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metals

Article

Wear and MnS Layer Adhesion in Uncoated Cutting Tools When Dry and Wet Turning Free-Cutting Steels

D. Martinez Krahmer 1,2,*, S. Hameed 3, A. J. Sánchez Egea 4,* , D. Pérez 1,2, J. Canales 5 and L. N. López de Lacalle 5

1 Center for Research and Development in Mechanics, National Institute of Industrial Technology (INTI), Avenida General Paz 5445, 1650 Miguelete, Provincia de Buenos Aires, Argentina; danielap@inti.gob.ar

2 Faculty of Engineering, Universidad Nacional de Lomas de Zamora, Juan XXIII y Camino de Cintura, 1832 Buenos Aires, Argentina

3 Department of Mechanical Engineering (EPSEVG), Universitat Politècnica de Catalunya, Av. de Víctor Balaguer, 1, Vilanova i la Geltrú, 08800 Barcelona, Spain; hameeds@tcd.ie

4 Department of Mechanical Engineering (EEBE), Universitat Politècnica de Catalunya, Av. Eduard Maristany, 16, 08019 Barcelona, Spain

5 Department of Mechanical Engineering, Aeronautics Advanced Manufacturing Center (CFAA), Faculty of Engineering of Bilbao, Alameda de Urquijo s/n, 48013 Bilbao, Spain; javier.canales@ehu.eus (J.C.); norberto.lzlacalle@ehu.eus (L.N.L.d.L.)

* Correspondence: mkrahmer@inti.gob.ar (D.M.K.); antonio.egea@upc.edu (A.J.S.E.); Tel.: +54-011-4754-4072 (D.M.K.); +34-934-054-024 (A.J.S.E.)

Received: 12 April 2019; Accepted: 8 May 2019; Published: 12 May 2019

Abstract: Free-cutting steels are developed to produce large quantities of parts with low mechanical behavior, mainly for automotive sector. These alloys contain phosphorous, lead, sulfur, and manganese that help to improve the machinability and surface roughness. However, due to the toxicity of lead, steel mills in recent years have been focusing on non-toxic steels to produce minimum environmental pollution and better machinability. The present work investigates the tool wear during dry and wet turning of free-cutting steels (SAE 1212, SAE 12L14, and SAE 1215) by using uncoated hard metal inserts at three cutting speeds. Additionally, a EDS analysis was performed to determine the presence of Mn and S elements at the rake face of the cutting tool that can induce a higher adhesion of manganese sulfide (MnS). The results show that the SAE 12L14 steel has the best performance in terms of tool life at different cutting speeds. This difference is maximum at the lowest cutting speed, which gradually decreases with the increase of the cutting speed. The wear behavior is evaluated in the three steel alloys at each cutting speed and, consequently, the tool wear exhibits a slightly better performance in the dry machining condition for higher cutting speeds (180 and 240 m/min), independent of the steel alloy. Finally, EDS analysis confirms the presence of Mn and S elements at the rake face of the inserts machined in dry condition. Hence, MnS is expected to interpose between the machined surface and cutting tool surface to behave similar to tribofilm by reducing the wear on the cutting edge.

Keywords: free-cutting steel; wear; dry turning; wet turning; uncoated carbide; adhesion layer



1. Introduction

The steel mills are developing some grades of steel called free-cutting steels (FCS) to reduce the use of cutting fluids during the cutting processes. It is well known that the use of cutting fluids in machining was initiated by Taylor in 1894 [1], who used water in the turning of steel to increase the cutting speed by 33%. However, the high oxidation nature of water and its lack of lubrication capacity could damage the cutting tool and increase the tool’s wear [2]. In recent years, other important



Metals 2019, 9, 556; doi:10.3390/met9050556



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aspects were also considered, such as health care of operators, environment, and the cost of liquids, which is between 7.5% and 17% of the cost of a machining part [3]. The present trend is to use alternative techniques, such as dry machining [4], electrocutting [5], cryogenic [6], cold compressed air [7], or minimum quantity of lubricant (MQL) [8], with the aim to reduce environmental impacts.

The machining processes are analyzed by considering the influential factors, such as the type of cutting processes, materials to be machined, and the material of the tool [9]. The selection of these factors would provide basic information for selecting the suitable cutting fluid [10]. Despite the fact, there are circumstances in which the best solution is obtained by using lubricant in particular conditions. For example, the materials with low thermal conductivity, such as titanium and nickel alloys require a system called “high-pressure coolant” (HPC) [11]. Their proper application in the cutting area helps to reduce the temperature on the cutting edge of tool [12], thus, increasing the tool life [13]. The results indicated that several parameters, such as cutting speed, chip breakage and thrust forces play a key role in improving the quality of machined surface [14]. Isik et al. [15] investigated the effect of cutting fluids during turning of steel SAE 1050 by using ISO P25 carbide tool and obtained a substantial reduction in tool wear under the wet machining. Priarone et al. [16] studied that the machinability of Ti-48Al-2Cr-2Nb alloy in terms of tool life is advantageous for emulsion mist, as compared to MQL and dry cutting. On the other hand, Gill et al. [17] analyzed the behavior of cryogenically treated tungsten carbide inserts utilized in dry and wet orthogonal turning. They found that these inserts performed significantly better under wet conditions for continuous as well as interrupted machining modes, especially at higher cutting speed. Jomaa et al. [18] compared the machinability and surface integrity of three mold steels during dry and wet machining. They observed that hardened mold steels can perform better in terms of tool wear and surface finish in dry machining, depending on the cutting speed. Ibrahim et al. [19] introduced the performance of ultrasonic-assisted turning of aluminum 6061-T6, which showed significant improvements in surface roughness and tool wear during wet machining. Moreover, Patrick et al. [20] performed turning under dry conditions and also used three coolants, such as oil, water, and palm oil at spindle speed of 355 rpm. They concluded that water as a cutting fluid reduced the heat generation, increased hardness of workpiece material, and produced the finest grain structure. Feed rates also have significant effects on surface roughness when groundnut oil based cutting fluid was used in turning of AISI 1330 alloy steel with a high-speed steel tool [21]. Kuram et al. [22] reported that the use of vegetable cutting oils reduced the thrust force and improved surface roughness at different spindle speeds and feed rates during drilling of AISI 304 stainless steel. Furthermore, the results indicated that an increase in spindle speed decreased the thrust force and surface roughness, while an increase in feed rate increased the thrust force, and hence the surface roughness.

In free-cutting steels, Luiz and Machado [23] explained in details according to the technological trends to improve their machinability and promote the replacement of lead to avoid toxicity. Thus, steel mills have developed new grades of free-cutting steels by adding sulphur, bismuth, calcium, selenium, and also zirconium to control the size and shape of manganese sulphides. They also referred MnS as microstructural compound, which helped in chip breakage and reduced the tool wear. Almeida et al. [24] studied the effect of machinability for AISI 12L14 with three residual elements (Cr, Ni, Cu) and found that these elements significantly influence its machinability but the lowest residual levels are not always good. On the other hand, Lane and his co-workers [25] tested the wear of polycrystalline diamond inserts (PCD) on alloys of aluminum AA6061 and steel AISI 1215. Additionally, examined that both the forces and wear rate were significantly higher during machining of steel AISI 1215. Furthermore, Leeba Varghese et al. [26] studied the influence of machining parameters on material removal rate and surface roughness during the dry turning of 11SMn30 free-cutting steel. Finally, Xu and coworkers investigated the cutting force and wear mechanism during high-speed turning of AISI 12L14 with Chemical Vapor Deposition (CVD) coated carbide tool GC4205 [27]. Later, they also studied wear mechanism by using Finite Element Method and experimental methods on high-speed turning of AISI 1215 steel with uncoated and multilayer carbide tools [28]. Following this last research topic, the present work is to



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investigate the importance of the cutting capabilities of free-cutting steels (FCS) during dry and wet machining. For this, three grades of carbon steel (SAE 12L14, SAE 1215, and SAE 1212) have been studied by using uncoated hard metal inserts and three commonly used cutting speeds: 150, 180, and 240 m/min. The wear evolution of the cutting tool is investigated experimentally to analyze the differences in wear rates for different FCS, machining conditions, and cutting speeds. In this end, the novelty of this work is to analyze the auto-lubrication characteristics in dry machining, which showed better cutting capabilities due to the adhesion of MnS, compared with the same machining configurations by using lubricant. These technological findings are interesting for industries with the aim to reduce the use of lubricants, which are associated with economic and environmental hazards.



2. Methodology

Three different grades of FSC, SAE 12L14, SAE 1215, and SAE 1212, have been studied in this work. The materials used in the turning experiments were drawn bars of 38.1 mm in diameter and 350 mm in length. Table 1 shows the chemical composition (% by weight) and Brinell HB hardness that were measured with optical emission spectroscopy (model: M8 spectrolab, Spectro, Kleve Germany) and Instron Wolpert durometer (model: S8-233971, Instron, Norwood, MA, USA) in our facilities. These three steels present similar chemical composition, except SAE 12L14 that contains lead.



Table 1. Chemical composition (wt%) and material hardness (HB) of the three free-cutting steels (FCS).



Material

SAE 12L14 SAE 1215 SAE 1212



C

0.074 0.065 0.070



Mn

1.065 1.000 1.050



S

0.313 0.318 0.303



P

0.055 0.052 0.055



Pb



Fe



HB



0.246 Balance 161



-



Balance 155



-



Balance 161



The metallographic analysis of the steel SAE 12L14 showed that it has a hot-rolled microstructure,



constituted by a matrix of equiaxed grains of ferrite. A lower proportion of perlite was uniformly



distributed in bands and heterogeneously in the matrix, which corresponded to a grain size equivalent



to



N◦



6



1 2



(ASTM



E112



[29]),



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Figure



1b



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type



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the



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a



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size, where plastically deformed grains were observed due to the cold working operation (drawing).



A numerical control lathe Promecor SMT 19 (Promecor, Córdoba, Argentina) was used to perform



experimental tests. Cutting tools with uncoated inserts (type CNMG120408 and quality ISO P40,



Kennametal, Latrobe, PA, USA) and specific tool-holder (type MCLNR-2525M12, Kennametal, Latrobe,



PA, USA) were used during the experiments. The CNMG insert on tool-holder presents a rake angle of −4◦, which is a common configuration for low and medium-carbon steels. The geometrical parameters



and chemical composition of the uncoated insert are shown in Table 2. The insert had a clearance angle of α = 5◦, rake angle of γ = −4◦, and inclination angle of λ = −5◦.



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3. Results and Discussion 3. Results and Discussion

The wear and the corresponding Taylor curves were determined for each of the three cutting speeTdhs.e wTheaerraensudlttsheexchoirbrietsepdonthdeinwgeTaaryelvorolcuutriovnesowf edrreydaentedrmwientemd afocrhienaicnhg otfestthseftohrreeeacchutsttienegl. sTpheeedsesc.oTnhdedreegsureletspeoxlhyniboimtedialthadejwusetamreenvtocluurtvioens woferderuysaendd(Rw2emt imniamchuimnin=g0t.9e5st8s) ftooroebatacihnsttheeelu.sTehfuel steocoolnlidfedfeogrrVeeBp=ol0y.5nommmiailnaedajuchstmcaesne.t Fcuorrveeaschwmereetaulsegdra(dRe2, m20inbiamrsuomf 1=.50.m95l8e)ntgothobwtaeirne tmheacuhsienfeudl . tSouobl sliefqeufeonrtVlyB, a=t0o.t5almomf 0i.8n Teaacnhdc3a0se7.mFoorfemacahtemriaeltawl agsramdaec, h2i0nbedards uorfin1.g5 tmheleenxpgethrimweernet.machined. SubseFqruoemnttlhye, aantoatlaylsoisf o0.f8FTigaunrdes330a7,m4aoafnmda5tear,iiatliws calseamratchhaitnfeodr dhuigrhinegr tchuetteinxgpesrpimeeedntt.he value of VB =Fr0o.5mmthme iasnraelaycshisedofiFnigleusrsetsim3–e5,aa,nitdissucblesaerqtuheanttfloy,rahfigashtewr ceuatrtienvgoslupteieodn tohne tvhaeluceutotifnVgBto=o0l.i5s mobmseirsvreeda.cIhneadllinsteleeslsgtriamdee,s,atnhde scuubttsineqguteonotlltyo,oakfmasotrwe etiamr eevtoolrueaticohnaown etahreecvuotltuintigontooofl VisBo=bs0e.r5vmedm. Idnuarlilnsgtederlygmraadcehsi,nthinegc.uTthtiinsgmtoeoanl stotohkatmdorryemtiamcehitnoinregaccohnadwitieoanr perveosleuntitoedn oafloVwBe=r 0w.5eamr mevdoluurtiinogn dsrloypme tahcahnintihnagt.oTbhtaisinmedeafnosr wtheattmdarychminainchgi,nwinhgichcomndaiytiboendpureesteonttheedfoarlmowateiornwoefaar seovloidluttriiobnofisllmopaet tthhaeninthteartfaocbetsai[n3e1d]. fHorowweetvemr,aicnhdinepinegn,dwenhticohf mthaeystbeeeldaulleotyotthheewfoeramr adtiiffoenreonfcaesboeltiwd etreinbothfielmdrayt athned iwnteetrcfaocnedsi[t3io1n].sHinocwreeavseers, ifnodr ehpigenhderencut totfinthgesspteeeedl asl(l2o4y0thoer 1w8e0amr d/miffienr)e.nIcnepbaerttwiceuelnart,hderydrmy aacnhdinwinegt ceoxnhdibitiitosnasbientctreeratsoeosl floifre hatighhigerhecructtuinttginsgpsepeedesd(s2t4h0anorth1e8w0 emt /mmaicnh).inIinngpacrotnicduiltaior,n.dRryegmaradcihnignitnhge eTxahyilboirtscuarvbeestt(eFrigtouorlesli3feb,a4tbhaignhde5rbc)u, itttiinsgshsopweendtshatht athnetwheeawrettremndacohfinthinegincsoenrtdditeipoenn. dRseognartdhiensgpteheed Taanydlotoroclulrifveeesv(oFliugtuiorensf3o–r5bbo)t,hitmisaschhoinwinngthcoant dthiteiownse.arSAtrEen1d2Lo1f4theexhinibsietretddtehpeebnedsst woneatrhpeesrpfoeermd aanncde tcoooml lpifaereedvowluitthionthfeorotbhoetrhtmwaocshtieneilnggrcaodneds,itipoanrst.icSuAlaErl1y2aLt14loewxhciubtittiendgthspeebeedstawndeadrrpyecrfoonrdmitainocnes. cAocmcopradriendglwy,itJhomthaea eotthale.r[1tw8]oalsstoeesltugdriaeddetsh, epwaretaicruelvarollyutaiot nlodwurcinugttidnrgy sapnededweatnmdadchryincinogndinititohnrese. Astceceolrgdriandgelys,. JTomheayafeotuanl.d[1l8o]waelsrowsetuadr ireadtetsheanwdeabreettveorlsuutirofancdeuprrinopgedrrtyieasnind wdreyt mmaacchhiinniinngg,inmtahirneley satteterlibgurtaeddesto. Tthheeymfaotuenridalloawdheerswioenaranradteths eanchdebmeitctaerl csoumrfapcoesiptiroonpeorftitehseisntederlys. mFiancahlilny,ining,omrdaeinr ltyo aetsttraibbulitsehdthtoe pthoessmiblaetecraiuasleasdbhyewsiohnichanthdetihnesecrhtsemreaiccahlecdotmhepcorsiitteiroina ooffVthBe=s0te.5elms.mFiinnallelyss, tiinmoerdduerrintog ewsteatbcloisnhdtihtieonp,otshseibEleDScaaunsaelsysbiys wwahsicpherthfoerminesedrotsnrtehaechraekdetfhaececroitfetrhiae ionfsVerBts=fo0r.5SAmEm12inL1le4scsatribmoen dsutereinl dguwrientgcownedtitainodn,dthrye cEoDnSdiatnioanlys.siFsiwguarsep6earfsohromwesdthone athveerraagkee wfaecieghoftsthine pinesrecretnstfaogreSoAfEsu1l2pLh1u4r c(aSr)baonndsmteaelndgaunriensge w(Ment )anodn rdarkyecfoancdeiitniodnrsy. Faingdurwe e6tacsohnodwitsiotnhse aatvderiffageerewnteciguhtttisnignsppeerecdens tiangSeAoEf s1u2l1p2haunrd(SS)AaEnd12mL1a4n(gSaAnEes1e2(1M2 nw)aosnserlaekcteedfaaces iitns dberyhaavniodrwweatscvoenrdyistiiomnislaarttodiSffAeEre1n2t1c5u)t.tTinhge smpaeregdisn ienrrSoArsEr1e2p1r2esaenndt tShAeEm1e2aLs1u4re(mSAenEt1d2e1v2iawtiaosnsoefletcetnedmaesasitusrbemeheanvtiso.rFwigausrvee6rby esximhiiblaitrsttoheSAelEec1t2ro1n5)ic. Tmhiecrmosacrogpine eimrroagrsesreopfrtewseonctuthtteinmgetoasoulsrewmitehntthdeetvoioatlitoinp odfetgernadmaetiaosnuraenmdetnhtes.aFdihgeusrieon6bofexMhnibSitaslothneg etlheecttrooonliecdmgeic.roscope images of two cutting tools with the tool tip degradation and the adhesion of MnS along the tool edge.



Metals 2019, 9, 556 MMeettaalsls22001199,,99,,xxFFOORRPPEEEERRRREEVVIIEEWW



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Metals 2019, 9, x FOR PEER REVIEW Metals 2019, 9, 556

Metals 2019, 9, x FOR PEER REVIEW



7 of 10 7 of 10

7 of 10



(b) (b)

Figure 6. (a) Average percentage of weight of S and Mn at the rake face for dry and wet machining cFoignFudirgietuior6en. s6(a.a)(taAd)viAfefveraererganegtpeceuprtectreicnnegtnatsgapgeeeoeodf fsw.we(beigi)ghMhttioocfrfoSSsacanondpdeMMimnn aaagttettshheeofrraatkhkeeefrfaaackceefofaorcrdedrwyryiatnahndtdhwewetteomtomlawcahceihnariinnagindg tchoencdaodnithdioietnsioisonanst oadtfiffdMiefnrfeeSnr.etnctuctutitntigngspspeeededs.s.(b(b))MMiiccrroossccooppee iimmaaggeessoofftthheerraakkeefafacecewwitihththtehetotoolowl weaeraarnadnd thethaedhadeshieosnioonfoMf MnSn.S.

The results obtained from EDS showed that S and Mn elements were found in a higher perceTnhtTaeghreeesiurneltstsuholetbstraaoikbneteadifnafecrdeomofrfEotmDheSEscDhuoSttwinsehgdowttoheoadlt.StThahanetdhSMiganhnedpleeMmrcneennettslaewgmeeernoetfsfoMwunnedraenindfoauShncidgohuienlrdpabeehrcidgenhueteargtoe minatptheeerricraealnkateadfghaeecesiniooftnhtaehtertachkueettrifanakcgeetofoaofclte.hTienhcetuhhtetiignfohgrpmtoeoroclf.enMTthaaegnehgiaognfheMspenerSacuneldnfitSdageceo(MuolfdnMSb)ne, adasunddeitsSocucmosausetleddribbaeyl adXduuheeetstoioaln. w[itchadrsmr2etutieiuo7gsbtstpm[thciir]dthhmr2cosu.ikriiyner7tgaefobtppT,aiir]ttghbvol.iiiernrhmteniefeeaortncTeicrigioddkvlseaeyhmaioieeltnsnettoiodltheanay.fhsaftoiedalahentIteltstnencahrt.hsehtoretlheIewMetefssttnhrseahooidtidecnwacnsteooteauehtoudSnlsdetprsetborehcaa,tulariolsriprurenncertnciateoribbdsghrtrgnfnseineheeoribdsgtcwnissdsetrheecuoitemtcwnsdaoaerqotuttsatnntroahpultitkktostcunntraehe[etipefk2zcgdurntnapifce8oMgdtyteaoMeii]lnncyc,ey.ofnMiaeeen,c,inftTndtteaainiiSfhdtgthinrntgoiShsteyirnaeterelsteyesuntrmshlnccesuerecbeoecouuerfefebosuarfneofantfdareniconttdSrtcictiedicertaniSoeintahsamn,itnhsungtg,ninagt,ioatlchodttoctfittntohnhteozfbozdMbonoenecMoooMcooesonsonltnwclteehamhe(mnheq[qwMn[e2Si2tutpupagfpfhh8e8oonereaaba–r]e]errnnSnrr..eeptmmeeppott)ehrTsTlld,dseooeyeyiaehheagrrdgl,dvt,tecsecnooaSrcaeerereitouodetondwefintwstnfnelntfiesctofesaosnetaiinarctdigotarutgtnemuhuecechnea,ceteoa,stseltois(ittysnliaMonthnnicaeohdncrfhhergddetfnheigSiihtitapSgStiMitobephto,aMi)–hhoya,ennw–ntcaeeanonntdu.SrwXohstod.TSwtriMoulitedTnbhiciMablebneihcihniesrasohoengcicntrspifihanwofsumtaavpretanwlfosecamolarevsrpto.rtctgecdeaoeesl[rtcrtrdc.ag2dooedestscat7Irviusbiunoregs]tmssaeyle.ihusrniidrtgdaoimsiheXlienTl,ninfdeaaoetiugihtixwchrl,oinfeappaencieeoxhwctrnyurltiotapalniewtthachtilansatlnhyolaetaieeil.ntnhcsianldnhyogaert winhdwyrhythyceothnwedewiatireoaonrfcotofomtoolpoialnrisenedsrettrsotsiwsiseletlsecssosinnidnditdriroyync.cooTnnhddiisittifiooancntttchhoaaunnldtthheeexwpwleeattinccoownndhdiytiittoihonen. .wInIneaadarddodiftiitotoinoo,nlti,hnteshreeerrtcesoicusollduelsds bine dbaernyaecgnoaentgidavitetiivoienntientrhtaearcnatictothinoenbwebteewttwceoeennendthittheioecncu.utIttitnninaggdffdlluuitiiiddonaan,ntddhetthhreee caaodduhhleedssiiobonenaoofnftehthgeeaMtMivnenSSionnotnetrhtaehcettoiotoonlo. blI.neIttnwhitesheins wthaewyc,autyht,teitnhagemaflomuuiondutanontfdocfotchmoempaopduohnuednsidtohtnhatoatfaadthdheheerMreesnsoSonnontthhteehreraatkkoeeofflaa. ccIeenddtheepipseenwnddasyso,ontnhmemaaacmhchioniuninningt go(df(rdcyoryomropwroweutn)etad)ntadhnadt tahdehthceueretctsuinottgninstghpeseperedaek.de. face depends on machining (dry or wet) and the cutting speed.

FFiiggFuuigrreeur7e7 7shshsohowowswssthttehheeinisinnesrseterrtttotoptpooopggroragaprphahypyhwywiittwhhiatahdhaedsihoennsiaaonnndd addniifdffeerredeninffttewrweenaertarpwrpoergaorrgersepssirosoingo.rneT.shsTiishoins. Tmheimassemuarseeuamrseuemrneetmnwteawnstadwsodanosendewownitehithwaaihthhigiaghhh-r-iergeshsoo-lruleutstioioolnnutssiccoaannnnscearn(nAelricc(ooAnnlaai,c,IoInnnffaiin,niItineteFfiFonociucteusF)s.o)T.cThuehs)ep. rpTorhtoeetcepticvrtoievtaeencatdinvde aauntdaoua-tluuot-bolur-ilbcurabitciraoitcniaotlniaoylnaeyrleaoryfoeMrf MonfSnMSwnwaSsawsooabbssseoerbrvvseedrdvooenndttohhnee trhaekerafkaeceefaoocffetthohefetthoooeoltltoitopipl. .tAiApft.fetArersfetseverevrseaerlvamelrmeatlemrtseerostfeorsf mofamchaaiccnhhiininngiinnigsgiosisnosonenstseoet ftootfhftehthewewewaeraeraorof fothfthetehteotootoollottilippt,i,paa,ssassshoshwonwinnn ittnhheethFFeiiggFuuirgreue7r7beb.7.AbAt. ttAhteht etehneedndeonfodaf oatefstaet,sttae,sat, parpoprmoromimnieninnetennttottotooloowll wewaeeraaranaadndmmicircor-oc-rccarracakcckkisiissdddeenennooottetededdiinnintthhtheeettootoooolllttitipipp,,,cccooommmbbibniinenededdwwwitihitthhmmmataaetrteeiarriliaaalldaahddehhseieossniioo, nn,, wwhhwiicchhhiciissh aaisllssaoolsffooouufonnuddndoonnontthhteeherraarkkaeekeffaafccaeec.e. .TTThhhiisissllalaayyyeeerrroooff MMnnSS ccaaannn rrreeetttaaarrrdddeeedddtththheeetottoooool llwwweaeeraarranaadnnddiniicnnrccerraeesaaessdeetddhetthhee pprroopccreeosscssessttsaasbbtiaillbiittiyyli,,tiyinn, ippnaaprrtatiircctuiuclluaarlrawrwwhhehennenuususisinningggdddrryryymmmaaaccchhhiininniiinnngggcccooonnndddiittiioonnss..

Figure 7. Characteristics found on the rake fake of the cutting tool: (a) adhesion on rake face; (b) FFiiggiuunrriteeia77ti..oCnChohafratarhcaetcetwreiresiatsirtcisacfsftoefruonu20dndmonionntohtfehteoraorklaelkiffeeakfwaekitoehfoatfhvetehlcoeucitcttuyintotgifnt1go8o0tlo:mo(la/:m) i(anad)ahaneddsihodenrsyioocnnonroadnkiteiroafnkasce;e(;fca)(cbe); (inbi)taiidanthiiteoisanitoionofnatnhodef ptwhroeemawrineaaeftnretarwf2tee0arrm2o0ifnmthoiefnitnoosofeltrotliowfelhlweifneitrhweaaicthhvienalgovctehitleoycsoittofyp1o8cfr0i1tme8r0/iamm. in/mainndadndrydcroyncdoitniodnitsi;on(cs); (acd)haedshioensioanndanpdropmroinmeinntewntewareoafr tohfethinesienrstewrthwenherenarcehaicnhginthgethsteosptocpritcerritiae.ria.

From the results, it is clear that the lubricating effect of the cutting fluid was negligible compared toFFthrrooammt pttrhhoeevirrdeeessuudllbttssy,, iittthiiess accldleehaaerrsttihhoanattotthfheMe llnuuSbb.rrOiiccanattitinhngeg eoeftfffheeeccrtthooaffntthdhe,etcchuuettttciionnogglifflnluugiidedffwwecaatsssnneeegmgllisiggtiiobbllbeeeccoloemmssppfaaorrreedd ttoo tthhaeattinppsrreoorvvtsiiddweedidthbbayy sttphheeeaadddrhhaeenssgiieoonnusooeffdMMinnntSSh..eOOpnnrettshheeentoottshhtueedrryhh.aaFnnidnda,, lttlhhye,eFccioogooullriienngg8 esehffffoeewccttsssteeheeemmTssayttoolobbreeculleerssvssesffoorr tthheecoiinnrrsseesrrpttssonwwdiiittnhhgaatossppSeeAeeEdd 1rr2aaLnn1gg4eeauunssdeeddSAiinnEtt1hh2ee12pprrmeessaeecnnhtitnssettduuddwyyi..thFFiidnniafafllellyrye,,nFFtiiggcuounrreedi88tiosshhnosowwanssdtthhcueetTTtiaanyyglloosprr ecceuudrrsvv.eess ccoorrrreessppoonnddiinngg ttoo SSAAEE 1122LL1144 aanndd SSAAEE 11221122 mmaacchhiinneedd wwiitthh ddiiffffeerreenntt ccoonnddiittiioonnss aanndd ccuuttttiinngg ssppeeeeddss..



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This graph will provide additional information (SAE 1212 was selected as its behavior was very

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2. In three free-cutting steels, the SAE 12L14 carbon steel, presented the best performance in terms of tool life for the lower cutting speeds, but no noticeable differences were found for cutting speed of 240 m/min. Additionally, the wear at the rake face of the cutting tool was lower at lower cutting speed and increased with the increase of the cutting speed at all machining condition of steel alloys.

3. The Taylor curves showed that SAE 12L14 was more sensitive to the cutting speed and type of machining condition. This difference can be noted to the lead, which enhanced the material’s machinability and, consequently, affected the slope of these curves that were associated to the material of the cutting tool and the workpiece to be machined.

4. Auto-lubrication characteristics of these steel grades have shown a better machining capabilities compare to the lubricated conditions. Consequently, lubrication did not bring any benefit for the studied machining conditions and materials; instead, it is showed economic and environmental disadvantages. Therefore, the lubrication should be considered for more challenging machining solicitations (high-speed machining) or hard-to-cut materials.

Author Contributions: Conceptualization, D.M.K. and D.P.; data curation, S.H., and A.J.S.E.; funding acquisition, A.J.S.E. and L.N.L.d.L.; methodology, D.M.K. and D.P.; validation, S.H. and D.P.; resources, J.C.; writing original draft, S.H., D.M.K., and D.P.; writing, review, and editing, A.J.S.E., J.C., and L.N.L.d.L.

Funding: This research was funded by Serra Húnter program (Generalitat de Catalunya), grant number UPC-LE-304.

Acknowledgments: This work is supported by the Serra Húnter program (Generalitat de Catalunya) reference number UPC-LE-304 and the Aeronautics Advanced Manufacturing Center (CFAA) of Bilbao. Thanks to Soledad Pereda from INTI-Mecánica for the valuable support with the electronic microscopy, Andrea Romano for helping with the microscopy analysis and X-ray spectroscopy analysis and Diego Russo for helping in machining activities.

Conflicts of Interest: The authors declare no conflict of interest.

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