ASTM A471/A471M-19(2024)

Standard Specification for Vacuum-Treated Alloy Steel Forgings for Turbine Rotor Disks and Wheels

ABSTRACT
This specification covers vacuum-treated alloy steel forgings intended for use as turbine rotor disks and wheels. The steel shall be made by the basic electric-furnace process. The molten steel shall be vacuum treated using either the vacuum stream degassing process, vacuum-lift process or ladle degassing process prior to or during the pouring of the ingot in order to remove objectionable gases, particularly hydrogen. The forgings shall receive their hot mechanical work under a press, hammer, or mill of sufficient power to work the metal throughout its section. Before reheating for heat treatment, the forging shall be allowed to cool in a manner to prevent damage and to accomplish transformation. The forgings shall be heated to a suitable temperature for a sufficient length of time for complete austenitization and shall be tempered to develop the specified properties. The forgings shall be preliminarily machined on all surfaces prior to heat treatment and shall be stress relieved after machining. To measure some mechanical properties, the specimens shall be subjected to tension test, impact test, and hardness test. A non-destructive test like an ultrasonic inspection shall be made on all available surfaces to demonstrate freedom from detrimental internal indications.
SCOPE
1.1 This specification covers vacuum-treated alloy steel forgings intended for use as turbine rotor disks and wheels.  
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 29-Feb-2024
• ICS: 77.140.85 - Iron and steel forgings
• Technical Committee: A01 - Steel, Stainless Steel and Related Alloys
• Drafting Committee: A01.06 - Steel Forgings and Billets

Relations

• Replaces: ASTM A471/A471M-19 - Standard Specification for Vacuum-Treated Alloy Steel Forgings for Turbine Rotor Disks and Wheels
• Effective Date: 01-Mar-2024
• Refers: ASTM A370-24 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Mar-2024
• Refers: ASTM A370-23 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-Sep-2023
• Referred By: ASTM A788/A788M-23 - Standard Specification for Steel Forgings, General Requirements
• Effective Date: 01-Mar-2024

Overview

ASTM A471/A471M-19(2024) is a standard specification developed by ASTM International that covers vacuum-treated alloy steel forgings used specifically for turbine rotor disks and wheels. This specification outlines the requirements for manufacturing, heat treatment, mechanical testing, and inspection to ensure the reliability and high performance of critical components in turbine machinery. The standard supports both SI and inch-pound units, which must be applied separately and not combined during application.

Vacuum treatment in the steel production process is emphasized in this standard to ensure the removal of objectionable gases - particularly hydrogen - which can adversely affect the integrity and mechanical properties of turbine components. The requirements also cover material ordering information, chemical composition, mechanical properties, non-destructive examination, and proper certification for quality assurance.

Key Topics

• Vacuum-Treated Alloy Steel: The standard mandates vacuum degassing processes such as vacuum stream, vacuum-lift, or ladle degassing to remove gases from molten steel prior to forging, significantly enhancing steel purity and reducing the risk of hydrogen embrittlement.
• Manufacturing Methods: Steel forgings must be produced using the electric-furnace process, with supplementary and secondary melting practices allowed as specified.
• Heat Treatment: Forgings undergo a precise heat treatment regime including austenitization and tempering to ensure optimal mechanical properties. Preliminary machining and stress relief procedures are also required for dimensional stability and performance.
• Mechanical and Non-destructive Testing: Materials must pass tension, impact, and hardness tests, with potential for creep or stress-rupture tests as supplements. Ultrasonic inspections are standard for detecting detrimental internal flaws. Additional non-destructive tests such as magnetic particle and dye penetrant tests may be implemented upon request.
• Ordering and Certification: The specification details ordering information, including the need for customer-provided drawings, class of steel, and test options. Manufacturers must provide documentation of chemical analyses, mechanical test results, and all heat treatment and inspection procedures.

Applications

ASTM A471/A471M-19(2024) is specifically designed for:

• Turbine Rotor Disks and Wheels: The primary application is in manufacturing critical rotating parts for turbines used in power generation, marine propulsion, and industrial equipment, where reliable performance under high mechanical and thermal stresses is essential.
• High-integrity Components: Due to stringent requirements for vacuum treatment and testing, the standard is ideal for alloy steel forgings that must withstand demanding operational environments, ensuring long service life and high safety margins.
• Global Supply Chains: The dual-unit approach and international development principles support broad adoption, facilitating the standard’s use in diverse global markets and compliance with international trade requirements.

Related Standards

Several other ASTM standards and specifications are referenced or complement ASTM A471/A471M-19(2024):

• ASTM A788/A788M: General requirements for steel forgings, including additional ordering, manufacturing, and supplementary requirements.
• ASTM A388/A388M: Practice for ultrasonic examination of steel forgings, crucial for internal quality assessment.
• ASTM A370: Methods and definitions for mechanical testing of steel products, used for tension, impact, and hardness test procedures.
• ASTM A275/A275M: Magnetic particle examination practice for surface inspection.
• ASTM E139: Methods for creep and stress-rupture tests of metallic materials.
• ASTM A751: Test methods for chemical analysis of steel products.

Keywords: vacuum-treated steel forgings, turbine rotor disks, turbine rotor wheels, mechanical properties, ultrasonic inspection, ASTM A471, alloy steel, electric-furnace process, power generation standards, non-destructive testing.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: A471/A471M − 19 (Reapproved 2024)
Standard Specification for
Vacuum-Treated Alloy Steel Forgings for Turbine Rotor
Disks and Wheels
This standard is issued under the fixed designation A471/A471M; 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 intended for use as turbine rotor disks and wheels.
3. Ordering Information
1.2 The values stated in either SI units or inch-pound units
3.1 Material supplied to this specification shall conform to
are to be regarded separately as standard. The values stated in
the requirements of Specification A788/A788M, which out-
each system are not necessarily exact equivalents; therefore, to
lines additional ordering information, manufacturing methods
ensure conformance with the standard, each system shall be
and procedures, marking, certification, production analysis
used independently of the other, and values from the two
variations, and additional supplementary requirements.
systems shall not be combined.
3.2 The purchaser shall specify in the inquiry and order the
1.3 This standard does not purport to address all of the
class of steel desired and test and purchase options (see 4.5.5,
safety concerns, if any, associated with its use. It is the
5.2.2, 6.1, 6.3, 6.4, and Section 7).
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3.3 Forging Drawing—Each forging shall be manufactured
mine the applicability of regulatory limitations prior to use.
in accordance with a purchaser-supplied drawing showing the
1.4 This international standard was developed in accor-
finished dimensions and the locations of mechanical test
dance with internationally recognized principles on standard-
specimens.
ization established in the Decision on Principles for the
3.4 Supplementary requirements are provided and shall
Development of International Standards, Guides and Recom-
apply only when specified in the purchaser’s order.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
4. Materials and Manufacture
2. Referenced Documents
4.1 Melting Process:
2.1 ASTM Standards: 4.1.1 The steel shall be made by the basic electric-furnace
A275/A275M Practice for Magnetic Particle Examination of process, with additional ladle refining being optional.
Steel Forgings 4.1.2 Provisions for subsequent secondary melting of the
A370 Test Methods and Definitions for Mechanical Testing steel by the consumable electrode-electroslag or vacuum-arc
of Steel Products remelting processes are included in Supplementary Require-
A388/A388M Practice for Ultrasonic Examination of Steel ment S4.
Forgings
4.2 The vacuum degassing requirements of Specification
A751 Test Methods and Practices for Chemical Analysis of
A788/A788M are mandatory.
Steel Products
4.3 Discard—Sufficient discard shall be taken from each
A788/A788M Specification for Steel Forgings, General Re-
ingot to secure freedom from pipe and undue segregation in the
quirements
finished forging.
This specification is under the jurisdiction of ASTM Committee A01 on Steel,
4.4 Forging Process—The forgings shall receive their hot
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee
mechanical work under a press, hammer, or mill of sufficient
A01.06 on Steel Forgings and Billets.
power to work the metal throughout its section. The forgings
Current edition approved March 1, 2024. Published March 2024. Originally
shall be upset by forming from a block having an axial length
approved in 1962. Last previous edition approved in 2019 as A471/A471M – 19.
DOI: 10.1520/A0471_A0471M-19R24.
before upsetting of at least two times the thickness of the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
forging after upsetting.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
4.4.1 The as-forged dimensions of each forging shall be
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. planned so the metal is shaped by forging as close as is
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A471/A471M − 19 (2024)
practical to the dimensions shown on the purchaser’s drawing 4.6.2 Machining to Purchaser’s Requirements for
so as to keep subsequent machining to a minimum. Shipment—After heat treatment for mechanical properties (see
4.4.2 The axial center of the forging shall be maintained in 4.5.3), the forgings shall be machined to the dimensions of the
common with the axial center of the ingot. purchaser’s forging drawing or instructions on the order.
4.5 Heat Treatment:
5. Chemical Composition
4.5.1 Cooling Prior to Heat Treatment—After forging and
5.1 The steel shall conform to the requirements for chemical
before reheating for heat treatment, the forging shall be
composition prescribed in Table 1.
allowed to cool in a manner to prevent damage and to
accomplish transformation. 5.2 Chemical Analysis:
4.5.2 Preliminary Heat Treatment—The forgings shall be 5.2.1 Heat Analysis—An analysis of each heat of steel shall
given such preliminary heat treatment as is proper for the be made by the manufacturer to determine the percentages of
design and composition. The forgings shall be heated to a those elements specified in Table 1. This analysis shall be made
suitable temperature for a sufficient length of time for complete from a test ingot taken during the pouring of the heat.
austenitization and shall be suitably cooled to bring about 5.2.1.1 If the test sample taken for the ladle analysis is lost
complete transformation. or declared inadequate for chemical determinations, the manu-
4.5.3 Heat Treatment for Mechanical Properties—The forg-
facturer may take alternative samples from appropriate loca-
ings shall be reheated to a temperature above the upper critical tions near the surface of the ingot or forging as necessary to
temperature, held a sufficient length of time for complete
establish the analysis of the heat in question.
austenitization, and liquid quenched. 5.2.2 Product Analysis—A product analysis may be re-
4.5.4 Tempering Temperature—The forgings shall be tem- quested by the purchaser on each forging. Sample for an
pered to develop the specified properties. The final tempering analysis may be taken from the forging at any point from the
temperature for Class 1 to 6 and 11 through 14 shall be not less mid-radius to the outside diameter or from a full-size
than 1100 °F [595 °C], and for Class 10 not less than 1200 °F prolongation, or turnings may be taken from a test specimen.
[650 °C]. The forgings shall be cooled under suitable condi- The chemical composition thus determined shall not vary from
tions from the tempering temperature. the requirements specified in Table 1 more than the amounts
4.5.5 Stress Relief—Unless otherwise specified by the prescribed in Table 1 of Specification A788/A788M.
purchaser, the forgings shall be stress relieved after machining
5.3 Test Methods of Analysis—Test Methods, Practices, and
(see 4.6.2) by heating slowly to a temperature within 100 °F
Terminology A751 shall be used for referee purposes.
[55 °C] below the final tempering temperature but in no case
below 1025 °F [550 °C] for Classes 1 to 6 and 11 through 14 6. Mechanical Properties
and 1150 °F [620 °C] for Class 10. They shall be held for a
6.1 Tension Test—The material shall conform to the require-
sufficient length of time and then cooled under suitable
ment for tensile properties prescribed in Table 2 when tested in
conditions. This stress-relief temperature may be omitted
accordance with Test Methods and Definitions A370. Tension
provided the metal removed in accordance with 4.6.2, exclud-
test specimens shall be the standard round, ⁄2 in. [12.5 mm]
ing test metal, does not exceed ⁄16 in. [5 mm] on any surface.
diameter, 2 in. [50 mm] gauge length as shown in Test Methods
4.6 Machining: and Definitions A370. The yield strength prescribed in Table 2
4.6.1 Preliminary Machining—The forgings shall be pre-
shall be determined by the 0.2 % offset method of Test
liminarily machined on all surfaces prior to heat treatment for Methods and Definitions A370. The offset shall be 0.2 %
mechanical properties (see 4.5.3). unless 0.02 % is specified in the ordering information.
TABLE 1 Chemical Requirements
Composition, %
Classes 1 to 6, Class 10 Classes 11 to 13, Class 14
incl incl
A
Carbon 0.28 max 0.27–0.37 0.38–0.43 0.45 max
Manganese 0.70 max 0.70–1.00 0.60–1.00 0.60–1.00
Phosphorus 0.012 max 0.012 max 0.012 max 0.012 max
Sulfur 0.015 max 0.015 max 0.015 max 0.015 max
B B B B B
Silicon
Nickel 2.00–4.00 0.50 max 0.50 max 1.65–3.50
Chromium 0.75–2.00 0.85–1.25 0.80–1.10 0.50–1.25
Molybdenum 0.20–0.70 1.00–1.50 0.15 min 0.20 min
Vanadium 0.05 min 0.20–0.30 0.06 max optional
C C C C
Antimony
D
Aluminum 0.015 max 0.015 max 0.015 max 0.015 max
A
0.35 % C max for Classes 4 and 5; 0.40 % C, max, for Class 6.
B
0.10 % max unless an alternative value, not in excess of 0.35 %, is specified in the purchase order.
C
To be reported for information only.
D
Total of soluble and insoluble.
A471/A471M − 19 (2024)
TABLE 2 Tensile and Charpy Impact Requirements
Class 1 Class 2 Class 3 Class 4 Class 5 Class 6
Tensile strength, min, ksi [MPa] 100 105 110 120 130 140
[690] [725] [760] [830] [900] [965]
Yield strength, ksi [MPa]
0.2 % offset 80–100 90–110 100–120 110–130 120–140 130–150
[550–690] [620–760] [690–825] [760–895] [825–965] [895–1035]
0.02 % offset 75–95 85–105 95–115 105–125 115–135 125–145
[520–655] [585–725] [655–790] [725–860] [790–930] [860–1000]
Elongation in 2 in. or 50 mm, min, % 20 19 18 17 16 15
Reduction of area, min, % 50 50 47 45 43 43
Charpy V-notch impact, room temperature, ft·lbf [J], min 50 [68] 50 [68] 45 [61] 45 [61] 40 [54] 40 [54]
Transition temperature, FATT , °F [°C], max 0 [–18] 0 [–18] 0 [–18] 0 [–18] 10 [–12] 10 [–12]
Brinell hardness number . . . . . . . . . . . . . . . . . .
Class 10 Class 11 Class 12 Class 13 Class 14
Tensile strength, min, ksi [MPa] 105 100 110 125 125
[725] [690] [760] [860] [860]
Yield strength, ksi [MPa]
0.2 % offset 90–105 . . . . . . . . .
...