1、Designation: A 768/A 768M 05Standard Specification forVacuum-Treated 12 % Chromium Alloy Steel Forgings forTurbine Rotors and Shafts1This standard is issued under the fixed designation A 768/A 768M; the number immediately following the designation indicates the yearof original adoption or, in the ca
2、se 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*1.1 This sp
3、ecification covers vacuum-treated 12 % chro-mium steel forgings for turbine rotors and shafts.1.2 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used indep
4、endently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety a
5、nd health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A 275/A 275M Test Method for Magnetic Particle Exami-nation of Steel ForgingsA 370 Test Methods and Definitions for Mechanical Testingof Steel ProductsA 418 Test Met
6、hod of Ultrasonic Examination of Turbineand Generator Steel Rotor ForgingsA 472 Test Method for Heat Stability of Steam TurbineShafts and Rotor ForgingsA 788 Specification for Steel Forgings, General Require-ments3. Ordering Information3.1 In addition to the ordering information required bySpecifica
7、tion A 788, the purchaser shall include with theinquiry and order a detailed drawing, sketch, or writtendescription of the forging, including the mechanical testspecimen location.4. General Requirements4.1 Material supplied to this specification shall conform tothe requirements of Specification A 78
8、8 which outlines addi-tional ordering information, manufacturing requirements, test-ing and retesting methods and procedures, marking, certifica-tion, product analysis variations, and additional supplementaryrequirements.4.2 If the requirements of this specification are in conflictwith the requireme
9、nts of Specification A 788, the requirementsof this specification shall prevail.5. Manufacture5.1 The melting processes of Specification A 788 shall beapplicable except that the open-hearth or basic oxygen methodsof primary melting shall not be used, and the molten steel shallbe vacuum degassed prio
10、r to or during pouring of the ingot.5.1.1 If the ESR process is used, then the electrodes shallhave been produced from vacuum degassed primary heat(s).5.2 In addition to the requirements of SpecificationA 788,itis important to maintain the axial center of the forging incommon with the axial center o
11、f the original ingot.5.3 Heat Treatment:5.3.1 The heat treatment for mechanical properties shallconsist of quenching and tempering.5.3.1.1 The preliminary heat treatment shall consist ofnormalizing well above the transformation temperature range.This operation may be performed before preliminary mac
12、hin-ing (see 5.4.1).5.3.1.2 The quenching treatment shall be from above thetransformation range but below the normalizing temperaturedescribed in 5.3.1.1. This treatment shall be performed afterpreliminary machining (see 5.4.1). Austenitizing temperaturesshall be in accordance with Table 1.5.3.1.3 T
13、he final tempering temperature shall be in accor-dance with Table 1.1This specification is under the jurisdiction of ASTM Committee A01 on Steel,Stainless Steel, and Related Alloys and is the direct responsibility of SubcommitteeA01.06 on Steel Forgings and Billets.Current edition approved Sept. 1,
14、2005. Published September 2005. Originallyapproved in 1979. Last previous edition approved in 2001 as A 768 95 (2001).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer t
15、o the standards Document Summary page onthe ASTM website.1*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.5.3.1.4 After heat treatment and subsequent rough machin-ing a
16、nd boring (see 5.4.2 and 5.4.3), the forging shall bestress-relieved at a temperature not more than 100F 55Cbelow the final tempering temperature, but not less than 1100F595C.5.3.1.5 With the prior approval of the purchaser, the stress-relief temperature may approach, equal, or slightly exceed thefi
17、nal tempering temperature as a means of adjusting finalstrength or toughness. If the stress relief temperature is within25F 15C of the final tempering temperature, or higher,additional tension tests must be obtained (see 7.1.3).5.3.1.6 The method of cooling during quenching and fromthe final temperi
18、ng and stress relieving temperatures shall bereported.5.4 Machining:5.4.1 Preliminary Rough MachiningAll exterior surfacesof the forging shall be machined prior to heat treatment formechanical properties.5.4.2 Second Rough MachiningAfter heat treatment formechanical properties, all surfaces of the f
19、orging shall be roughmachined prior to stress relief and the stability test.5.4.3 Boring:5.4.3.1 Forgings shall be bored to permissible bore size andtolerance when required by the purchasers drawing.5.4.3.2 Forgings may be bored to limits agreed to by thepurchaser or indicated on the purchasers draw
20、ing, to removeobjectionable center conditions revealed by ultrasonic inspec-tion.5.4.3.3 Unless otherwise specified by the purchaser, themanufacturer may bore the forging at any time prior to stressrelief (see Supplementary Requirement S1).5.4.4 Machining to Purchasers Requirements forShipmentThe fo
21、rging as shipped shall conform to the finishand dimension requirements specified on the purchasersdrawing or order.6. Chemical Composition6.1 The steel shall conform to the requirements for chemicalcomposition prescribed in Table 2.6.2 Product AnalysisThe manufacturer shall make a prod-uct analysis
22、from each forging. The chemical composition thusdetermined shall not vary from the requirements specified inTable 1 by more than the amounts prescribed in SpecificationA 788.7. Mechanical Properties7.1 Tension Test:7.1.1 The steel shall conform to the tensile requirements ofTable 3.7.1.2 The number
23、and location of tension test specimensshall be as specified on the forging drawings furnished by thepurchaser.7.1.3 Final acceptance tests shall be made after heat treat-ment of the forging for mechanical properties prior to stressrelief, unless the stress relief temperature is within 25F 15Cof the
24、tempering temperature, or higher, in which case checktests shall be made after the stress relief treatment and reportedto the purchaser. The purchaser may require check tests aftercompletion of all heating cycles, including stress relief and theheat stability tests.7.1.4 The yield strength prescribe
25、d in Table 3 shall bedetermined 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 notchtoughness (both transition temperature and room temperatureimpact values) prescribed in Table 3.7.2.2 The notch toughness specimens s
26、hall be machinedfrom radial bars taken from the main body of the forging, asshown in the forging drawing. The specimens shall be CharpyV-notch, Type A, as shown in Test Methods and DefinitionsA 370. The notch direction of the Charpy bars shall betangential.8. Nondestructive Tests8.1 General Requirem
27、ents:TABLE 1 Heat Treating Temperature, F C, RequirementsGrade Austenitizing 1stTempering,min2ndTempering1 17251825 1125 1100940995 605 5952 19001940 1040 1010104010351060 560 5455603 17001800 1120 1100925980 605 5954 17001800 975 950925980 525 510TABLE 2 Chemical RequirementsComposition, % Grade 1
28、Grade 2 Grade 3 Grade 4Carbon 0.15 max 0.080.15 0.100.16 0.050.07Manganese 1.0 max 0.500.90 0.251.00 0.701.00Phosphorus 0.018 max 0.02 max 0.015 max 0.015 maxSulfur 0.015 max 0.015 max 0.012 max 0.012 maxSilicon 0.35 max 0.30 max 0.150.45 0.300.50Nickel 0.400.75 2.03.0 0.75 max 3.54.25Chromium 11.51
29、3.0 11.013.0 11.013.0 11.2512.25Molybdenum 0.50 max 1.52.0 0.20 max 0.300.50Vanadium . 0.250.40 . 0.03 maxColumbium . . 0.15 min .Aluminum . . . 0.03 maxNitrogen . 0.06 max . .A 768/A 768M 0528.1.1 The forgings shall be free of cracks, seams, laps,shrinkage, and other injurious imperfections.8.1.2 T
30、he purchaser may request ultrasonic, magnetic par-ticle, dye penetrant, etch, or other accepted nondestructiveinspection necessary to evaluate imperfections and to ensurecompliance with this requirement.8.2 Ultrasonic Inspection:8.2.1 An ultrasonic inspection shall be made on the ma-chined forging a
31、t the manufacturers plant. This inspectionshall be made in accordance with Test Method A 418 todemonstrate freedom from detrimental internal defects.8.2.2 The ultrasonic inspection shall be made from allavailable surfaces prior to removal of test specimens thatwould interfere with complete testing o
32、f the forging.8.2.3 Forgings with recordable ultrasonic indications shallbe referred to the purchaser for evaluation based on the nature,frequency, and location of indications, both stationary andtraveling. If the ultrasonic indications are considered objection-able, it shall be determined by conven
33、tional or mutuallyacceptable inspection procedures whether the forging will berejected.8.3 Internal Inspection:8.3.1 Boring, when specified for internal periscopic inspec-tion, shall be in accordance with the drawings furnished by thepurchaser. The drawings shall specify the nominal dimensionsof the
34、 bore hole.8.3.2 If objectionable conditions are encountered during theinternal inspection of the bore hole, the manufacturer shallnotify the purchaser of the location and nature of the condition.Further action shall be taken only after mutual agreementbetween the manufacturer and purchaser.9. Stabi
35、lity Test9.1 Each forging shall be subjected to a heat stability test atthe manufacturers plant in accordance with the latest issue ofTest Method A 472 to determine the stability or freedom fromtendency to distort during high temperature operating condi-tions.9.2 The stability test shall be conducte
36、d after the forging hasbeen stress relieved in accordance with 5.3.1.4.NOTE 1If agreed to by the purchaser, the stress relief may beperformed as part of the stability test.9.3 Stability Test Requirements:9.3.1 The purchasers drawings shall indicate the minimumportion of the forging to be included wi
37、thin the heatingchamber during the stability test.9.3.2 The purchasers drawings or order shall indicate theminimum stability test temperature.10. Retreatment10.1 If the results of the mechanical tests of any forging donot conform to the requirements specified, the manufacturermay retreat the forging
38、 one or more times, but not more thanthree additional times, without the approval of the purchaser.10.2 If bore core properties are specified under Supplemen-tary Requirement S1 and retemper is necessary after boring,the remaining portions of the bore core shall be replaced in thebore during retempe
39、r.10.3 If complete retreatment, including normalizing orquenching, is necessary after boring, the feasibility of retreat-ing portions of the bore core in the bore of the forging shall bediscussed between manufacturer and purchaser and a proce-dure agreed upon before treatment.11. Certification and R
40、eports11.1 In addition to the certification requirements of Speci-fication A 788, the following shall be reported:11.1.1 Product analysis results.12. Package Marking, Packaging, and Loading12.1 In addition to the marking requirements in Specifica-tion A 788, test specimens shall be identified with n
41、umberscorresponding to the forging identification numbers and num-bers corresponding to test location and type if specified on thepurchasers drawings or order.12.2 In addition, the axial bores of bored forgings shall beprotected and suitably plugged to prevent damage or corrosionduring shipment or s
42、torage.TABLE 3 Tensile and Notch Toughness RequirementsGrade 1Grade 2Grade 3 Grade 4Class 1 Class 2 Class 1 Class 2 Class 1 Class 2Tensile strength, ksi MPa 90110 85 min 150 min 90110 105125 110140 120150620760 585 1035 620760 725860 760965 8251035Yield strength (0.2 % offset) ksiMPa, min70631070808
43、595485 435 760 485 550 585 655minElongation, min, % 16 18 15 15 16 16 15Reduction of area, min, % 45 45 45 45 45 45 42FATT50, max, F C 175 140 25 140 175 60 8080 60 -4 60 80 15 25Room temperature impact, min, ft-lbJ15 20 50 15 15 35 2520 28 70 20 20 49 35A 768/A 768M 053SUPPLEMENTARY REQUIREMENTSThe
44、 following supplementary requirement shall apply only when specified by the purchaser in theinquiry, contract, and order. Details of this supplementary requirement shall be agreed upon betweenthe manufacturer and the purchaser.S1. Bore Core PropertiesS1.1 The purchaser may require the removal of the
45、 longi-tudinal bore core from the forging after heat treatment formechanical properties and subsequent approval of the usualsurface mechanical property tests.S1.1.1 The diameter of the longitudinal bore core shall besubject to agreement between the manufacturer and the pur-chaser.S1.1.2 The purchase
46、r may require mechanical tests ontension of impact specimens from locations in the longitudinalbore core as specified on the forging drawings furnished by thepurchaser.S1.1.3 The acceptable level of mechanical properties ob-tained from specimens from the longitudinal bore core shall beas agreed upon
47、 between the manufacturer and the purchaser.S2. Magnetic Particle ExaminationS2.1 A magnetic particle examination of the completeexterior and bore surfaces of the machined forging shall bemade at the forging manufacturers plant. The examinationshall be performed in accordance with the latest issue o
48、f TestMethod A 275/A 275M.S2.2 Forgings with either cracks or linear indications of anylength are subject to rejection unless they can be removed tothe purchasers satisfaction.SUMMARY OF CHANGESCommittee A01 has identified the location of several changes made to this standard since the last issue(A
49、768 95 (2001) that may impact its use.(1) Converted the standard to dual unit format.(2) Deleted several sections that are already covered in thegeneral requirements specification, A 788.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any su
