ASTM A768-95
(Specification)Standard Specification for Vacuum-Treated 12% Chromium Alloy Steel Forgings for Turbine Rotors and Shafts
Standard Specification for Vacuum-Treated 12% Chromium Alloy Steel Forgings for Turbine Rotors and Shafts
SCOPE
1.1 This specification covers vacuum-treated 12 % chromium steel forgings for turbine rotors and shafts.
1.2 The values stated in inch-pound units are to be regarded as the standard.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: A 768 – 95 An American National Standard
Standard Specification for
Vacuum-Treated 12 % Chromium Alloy Steel Forgings for
Turbine Rotors and Shafts
This standard is issued under the fixed designation A 768; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 5. Manufacture
1.1 This specification covers vacuum-treated 12 % chro- 5.1 The melting processes of Specification A 788 shall be
mium steel forgings for turbine rotors and shafts. applicable except that the open-hearth or basic oxygen methods
1.2 The values stated in inch-pound units are to be regarded of primary melting shall not be used, and the molten steel shall
as the standard. be vacuum degassed prior to or during pouring of the ingot.
5.1.1 If the ESR process is used, then the electrodes shall
2. Referenced Documents
have been produced from vacuum degassed primary heat(s).
2.1 ASTM Standards: 5.2 In addition to the requirements of Specification A 788, it
A 275/A 275M Test Method for Magnetic Particle Exami-
is important to maintain the axial center of the forging in
nation of Steel Forgings common with the axial center of the original ingot.
A 370 Test Methods and Definitions for Mechanical Testing
5.3 Heat Treatment:
of Steel Products 5.3.1 The heat treatment for mechanical properties shall
A 418 Test Method of Ultrasonic Examination of Turbine
consist of quenching and tempering.
and Generator Steel Rotor Forgings 5.3.1.1 The preliminary heat treatment shall consist of
A 472 Test Method for Heat Stability of Steam Turbine
normalizing well above the transformation temperature range.
Shafts and Rotor Forgings This operation may be performed before preliminary machin-
A 788 Specification for Steel Forgings, General Require-
ing (see 5.4.1).
ments 5.3.1.2 The quenching treatment shall be from above the
transformation range but below the normalizing temperature
3. Ordering Information
described in 5.3.1.1. This treatment shall be performed after
3.1 In addition to the ordering information required by
preliminary machining (see 5.4.1). Austenitizing temperatures
Specification A 788, the purchaser shall include with the
shall be in accordance with Table 1.
inquiry and order a detailed drawing, sketch, or written
5.3.1.3 The final tempering temperature shall be in accor-
description of the forging, including the mechanical test
dance with Table 1.
specimen location.
5.3.1.4 After heat treatment and subsequent rough machin-
ing and boring (see 5.4.2 and 5.4.3), the forging shall be
4. General Requirements
stress-relieved at a temperature not more than 100°F (55°C)
4.1 Material supplied to this specification shall conform to
below the final tempering temperature, but not less than 1100°F
the requirements of Specification A 788 which outlines addi-
(593°C).
tional ordering information, manufacturing requirements, test-
5.3.1.5 With the prior approval of the purchaser, the stress-
ing and retesting methods and procedures, marking, certifica-
relief temperature may approach, equal, or slightly exceed the
tion, product analysis variations, and additional supplementary
final tempering temperature as a means of adjusting final
requirements.
strength or toughness. If the stress relief temperature is within
4.2 If the requirements of this specification are in conflict
25°F (14°C) of the final tempering temperature, or higher,
with the requirements of Specification A 788, the requirements
additional tension tests must be obtained (see 7.1.3).
of this specification shall prevail.
5.3.1.6 The method of cooling during quenching and from
the final tempering and stress relieving temperatures shall be
reported.
This specification is under the jurisdiction of ASTM Committee A-1 on Steel,
5.4 Machining:
Stainless Steel, and Related Alloys and is the direct responsibility of Subcommittee
A01.06 on Steel Forgings and Billets.
5.4.1 Preliminary Rough Machining—All exterior surfaces
Current edition approved Jan. 15, 1995. Published March 1995. Originally
of the forging shall be machined prior to heat treatment for
published as A 768 – 79. Last previous edition A 768 – 93.
mechanical properties.
Annual Book of ASTM Standards, Vol 01.05.
Annual Book of ASTM Standards, Vol 01.03. 5.4.2 Second Rough Machining—After heat treatment for
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
A 768
TABLE 1 Heat Treating Requirements
of the tempering temperature, or higher, in which case check
Grade Austenitizing 1st Tempering 2nd tests shall be made after the stress relief treatment and reported
Temperature, Temperature, Tempering
to the purchaser. The purchaser may require check tests after
°F min Temperature
completion of all heating cycles, including stress relief and the
1 1725–1825 1125 1100
heat stability tests.
2 1900–1940 1040 1010–1040
7.1.4 The yield strength prescribed in Table 3 shall be
3 1700–1800 1120 1100
4 1700–1800 975 950
determined by the offset method of Test Methods and Defini-
tions A 370.
7.2 Impact Test:
7.2.1 The steel shall conform to the requirements for notch
mechanical properties, all surfaces of the forging shall be rough
toughness (both transition temperature and room temperature
machined prior to stress relief and the stability test.
impact values) prescribed in Table 3.
5.4.3 Boring:
7.2.2 The notch toughness specimens shall be machined
5.4.3.1 Forgings shall be bored to permissible bore size and
from radial bars taken from the main body of the forging, as
tolerance when required by the purchaser’s drawing.
shown in the forging drawing. The specimens shall be charpy
5.4.3.2 Forgings may be bored to limits agreed to by the
V-notch, Type A, as shown in Test Methods and Definitions
purchaser or indicated on the purchaser’s drawing, to remove
A 370. The notch direction of the charpy bars shall be
objectionable center conditions revealed by ultrasonic inspec-
tangential.
tion.
5.4.3.3 Unless otherwise specified by the purchaser, the
8. Nondestructive Tests
manufacturer may bore the forging at any time prior to stress
relief (see Supplementary Requirement S1).
8.1 General Requirements:
5.4.4 Machining to Purchaser’s Requirements for
8.1.1 The forgings shall be free of cracks, seams, laps,
Shipment—The forging as shipped shall conform to the finish
shrinkage, and other injurious imperfections.
and dimension requirements specified on the purchaser’s
8.1.2 The purchaser may request ultrasonic, magnetic par-
drawing or order.
ticle, dye penetrant, etch, or other accepted nondestructive
inspection necessary to evaluate imperfections and to ensure
6. Chemical Composition
compliance with this requirement.
6.1 The steel shall conform to the requirements for chemical
8.2 Ultrasonic Inspection:
composition prescribed in Table 2. 8.2.1 An ultrasonic inspection shall be made on the ma-
6.2 Product Analysis—The manufacturer shall make a prod-
chined forging at the manufacturer’s plant. This inspection
uct analysis from each forging. The chemical composition thus shall be made in accordance with Test Method A 418 to
determined shall not vary from the requirements specified in
demonstrate freedom from detrimental internal defects.
Table 1 by more than the amounts prescribed in Specification 8.2.2 The ultrasonic inspection shall be made from all
A 788.
available surfaces prior to removal of
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