature and maintaining it at approx. 20 C. above the liquidus of the alloy, or at at least 20 C. above the liquidus of the alloy, adding the ferrochromium to the low carbon nitrogen, which is the main source of nitrogen, controlling the temperature and maintaining it at approx. 20 C. above the liquidus of the alloy, or at at least 20 C. above the liquidus of the alloy, implementing the casting of the ingot.

(16) The invention also relates to the use of such an alloy for producing a timepiece balance spring, in particular a balance spring for an oscillator.