INFLUENCE OF GRINDING TREATMENTS ON THE SUR FACE HARDNESS OF INTAGLIO PRINTING PLATES OF 0.33.PERCENT CARBON STEEL

U. S. DEPARTMENT OF COMMERCE NATIONAL BUREAU OF STANDARDS RESEARCH PAPER RP1374 Pat f Junal f Reseach f the }{atinal Bueau f Standads, Vlume 26, Mach 1941 INFLUENCE OF GRINDING TREATMENTS ON THE SUR FACE HARDNESS OF INTAGLIO PRINTING PLATES OF 0.33.PERCENT CARBON STEEL By Hay K. Heschman and Fedeick Knp ABSTRACT A study was made f the suface-hadening effects in plates used f intagli pinting. These plates wee f O.33-pecent cabn steels having diffeent metallgaphic stuctues and finished unde diffeent ginding cnditins. The influence f the fllwing facts in the ginding cnditins n the suface hadness f the steels was investigated: (1) cling cnditins duing ginding, (2) gain sie f the abasive (3), depth f cut, and (4) ate at which the abasive wheel passes ve the specimens. Vaiatins in the hadness f the steels at diffeent levels beneath the gund sufaces wee detemined by applying diffeent lads n an elngated pyamidal-diamnd indente. The gemetical iegulaities f the sufaces f the gund specimens, evaluated by the "tace" methd, wee cnsideed with espect t thei influence n the accuacy f measuement f suface hadness by the indentatin means emplyed and thei elatinship t suface hadness. CONTENTS Page 1. Intductin 261 II. ateial 262 III. ethd s f tesl 262, 1. Ginding teatments 262 2. Hadness indentatin tests 264 3. Suface measuements 264 IV. Results and discussin 265 V. Summay 271 VI. Refeences 272 I. INTRODUCTION Incised symbls, insciptins, and pictial epesentatins in steel plates intended f intagli pinting may be cut with an engaving instument impessed fm a hadened steel ll beaing the embssed design. These pcesses f cutting and impessing ae usually designated as "engaving" and "mechanical-tansfeing," espectively. The espnse f plate steel t the engaving and mechanicaltansfeing teatments is influenced by the gemetical as well as the plastic defmatin chaacteistics f the suface layes f the steel. The hadness f the steel at and nea its suface, which may diffe significantly fm that f the undelying steel, is ne f the facts believed t have an imptant beaing in espect t this behavi. The mechanical finishing f the sufaces f engaving and tansfeplate steels by machining, ginding, and plishing, affects the hadness f the suface layes. These effects may diffe accding t the seveity f the plastic defmatin and themal effects caused by the finishing pcess and the espnse f the metal t wk-hadening. 261

262 Junal j Reseach j the Natinal Bueau j Standads [Vl..t6 This pape pesents esults f hadness tsts with indentatins penetating t diffeent levels beneath the gund sufaces f plates f 0.33-pecent cabn steels having diffeent metallgaphic stuctues and finished unde diffeent ginding cnditins. This is ne phase f an investigatin f suface finishes being cnducted by the Natinal Bueau f Standads in cpeatin with the Bueau f Engaving and Pinting. Because the depth f penetatin f the hadening effect belw the gund suface f the steel was vey small, hadness measuements had t be cnfined t the suface layes at cespndingly shallw depths. The depths f penetatin f the ball and the cnical pyamidaldiamnd indentes used with the well-knwn Binell, Rckwell, and Vickes testes wee entiely t geat f the pupse. The elngated pyamidal-diamnd indente ecently develped at the Natinal Bueau f Standads t pemit the accuate measuements f indentatins made unde small lads [1] 1 was used t evaluate the hadness changes in the suface layes f metals accmpanying defmatinal and stuctual changes caused by ginding. The aveage depths f indentatins made with this tl in the expeiments wee 0.0001, 0.00015,0.00025, and 0.00035 inch at lads f 100,200,500, and 1,000 gams, espectively. It is evident that the me shallw the indentatin, the me significant becmes the influence f the gemetical iegulaities f the suface n the depth f penetatin f the indente. In the pesent study, the suface finishes f the specimen plates wee evaluated by the "tace" methd. II. MATERIAL The 0.33-pecent plain cabn steel investigated is typical f the steel used f tay-pess pinting plates by the Bueau f Engaving and Pinting. Othe than in, the significant cnstituents detemined by chemical analysis wee as fllws: Pecent Cabn Manganese Phsphus _ Sulfu SilicOD O. 33. 55. 028. 027.23 All specimens f the vaius teatments wee cut fm a single plate f the steel t the dimensins 6 by 5 by X inch thick. Five specimens, each heat-teated t pduce a diffeent micstuctue, wee used f each f the ginding cnditins descibed belw. The micstuctues ae shwn in figue 1. A laye, at least 0.020 inch thick, was emved by ginding fm the test suface f each specimen, afte heat teatment, t eliminate the xidied decabuied metal that might have develped in this ptin duing heat teatment. III. METHODS OF TEST 1. GRINDING TREATMENTS All ginding tests wee made n a hydaulically peated sufaceginding machine having a magnetic chuck f sufficient length t pemit the simultaneus ginding f five specimens placed in tandem aangement. In this manne, pactically identical cnditins wee I Figues in backets indicate the liteatue efeences at the end f this pape. <

Junal f Reseac h f the Natinal Bueau f Standads FIG U R E Resea ch Pape 13 74 l.- Chamcteistic micstuctw'es f O. SS-pecent cabn steel develped by diffeent heat teatments. Etched in I-pecent Nita!. Magnificatin X IOO. ", Funace-cled fm 1,925 0 F (1,050 0 C); b, funacecled fm 1,600 0 F (8700 C); c, ai-cled fm 1,6000 F (870 0 C); d, wate-qu enchcd fm 1,600 0 F (870 0 C) and d awn at 1,400 0 F (760 0 C); e, wa te -q ucnchcd fm 1,600 0 F (870 0 C) and d awn at 1,200 0 F (650 0 C).

HeSchman] Knp Effect j Ginding n Sujace Hadness j Steel 263 maintained f all f the specimens duing each ginding teatment. The machine was equipped with cntls f vaying the table speed, css feed, and depth f cut, but the peipheal speed f the abasive wheel was appximately the same (5,600 feet pe minute) f all tests. Wheels f thee diffeent git sies wee emplyed. All wheels wee 12 inches in diamete with cutting faces 1 inch wide. Futhe details f the wheels ae given in table 1. TABLE l.- Ginding cnditins emplyed n specimens Gind ing test desig natin Table speed, ftlmin, f Css feed f cut Wheel feed f cu t cut num numbe 1_ numbe 1_ Abasive wheel specificatin be l - 1 2 3 4 1 2 3 4 1 2 3 4 - -- - - - - ---------- in,. in. in. in. in. in. in. in. gain, vitified bnd. sft. }45 45 --- 0.04 0.04. ----. -. -- 0.001.0002 ------ ----- - a {AlUndUm abasive, N. 46 b, {AlUndUm abasive, N. 60 gain, vitified bnd, sft, }45 45 45 45.02. 02 0.02 O. Ol. 0004.0003. 0002.0001 peu stuctue. c {AlUndUm abasive, N. 80 :t gain, vitified bnd, sft, }3S 35 35 25. 02.015.015.01. OOO J. 0003.0002.0001 pen stuctue. IL _ {Alundum abasive, N. 46 gain, vitified bnd, sft. 35 35 30.02. 015.015.015. 0004.0003.0002.0001 e t {Alundum abasive, N. 46 gain, vitified bnd, sft. t 35 35 35 35 30.02. 015.015.015. 0004.0003.0002.0001 {Alundum abasive, N. 46 }45 45 gain, vitified bnd, sft. ---.010.010 ---_..----.0002. 0001 ---'.- ----.- g-------. {Alundum abmsive, N. 46 }70 70 70.0lD.010.010.0002.0001.0001 gain, vitified bnd, sft. --.-. "._--- 1 Last cut indicated epesents finishing cut. Specimens pegund with N. 46 git wbel, same as cnditins tes t "a". Specimens pegund with N09. 46 and 60 git wbeels, s!tme as cnditins "a" and "b" espectively. Gnnd dy, that is, witbut liquid clant. A Iiqnid cmmecial ginding cmpnnd was emplyed f all the tests. Each wheel was munted n a sepaate hub, which fitted within clse tleance n the spindle f the ginding machine. The wheels wee caefully balanced t pemit the intechange f wheels with a minimum influence f the vibatin fact. Pi t each ginding test, the wheels wee dessed with a shap diamnd tl. One seies f ginding t ests was made dy, that is, withut the use f a cling liquid. F all the tests, a cmmecial ginding cmpund was used. This liquid, "clant", was fed in tw ppsite diectins fm a fced-ciculatin system t the cutting face f the wheel at appximately the aea f cntact with the specimen. A suitable filte in the ciculatin system effectively emved abasive matte fm the used liquid pi t its eciculatin t the wk. The specimens wee dessed befe each ginding test in de t eliminate the effects f the pevius tests and t insue cntinued flatness f the sufaces. The depth f these cuts was cnsideably less than the initial cut f the fllwing test, thus minimiing the influence f the dessing teatment n the test esults. The effects f the fllwing facts in the ginding cnditins n the suface hadness f the specimens wee investigated: (1) scillating ate f the specimen with espect t the abading suface f the wheel, (2) depth f cut, (3) gain sie f the abasive, and (4) cling cnditins duing ginding. Futhe details f the individual test cnditins ae given in table 1.

264 Junal j Reseach j the Natinal Bueau j Standads [Vl. tlj 2. HARDNESS INDENTATION TESTS Imptant facts influencing the accuacy f suface-hadness tests ae the effect f elastic ecvey n small indentatins and vaiatins f this effect f metals f diffeent hadness. It has been demnstated that hadness measuements made with the elngated pyamidal-diamnd indente used in this investigatin ae nt significantly influenced by these facts [1]. Since, with diffeent lads, the same indentatin numbes ae secued n metal f unifm hadness, the existence f hadness gadients in diffeent levels f the suface layes is eadily detected. Indentatin deteminatins wee made unde fu diffeent lads, namely 100, 200, 500, and 1,000 gams, with the indenting appaatus descibed in a pevius Bueau publicatin [1]. The time f cntact f the indente with the specimen f each indentatin test was 20 secnds. In evey case the indentatins wee made with the lng axis f the indente appximately paallel t the diectin f the ginding maks. The hadness indentatin numbes wee cmputed by dividing the lad, in kilgams, by the unecveed pjected aea, in squae millimetes [1]. The cnstant Cp, which elates the length f the indentatin t its pjected aea, was 0.0694 f the indente used. Decease in identatin numbe with incease in lad was an indicatin f the depth f the hadening effect f the ginding teatment. Data supplementing this infmatin wee btained by making simila indentatin tests afte the emval f layes fm the gund suface by plishing with 3/0 emey pape unde light pessues until the ginding maks wee baely visible. The thickness f the suface metal thus emved was estimated by the measue f the depths f the ginding maks detemined by the tace methd. Micstuctual inhmgeneities f the specimens influenced the depth f penetatin f the indente. This is illustated in figue 2 by the diffeences in the sies f the indentatins in the feitic- and cabn-ich aeas, espectively. In de t secue a epesentative aveage value f each f the sufaces tested, 10 me indentatins wee made with each lad n the indente. 3. SURFACE MEASUREMENTS It was essential, f the ppe intepetatin f the esults f the indentatin tests, t evaluate the suface "ughness" f the gund specimens. Such data als seved t eveal any existing celatin f the fact f suface finish with suface hadness. The pfilmete, embdying the tace pinciple, used f evaluating the suface finishes did nt diectly detemine the "peak t valley" heights f the suface makings, which ae chaacteied in figue 3, but athe indicated the t-mean-squae aveage values in micinches (10-6) f the deviatins fm the nminal suface. Accding t Abbtt [2], the actual "peak t valley" heights ae 3 t 4 times the t-mean-squae values. The highe fact is cnsideed me nealy cect f the limits f finish dealt with in this study.

------------------------------- ----------------- ---, Junal f Reseach f the Natinal Bueau f Standads Reseach Pape 1374 Effect f micstnlct-ual inhmgeneity f steel n the magnitude f indentatin made with the elngated py'amidal-diamnd indenting tl. FIGURE 2.- l'he length f the indentatin and the cespnding hadness indentatin numbe fl' each f the a.eas indicat.ed by lettes in the micgaph wee s fllw s: Aea Pedminating micstuctual cnstituent Length f iclcntatill Cmputed had ness indentatin numbe A B C Feite _ Feite and pealite Pealite _ mic inches 325 305 290 135 l 5G 17l Etched in I-pecent Nita!. Magnificatin XIOO.

Reseach Pape 1374 Junal f Reseach f the Natinal Bueau f Standads FIGURE 3.- Chamcteistic appeamnces f slujace finishes pduced by ginding with diffeent git sie abasive wheels. Une!chcd. Magnificatin X20. I Abasive git sie I Pfile eading I --::i:o I a 46 6 t 9 I M icgapb '\- ------ b 1 c 60 80 in. 8 t 14 3 t 4.5

FIeBChman] Knp Effect f Ginding n Suface Hadness f Steel 265 IV. RESULTS AND DISCUSSION The esults f the indentatin tests and the evaluatins f suface "ughness" f each f the specimens pepaed by the seveal ginding teatments ae listed in table 2. The changes f indentatin numbes with inceased lad n the indente f the diffeent ginding and heat teatments ae shwn in figues 4 t 8. These cuves, in geneal, shw a decease f indentatin numbe with inceasing lad. This indicates a decease f hadness with inceasing depths f the suface layes. These data must, hweve, be intepeted with espect t the influences f the gemetical chaacteistics f the suface finishes. TABLE 2.-Aveage suface-hadness values f 0.33-pccent cabn steel specimens heat teated t develp diffeent stuctual cnditins: (1) "as gund," (2) afte emval f supeficial laye f metal fm gund suface by light plishing with 3/0 emey pape Hadness indentatin numbe (elngated pyamidal-diamnd indente), Gind Speci H As gund" sufaces Plished sufaces' Evalna ing I men tins f teat identifi- Heat teatment suface ment catin T est lad, gams Test lad, gams finish 100 200 500 1, 000 100 200 500 1,000 --- ----------------- ms 10-' in. a. MB-8 219 191 187 178 169 159 b 157 6 t 9 MB-8 194 177 173 157 183 170 159 152 5 t 11 c. d MB-8 188 176 176 152 177 165 163 148 3 t 6 In 00'00 " ',,' F, """ Ome MB-8 peatue f 1 h, and funace- 220 198 183 164 176 184 162 158 6 t 9 MB-8 cled. 175 165 161 159 196 175 172 161 6 t 8 t --------- MB-8 216 196 171 164 ----- -.--- ----- ----- 4 t 7 g-------- MB-8 216 197 182 172 ----- ----- ----- ----- 6 t 10 a MB-4 207 185 176 193 194 177 165 6 t 10 b MB-4 195 184 171 156 179 172 157 155 c. 8 t 14 MB-4 Heated t 1,600 0 F, held at tem- 199 179 165 153 177 169 160 153 2 t 4 d._ MB-4 peatue f 1 h, and funace- 209 200 172 166 194 184 167 158 6 t 9 e. MB-4 cled. 178 175 158 150 189 175 161 154 4 t 6 t.------ -- MB-4 208 199 178 171 -.--- ---- - --- -- ----- 5 t 7 g- - ------ MB-4 236 203 ISO 168 ----- ----- ----- ----- 7 t 11 a. MB-8 223 214 190 222 b 212 203 187 6 t 11 c MB-8 205 208 193 189 187 184 182 170 7 t 12 d MB-6 lum,,,, "',&n' F, >."., Om- 210 202 189 177 199 191 182 176 3 t 5 e MB-6 peatue f 1 h, and ai- 223 209 202 187 210 200 193 ISO 6 t 8 MB-6 cled. 188 186 174 172 191 189 182 177 4 t 7 t--------- MB-6 217 210 192 186 ----- ----- ----- --- -- 5 t 7 0- ------- MB-6 231 231 194 192 ----- ----- --- -- ----- 7 t 9 a MB-7 253 231 208 235 230 214 202 6 t 10 b. c MB-7 219 218 195 186 203 192 190 184 8 t 13 d MB-7 215 218 198 188 206 202 189 183 3 t 6 MB-7 IH'" in wate, '" ',n' and dawn F, '"" f... 1 h, e 237 217 205 189 205 204 193 187 6 t 9 MB-7 at 1,400 0 F. 209 204 186 182 207 201 189 183 5t 7 t-.------- MB-7 228 212 198 192 ----- ----- -- --- --- -- 5 t 8 0---.. --- MB-7 231 219 206 198 ----- ----- ----- --- -- 6 t 9 a MB-6 269 241 239 270 241 226 223 6 t 9 b MB-6 246 236 222 222 207 207 208 202 7 t 14 0. d MB-6 232 226 216 214 213 214 209 202 3 t 4 e MB-6 lnm'" in wate, '" ',000' and dawn F,,"","'" f 1 h 247 246 241 233 219 216 228 226 6 t 9 MB-6 at 1,200 0 F. 222 219 222 219 217 217 213 208 4 t 6 t-------- MB-6 240 243 232 234 ----- ----- ----- ----- 5 t 7 g-- ----_. MB-6 238 244 224 215 ----- ----- --- -- --- -- 7 t 10 I See tahle 1 f details f ginding teatments., Each value given is the aveage f 10 me eadings., Fli s bin was cntinued until ginding maks wee baely visible t unaided eye.

266 J unal j Reseach j the Natinal Bueau j Standads [Vl. 16 175 - "" POLISHED WITH 3/0 EMERY AFTER GRINDING ----- I-- ----:= ---- ----. =---.. 1 f --- -..., 125 250 a:: w 200 ::;:) LJJ \ P:: f-...- "AS GROUND" CONDITION KEY SYMBOL GRINDING TEST DESIGNATION a x b.c. c 0 d 0 e f A 9 ::::::::::--- II -... "-- ----...,. --l t::-- I '-... 1500 100 200 500 1000 LOAD GRAMS FIGURE 4.-Effect f diffeent cnditins f ginding n the suface-indentatin (hadness) values f 0.33-pecent cabn steel, funace-cled fm 1,925 F (1,050 C), as detemined unde diffeent lads n the indente. The cuves in the uppe ptin f the figue indicate the suface-hadness values afte emving a supeficiallaye f metal fm each f the gund sufaces by light plisbing with 3/0 emey pape. (See tatile 1 f details f test cnditins cespnding t tbe ginding-test designatins listed in tbe "key.") Applying the fact f 4 t the suface-finish values given in table 2, the aveage" peak t valley" heights f the suface cntus wee estimated t be abut 0.000012 t 0.000024 inch f the smthe sufaces and appximately 0.00003 t 0.00005 inch f the case nes. Cmpaing the dimensins f the suface seatins with thse

HeSchman] Knp Effect j Ginding n Sujace Hadness j Steel 267 200,--,---,---,---,---,--,----------------------,----, POLISHED WitH 3/0 EMERY AFTER GRINDING 2501-----------------i-----+---- 1 'As GROUND" CONDITION GRINDING TEST DESIGNATION a x b t:.. c 0 d 0 e f A 0:: 9 W 200---*---+---,---,---,,------.------+---+-- :l Z Z i:e w KEY 1500 100 200 500 1000 LOAD GRAMS FIGURE 5.- Effect f diffeent cnditins f ginding n the suface-indentatin (hadness) values f O.SS-pecent cabn steel, funace-cled fm 1,600 F (870 C), as detemined unde dl:ffeent lads n the indente. The cuves in the uppe ptin f the figue indicate tbe suface-bad ness values afte emving a supeficiallaye f metal fm eacb f tbe gund sufaces by ligbt polisbing witb 3/0 emey pape. (See table 1 f details f test cnditins cespnding t tbe ginding-test designatins listed in tbe "key.") f the depths f the indentatins made with the 100- and 200-gam lads, it is appaent that nly patial cntact was maintained between the metal and the suface f the penetating ptin f the indente. Unde such cnditins, a lnge indentatin wuld be btained than if a me cmplete beaing cntact wee maintained. Theefe, the indentatin numbes, paticulaly f the lighte lads, wee undubtedly smalle than the tue values. Nevetheless, the distinct decease in indentatin numbe with incease in lad (figues 4 t 8) indicated that the hadening effect was supeficial.

268 Junal j Reseach j the Natinal Bueau j Standads [VUIf 200 I---- I-- 01- -- -- N --"'=- II POLISHED WITH 3/0 EMERY AFTER GRINDING ------ ---- ---- I--. I------, --.::: -- --- I-- 150 I I I I I 250 a:: 200 5 w 2 '", l\... t:::: I------,,/ M GROUND" CONDITIOf'J KEY SYMBOL a X b t:.. c c e f 9 I'--.. GJ?{161 -- 0 d -- ---- --,j ---c----- --- -- 1 -- 150 100 200 500 LOAD GRAMS 1000 FIGURE 6.-Effect f diffeent cnditins f ginding n the suface. indentatin (hadness) values f O.SS-pecent cabn steel, ai-cled fm 1,600 F, (870 C) as detemined unde diffeent lads n the indente. The cuves in the uppe ptin f the figue indicate the suface hadness values afte emving a supeficiallaye f metal fm each f the gund sufaces by light plishing with 3/0 emey pape. (See ta.ble 1 f details f test cnditins cespnding t ginding test designatins listed in the "key.")

HtT8chman] Knp Effect j Ginding n Sujace Hadness j Steel 269 22 5 I POLISHED WITH 3/0 EMERY AFTER GRINDING "" --- --. ---N 175 I 0 Jl: a --<;> AJ 4 0:: W!D ::> Q 275 250 I 200 w.?- "'- I IP t?1 A S GROUND' CONDITION KEY SYMBOL GRINDING TEST DESIGNATION a X b I::. c 0 d 0 e f.ii. 9... "". -:::: t-- I """ i===== t::-: I t--- t=:=:::: t--: --:::: 175 0 100 200 500 1000 LOAD GRAMS FIGURE 7.-Effect f diffeent cnditins f ginding n the suface-indentatin (hadness) values f O.SS-pecent cabn steel, wate-quenched fm 1,600 F (870 C), and dawn at 1400 F (760 C), as detemined unde diffeent lads n the indente. The cuves in the uppe ptin f the figue indicate the suface hadness values afte emving a supeficial laye f metal fm each f the gund sufaces by light plishing with 3/0 emey pape. (See table 1 f details f test cnditins cespnding t ginding-test designatins listed in the "key.") 291547-41--7

270 Junal j Reseach j the Natinal Bueau j Standads [VU16 250 200 1\ \ POLISHED WITH 3/0 EMERY AFTER GRINDING i'--.. 1 ---- V 1 I t-- I - t--, t----b- I 1 ===le: 0:: W III 300 250 t «i- s 4 AS GROUND" CONDITION 1\ KEY SYMBOL GRINDING TEST DESiGNATION., a X b \ L\ c ;}--- 0 d 0 e II f A 9 R -- I I I t-- -- l t-- -... i I b ---h. '---- -'1 \-----::1 --:.::: --1-- 1' 20 0 100 200 500 LOAD-GRAMS 1000 FIGURE S.-Effect f diffeent cnditins f ginding n the suface-indentatin (hadness) values f O.SS-pecent cabn steel, wate-quenched fm 1,600 F (870 C) and dawn at 1,200 F (650 C), as detemined unde diffeent lads n the indente. The cuves in the uppe ptin f the figue Indicate the suface hadness values afte emving a supeficial laye f metal fm each f the gund sufaces by light plishing with 3/0 emey pape. (See table 1 f details f test cnditins cespnding t ginding test designatins listed in the "key.")

He&ehman] Knp Effect j Ginding n Sujace Hadness j Steel 271 Evidence in futhe suppt f this view was secued fm the indentatin tests n the specimens plished with 3/0 emey pape afte ginding. The plishing teatments emved a thickness f metal fm the gund sufaces equivalent t the" peak t valley" heights f the ginding maks, which in n case appeciably exceeded 0.00005 inch. Despite the wk-hadening effects f the plishing teatments, the esults f the indentatin tests n the plished sufaces wee cnsistently lwe than thse f the gund cnditins (table 2 and figues 4 t 8). It is wthy f nte that the vaiatins f the individual indentatin numbes fm the aveage values wee n geate f the" as gund" sufaces than f the plished sufaces. It is likely that the tue diffeences in indentatin numbe f cespnding lads between the gund and plished specimens wee geate than indicated, because me cmplete cntact was b tained between the indente and the smthe plished sufaces. Althugh the degee f finish may influence the accuacy f small indentatin hadness tests f a metal, the esults listed in table 2 did nt shw any celatin between hadness and degee f finish f the suface. In sme cases, simila hadness numbes wee 0 btained n the same specimen having sufaces f significantly diffeing finishes pduced with diffeent ginding cnditins (teatments band c, table 2). On the the hand, thee wee a numbe f tests in which diffeent hadness esults wee btained, despite the similaity f suface finish (table 2). The hadness cuves (figs. 4 t 8) in mst cases shw that the facts f cling, depth f cut, and gain sie f the wheel significantly influenced the suface hadness f the steel. Within the limitatins f the tests made, the suface hadening appeaed t be independent f the micstuctual chaacteistics f the mateial. The diffeences in the indentatin numbes f the" dy" and "wet" gund specimens (cuves d and e, espectively) may be attibuted in a lage measue t the themal influences, as the the facts cntlling the wkhadening effects wee the same f bth cases. The hadness data btained f the sufaces, which wee gund unde identical cnditins except as t the depth f cut (cuves a and d), shwed that a highe degee f hadening was btained as the depth f cut was inceased. The suface-hadening effect pduced with the N. 46 gain abasive (cuve a) was cnsideably geate than was btained by ginding with eithe the Ns. 60- and 80-gain abasives (cuves b and c). The hadening effects pduced with the last tw abasiv,es wee appximately the same. The indentatin tests made n the specimens gund at scillating speeds anging fm 38 t 71 feet pe minute (table 1) indicated that this fact exeted n appeciable influence. The esults ae pesented in cuves d, j, and g, figues 4 t 8. V. SUMMARY Mechanical-tansfe plates f 0.33-pecent cabn steel having diffeent metallgaphic stuctues wee investigated t detemine the influence f diffeent ginding cnditins n the suface hadness f the steel. Hadness indentatin tests wee made with diffeent lads n an elngated pyamidal-diamnd indente develped at the

272 Junal j Reseach j the Natinal Bueau j Standads [Vl.!11 Natinal Bueau f Standads. The gemetical iegulaities f the gund sufaces evaluated by the "tace" methd as the t-meansquae aveage deviatin fm a nminal suface wee cnsideed with espect t thei influence n the accuacy f the hadness measuements. Expeimental data ae pesented t shw that the hadness f the suface metal, distinguished fm that f the undelying metal, may be significantly influenced by (1) the cling cnditins duing ginding, (2) the depth f cuts, and (3) the gain sie f the abasive. Hweve, the ate at which the stne passed ve the specimens did nt appea t influence the hadening effects. The esults btained within the limitatins f the tests suggested that suface hadness is independent f the gemetical cnditin f the suface. Hweve, the accuacy f the measuements f suface hadness by indentatin means may be influenced by the degee f finish f the suface. The hadening effects f the ginding teatments n the steel investigated did nt appea t be influenced by diffeences f the micstuctues f the mateial. The hadness data secued suggested that the mst significant hadening effects f ginding ae supeficial and that these influences ae pgessively less f the successively deepe adjacent layes,'f the steel. VI. REFERENCES [1J F. Knp, C. Petes, and W. Emesn. A sensitive pyamidal-diamnd tl f indentatin measuements, J. Reseach NBS 23, 39 (1939) RP1220. [2] E. J. Abbtt, S. Busky, and D. Williamsn. The Pfilmete, a new instumentf the apid measuement f sufaces, Mech. Eng. 60, 205 (1938). WASHINGTON, Decembe 12,1940.