ASTM A940-96(2001)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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: A 940 – 96 (Reapproved 2001)
Standard Specification for
Vacuum Treated Steel Forgings, Alloy, Differentially Heat
Treated, for Turbine Rotors
This standard is issued under the fixed designation A 940; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope E 139 Practice 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 A 788, the purchaser shall include with the
different austenitizing temperatures followed by two different
inquiry and order a detailed drawing, sketch, or written
cooling rates for normalizing and quenching, and then temper-
description of the forging, including the mechanical test
ing, to achieve creep resistance in the high pressure (HP)
2 locations, the portion of the forging to be included in the
portion and high toughness in the low pressure (LP) portion.
heating chamber during the stability test, and the minimum
1.3 The values stated in inch-pound units are to be regarded
stability test temperature.
as the standard. The values given in parentheses are for
3.2 Thepurchasershallspecifyifchecktestsformechanical
information only.
properties are required after stress relief or heat stability tests.
2. Referenced Documents 3.3 Supplementary Requirements—Supplementary require-
ments are provided. These requirements shall apply only when
2.1 ASTM Standards:
specified in the purchase order.
A 275/A 275M Test Methods for Magnetic Particle Exami-
nation of Steel Forgings
4. General Requirements
A 370 Test Methods and Definitions for MechanicalTesting
4.1 Material supplied to this specification shall conform to
of Steel Products
the requirements of Specification A 788, which outlines addi-
A 418 TestMethodofUltrasonicExaminationInspectionof
3 tional ordering information, manufacturing requirements, test-
Turbine and Generator Steel Rotor Forgings
ing and retesting methods and procedures, marking, certifica-
A 470 Specification for Vacuum-Treated Carbon and Alloy
3 tion, product analysis variations, and additional supplementary
Steel Forgings for Turbine Rotors and Shafts
requirements.
A 472 Test Method for Heat Stability of Steam Turbine
3 4.2 If the requirements of this specification are in conflict
Shafts and Rotor Forgings
with the requirements of SpecificationA 788, the requirements
A 751 Test Methods, Practices, and Terminology for
4 of this specification shall prevail.
Chemical Analysis of Steel Products
A 788 Specification for Steel Forgings, General Require-
5. Manufacture
ments
5.1 Melting processes of SpecificationA 788 shall be appli-
cable, except that the open hearth or basic oxygen methods of
primary melting shall not be used and the molten steel shall be
This specification is under the jurisdiction of ASTM Committee A01 on Steel,
Stainless Steel, and RelatedAlloys and is the direct responsibility of Subcommittee
vacuum treated during processing. When the ladle degassing
A01.06 on Steel Forgings and Billets.
process is used, the evacuation system shall be capable of
Current edition approved Sept. 10, 1996. Published July 1997. Originally
reducing the system vacuum pressure to a low level (usually
published as A 940–95. Last previous edition A 940–95.
Symposium on Steel Forgings,ASTM STP903,ASTM, Philadelphia, PA, 1984,
pp. 59-86.
Annual Book of ASTM Standards, Vol 01.05.
4 5
Annual Book of ASTM Standards, Vol 01.03. Annual Book of ASTM Standards, Vol 03.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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.
A 940 – 96 (2001)
less than 1000 µm). The molten metal shall be stirred ad- 5.4.4 Machining to Purchaser’s Requirements for
equately for a sufficient length of time to maximize exposure to Shipment—The forging, as shipped, shall conform to the finish
theevacuatedatmosphere.Whenthisprocessisused,hydrogen and dimensions specified on the purchaser’s drawing or order.
testing per Supplementary Requirement S4 is mandatory.
6. Chemical Composition
5.1.1 If the ESR process is used, the electrodes shall have
6.1 Heat Analysis—An analysis of each heat of steel shall
been produced from vacuum treated primary heat(s), and
be made by the manufacturer.This analysis shall be made from
Supplementary Requirement S4 is mandatory.
a test sample taken preferably during the pouring of the heat.
5.2 In addition to the requirements of SpecificationA 788,it
The steel shall conform to the requirements for chemical
is important to maintain the axial center of the forging in
composition prescribed in Table 1.
common with the axial center of the original ingot.
6.2 ProductAnalysis—The manufacturer shall make a prod-
5.3 Differential Heat Treatment—The heat treatment for
uct analysis from each forging. The chemical composition thus
mechanical properties shall consist of normalizing and temper-
determined shall not vary from the requirements specified in
ing of the creep resistant portion, HP portion, and quenching
Table 1 by more than the amounts prescribed in Specification
and tempering of the high toughness portion, LP portion.
A 788.
5.3.1 The preliminary heat treatment shall consist of nor-
6.3 Referee Analysis—Test Methods, Practices, and Termi-
malizing well above the transformation temperature range.
nology A 751 shall be used.
5.3.2 The normalizing and quenching treatments shall be
fromabovethetransformationrangebutbelowthenormalizing
7. Mechanical Properties
temperature described in 5.3.1. This treatment shall be per-
7.1 Tension Test:
formed after preliminary machining.
7.1.1 The steel shall conform to the tensile requirements of
5.3.2.1 The heat treatment for the HP portion shall consist
Table 2.
of normalizing, accelerated air cooling, and tempering.
7.1.2 The number and location of tension test specimens
5.3.2.2 For the high toughness LP portion, the heat treat-
shall be as specified on the forging drawings furnished by the
ment shall consist of water quenching (or water-spray quench-
purchaser.
ing) and tempering.
7.1.3 Final acceptance tests shall be performed after heat
5.3.3 The final tempering temperature for all zones shall not
treatment of the forging for mechanical properties prior to
be below 1200°F (649°C).
stress relief. If the stress relief temperature is within 25°F
5.3.4 After heat treatment and subsequent rough machining
(14°C) of the tempering temperature, or higher, check tests
and boring, the forging shall be stress relieved at a temperature
shall be made after the stress relief treatment and reported to
not more than 100°F (55°C) below the final tempering tem-
the purchaser. The purchaser may require check tests after the
perature, but not below 1100°F (593°C).
completion of all heating cycles, including stress relief and the
5.3.5 With the prior approval of the purchaser, the stress
heat stability tests.
relieving temperature may approach, equal, or slightly exceed
7.1.4 The yield strength prescribed in Table 2 shall be
the final tempering temperature as a means of adjusting final
determined by the offset method of Test Methods and Defini-
strength or toughness. If the stress relieving temperature is
tions A 370.
within 25°F (14°C) of the final tempering temperature, or
7.2 Impact Test:
higher, acceptance tests shall be obtained after the stress
7.2.1 The steel shall conform to the requirements for notch
relieving operation.
toughness (both transition temperature and room temperature
5.3.6 The method of cooling the HP and LP portions during
impact values) prescribed in Table 3.
the normalizing, quenching, tempering, and stress relieving
7.2.2 The notch toughness specimens shall be machined
heat treating cycles shall be reported.
from radial bars taken from the main body of the forging, as
5.4 Machining:
shown in the forging drawing. The specimens shall be Charpy
5.4.1 Preliminary Rough Machining—All exterior surfaces
V-notch, Type A, as shown in Test Methods and Definitions
of the forging shall be machined prior to heat treatment for
A 370. The notch direction of the Charpy bars shall be as
mechanical properties.
prescribed in Specification A 470.
5.4.2 Second Rough Machining—After heat treatment for
mechanicalproperties,allsurfacesoftheforgingshallberough
TABLE 1 Chemical Composition
machined prior to stress relief and the stability test.
Composition, % Grade 1
5.4.3 Boring:
Carbon 0.23–0.31
5.4.3.1 Forgings shall be bored to permissible bore size and
Manganese 0.50–1.00
tolerances when required by the purchaser’s drawing.
Phosphorus, max 0.012
5.4.3.2 Forgings may be bored to limits agreed to by the Sulfur, max 0.015
Silicon, max 0.10
purchaser or indicated on the purchaser’s drawing, to remove
Nickel 0.80–1.10
objectionable center conditions revealed by ultrasonic inspec-
Chromium 0.90–1.50
tion.
Molybdenum 1.10–1.50
Vanadium 0.20–0.30
5.4.3.3 Unless otherwise specified by the purchaser, the
Columbium (Niobium) 0.01–0.05
manufacturer may bore the forging at any time after quenching
Aluminum 0.010 max
and prior to stress relief.
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.
A 940 – 96 (2001)
TABLE 2 Tensile Requirem
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