ASTM A1091/A1091M-21

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
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Designation: A1091/A1091M − 16 A1091/A1091M − 21
Standard Specification for
Steel Castings, Creep-Strength Enhanced Ferritic Alloy, for
Pressure-Containing Parts, Suitable for High Temperature
High-Temperature Service
This standard is issued under the fixed designation A1091/A1091M; 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.
ε NOTE—Table 3 was editorially corrected in April 2017.
1. Scope Scope*
1.1 This specification covers creep-strength enhanced alloy steel castings for valves, flanges, fittings, and other pressure-
containing parts intended primarily for high-temperature service (see Note 1). However, they are not restricted to such
applications,applications and the castings may be used for other applications for which the attributes of the material, as defined
by this specification, are suitable.
1.2 One grade of martensitic alloy steel, Grade C91, C91 (UNS Number J84090), is covered (see Note 2). It is provided in two
classes, differentiated by the type of heat treatment after weld repairs. welding. This and similar steels are characterized by a
predominantly tempered martensitic or tempered Bainitic microstructure that is stabilized by the precipitation of temper-resistant
particles at various precipitate nucleation sites in the microstructure. Such steels are designed to have creep-rupture strengths
significantly superior to those of alloys of nominally similar compositions, but in which the precipitates or nucleation sites are
absent. Since this crucial difference cannot be revealed by room-temperature mechanical property tests, these alloys require tighter
controls on manufacturing and processing.
NOTE 1—The grades covered by this specification represent materials that are generally suitable for assembly with other castings or wrought steel parts
by fusion welding. It is not intended to imply that these grades possess equal degrees of weldability; therefore, it is the responsibility of the purchaser
to establish a suitable welding technique. Since these grades possess varying degrees of suitability for high-temperature service, it is also the responsibility
of the purchaser to determine which grade shall be furnished, due consideration being given to the requirements of the applicable construction codes.
NOTE 2—The committee formulating this specification has included one grade of material that is considered to represent a type of ferritic alloy steel
suitable for valves, flanges, fittings, and other pressure-containing parts. Additional alloy steels will be considered for inclusion in this specification by
the committee as the need becomes apparent.
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-conformancenonconformance with the standard.
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.
This specification is under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee A01.18
on Castings.
Current edition approved May 1, 2016May 1, 2021. Published May 2016June 2021. Originally approved in 2016. Last previous edition approved in 2016 as
A1091/A1091M – 16. DOI: 10.1520/A1091_A1091M-16E01.10.1520/A1091_A1091M-21.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A1091/A1091M − 21
2. Referenced Documents
2.1 ASTM Standards:
A335/A335M Specification for Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service
A703/A703M Specification for Steel Castings, General Requirements, for Pressure-Containing Parts
A802/A802M Practice for Steel Castings, Surface Acceptance Standards, Visual Examination
A985/A985M Specification for Steel Investment Castings General Requirements, for Pressure-Containing Parts
A999/A999M Specification for General Requirements for Alloy and Stainless Steel Pipe
2.2 ANSI StandardsStandard:
ANSI B46.1 Surface Texture
2.3 ASME Boiler and Pressure Vessel CodeCode:
ASME Boiler and Pressure Vessel Code Section I
ASME Boiler and Pressure Vessel Code Section III
ASME Boiler and Pressure Vessel Code Section IV
ASME Boiler and Pressure Vessel Code Section VIII
ASME Boiler and Pressure Vessel Code Section IX
ASME Boiler and Pressure Vessel Code Section XII
2.4 Other ASME CodesCodes:
B16.34 Valves Flanged, Threaded and Welding End
B31.1 Power Piping
B31.3 Process Piping
2.5 AWS SpecificationsSpecifications:
A5.5/A5.5M Low Alloy Low-Alloy Steel Electrodes for Shielded Metal Arc Welding
A5.23/A5.23M Low Alloy Low-Alloy Steel Electrodes and Fluxes for Submerged Arc Welding
A5.28/A5.28M Low Alloy Low-Alloy Steel Electrodes and Rods for Gas Shielded Arc Welding
A5.29/A5.29M Low Allow Low-Alloy Steel Electrodes for Flux Cored Arc Welding
3. General Conditions for Delivery
3.1 Except for investment castings and centrifugally cast pipe, castings furnished to this specification shall conform to the
requirements of Specification A703/A703M, including any supplementary requirements that are indicated in the purchase order.
Failure to comply with the general requirements of Specification A703/A703M constitutes nonconformance with this specification.
In case of conflict between the requirements of this specification and Specification A703/A703M, this specification shall prevail.
3.2 Investment castings furnished to this specification shall conform to the requirements of Specification A985/A985M, including
any supplementary requirements that are indicated in the purchase order. Failure to comply with the general requirements of
Specification A985/A985M constitutes nonconformance with this specification. In case of conflict between the requirements of this
specification and Specification A985/A985M, Specification A985/A985M shall prevail.
3.3 Centrifugally cast pipe furnished under this specification shall conform to the requirements of Specification A999/A999M,
including any supplementary requirements that are indicated in the purchase order. Failure to comply with the general requirements
of Specification A999/A999M constitutes nonconformance with this specification. In case of conflict between the requirements of
this specification and Specification A999/A999M, this specification shall prevail.
4. Ordering Information
4.1 Orders for material under this specification shall include the following, as required, to describe the desired material adequately:
4.1.1 Except for centrifugally cast pipe,pipe:
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Available from American Society of Mechanical Engineers (ASME), ASME International Headquarters, Two Park Ave., New York, NY 10016-5990, http://
www.asme.org.
Available from American Welding Society (AWS), 8669 NW 36 St., #130, Miami, FL 33166-6672, http://www.aws.org.
A1091/A1091M − 21
4.1.1.1 A description of the casting by pattern number or drawing (dimensional tolerances shall be included on the casting
drawing),
4.1.1.2 Grade and Classclass of steel,
4.1.1.3 Options in the specification (see 5.1.5, 5.2, 7.1.4, 8.4, 10.3.5, and 10.3.7, 10.3.8.2, and 10.3.8.3),
4.1.1.4 Whether the castings are to be produced using the investment casting process, and
4.1.1.5 The supplementary requirements desired including the standards of acceptance.
4.1.2 Centrifugally cast pipe,pipe:
4.1.2.1 Quantity (feet, centimeters, or number of lengths),
4.1.2.2 Name of material (centrifugally cast pipe),
4.1.2.3 Grade of steel,
4.1.2.4 Size (outside or inside diameter and minimum wall thickness),
4.1.2.5 Length (specific or random) (Section on Permissible Variations in Length of Specification A999/A999M),
4.1.2.6 End finish (Section on Ends of Specification A999/A999M),
4.1.2.7 Options in the specification (see 5.1.5, 5.2, 7.1.4, 8.4, 10.3.5, and 10.3.7, 10.3.8.2, and 10.3.8.3),
4.1.2.8 Whether the castings are to be used in ASME Boiler &and Pressure Vessel Code Sections I, III, IV, VIII, and XII
construction; or in ASME Codes B16.34, B31.1, B31.3, or other ASME construction codes,and,codes, and
4.1.2.9 The supplementary requirements desired.
5. Materials and Manufacture
5.1 Heat-Treatment—Heat Treatment—Castings shall be furnished in the austenitized and tempered condition.
5.1.1 Before heat treatment, castings shall be allowed to cool to a temperature below the transformation range.
5.1.2 Castings shall be heat treated by heating to a temperature range of 1900 to 1975°F1975 °F [1040 to 1080°C]1080 °C] and
either air cooled or accelerated cooled from the austenitizing temperature by air blasting or liquid quenching, to a temperature of
200°F [95°C]200 °F [95 °C] or below, followed by tempering at 1350 to 1470°F1470 °F [730 to 800°C].800 °C].
5.1.3 Compliance with the temperature ranges specified in 5.1.2, for castings heat treated singly, shall be verified by a
thermocouple or thermocouples placed directly on the castings.
5.1.4 Compliance with the temperature ranges specified in 5.1.2, for castings heat treated in batches, shall be verified by
thermocouples placed on selected castings in each batch.
5.1.5 Unless specified by the purchaser, the number and locations of thermocouples to be placed on each casting, or on castings
in each heat-treatment batch, shall be at the discretion of the producer.
5.1.6 A record of the final austenitizing and tempering heat treatment,treatment and, if specified in the order (see 10.3.7),) of any
and all subsequent sub-criticalsubcritical heat treatments, shall be made and shall be shown on the material test report. The record
shall include both the number and locations of thermocouples applied to each casting, or to each heat-treatment batch of castings.
5.2 Machining—Centrifugally cast pipe shall be machined on the inner and outer surfaces to a roughness value no greater than
250μ in.250 μin. [6.35 μm] arithmetical average deviation (AA) from the mean line unless otherwise specified as in ANSI B46.1.
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6. Chemical Composition
6.1 Heat Analysis—An analysis of each heat shall be made by the manufacturer to determine the weight percentages of elements
specified in Table 1. The analysis shall be made on a test sample taken from the ladle. The chemical composition thus determined
shall steel shall conform to the requirements specified in Table 1 (see Note 3).
NOTE 3—The role of alloying elements in the development of Grade C91has C91 has been extensively investigated. V and Cb (Nb) contribute to
precipitation strengthening by forming fine and coherent precipitation of M(C, N)X carbo-nitrides in the ferrite matrix. V also precipitates as VN during
tempering or during creep. The two elements are more effective in combination. Therefore, the addition of strong nitride-forming elements, those with
a stronger affinity for nitrogen than Cb (Nb) and V, as de-oxidation agents,agents interferes with these high-temperature strengthening mechanisms.
7. Mechanical Properties
7.1 Tensile Testing—Testing:
7.1.1 One tension test shall be made from each heat per heat treatment lot. Test results shall conform to the tensile requirements
specified in Table 2.
7.1.2 If a specimen is machined improperly or if flaws are revealed by machining or during testing, the specimen may be discarded
and another substituted from the same heat.
7.1.3 Except as permitted by 7.1.4, and except for investment castings, test coupons from which tension test specimens are
prepared shall be removed from heat-treated casting prolongations.
7.1.4 When agreed upon between the manufacturer and the purchaser, test coupons from which test specimens are prepared shall
be cast as separate blocks from the same heat as the casting represented. The test blocks shall be heat treated in the same manner
as the casting represented.
TABLE 1 Chemical RequirementsComposition Requirements for
A
Grade C91 (UNS Number J84090)
Composition, %
Element Weight %
Grade Identification Symbol C91
UNS Number J84090
Carbon 0.08-0.12
Carbon 0.08–0.12
Manganese 0.30–0.60
Phosphorus 0.025
Sulfur 0.010
Silicon 0.20–0.50
Nickel 0.40
Chromium 8.0–9.5
Molybdenium 0.85–1.05
Molybdenum 0.85–1.05
A
Columbium
A
(Niobium) 0.060–0.10
B
Niobium 0.060–0.10
Nitrogen 0.030–0.070
Vanadium 0.18–0.25
Aluminum 0.02
Titanium 0.01
Zirconium 0.01
A
All values are maximums unless a range is provided.
B
Columbium (Cb) and Niobium (Nb) refer to the same Element 41.are inter-
changeable names for element 41
...