ASTM_E_1921_-_15.pdf

Designation:E192115Standard Test Method forDetermination of Reference Temperature,To,for FerriticSteels in the Transition Range1This standard is issued under the fixed designation E1921;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the determination of a referencetemperature,To,which characterizes the fracture toughness offerritic steels that experience onset of cleavage cracking atelastic,or elastic-plastic KJcinstabilities,or both.The specifictypes of ferritic steels(3.2.1)covered are those with yieldstrengths ranging from 275 to 825 MPa(40 to 120 ksi)andweld metals,after stress-relief annealing,that have 10%orless strength mismatch relative to that of the base metal.1.2 The specimens covered are fatigue precracked single-edge notched bend bars,SE(B),and standard or disk-shapedcompact tension specimens,C(T)or DC(T).A range ofspecimen sizes with proportional dimensions is recommended.The dimension on which the proportionality is based isspecimen thickness.1.3 Median KJcvalues tend to vary with the specimen typeat a given test temperature,presumably due to constraintdifferences among the allowable test specimens in 1.2.Thedegree of KJcvariability among specimen types is analyticallypredicted to be a function of the material flow properties(1)2and decreases with increasing strain hardening capacity for agiven yield strength material.This KJcdependency ultimatelyleads to discrepancies in calculated Tovalues as a function ofspecimen type for the same material.Tovalues obtained fromC(T)specimens are expected to be higher than Tovaluesobtained from SE(B)specimens.Best estimate comparisons ofseveral materials indicate that the average difference betweenC(T)and SE(B)-derived Tovalues is approximately 10C(2).C(T)and SE(B)Todifferences up to 15C have also beenrecorded(3).However,comparisons of individual,small data-sets may not necessarily reveal this average trend.Datasetswhich contain both C(T)and SE(B)specimens may generateToresults which fall between the Tovalues calculated usingsolely C(T)or SE(B)specimens.It is therefore stronglyrecommended that the specimen type be reported along withthe derived Tovalue in all reporting,analysis,and discussion ofresults.This recommended reporting is in addition to therequirements in 11.1.1.1.4 Requirements are set on specimen size and the numberof replicate tests that are needed to establish acceptablecharacterization of KJcdata populations.1.5 Tois dependent on loading rate.Tois evaluated for aquasi-static loading rate range with 0.1 dK/dt 2 MPam/s.Slowly loaded specimens(dK/dt 2MPam/s)in Annex A1.1.6 The statistical effects of specimen size on KJcin thetransition range are treated using weakest-link theory(4)applied to a three-parameter Weibull distribution of fracturetoughness values.A limit on KJcvalues,relative to thespecimen size,is specified to ensure high constraint conditionsalong the crack front at fracture.For some materials,particu-larly those with low strain hardening,this limit may not besufficient to ensure that a single-parameter(KJc)adequatelydescribes the crack-front deformation state(5).1.7 Statistical methods are employed to predict the transi-tion toughness curve and specified tolerance bounds for 1Tspecimens of the material tested.The standard deviation of thedata distribution is a function of Weibull slope and median KJc.The procedure for applying this information to the establish-ment of transition temperature shift determinations and theestablishment of tolerance limits is prescribed.1.8 This test method assumes that the test material ismacroscopically homogeneous such that the materials haveuniform tensile and toughness properties.The fracture tough-ness evaluation of nonuniform materials is not amenable to thestatistical analysis methods employed in the main body of thistest method.Application of the analysis of this test method toan inhomogeneous material will result in an inaccurate esti-mate of the transition reference value Toand non-conservativeconfidence bounds.For example,multipass weldments cancreate heat-affected and brittle zones with localized propertiesthat are quite different from either the bulk material or weld.Thick section steel also often exhibits some variation in1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of E08.07 on Fracture Mechanics.Current edition approved Feb.1,2015.Published June 2015.Originallyapproved in 1997.Last previous edition approved in 2014 as E1921 14a.DOI:10.1520/E1921-15.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959