Standard Specification for Vacuum Treated Steel Forgings, Alloy, Differentially Heat Treated, for Turbine Rotors

ABSTRACT
This specification covers vacuum treated and differentially heat treated alloy steel forgings for turbine rotors. Materials shall be manufactured by melting process, heat treatment (consisting of normalizing and tempering to achieve creep resistance in the high pressure portion, and quenching and tempering to achieve high toughness in the low pressure portion), rough machining, and boring. Heat and product analyses shall be performed to evaluate conformance of the steel to required chemical compositions. Tension and impact tests shall also be executed to make sure that forgings adhere to tensile and notch toughness requirements, including tensile strength, yield strength, elongation, and reduction of area. Final products shall be free of cracks, seams, laps, shrinkage, and other injurious imperfections. To evaluate such imperfections, nondestructive tests, such as ultrasonic and internal inspection procedures, may be conducted at the preference of the purchaser. Forgings that do not meet the requirements specified, may be retreated one or more times, but not more than three additional times.
SCOPE
1.1 This specification covers vacuum treated, alloy steel forgings, differentially heat treated for turbine rotors.  
1.2 Differential heat treatment of a rotor forging involves subjecting two portions of the forging concurrently to two different austenitizing temperatures followed by two different cooling rates for normalizing and quenching, and then tempering, to achieve creep resistance in the high pressure (HP) portion and high toughness in the low pressure (LP) portion.  
1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

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ASTM A940/A940M-06(2011) - Standard Specification for Vacuum Treated Steel Forgings, Alloy, Differentially Heat Treated, for Turbine Rotors
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:A940/A940M −06(Reapproved 2011)
Standard Specification for
Vacuum Treated Steel Forgings, Alloy, Differentially Heat
Treated, for Turbine Rotors
This standard is issued under the fixed designationA940/A940M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E139 Test Methods for Conducting Creep, Creep-Rupture,
and Stress-Rupture Tests of Metallic Materials
1.1 This specification covers vacuum treated, alloy steel
forgings, differentially heat treated for turbine rotors.
3. Ordering Information
1.2 Differential heat treatment of a rotor forging involves
3.1 In addition to the ordering information required by
subjecting two portions of the forging concurrently to two
Specification A788/A788M, the purchaser shall include with
different austenitizing temperatures followed by two different
the inquiry and order a detailed drawing, sketch, or written
cooling rates for normalizing and quenching, and then
description of the forging, including the mechanical test
tempering, to achieve creep resistance in the high pressure
locations, the portion of the forging to be included in the
(HP) portion and high toughness in the low pressure (LP)
heating chamber during the stability test, and the minimum
portion.
stability test temperature.
1.3 The values stated in either SI units or inch-pound units
3.2 The purchaser shall specify if check tests for mechanical
are to be regarded separately as standard. The values stated in
properties are required after stress relief or heat stability tests.
each system may not be exact equivalents; therefore, each
system shall be used independently of the other. Combining
3.3 Supplementary Requirements—Supplementary require-
values from the two systems may result in non-conformance
ments are provided. These requirements shall apply only when
with the standard.
specified in the purchase order.
2. Referenced Documents
4. General Requirements
2.1 ASTM Standards:
4.1 Material supplied to this specification shall conform to
A275/A275M Practice for Magnetic Particle Examination of
the requirements of Specification A788/A788M, which out-
Steel Forgings
lines additional ordering information, manufacturing
A370 Test Methods and Definitions for Mechanical Testing
requirements, testing and retesting methods and procedures,
of Steel Products
marking, certification, product analysis variations, and addi-
A418/A418M Practice for Ultrasonic Examination of Tur-
tional supplementary requirements.
bine and Generator Steel Rotor Forgings
A470/A470M Specification for Vacuum-Treated Carbon and
4.2 If the requirements of this specification are in conflict
Alloy Steel Forgings for Turbine Rotors and Shafts
with the requirements of Specification A788/A788M, the
A472/A472M Specification for Heat Stability of Steam Tur-
requirements of this specification shall prevail.
bine Shafts and Rotor Forgings
A788/A788M Specification for Steel Forgings, General Re-
5. Manufacture
quirements
5.1 Melting processes of Specification A788/A788M shall
be applicable, except that the open hearth or basic oxygen
This specification is under the jurisdiction of ASTM Committee A01 on Steel,
methods of primary melting shall not be used and the molten
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee
A01.06 on Steel Forgings and Billets. steel shall be vacuum treated during processing. Except for
Current edition approved April 1, 2011. Published June 2011. Originally
vacuum stream degassed ingots, the hydrogen content shall be
approved in 1995. Last previous edition approved in 2006 as A940/A940M – 06.
determined. The acceptable hydrogen limit as well as the stage
DOI: 10.1520/A0940_A0940M-06R11.
2 in processing when sampling, the sample preparation proce-
Symposium on Steel Forgings, ASTM STP 903, ASTM International, West
Conshohocken, PA, 1984, pp. 59–86.
dure and the method of analysis shall be established between
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
the manufacturer and the purchaser.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
5.1.1 If the ESR process is used, the electrodes shall have
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. been produced from vacuum treated primary heat(s).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A940/A940M−06 (2011)
5.2 In addition to the requirements of Specification A788/ testsampletakenpreferablyduringthepouringoftheheat.The
A788M, it is important to maintain the axial center of the steel shall conform to the requirements for chemical composi-
forging in common with the axial center of the original ingot. tion prescribed in Table 1.
5.3 Differential Heat Treatment—The heat treatment for 6.2 ProductAnalysis—The manufacturer shall make a prod-
mechanical properties shall consist of normalizing and temper- uct analysis from each forging. The chemical composition thus
ing of the creep resistant portion, HP portion, and quenching determined shall not vary from the requirements specified in
and tempering of the high toughness portion, LP portion. Table 1 by more than the amounts prescribed in Specification
5.3.1 The preliminary heat treatment shall consist of nor- A788/A788M.
malizing well above the transformation temperature range.
7. Mechanical Properties
5.3.2 The normalizing and quenching treatments shall be
fromabovethetransformationrangebutbelowthenormalizing 7.1 Tension Test:
7.1.1 The steel shall conform to the tensile requirements of
temperature described in 5.3.1. This treatment shall be per-
formed after preliminary machining. Table 2.
7.1.2 The number and location of tension test specimens
5.3.2.1 The heat treatment for the HP portion shall consist
of normalizing, accelerated air cooling, and tempering. shall be as specified on the forging drawings furnished by the
5.3.2.2 For the high toughness LP portion, the heat treat- purchaser.
ment shall consist of water quenching (or water-spray quench- 7.1.3 Final acceptance tests shall be performed after heat
ing) and tempering. treatment of the forging for mechanical properties prior to
5.3.3 The final tempering temperature for all zones shall not stress relief. If the stress relief temperature is within 25°F
be below 1200°F [650°C]. [15°C] of the tempering temperature, or higher, check tests
5.3.4 After heat treatment and subsequent rough machining shall be made after the stress relief treatment and reported to
and boring, the forging shall be stress relieved at a temperature the purchaser. The purchaser may require check tests after the
completion of all heating cycles, including stress relief and the
not more than 100°F [55°C] below the final tempering
temperature, but not below 1100°F [595°C]. heat stability tests.
7.1.4 The yield strength prescribed in Table 2 shall be
5.3.5 With the prior approval of the purchaser, the stress
relieving temperature may approach, equal, or slightly exceed determined by the offset method of Test Methods and Defini-
tions A370.
the final tempering temperature as a means of adjusting final
strength or toughness. If the stress relieving temperature is
7.2 Impact Test:
within 25°F [15°C] of the final tempering temperature, or
7.2.1 The steel shall conform to the requirements for notch
higher, acceptance tests shall be obtained after the stress
toughness (both transition temperature and room temperature
relieving operation.
impact values) prescribed in Table 3.
5.3.6 The method of cooling the HP and LP portions during
7.2.2 The notch toughness specimens shall be machined
the normalizing, quenching, tempering, and stress relieving
from radial bars taken from the main body of the forging, as
heat treating cycles shall be reported.
shown in the forging drawing. The specimens shall be Charpy
5.4 Machining: V-notch, Type A, as shown in Test Methods and Definitions
5.4.1 Preliminary Rough Machining—All exterior surfaces A370. The notch direction of the Charpy bars shall be as
of the forging shall be machined prior to heat treatment for prescribed in Specification A470/A470M.
mechanical properties.
8. Nondestructive Tests
5.4.2 Second Rough Machining—After heat treatment for
8.1 General Requirements:
mechanicalproperties,allsurfacesoftheforgingshallberough
machined prior to stress relief and the stability test. 8.1.1 The forgings shall be free of cracks, seams, laps,
shrinkage, and other injurious imperfections.
5.4.3 Boring:
5.4.3.1 Forgings shall be bored to permissible bore size and 8.1.2 The purchaser may request ultrasonic, magnetic
particle, dye penetrant, etch, or other nondestructive inspec-
tolerances when required by the purchaser’s drawing.
5.4.3.2 Forgings may be bored to limits agreed to by the tions necessary to evaluate imperfections and to ensure com-
pliance with this requirement.
purchaser or indicated on the purchaser’s drawing, to remove
objectionable center conditions revealed by ultrasonic inspec-
TABLE 1 Chemical Composition
tion.
Composition, % Grade 1
5.4.3.3 Unless otherwise specified by the purchaser, the
Carbon 0.23–0.31
manufacturer may bore the forging at any time after quenching
Manganese 0.50–1.00
and prior to stress relief.
Phosphorus, max 0.012
5.4.4 Machining to Purchaser’s Requirements for
Sulfur, max 0.015
Silicon, max 0.10
Shipment—The forging, as shipped, shall conform to the finish
Nickel 0.80–1.10
and dimensions specified on the purchaser’s d
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