Paramagnetic hard stainless steel and manufacturing process thereof

Patent metadata

Field	Value
Publication number	US-11591663-B2
Application number	US-202016983227-A
Country	US
Kind code	B2
Filing date	Aug 3, 2020
Priority date	Dec 13, 2019
Publication date	Feb 28, 2023
Grant date	Feb 28, 2023

Abstract

A paramagnetic stainless steel with a chemical composition including by weight: 26≤Cr≤40%, 5≤Ni≤20%, 0≤Mn≤5%, 0≤Al≤5%, 0≤Mo≤3%, 0≤Cu≤2%, 0≤Si≤5%, 0≤Ti≤1%, 0≤Nb≤1%, 0≤C≤0.1%, 0≤N≤0.1%, 0≤S≤0.5%, 0≤P≤0.1%, the remainder consisting of iron and any impurities each having a content less than or equal to 0.5%, the steel having a hardness HV10 between 500 and 900. It also relates to a part particularly a horological component made of this steel and to the process for manufacturing the part.

First claim

The invention claimed is:

1. A paramagnetic stainless steel with a chemical composition comprising by weight:
26≤Cr≤40%,
5≤Ni≤20%,
0≤Mn≤5%,
0≤Al≤5%,
0≤Mo≤3%,
0≤Cu≤2%,
0≤Si≤5%,
0≤Ti≤1%,
0≤Nb≤1%
0≤C≤0.1%,
0≤N≤0.1%,
0≤S≤0.5%,
0≤P≤0.1%,
the remainder consisting of iron and any impurities each having a content less than or equal to 0.5%,
wherein the steel has a hardness HV10 in a range of from 500 to 900,
wherein the steel has a microstructure consisting of a sigma phase with a mass percentage in a range of from 40 to 80% and an austenitic phase within a mass percentage in a range of from 20 to 60%, the austenitic phase originating from transforming an alloy having a structure including 100% ferrite.

2. The steel of claim 1 , with a chemical composition comprising by weight:
28≤Cr≤38%,
5≤Ni≤15%,
0≤Mn≤3%,
0≤Al≤3%,
0≤Mo≤3%,
0≤Cu≤2%,
0≤Si≤5%,
0≤Ti≤1%,
0≤Nb≤1%
0≤C≤0.05%,
0≤N≤0.05%,
0≤S≤0.5%,
0≤P≤0.1%.

3. The steel of claim 1 , with a chemical composition comprising by weight:
30≤Cr≤36%,
5≤Ni≤10%,
0≤Mn≤3%,
0≤Al≤1%,
0≤Mo≤1%,
0≤Cu≤1%,
0≤Si≤3%,
0≤Ti≤1%,
0≤Nb≤1%
0≤C≤0.05%,
0≤N≤0.05%,
0≤S≤0.05%,
0≤P≤0.1%.

4. A part, made of the paramagnetic stainless steel claim 1 .

5. The part of claim 4 , comprising horological component of external parts or of a movement of a timepiece.

6. A watch, comprising:
a horological component made of the paramagnetic stainless steel of claim 1 .

7. A process for manufacturing a part formed from the paramagnetic stainless steel of claim 1 , comprising: heat treating or hardening a blank having substantially a shape of the part to be manufactured, to obtain the part, the hardening being carried out at a temperature in a range of from 650 to 900° C. for a time in a range of from 30 minutes to 24 hours, thereby transforming a ferrite of the structure into an austenitic phase and an intermetallic sigma phase, the hardening being followed by cooling to ambient temperature.

8. The process of claim 7 , wherein a mostly or completely ferritic structure of the blank prior to the heat treating or hardening has been produced by performing a heat or thermomechanical treatment on a base material at a temperature in a range of from 950 to 1450° C. for a time in a range of from 1 minute to 24 hours,
wherein the heat or thermomechanical treatment is followed by a hardening to a temperature less than 500° C. to retain the ferritic structure at ambient temperature.

9. The process of claim 8 , wherein the base material is in the form of a powder or a consolidated material.

10. The process of claim 8 , wherein the base material has been obtained by casting, by pressing, by metal injection molding, by additive manufacturing, or by powder metallurgy.

11. The process of claim 7 , further comprising;
producing the blank by selective laser melting.

12. The process of claim 7 , wherein, prior to the heat treating or hardening, the blank has a hardness in a range of from 150 to 400 HV10.

13. The process of claim 7 , further comprising, prior to the heat treating or hardening: forming a blank of the paramagnetic stainless steel by one or more plastic deformation sequences at a temperature less than 650° C.

14. The process of claim 7 , further comprising, prior to the heat treating or hardening: forming a blank of the paramagnetic stainless steel by forging, blanking, or machining.

15. The process of claim 8 , wherein the heat treating or hardening is carried out in several cycles.

16. The process of claim 7 , further comprising:
before the heat treating or hardening, a heat or thermomechanical treating on an initial blank, at least partially comprising austenite, at a temperature in a range of from 950 to 1450° C. for a time in a range of from 1 minute to 24 hours to obtain a completely ferritic structure in the blank,
wherein the heat or thermomechanical treating is followed by a hardening to a temperature less than 500′C to retain the completely ferritic structure at ambient temperature.

Assignees

• Swatch Group Res & Dev Ltd

Inventors

• Porret Joel

Classifications

• C21D8/00 Primary

  Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02) · CPC title

• B22F10/64

  by thermal means (control of energy beam parameters for post heating B22F10/364) · CPC title

• G04B19/12

  Selection of materials for dials or graduations {markings} · CPC title

• B33Y40/20

  Post-treatment, e.g. curing, coating or polishing · CPC title

• C21D2211/001

  Austenite · CPC title