ASTM_B_344_-_14.pdf

Designation:B34414Standard Specification forDrawn or Rolled Nickel-Chromium and Nickel-Chromium-Iron Alloys for Electrical Heating Elements1This standard is issued under the fixed designation B344;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.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope1.1 This specification covers annealed,drawn,or rolledshapes for electrical heating purposes,of alloys having thenominal compositions of 80%nickel and 20%chromium;60%nickel,16%chromium,and remainder iron;and 35%nickel,20%chromium,and remainder iron;38%nickel,21%chromium,and remainder iron;and 35%nickel,20%chro-mium remainder iron.1.2 The values stated in inch-pound units are to be regardedas standard.The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.2.Referenced Documents2.1 ASTM Standards:2A751 Test Methods,Practices,and Terminology for Chemi-cal Analysis of Steel ProductsB63 Test Method for Resistivity of Metallically ConductingResistance and Contact MaterialsB70 Test Method for Change of Resistance With Tempera-ture of Metallic Materials for Electrical HeatingB76 Test Method for Accelerated Life of Nickel-Chromiumand Nickel-Chromium-Iron Alloys for Electrical Heating3.Significance and Use3.1 This specification on nickel-chromium and nickel-chromium-iron alloys contains the requirements for chemistry,electrical resistance,mechanical properties,and packaging.4.Requirements4.1 The alloys shall conform to the requirements as tochemical composition prescribed in Table 1.4.2 Samples for Chemical AnalysisSpecimens for chemi-cal analysis may be taken from either the melt or from a sampleof finished wire that is representative of the lot.4.2.1 The lot size for determining compliance with therequirements of this specification shall be one heat.4.3 Chemical AnalysisThe chemical analysis shall bemade in accordance with Test Methods A751,or by otheranalytical methods approved by the purchaser.4.4 Actual chemical analysis is not required for routineacceptance.5.Physical Requirements5.1 The material shall be thoroughly and uniformly an-nealed.5.2 Wire shall conform to the following elongation require-ments:SizeElongation in 10 in.,min,%0.0035 in.(0.0889 mm)(No.39 Awg)and larger200.0031 in.(0.0787 mm)to 0.002 in.(0.0508 mm)(Nos.40 to 44 Awg)105.3 Determination is not required for routine acceptance.6.Nominal Resistivity6.1 The nominal resistivity(Note 1)shall be the resistivityof the wire as quenched from a temperature above 1450F(788C).The numerical value of the nominal resistivity shallbe as shown in Table 2.6.2 Determination is not required for routine acceptance.NOTE1The characteristics of these alloys are such that the actualresistivity of annealed wire may be as much as 6%higher than thenominal,depending on its method of manufacture.7.Test for Resistivity7.1 The resistivity shall be determined in accordance withTest Method B63.7.2 Determination is not required for routine acceptance.1This specification is under the jurisdiction of ASTM Committee B02 onNonferrous Metals and Alloys and is the direct responsibility of SubcommitteeB02.10 on Thermostat Metals and Electrical Resistance Heating Materials.Current edition approved Oct.1,2014.Published October 2014.Originallyapproved in 1959.Last previous edition approved in 2011 as B344 11.DOI:10.1520/B0344-14.2For 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 8.Nominal Electrical Resistance for Unit Length8.1 The nominal resistance per unit length for round wireshall be calculated from the nominal resistivity and the nominalcross-sectional area.NOTE2When ribbon or flat wire is produced by rolling from roundwire,the cross section departs from that of a true rectangle by an amountdepending on the width-to-thickness ratio and the specific manufacturingpractice.The conventional formula for computing ohms per foot and feetper pound is to consider the cross section as 17%less than a true rectanglewhen width is more than 15 times the thickness and 6%less than a truerectangle in other cases.This is not valid in view of modern rollingequipment and practices,but still is widely used as a basis of description.Ribbon actually is made to a specified resistance per foot,and no toleranceis specified for thickness.An alternative and a closer approximation wouldbe that for ribbon rolled from round wire,the electrical resistance wouldbe calc