ASTM A768-95(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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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 768 – 95 (Reapproved 2001)
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 4.2 If the requirements of this specification are in conflict
with the requirements of SpecificationA 788, the requirements
1.1 This specification covers vacuum-treated 12 % chro-
of this specification shall prevail.
mium steel forgings for turbine rotors and shafts.
1.2 The values stated in inch-pound units are to be regarded
5. Manufacture
as the standard.
5.1 The melting processes of Specification A 788 shall be
2. Referenced Documents applicableexceptthattheopen-hearthorbasicoxygenmethods
of primary melting shall not be used, and the molten steel shall
2.1 ASTM Standards:
be vacuum degassed prior to or during pouring of the ingot.
A 275/A 275M Test Method for Magnetic Particle Exami-
5.1.1 If the ESR process is used, then the electrodes shall
nation of Steel Forgings
have been produced from vacuum degassed primary heat(s).
A 370 Test Methods and Definitions for MechanicalTesting
5.2 In addition to the requirements of SpecificationA 788,it
of Steel Products
is important to maintain the axial center of the forging in
A 418 Test Method of Ultrasonic Examination of Turbine
common with the axial center of the original ingot.
and Generator Steel Rotor Forgings
5.3 Heat Treatment:
A 472 Test Method for Heat Stability of Steam Turbine
5.3.1 The heat treatment for mechanical properties shall
Shafts and Rotor Forgings
consist of quenching and tempering.
A 788 Specification for Steel Forgings, General Require-
5.3.1.1 The preliminary heat treatment shall consist of
ments
normalizing well above the transformation temperature range.
3. Ordering Information This operation may be performed before preliminary machin-
ing (see 5.4.1).
3.1 In addition to the ordering information required by
5.3.1.2 The quenching treatment shall be from above the
Specification A 788, the purchaser shall include with the
transformation range but below the normalizing temperature
inquiry and order a detailed drawing, sketch, or written
described in 5.3.1.1. This treatment shall be performed after
description of the forging, including the mechanical test
preliminary machining (see 5.4.1). Austenitizing temperatures
specimen location.
shall be in accordance with Table 1.
4. General Requirements
5.3.1.3 The final tempering temperature shall be in accor-
dance with Table 1.
4.1 Material supplied to this specification shall conform to
5.3.1.4 After heat treatment and subsequent rough machin-
the requirements of Specification A 788 which outlines addi-
ing and boring (see 5.4.2 and 5.4.3), the forging shall be
tional ordering information, manufacturing requirements, test-
stress-relieved at a temperature not more than 100°F (55°C)
ing and retesting methods and procedures, marking, certifica-
belowthefinaltemperingtemperature,butnotlessthan1100°F
tion, product analysis variations, and additional supplementary
(593°C).
requirements.
5.3.1.5 With the prior approval of the purchaser, the stress-
relief temperature may approach, equal, or slightly exceed the
This specification is under the jurisdiction of ASTM Committee A01 on Steel,
final tempering temperature as a means of adjusting final
Stainless Steel, and RelatedAlloys and is the direct responsibility of Subcommittee
strength or toughness. If the stress relief temperature is within
A01.06 on Steel Forgings and Billets.
25°F (14°C) of the final tempering temperature, or higher,
Current edition approved Jan. 15, 1995. Published March 1995. Originally
published as A 768 – 79. Last previous edition A 768 – 93. additional tension tests must be obtained (see 7.1.3).
Annual Book of ASTM Standards, Vol 01.05.
Annual Book of ASTM Standards, Vol 01.03.
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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.
A 768 – 95 (2001)
TABLE 1 Heat Treating Requirements
7.1.1 The steel shall conform to the tensile requirements of
Grade Austenitizing 1st Tempering 2nd Table 3.
Temperature, Temperature, Tempering
7.1.2 The number and location of tension test specimens
°F min Temperature
shall be as specified on the forging drawings furnished by the
1 1725–1825 1125 1100
purchaser.
2 1900–1940 1040 1010–1040
7.1.3 Final acceptance tests shall be made after heat treat-
3 1700–1800 1120 1100
4 1700–1800 975 950
ment of the forging for mechanical properties prior to stress
relief,unlessthestressrelieftemperatureiswithin25°F(14°C)
of the tempering temperature, or higher, in which case check
tests shall be made after the stress relief treatment and reported
5.3.1.6 The method of cooling during quenching and from
to the purchaser. The purchaser may require check tests after
the final tempering and stress relieving temperatures shall be
completion of all heating cycles, including stress relief and the
reported.
heat stability tests.
5.4 Machining:
7.1.4 The yield strength prescribed in Table 3 shall be
5.4.1 Preliminary Rough Machining—All exterior surfaces
determined by the offset method of Test Methods and Defini-
of the forging shall be machined prior to heat treatment for
tions A 370.
mechanical properties.
7.2 Impact Test:
5.4.2 Second Rough Machining—After heat treatment for
7.2.1 The steel shall conform to the requirements for notch
mechanicalproperties,allsurfacesoftheforgingshallberough
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 Thesteelshallconformtotherequirementsforchemical
8.2 Ultrasonic Inspection:
composition prescribed in Table 2.
8.2.1 An ultrasonic inspection shall be made on the ma-
6.2 ProductAnalysis—Themanufacturershallmakeaprod-
chined forging at the manufacturer’s plant. This inspection
uct analysis from each forging. The chemical composition thus
shall be made in accordance wi
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