1 1ENGINEERING MATERIALS IENGINEERING MATERIALS ICH-5 HARDNESS & HARDNESS CH-5 HARDNESS & HARDNESS TESTINGTESTING2 2IntroductionIntroductionHardness measurements widely used in Hardness measurements widely used in laboratory and as industrial tests laboratory and as industrial tests (widely used on castings and orgings! (widely used on castings and orgings! as a tool c"aracteri#ing t"e mec"anical as a tool c"aracteri#ing t"e mec"anical $ro$erties o materials%$ro$erties o materials%It can be used to classiy t"e materials It can be used to classiy t"e materials or to identiy a material in a grou$%or to identiy a material in a grou$%Hardness tests are em$loyed at a &ery Hardness tests are em$loyed at a &ery large scale to assess t"e useul large scale to assess t"e useul $ro$erties o materials%$ro$erties o materials%3 3'E(INITI)N'E(INITI)NHardness is de*ned as t"e resistance o a Hardness is de*ned as t"e resistance o a material to $ermanent deormation suc" as+material to $ermanent deormation suc" as+,IndentationIndentation,-ear-ear,AbrassionAbrassion,Scratc"Scratc"Hardness is a mec"anical $ro$erty t"at is Hardness is a mec"anical $ro$erty t"at is related to+related to+,-ear resistance o a material-ear resistance o a material,Its ability to abrade or indent anot"er material Its ability to abrade or indent anot"er material oror,Its resistance to $ermanent or $lastic Its resistance to $ermanent or $lastic deormationdeormation4 4T"ere are many "ardness tests T"ere are many "ardness tests currently in use%T"e neccessity or all currently in use%T"e neccessity or all t"ese di.erent "ardness tests is due to t"ese di.erent "ardness tests is due to t"e need or categori#ing t"e great t"e need or categori#ing t"e great range o "ardness rom sot rubber to range o "ardness rom sot rubber to "ard ceramics%"ard ceramics%Selecting o t"e a$$ro$irate "ardnees Selecting o t"e a$$ro$irate "ardnees test is de$endent u$on t"etest is de$endent u$on t"e,Relati&e "ardness o t"e material being Relati&e "ardness o t"e material being tested andtested and,Amount o damage t"at can be tolerated on Amount o damage t"at can be tolerated on t"e surace o t"e s$ecimen (or material!t"e surace o t"e s$ecimen (or material!5 5T/0ES )( HAR'NESS TESTST/0ES )( HAR'NESS TESTS T"e ty$es o "ardness testers in use o $roduct T"e ty$es o "ardness testers in use o $roduct are based on a number o 1arbitrary de*nitions2 are based on a number o 1arbitrary de*nitions2 o "ardness% o "ardness% Some o t"ese de*nitions are+Some o t"ese de*nitions are+ 34 Resistance to $ermanent indentation 34 Resistance to $ermanent indentation (indentation test ! (indentation test ! 54Resistance to scratc"ing (scratc" test!54Resistance to scratc"ing (scratc" test! 64Energy absor$tion under im$act loads 64Energy absor$tion under im$act loads (dynamic "ardness test!(dynamic "ardness test! 74Rebound o a alling weig"t (rebound test!74Rebound o a alling weig"t (rebound test! 3&4 : Same principle collision&absorbed energy 3&4 : Same principle collision&absorbed energy of one hard metal by the other soft metalof one hard metal by the other soft metal6 6) t"ese met"ods8 indentation test is ) t"ese met"ods8 indentation test is em$loyed t"e most%em$loyed t"e most%(or t"is ty$e o test8 "ardness is de*ned (or t"is ty$e o test8 "ardness is de*ned as t"e resistance o a material to as t"e resistance o a material to $ermanent indentation%$ermanent indentation%The general principle of the indentation The general principle of the indentation testtest is t"at a "ard indenter (a small is t"at a "ard indenter (a small s$"ere8 $yramid or cone! is $ressed into s$"ere8 $yramid or cone! is $ressed into t"e surace o t"e material to be tested t"e surace o t"e material to be tested under a s$eci*c load or a de*nite under a s$eci*c load or a de*nite inter&all o time8 and t"e si#e or t"e inter&all o time8 and t"e si#e or t"e de$t" o t"e indentation is measured%de$t" o t"e indentation is measured%7 7Brinell-indentersRockcell Ball indentersRockcell Diamond indenters2.5 mm carbide ball indenter5 mm carbide ball indenter8 8Hardness test is one o t"e $rominent Hardness test is one o t"e $rominent tests in determining t"e $ro$erties o tests in determining t"e $ro$erties o materials%materials%9ecause8 a reasonable relations"i$ e:ists 9ecause8 a reasonable relations"i$ e:ists between t"e "ardness and ot"er $"ysical between t"e "ardness and ot"er $"ysical $ro$erties o a material%$ro$erties o a material%(or e:am$le8 "ardness and t"e tensile (or e:am$le8 "ardness and t"e tensile test bot" measure t"e resistance o a test bot" measure t"e resistance o a material to $lastic deormation%T"ereore material to $lastic deormation%T"ereore a correlation e:ists between t"e "ardness a correlation e:ists between t"e "ardness and tensile strengt" o t"e steels +and tensile strengt" o t"e steels +SSt t = = ;%66 : 9HN;%66 : 9HN9 9Howe&er8 "ardness is not a undamental Howe&er8 "ardness is not a undamental $ro$erty o a material%$ro$erty o a material%It de$ends u$on t"e $articular treatment to It de$ends u$on t"e $articular treatment to w"ic" t"e material "as been subsed Indentation Hardness Tests Are +Hardness Tests Are + 34Macro Hardness34Macro Hardness TestersTesters Loads ? 3 @g54Micro Hardness Testers 54Micro Hardness TestersLoads A 3 @g9RINELL H%T%R)=B-ELL H%T%CI=BERS H%TCI=BERS 'IAM)N'0/RAMI' H%T%BN))0 'IAM)N' H%T%11 11Micro "ardness testMicro "ardness testT"e si#e o indentation $roduced is so T"e si#e o indentation $roduced is so small t"at a $owerull microsco$e is small t"at a $owerull microsco$e is reDuired to reDuired to measure t"e si#e o indentation%measure t"e si#e o indentation%T"is met"od is used or testing &ery T"is met"od is used or testing &ery t"in materials (down to ;%;3 mm!8 t"in materials (down to ;%;3 mm!8 e:tremely small $arts8 t"in e:tremely small $arts8 t"in su$er*cially "ardened $arts8 $lated su$er*cially "ardened $arts8 $lated suraced and in researc" a$$lications%suraced and in researc" a$$lications%12 12In indentation ty$e o testers8 t"e In indentation ty$e o testers8 t"e s"a$e and si#e o t"e indenter and t"e s"a$e and si#e o t"e indenter and t"e magnitude o t"e load a$$lied are magnitude o t"e load a$$lied are selected in accordance wit" t"eselected in accordance wit" t"e ++,0ur$ose o t"e test0ur$ose o t"e test,T"e structural $ro$erties o t"e material T"e structural $ro$erties o t"e material being testedbeing tested,T"e state o its surace andT"e state o its surace and,T"e si#e o t"e $art or s$ecimenT"e si#e o t"e $art or s$ecimen All of which shall be dealt with in appropriate All of which shall be dealt with in appropriate placesplaces13 13 T"e A'CANTAGES o T"e Hardness T"e A'CANTAGES o T"e Hardness Measurements can be summari#ed as +Measurements can be summari#ed as +3!3!T"e "ardness o a T"e "ardness o a Ductile Material, Ductile Material, determined by t"e indentation test8 is determined by t"e indentation test8 is related wit" its ot"er mec"anical related wit" its ot"er mec"anical $ro$erties (in $articular wit" t"e ultimate $ro$erties (in $articular wit" t"e ultimate tensile strengt"!% T"e tensile strengt"!% T"e SSut ut o most steels o most steels (e:ce$t or t"ose "a&ing austenitic or (e:ce$t or t"ose "a&ing austenitic or mantensitic structure! and many non4mantensitic structure! and many non4errous alloys can be assessed Duic@ly by errous alloys can be assessed Duic@ly by "ardnessmeasurements%"ardnessmeasurements%14 14T"oug" t"eT"oug" t"e rittle Materialsrittle Materials undergo $lasticundergo $lastic deormation in indentation tests8 a correlationdeormation in indentation tests8 a correlation between "ardness andbetween "ardness and S Suu is not obser&ed or brittleis not obser&ed or brittle materials% A limited e:ce$tion is t"e gray iron ormaterials% A limited e:ce$tion is t"e gray iron or w"ic" a Dualitati&e relations"i$ e:ists% A "ig"w"ic" a Dualitati&e relations"i$ e:ists% A "ig" indentation "ardness is usually an indication o "ig"indentation "ardness is usually an indication o "ig" ultimate com$ressi&e strengt" ( ultimate com$ressi&e strengt" (S Suc uc! or t"is material! or t"is material (gray iron!% (gray iron!%,Hardness8 as determined by indentation tests8 isHardness8 as determined by indentation tests8 is also s"own to be correlated wit" t"ealso s"own to be correlated wit" t"e E Efatiguefatigue strength! strength!o some metals suc" as annealed steels8 co$$er ando some metals suc" as annealed steels8 co$$er and duraluminum% duraluminum%,T"ese correlations8 bot" or S T"ese correlations8 bot" or Suu and atigue strengt"s8and atigue strengt"s8 a$$ly only o&er a range o materials on w"ic" tests a$$ly only o&er a range o materials on w"ic" tests"a&e $re&iously been made% T"ereore8 users s"ould"a&e $re&iously been made% T"ereore8 users s"ould rerain rom ma@ing o&er generali#ation% rerain rom ma@ing o&er generali#ation%15 1554Hardness tests are substantially sim$lier t"an ot"er54Hardness tests are substantially sim$lier t"an ot"er mec"anical tests% S$ecially $re$ared s$ecimens aremec"anical tests% S$ecially $re$ared s$ecimens are not needed% T"e mac"ine $arts can usually be testednot needed% T"e mac"ine $arts can usually be tested directly% T"oug" de$ends on t"e si#e o t"e $art anddirectly% T"oug" de$ends on t"e si#e o t"e $art and ty$e o test8 t"e $arts tested are not demaged%ty$e o test8 t"e $arts tested are not demaged% (urt"ermore8 "ardness tests can be made Duic@ly8(urt"ermore8 "ardness tests can be made Duic@ly8 ta@ing about in t"e order o seconds to ew minutes ta@ing about in t"e order o seconds to ew minutes64 64Similar materials may be graded according toSimilar materials may be graded according to "ardness8 t"us ma@ing s$eci*cations or a certain ty$e"ardness8 t"us ma@ing s$eci*cations or a certain ty$e o a$$lication clear4cut% Li@ewise8 t"e Duality le&el oo a$$lication clear4cut% Li@ewise8 t"e Duality le&el o materials or $roducts may be controlled e.ecti&ely bymaterials or $roducts may be controlled e.ecti&ely by "ardness tests% "ardness tests%7474 Hardness can be measured on $arts o small t"ic@nessHardness can be measured on $arts o small t"ic@ness and in &ery t"in layers8 or o&er microsco$ic sections% and in &ery t"in layers8 or o&er microsco$ic sections%16 16T/0ES )( HAR'NESS TESTST/0ES )( HAR'NESS TESTSIN'ENTATI)N TESTSMA=R)MI=R)F4SH)RE S=LERS=)0EG4S=RAT=H H4>LTRAS)NI=3;4H)T HAR'NESSI4BN))0 'IAM)N'74CI=BERS 'IAM)N'64CI=BERS54R)=B-ELL349RINELLJ4'>R)METER17 17THE 9RINELL HAR'NESS TESTTHE 9RINELL HAR'NESS TESTT"e 9rinell met"ods consists o indenting T"e 9rinell met"ods consists o indenting t"e metal (usually! wit" a 3; mm t"e metal (usually! wit" a 3; mm diameter steel ball sub