# US 11,111,552 B2 · Methods for processing metal alloys

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- Number: US 11,111,552 B2
- Document ID: US11111552B2
- Status: Granted
- Kind: B2
- Application number: 14/077,699
- Filed: 2013-11-12
- Published: 2015-05-14
- Granted: 2021-09-07
- Earliest claimed: 2013-11-12
- Assignees: ATI Properties, Inc.
- Applicants: ATI Properties LLC
- Inventors: Robin M. Forbes Jones; Ramesh S. Minisandram
- Web page: https://patentgrep.com/patent/US11111552B2

## CPC

- C21D 8/00: 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)
- C21D 1/18: Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62)
- C21D 6/004: {containing Cr and Ni}
- C21D 6/005: {containing Mn}
- C21D 7/13: by hot working
- C21D 8/021: involving particular fabrication steps or treatments of ingots or slabs
- C21D 8/0247: characterised by the heat treatment
- C22C 19/056: {with the maximum Cr content being at least 10% but less than 20%}
- C22C 30/02: containing copper
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/004: {Very low carbon steels, i.e. having a carbon content of less than 0,01%}
- C22C 38/02: containing silicon
- C22C 38/40: with nickel
- C22C 38/42: with copper
- C22C 38/44: with molybdenum or tungsten
- C22C 38/58: with more than 1.5% by weight of manganese
- C22F 1/002: {by rapid cooling or quenching; cooling agents used therefor}
- C22F 1/10: of nickel or cobalt or alloys based thereon
- C22F 1/183: {of titanium or alloys based thereon}
- C21D 2211/001: Austenite
- C21D 2211/004: Dispersions; Precipitations
- C22C 14/00: Alloys based on titanium
- C22C 19/05: with chromium
- C22C 19/051: {and Mo or W}
- C22C 19/07: based on cobalt
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- C22F: CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass, C23F17/00)

## Abstract

A method of processing a metal alloy includes heating to a temperature in a working temperature range from a recrystallization temperature of the metal alloy to a temperature less than an incipient melting temperature of the metal alloy, and working the alloy. At least a surface region is heated to a temperature in the working temperature range. The surface region is maintained within the working temperature range for a period of time to recrystallize the surface region of the metal alloy, and the alloy is cooled so as to minimize grain growth. In embodiments including superaustenitic and austenitic stainless steel alloys, process temperatures and times are selected to avoid precipitation of deleterious intermetallic sigma-phase. A hot worked superaustenitic stainless steel alloy having equiaxed grains throughout the alloy is also disclosed.

## Claims

### Claim 1

A method of processing a superaustenitic stainless steel alloy, the method comprising:
heating a superaustenitic stainless steel alloy to a temperature in a working temperature range, wherein the working temperature range is from a recrystallization temperature of the superaustenitic stainless steel alloy to a temperature below an incipient melting temperature of the superaustenitic stainless steel alloy;
working the superaustenitic stainless steel alloy in the working temperature range to provide a superaustenitic stainless steel article comprising a surface region and a central region, wherein the surface region comprises a mixture of recrystallized grains and unrecrystallized grains, and wherein the central region is fully recrystallized;
transferring the superaustenitic stainless steel alloy article to a heating apparatus within a time that does not exceed the time to an apex of a time-temperature-transformation curve for dissolution of an intermetallic sigma-phase precipitate of the superaustenitic stainless steel alloy;
heating the surface region of the superaustenitic stainless steel alloy article to a temperature range of greater than 1900° F. to 2000° F.;
maintaining the surface region of the superaustenitic stainless steel alloy article in the temperature range of greater than 1900° F. to 2000° F. for 1 minute to 30 minutes to recrystallize only grains in the surface region of the superaustenitic stainless steel alloy article and provide a fully recrystallized surface region; and
cooling the superaustenitic stainless steel alloy article from the temperature range of greater than 1900° F. to 2000° F. at a cooling rate and to a temperature that minimizes grain growth in the superaustenitic stainless steel alloy article;
wherein after the cooling the superaustenitic stainless steel alloy article, an average grain size of the superaustenitic stainless steel alloy article is in an ASTM grain size number range of 00 to less than 3 wherein the cooling rate comprises a range from 0.3 Fahrenheit degrees per minute to 10 Fahrenheit degrees per minute.

### Claim 2 (depends on 1)

The method of claim 1, wherein the superaustenitic stainless steel alloy comprises, in percent by weight based on total alloy weight: up to 0.2 carbon; up to 20 manganese; 0.1 to 1.0 silicon; 14.0 to 28.0 chromium; 15.0 to 38.0 nickel; 2.0 to 9.0 molybdenum; 0.1 to 3.0 copper; 0.08 to 0.9 nitrogen; 0.1 to 5.0 tungsten; 0.5 to 5.0 cobalt; up to 1.0 titanium; up to 0.05 boron; up to 0.05 phosphorus; up to 0.05 sulfur; iron; and incidental impurities.

### Claim 3 (depends on 1)

The method of claim 1, wherein the superaustenitic stainless steel alloy comprises, in percent by weight based on total alloy weight: up to 0.05 carbon; up to 1.0 silicon; 10 to 20 manganese; 13.5 to 18.0 chromium; 1.0 to 4.0 nickel; 1.5 to 3.5 molybdenum; 0.2 to 0.4 nitrogen; iron; and incidental impurities.

### Claim 4 (depends on 1)

The method of claim 1, wherein the superaustenitic stainless steel alloy comprises one of a UNS N08367 alloy, a UNS N06600 alloy; a UNS N06975 alloy; a UNS N06625 alloy; a UNS N08800 alloy; a UNS N08810 alloy, a UNS N08811 alloy; a UNS N08825 alloy; a UNS N06985 alloy; a UNS N08535 alloy; a UNS N06255 alloy; and a UNS S31603 alloy.

### Claim 5 (depends on 1)

The method of claim 1, wherein working the superaustenitic stainless steel alloy comprises at least one of forging, rolling, blooming, extruding, and forming the superaustenitic stainless steel alloy.

### Claim 6 (depends on 1)

The method of claim 1, wherein working the superaustenitic stainless steel alloy comprises at least one of roll forging, swaging, cogging, open-die forging, impression-die forging, press forging, automatic hot forging, radial forging, and upset forging the superaustenitic stainless steel alloy.

### Claim 7 (depends on 1)

The method of claim 1, wherein heating the surface region of the superaustenitic stainless steel alloy article comprises at least one of furnace heating, flame heating, and induction heating the surface region of the superaustenitic stainless steel alloy article.

### Claim 8 (depends on 1)

The method of claim 1, wherein maintaining the surface region of the superaustenitic stainless steel alloy article comprises maintaining the surface region of the superaustenitic stainless steel alloy article in the temperature range of greater than 1900° F. to 2000° F. for 5 minutes to 30 minutes.

### Claim 9 (depends on 1)

The method of claim 1, wherein:
heating the superaustenitic stainless steel alloy to the working temperature range comprises heating the superaustenitic stainless steel alloy to a temperature range from a solvus temperature of the intermetallic sigma-phase precipitate of the superaustenitic stainless steel alloy to below the incipient melting temperature of the superaustenitic stainless steel alloy;
the working temperature range for working the superaustenitic stainless steel alloy is from above the apex temperature of the time-temperature-transformation diagram for the intermetallic sigma-phase precipitate of the superaustenitic stainless steel alloy to below the incipient melting temperature of the superaustenitic stainless steel alloy; and
the temperature of the superaustenitic stainless steel alloy does not intersect the time-temperature-transformation diagram for the intermetallic sigma-phase precipitate of the superaustenitic stainless steel alloy during the working the superaustenitic stainless steel alloy and prior to heating the surface region of the superaustenitic stainless steel alloy article.

### Claim 10 (depends on 9)

The method of claim 9, wherein working the superaustenitic stainless steel alloy comprises at least one of forging, rolling, blooming, extruding, and forming the superaustenitic stainless steel alloy.

### Claim 11 (depends on 9)

The method of claim 9, wherein working the superaustenitic stainless steel alloy comprises at least one of roll forging, swaging, cogging, open-die forging, impression-die forging, press forging, automatic hot forging, radial forging, and upset forging the superaustenitic stainless steel alloy.

### Claim 12 (depends on 9)

The method of claim 9, wherein heating the surface region of the superaustenitic stainless steel alloy article comprises at least one of furnace heating, flame heating, and induction heating the surface region.

### Claim 13 (depends on 9)

The method of claim 9, wherein maintaining the surface region of the superaustenitic stainless steel alloy article comprises maintaining the surface region of the superaustenitic stainless steel alloy article in the temperature range of greater than 1900° F. to 2000° F. for a time sufficient to fully recrystallize the surface region, solutionize the intermetallic sigma-phase precipitate of the superaustenitic stainless steel alloy in the surface region, and minimize grain growth in the superaustenitic stainless steel alloy.

### Claim 14 (depends on 9)

The method of claim 9, wherein maintaining the surface region of the superaustenitic stainless steel alloy article comprises maintaining the surface region of the superaustenitic stainless steel alloy article in the temperature range of greater than 1900° F. to 2000° F. for 5 minutes to 30 minutes.

### Claim 15 (depends on 9)

The method of claim 9, wherein cooling the superaustenitic stainless steel alloy article comprises cooling at a rate sufficient to inhibit precipitation of an intermetallic sigma-phase precipitate in the superaustenitic stainless steel alloy article.

### Claim 16 (depends on 9)

The method of claim 9, wherein cooling the superaustenitic stainless steel alloy article comprises one of quenching, forced air cooling, and air cooling the superaustenitic stainless steel alloy.

### Claim 17 (depends on 9)

The method of claim 9, wherein cooling the superaustenitic stainless steel alloy article comprises one of water quenching and oil quenching the superaustenitic stainless steel alloy article.

### Claim 18 (depends on 9)

The method of claim 9, wherein the superaustenitic stainless steel alloy comprises one of a UNS N08367 alloy; a UNS N06600 alloy; a UNS N06975 alloy; a UNS N06625 alloy; a UNS N08800 alloy; a UNS N08810 alloy, a UNS N08811 alloy; a UNS N08825 alloy; a UNS N06985 alloy; a UNS N08535 alloy; a UNS N06255 alloy; and a UNS S31603 alloy.

### Claim 19 (depends on 1)

The method of claim 1, wherein the surface region of the superaustenitic stainless steel alloy article extends from a surface of the superaustenitic stainless steel alloy article to a depth of 1 inch into an interior of the superaustenitic stainless steel alloy article.

### Claim 20 (depends on 1)

The method of claim 1, wherein the average grain size of the superaustenitic stainless steel alloy article is in an ASTM grain size number range of 00 to 2.

### Claim 21

A method of processing a superaustenitic stainless steel alloy, the method comprising:
heating a superaustenitic stainless steel alloy to an intermetallic phase precipitate dissolution temperature in an intermetallic phase precipitate dissolution temperature range, wherein the intermetallic phase precipitate dissolution temperature range is from a solvus temperature of an intermetallic phase precipitate of the superaustenitic stainless steel alloy to a temperature just below an incipient melting temperature of the superaustenitic stainless steel alloy;
maintaining the superaustenitic stainless steel alloy in the intermetallic phase precipitate dissolution temperature range for a time sufficient to dissolve the intermetallic phase precipitate and to minimize grain growth in the superaustenitic stainless steel alloy;
working the superaustenitic stainless steel alloy at a working temperature in a working temperature range from just above an apex temperature of a time-temperature-transformation curve for the intermetallic phase precipitate of the superaustenitic stainless steel alloy to just below the incipient melting temperature of the superaustenitic stainless steel alloy to provide a superaustenitic stainless steel article comprising a surface region and a central region, wherein the surface region comprises a mixture of recrystallized grains and unrecrystallized grains, and wherein the central region is fully recrystallized;
transferring the superaustenitic stainless steel alloy article to a heating apparatus without letting the superaustenitic stainless steel article cool to the apex temperature of the time-temperature-transformation curve;
heating the surface region of the superaustenitic stainless steel alloy article to a temperature in a temperature range of greater than 1900° F. to 2000° F.;
maintaining the surface region of the superaustenitic stainless steel alloy article in the temperature range of greater than 1900° F. to 2000° F. for 1 minute to 30 minutes to recrystallize only grains in the surface region and provide a fully recrystallized surface region; and
cooling the superaustenitic stainless steel alloy article to a cooling temperature at a cooling rate and to a temperature that inhibits formation of the intermetallic phase precipitate and minimizes grain growth;
wherein after the cooling the superaustenitic stainless steel alloy article, an average grain size of the superaustenitic stainless steel alloy article is in an ASTM grain size number range of 00 to less than 3 wherein the cooling rate comprises a range from 0.3 Fahrenheit degrees per minute to 10 Fahrenheit degrees per minute.

### Claim 22 (depends on 21)

The method of claim 21, wherein the intermetallic phase precipitate comprises sigma-phase.

### Claim 23 (depends on 22)

The method of claim 22, wherein cooling the superaustenitic stainless steel alloy article comprises one of water quenching and oil quenching the superaustenitic stainless steel alloy article.

### Claim 24 (depends on 21)

The method of claim 21, wherein working the superaustenitic stainless steel alloy comprises at least one of forging, rolling, blooming, extruding, and forming the superaustenitic stainless steel alloy.

### Claim 25 (depends on 21)

The method of claim 21, wherein working the superaustenitic stainless steel alloy comprises at least one of roll forging, swaging, cogging, open-die forging, impression-die forging, press forging, automatic hot forging, radial forging, and upset forging the superaustenitic stainless steel alloy.

### Claim 26 (depends on 21)

The method of claim 21, wherein working the superaustenitic stainless steel alloy comprises radial forging the superaustenitic stainless steel alloy.

### Claim 27 (depends on 21)

The method of claim 21, wherein heating the surface region of the superaustenitic stainless steel alloy article comprises at least one of furnace heating, flame heating, and induction heating the surface region of the superaustenitic stainless steel alloy.

### Claim 28 (depends on 21)

The method of claim 21, wherein cooling the superaustenitic stainless steel alloy article comprises one of quenching, forced air cooling, and air cooling the superaustenitic stainless steel alloy article.

### Claim 29 (depends on 21)

The method of claim 21, wherein the superaustenitic stainless steel alloy comprises, in percent by weight based on total alloy weight: up to 0.2 carbon; up to 20 manganese; 0.1 to 1.0 silicon; 14.0 to 28.0 chromium; 15.0 to 38.0 nickel; 2.0 to 9.0 molybdenum; 0.1 to 3.0 copper; 0.08 to 0.9 nitrogen; 0.1 to 5.0 tungsten; 0.5 to 5.0 cobalt; up to 1.0 titanium; up to 0.05 boron; up to 0.05 phosphorus; up to 0.05 sulfur; iron; and incidental impurities.

### Claim 30 (depends on 21)

The method of claim 21, wherein the surface region of the superaustenitic stainless steel alloy article extends from a surface of the superaustenitic stainless steel alloy article to a depth of 1 inch into an interior of the superaustenitic stainless steel alloy article.

### Claim 31 (depends on 21)

The method of claim 21, wherein maintaining the surface region of the superaustenitic stainless steel alloy article comprises maintaining the surface region of the superaustenitic stainless steel alloy article in the temperature range of greater than 1900° F. to 2000° F. for 5 minutes to 30 minutes.

### Claim 32 (depends on 21)

The method of claim 21, wherein the average grain size of the superaustenitic stainless steel alloy article is in an ASTM grain size number range of 00 to 2.

### Claim 33

A method of processing a superaustenitic stainless steel alloy, the method comprising:
heating a superaustenitic stainless steel alloy to a temperature in a working temperature range, wherein the working temperature range is from a recrystallization temperature of the superaustenitic stainless steel alloy to a temperature below an incipient melting temperature of the superaustenitic stainless steel alloy;
working the superaustenitic stainless steel alloy in the working temperature range to provide a superaustenitic stainless steel article comprising a surface region and a central region, wherein the surface region comprises a mixture of recrystallized grains and unrecrystallized grains, and wherein the central region is fully recrystallized;
transferring the superaustenitic stainless steel alloy article to a heating apparatus within a time that does not exceed the time to an apex of a time-temperature-transformation curve for dissolution of an intermetallic sigma-phase precipitate of the superaustenitic stainless steel alloy;
heating the surface region of the superaustenitic stainless steel alloy article to a temperature in a temperature range of greater than 2000° F. to 2150° F.;
maintaining the surface region of the superaustenitic stainless steel alloy article in the temperature range of greater than 2000° F. to 2150° F. for 1 minute to 30 minutes to recrystallize only grains in the surface region and provide a fully recrystallized surface region; and
cooling the superaustenitic stainless steel alloy article from the temperature range of greater than 2000° F. to 2150° F. at a cooling rate and to a temperature that minimizes grain growth in the superaustenitic stainless steel alloy article;
wherein after the cooling the superaustenitic stainless steel alloy article, an average grain size of the superaustenitic stainless steel alloy article is in an ASTM grain size number range of 00 to less than 3 wherein the cooling rate comprises a range from 0.3 Fahrenheit degrees per minute to 10 Fahrenheit degrees per minute.

### Claim 34

A method of processing a superaustenitic stainless steel alloy, the method comprising:
heating a superaustenitic stainless steel alloy to an intermetallic phase precipitate dissolution temperature in an intermetallic phase precipitate dissolution temperature range, wherein the intermetallic phase precipitate dissolution temperature range is from a solvus temperature of an intermetallic phase precipitate of the superaustenitic stainless steel alloy to a temperature just below an incipient melting temperature of the superaustenitic stainless steel alloy;
maintaining the superaustenitic stainless steel alloy in the intermetallic phase precipitate dissolution temperature range for a time sufficient to dissolve the intermetallic phase precipitate and to minimize grain growth in the superaustenitic stainless steel alloy;
working the superaustenitic stainless steel alloy at a working temperature in a working temperature range from just above an apex temperature of a time-temperature-transformation curve for the intermetallic phase precipitate of the superaustenitic stainless steel alloy to just below the incipient melting temperature of the superaustenitic stainless steel alloy to provide a superaustenitic stainless steel article comprising a surface region and a central region, wherein the surface region comprises a mixture of recrystallized grains and unrecrystallized grains, and wherein the central region is fully recrystallized;
transferring the superaustenitic stainless steel alloy article to a heating apparatus without letting the superaustenitic stainless steel article cool to the apex temperature of the time-temperature-transformation curve;
heating the surface region of the superaustenitic stainless steel alloy article to a temperature in a temperature range of greater than 2000° F. to 2150° F.;
maintaining the surface region of the superaustenitic stainless steel alloy article in the temperature range of greater than 2000° F. to 2150° F. for 1 minute to 30 minutes to recrystallize only grains in the surface region and provide a fully recrystallized surface region; and
cooling the superaustenitic stainless steel alloy article to a cooling temperature at a cooling rate and to a temperature that inhibits formation of the intermetallic phase precipitate and minimizes grain growth;
wherein after the cooling the superaustenitic stainless steel alloy article, an average grain size of the superaustenitic stainless steel alloy article is in an ASTM grain size number range of 00 to less than 3 wherein the cooling rate comprises a range from 0.3 Fahrenheit degrees per minute to 10 Fahrenheit degrees per minute.