Definition
Carbonsteelisasteelwithcarboncontentupto2.1%byweightandnominimumspecifiedalloyingelementadded. SometimesalsobecalledPlaincarbonsteelorcarbonsteel.Carbonsteelmeanstheiron-carbonalloywithcarboncontentWclessthan2.11%.Carbonsteel,inadditiontocarbon,usuallycontainsasmallamountofsilicon,manganese,sulfurandphosphorus.
Classification
(1)Carbonsteelscanbeclassifiedbyuse:carbonstructuralsteel,carbontoolsteelandfree-cuttingstructuralsteel. Carbonstructuralsteelisdividedintotwocategories:constructionsteelandmachinebuildingstructuralsteel;
(2)Byrefiningmethods,itcanbedividedintoopenhearthsteelandconvertersteel;
(3)Bymethodofdeoxidation,itcanbedividedintoboilingsteel(F),killedsteel(Z),semikilledsteel(b)andspecialkilledsteel(TZ);
(4)Bycarboncontent,itcanbedividedintomildorlow-carbonsteel（WC≤0.25%）,medium-carbonsteel（WC0.25%—0.6%）andhigher-carbonsteel（WC>0.6%）;
(5)Bythequalityofsteel,Carbonsteelsareclassifiedintoplaincarbonsteels(highinphosphorusandsulfur),highqualitycarbonsteels(lowinphosphorusandsulfur)andhighqualitysteels(lowerinphosphorusandsulfur)andsuperiorqualitysteel.
Commonly,thehighercarboncontentcarbonsteelcontains,thegreaterhardnessitisandductilityislow.
Commoncarbonsteel
1.carbonstructuralsteel
Grade:forexampleQ235-AF,suggestsσs≥235MPaGradenote:Qisyieldstrength,Aisqualitygrade(withABCDfourgrades),Fisrimmedsteel.Features:lowcost,goodperformance(suchasweldabilityandcoldformability). Applications:generalengineeringstructuresandgeneralmechanicalparts.SuchasQ235canmakebolts,nuts,pins, hooksand lessimportantmechanicalparts,aswellastheconstructionofthethreadsteel,structuralsteel,rebar andsoon.
2.Qualitycarbonstructuralsteel
Grade:forexample45、65Mn、08F,Gradenote:Adirectexpressionofthefractionofcarbonamountcontainedin themetals.Application:nonalloysteelwhichisusedtomakeimportantmechanicalpartsisusuallyusedafterheat treatment.Commongradeanduse:Carbonhaslowmassfraction,goodplasticityandlowstrength,usedin stampingparts,suchasautomobilesandinstrumenthousings;Becauseofitsgoodplasticityandweldability,itcan beusedforpartsandcarburizingpartswhichstrengthrequirementisnothigh,suchashood,weldingcontainer,smallshaft,nut,washerandcarburizedgearetc.45，40Mn，afterquenchingandtempering,thecompositehasgoodmechanicalpropertiesandisappliedtothemechanicalpartswithhigherforce,suchasGear,connectingrod, machinetoolmainshaft,etc.60、65Mnsteelhavingahighstrength;usedinthemanufactureofsprings,locomotive rims,andlowspeedwheels.
3.Carbontoolsteel
Grade:forexampleT12steelrepresentsWc=1.2%carbontoolsteel.Gradenote:Tplusthousandsoffractionsofmetalcontainingcarbon.
Features:belongstoeutectoidsteelandhyper-eutectoidsteel,withhighstrength,highhardnessandgoodwearresistance,andissuitableformanufacturingvariouslowspeedcuttingtools.Commongradeanduse:T7,T8:makeparts thatrequireimpactandrequiretoughness,suchashammer,chisel,punch,woodworkingtools,scissors.T9、T10、 T11： Smallimpactresistanttoolsrequiringhighhardnessandhighwearresistance,suchassmalldrill,tap,die, handsaw. T12、T13：Maketoolsthatarefreefromimpact,suchasfile,scraper,razor,gage.
4.CastSteel
Grade:forexampleZG200-400，suggestsσs≥200MPa，σb≥400MPacaststeel,Features:castingperformanceisworsethancastiron,butmechanicalpropertyisbetterthancastiron.Applications:mainlyusedinmanufacturingthe importantmachinerypartswithcomplexshape,highmechanicalperformancerequirementsyetdifficulttoformbyforging orpressing,suchasthecartransmissionhousing,thecouplerandcouplerofarollingstock,etc.
Effectofimpurityelementsonpropertiesofcarbonsteel
1.manganese
About0.25%~0.80%.Solidsolutionstrengthening,removeFeOandreducethebrittlenessofsteel,chemical combinationwithSulphurtoMnS,toreducetheharmfuleffectofsulfur.Itisbeneficial.
2.silicon
About0.10%~0.40%,Solidsolutionstrengthening,removetheadverseeffectsofFeOonthequalityofsteel. Itis beneficial.
3.sulfur
FeSandFeformlowmeltingpointeutectic(985meltingpoint),thesteelisbrittleandcrackedwhenitishotworking at1000~1250℃,hotshortness.Itisharmful.
4.phosphorus
Increaseinstrengthandhardness,butitreducesplasticityandtoughness,coldshortness.Itisharmful.
