Active Standard ASTM A940 / A940M | Developed by Subcommittee: A01.06
Book of Standards Volume: 01.05
Historical (view previous versions of standard)
This specification covers vacuum treated and differentially heat treated alloy steel forgings for turbine rotors. Materials shall be manufactured by melting process, heat treatment (consisting of normalizing and tempering to achieve creep resistance in the high pressure portion, and quenching and tempering to achieve high toughness in the low pressure portion), rough machining, and boring. Heat and product analyses shall be performed to evaluate conformance of the steel to required chemical compositions. Tension and impact tests shall also be executed to make sure that forgings adhere to tensile and notch toughness requirements, including tensile strength, yield strength, elongation, and reduction of area. Final products shall be free of cracks, seams, laps, shrinkage, and other injurious imperfections. To evaluate such imperfections, nondestructive tests, such as ultrasonic and internal inspection procedures, may be conducted at the preference of the purchaser. Forgings that do not meet the requirements specified, may be retreated one or more times, but not more than three additional times.
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1.1 This specification covers vacuum treated, alloy steel forgings, differentially heat treated for turbine rotors.
1.2 Differential heat treatment of a rotor forging involves subjecting two portions of the forging concurrently to two different austenitizing temperatures followed by two different cooling rates for normalizing and quenching, and then tempering, to achieve creep resistance in the high pressure (HP) portion and high toughness in the low pressure (LP) portion.
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-conformance with the standard.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
A275/A275M Practice for Magnetic Particle Examination of Steel Forgings
A370 Test Methods and Definitions for Mechanical Testing of Steel Products
A418/A418M Practice for Ultrasonic Examination of Turbine and Generator Steel Rotor Forgings
A470/A470M Specification for Vacuum-Treated Carbon and Alloy Steel Forgings for Turbine Rotors and Shafts
A472/A472M Specification for Heat Stability of Steam Turbine Shafts and Rotor Forgings
A788/A788M Specification for Steel Forgings, General Requirements
E139 Test Methods for Conducting Creep, Creep-Rupture, and Stress-Rupture Tests of Metallic Materials
ICS Number Code 77.140.85 (Iron and steel forgings)