US3062692A

US3062692A - Austenitic steel generator rings and steel therefor

Info

Publication number: US3062692A
Application number: US850792A
Authority: US
Inventors: Samuel J Manganello; Matti H Pakkala
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1959-11-04
Filing date: 1959-11-04
Publication date: 1962-11-06
Anticipated expiration: 1979-11-06
Also published as: GB923844A

Description

United States Patent Ofiice 3,062,692 Patented Nov. 6, 1962 I AUSTENITIC STEEL GENERATOR RINGS AND This invention relates to generator rings and steels therefor capable of developing high yield strengths by cold working and aging coupled with sufficient ductility to permit large amounts of cold work and more particularly to generator rings and forgings having such properties along with a grain size no larger than ASTM #4.

So-called generator rings or retaining rings used as coil supports in generator rotors must be formed of austenitic, i.e. nonmagnetic, steels to avoid electrical losses. It is necessary that these rings possess high yield point in excess of 125,000 p.s.i. (0.2% offset) which require that the rings after forging and heat treating must be warm or cold expanded 25% or more to develop the required strength limit. These rings are subjected to rigid inspections because of the serious nature of failure in use. Ultrasonic inspection is one of the preferred types of inspection but this cannot be used satisfactorily on steels having a grain size larger than ASTM #1.

It is accordingly an object of the present invention to provide austenitic generator ring steels having a grain size no larger than ASTM #4 along with good hot and cold forging properties.

The foregoing and further objects will be apparent from the following specification.

We have discovered that the desired combination of properties can be achieved with a steel composition containing:

.60 to .80% carbon 8.00 to' 10.00% manganese .20 to .60% silicon 6.00 to 7.00% nickel 4.00 to 5.00% chromium .30 to .60% eolumbium with the balance substantially iron and other elements in amounts which are not harmful to the properties.

As a specific example, steel of the following composition was treated in accordance with our invention:

0.70% carbon 9.00% manganese .035% phosphorus .015% sulphur 0.50% silicon 6.50% nickel 4.25% chromium 0.010% aluminum 0.010% nitrogen 0.30% columbium with balance substantially iron.

Ring specimens of this steel were heated to 2000 F. for 2 hours and air cooled. After heating and cooling, the specimens had a grain size of 5-6 according to the ASTM chart. One specimen was cold expanded and the other The 30% expanded steel was then Solution temperature:

subjected to an aging treatment at 600 F. for 2 hours. The results were as follows:

Yield Strength (0.02% offset); p.s.i.

Yield Elonga- Strength Tensile tion in (0.2% Strength, 2 onset), p.s.i. percent p.s.i.

Reduc- Cold Worked, of percent Area,

percent These tests indicate that the steel of our invention may be cold expanded 25 to 30% to obtain the desired tensile strength and 0.2% offset yield strength. Considerable improvement in the .02% offset yield is obtained by aging along with minor improvements in .2% offset yield, tensile strength, elongation and reduction of area. The aging should be in the range of 500 to 650 F. for sufficient time to achieve uniformity of temperature.

The grain size above stated is a true inherent grain Size and remains substantially the same after difierent solution temperatures as can be seen from the following tabulation.

ASTM grain size 1800 F. 6 2000 F. 22000 F. 46

While we have shown and described one specific embodiment of our invention, it will be understood that this embodiment is merely for the purpose of illustration and description and that various other forms may be devised within the scope of our invention, as defined in the appended claims.

We claim:

1. A cold expanded austenitic steel generator rotor coil support retaining ring characterized by a grain size no coarser than ASTM #4 containing .60 to .80% carbon, 8.00 to 10.00% manganese, .20 to .60% silicon, 6.00 to 7.00% nickel, 4.00 to 5.00% chromium and .30 to .60% eolumbium with the balance iron and other elements in amounts which do not have a harmful effect on the properties.

2. An austenitic steel generator rotor coil support retaining ring characterized by a grain size no coarser than ASTM #4 and by having been cold expanded over 25% containing .60 to .80% carbon, 8.00 to 10.00% manganese, .20 to .60% silicon, 6.00 to 7.00% nickel, 4.00 to 5.00% chromium and .30 to .60% eolumbium, balance substantially iron.

3. A method of producing austenitic steel generator rotor coil support retaining rings characterized by a grain size no coarser than ASTM #4 and 0.2% yield strength greater than 125,000 p.s.i. comprising forming a ring of steel containing .60 to .80% carbon, 8.00 to 10.00% manganese, .20 to .60% silicon, 6.00 to 7.00% nickel, 4.00 to 5.00% chromium and .30 to .60% columbium, balance substantially iron, and cold expanding said ring at least 25 4. A method of producing austenitic steel generator rotor coil support retaining rings characterized by a grain size no coarser than ASTM #4 and 0.2% yield strength greater than 125,000 p.s.i. comprising forming a ring of steel containing .60 to .80% carbon, 8.00 to 10.00% manganese, .20 to .60% silicon, 6.00 to 7.00%

a nickel, 4.00 to 5.00% chromium and .30 to .60% columbium, balance substantially iron, cold expanding said ring between 25% and 30% and then aging it at a temperature between 500 and 650 F.

5. An austenitic steel characterized by good cold formability and a grain size no coarser than ASTM #4 containing .60 to .80% carbon, 8.00 to 10.00% manganese, .20 to .60% silicon, 6.00 to 7.00% nickel, 4.00 to 5.00% chromium and .30 to .60% columbium, balance substantially iron.

6. An austenitic steel characterized by being hardenable by cold working and aging and having a grain size no coarser than ASTM #4 in the hardened condition,

References Cited in the file of this patent UNITED STATES PATENTS 1,561,306 Brace Nov. 10, 1925 1,574,782 Becker Mar. 2, 1926 2,449,023 Thornton Sept. 7, 1948 2,859,149 Straumann Nov. 4, 1958 :UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,062,692 November 6, 1962 Samuel J. Manganello et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 28, for "ASTM #1" read ASTMJM column 2, line -:29, for "22000 F. read 2200 F. Y

Signed and sealed this 9th day of April 1963.

(SEAL) Attest:

ESTON e. JOHNSON DAVID L. LADD I v Commissioner of Patents Attesting Officer :UNITED STATES PATENT CFFICE CERTIFICATE OF CORRECTION Patent N 3,062,692 November 6, 1962 Samuel J Manganello et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 line 28 for "ASTM 1" read ASTM. 4 v

column 2, line x29, for "22000 F." read 2200 F.

Signed and sealed this 9th day of April 1963,,

(SEAL) Attest: I r

ESTON G. JOHNSON DAVID L. LADD V Commissioner of Patents Attesting Officer

Claims

1. A COLD EXPANDED AUSTENITIC STEEL GENERATOR ROTOR COIL SUPPORT RETAINING RING CHARACTERIZED BY A GRAIN SIZE NO COARSER THAN ASTM #4 CONTAINING .60 TO .80% CARBON, 8.00 TO 10.00% MANGANESE, .20 TO .60% SILICON, 6.00 TO 7.00% NICKEL, 4.00 TO 5.00% CHROMIUM AND .30 TO .60% COLUMBIUM WITH THE BALANCE IRON AND OTHER ELEMENTS IN AMOUNTS WHICH DO NOT HAVE A HARMFUL EFFECT ON THE PROPERTIES.