ASTM_A_768_-_A_768M_-_05_2015.pdf

Designation:A768/A768M05(Reapproved 2015)Standard Specification forVacuum-Treated 12%Chromium Alloy Steel Forgings forTurbine Rotors and Shafts1This standard is issued under the fixed designation A768/A768M;the number immediately following the designation indicates the yearof 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.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope1.1 This specification 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 independently 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 and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2A275/A275M Practice for Magnetic Particle Examination ofSteel ForgingsA370 Test Methods and Definitions for Mechanical Testingof Steel ProductsA418/A418M Practice for Ultrasonic Examination of Tur-bine and Generator Steel Rotor ForgingsA472/A472M Specification for Heat Stability of Steam Tur-bine Shafts and Rotor ForgingsA788/A788M Specification for Steel Forgings,General Re-quirements3.Ordering Information3.1 In addition to the ordering information required bySpecification A788/A788M,the purchaser shall include withthe inquiry 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 A788/A788M which outlinesadditional ordering information,manufacturing requirements,testing and retesting methods and procedures,marking,certification,product analysis variations,and additional supple-mentary requirements.4.2 If the requirements of this specification are in conflictwith the requirements of Specification A788/A788M,therequirements of this specification shall prevail.5.Manufacture5.1 The melting processes of Specification A788/A788Mshall be applicable except that the open-hearth or basic oxygenmethods of primary melting shall not be used,and the moltensteel shall be vacuum degassed prior to or during pouring of theingot.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 Specification A788/A788M,it is important to maintain the axial center of theforging in common with the axial center of 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 machin-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 The 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 March 1,2015.Published March 2015.Originallyapproved in 1979.Last previous edition approved in 2010 as A768/A768M 05(2010).DOI:10.1520/A0768_A0768M-05R15.2For 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 to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.3.1.4 After heat treatment and subsequent rough machin-ing and 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 thefinal 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 c