# US 10,870,910 B2 · Ferritic nitrocarburized part and methods of making and using the same

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- Number: US 10,870,910 B2
- Document ID: US10870910B2
- Status: Granted
- Kind: B2
- Application number: 15/866,814
- Filed: 2018-01-10
- Published: 2019-07-11
- Granted: 2020-12-22
- Earliest claimed: 2018-01-10
- Assignees: GM Global Technology Operations LLC; Woodworth Inc.
- Applicants: GM Global Technology Operations LLC; Woodworth Inc.
- Inventors: Michael L. Holly; Dennis Deciechi; James J. Gentile; David M. Cummings; Charles M. Enloe
- Web page: https://patentgrep.com/patent/US10870910B2

## CPC

- C23C 8/28: more than one element being applied in one step
- B62D 29/007: {predominantly of special steel or specially treated steel, e.g. stainless steel or locally surface hardened steel}
- C23C 8/02: Pretreatment of the material to be coated (C23C8/04 takes precedence)
- C23C 8/32: of ferrous surfaces
- C23C 8/38: Treatment of ferrous surfaces
- C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04)
- B62D: MOTOR VEHICLES; TRAILERS (steering, or guiding on a desired track, of agricultural machines or implements A01B69/00; wheels, castors, axles, increasing wheel adhesion B60B; vehicle tyres, tyre inflation or tyre changing B60C; connections between vehicles of a train or the like B60D; vehicles for use on rail and road, amphibious or convertible vehicles B60F; suspension arrangements B60G; heating, cooling, ventilating or other air treating devices B60H; windows, windscreens, non-fixed roofs, doors or similar devices, protective coverings for vehicles not in use B60J; propulsion plant arrangements, auxiliary drives, transmissions, controls, instrumentation or dashboards B60K; electric equipment or propulsion of electrically-propelled vehicles B60L; power supply for electrically-propelled vehicles B60M; passenger accommodation not otherwise provided for B60N; adaptations for load transportation or to carry special loads or objects B60P; arrangement of signalling or lighting devices, the mounting or supporting thereof or circuits therefor, for vehicles in general B60Q; vehicles, vehicle fittings or vehicle parts not otherwise provided for B60R; servicing, cleaning, repairing, supporting, lifting, or manoeuvring, not otherwise provided for, B60S; brake arrangements, brake control systems or parts thereof B60T; air-cushion vehicles B60V; motor-cycles, accessories therefor B62J, B62K; testing of vehicles G01M)

## Abstract

A number of variations may include a ferritic nitrocarburized part comprising steel, wherein the ferritic nitrocarburized steel has a tensile strength exceeding the parent steel material and sufficient ductility, bendability, and flangeability to support subsequent flanging and press-fitting of bushings. Exact strength increases and bendability will be dependent on exact process and alloy combinations.

## Claims

### Claim 1

A product comprising:
a ferritic nitrocarburized part including a parent steel material that is subcritically annealed;
wherein the ferritic nitrocarburized part has a tensile strength exceeding that of the parent steel material, and the ferritic nitrocarburized part has characteristics of ductility, bendability, and flangeability to support subsequent flanging and press-fitting of bushings; and
wherein the ferritic nitrocarburized part includes a compound zone and a surface at an outer edge of the compound zone, wherein the surface is configured for engagement with a corresponding friction material, and wherein the compound zone includes a nitride layer having epsilon iron nitride, Fe2-3N and gamma prime iron nitride Fe4N.

### Claim 2 (depends on 1)

The product as defined in claim 1 wherein the ferritic nitrocarburized part includes a structural component for a vehicle.

### Claim 3 (depends on 2)

The product as defined in claim 2 wherein the structural component defines a hole, and further includes an insert disposed in the hole.

### Claim 4 (depends on 1)

The product as defined in claim 1 wherein the nitride layer includes an outer surface.

### Claim 5 (depends on 1)

The product as defined in claim 1 wherein the compound zone further includes an iron oxide layer overlying the nitride layer, and the iron oxide layer includes an outer surface.

### Claim 6 (depends on 1)

The product as defined in claim 1 wherein the nitride layer has a depth of at least 10 microns.

### Claim 7

A product comprising:
a parent steel that is cold-rolled and subcritically annealed;
a compound zone disposed on the parent steel to form a ferritic nitrocarburized part, and the compound zone includes a nitride layer disposed on the parent steel;
wherein the nitride layer includes epsilon iron nitride, Fe2-3N, and gamma prime iron nitride Fe4N; and
wherein the ferritic nitrocarburized part has a tensile strength that exceeds that of the parent steel.

### Claim 8 (depends on 7)

The product as defined in claim 7 wherein the ferritic nitrocarburized part includes a structural component for a vehicle.

### Claim 9 (depends on 8)

The product as defined in claim 8 wherein the structural component defines a hole, and further includes an insert disposed in the hole.

### Claim 10

A method comprising:
providing a part that includes a parent steel material;
preheating the part to about 400° C. 500° C. for about 2-4 hours;
subcritically annealing the part that includes heating that part to about 500° C. 725° C. for about 1-5 hours and cooling the part to about 350° C.-500° C.;
heating the part to about 500° C.-650° C.;
ferritic nitrocarburizing the part at about 500° C.-650° C. to form an iron nitride layer on a surface of the part;
cooling the part to provide a ferritic nitrocarburized part that includes the parent steel material, wherein the ferritic nitrocarburized part has a tensile strength exceeding that of the parent steel material, and the ferritic nitrocarburized part has characteristics of ductility, bendability, and flangeability to support subsequent flanging and press-fitting of bushings; and
wherein ferritic nitrocarburizing the part includes forming a compound zone and a surface at an outer edge of the compound zone, wherein the surface at the outer edge is configured for engagement with a corresponding friction material, and wherein the compound zone includes a nitride layer having epsilon iron nitride, Fe2-3N and gamma prime iron nitride Fe4N.

### Claim 11 (depends on 10)

The method as defined in claim 10 wherein ferritic nitrocarburizing includes a gas nitrocarburizing process, a plasma nitrocarburizing process, a fluidized bed nitrocarburization process, or a salt bath nitrocarburizing process.

### Claim 12 (depends on 10)

The method as defined in claim 10 wherein the ferritic nitrocarburized part includes a structural component for a vehicle.

### Claim 13 (depends on 10)

The method as defined in claim 10 wherein the nitride layer includes an outer surface.

### Claim 14 (depends on 10)

The method as defined in claim 10 wherein ferritic nitrocarburizing the part further includes forming an iron oxide layer in the compound zone overlying the nitride layer, wherein the iron oxide layer includes an outer surface.

### Claim 15 (depends on 14)

The method as defined in claim 14 wherein the iron oxide layer includes oxidized nitrocarburized iron having a formula of Fe3O4.

### Claim 16 (depends on 10)

The method as defined in claim 10 wherein the nitride layer has a depth of at least 10 microns.

### Claim 17 (depends on 10)

The method as defined in claim 10 wherein ferritic nitrocarburizing the part further includes heat treatment of the part in an atmosphere rich in nitrogen and carbon in a mixture.