Nkag siab txog Kev Hloov Txias Txias ntawm Hlau

 

Kuv Txoj Kev Txias

 

Hlau feem ntau dhau ob hom kev ua kom txias: isothermal txias thiab tas li txias.

 

Isothermal txias

Nyob rau hauv txoj kev no, cov hlau yog rhuab mus rau lub xeev austenitic thiab tom qab ntawd txias sai sai rau qhov kub thiab txias, qhov twg nws tau tuav rau qee lub sijhawm, tso cai rau lub austenite hloov ua ntej txias mus rau chav sov. Txoj hauv kev no ua rau muaj kev tswj xyuas meej ntawm kev hloov pauv kub thiab lub sijhawm, ua rau muaj qhov tshwj xeeb microstructures thiab cov khoom.

 

▲ Isothermal Cooling thiab Kub

 

Kev ua kom txias tsis tu ncua

Ntawm no, cov hlau, pib nyob rau hauv lub xeev austenitic, tsis tu ncua txias rau chav tsev kub ntawm cov nqi sib txawv (piv txwv li, cua txias, cua sov cua sov, roj txias, dej txias, thiab lwm yam). Tus nqi cua txias hauv txoj kev no cuam tshuam cov txheej txheem hloov pauv ntawm austenite thiab microstructure kawg.

 

▲ Kev ua kom txias thiab kub tsis tu ncua

 

 

II Isothermal Transformation Curves ntawm Supercooled Austenite

 

▲ Supercooled austenite isothermal transformation nkhaus ntawm eutecoid steel

 

C-nqaj (tseem hu ua isothermal transformation curve of supercooled austenite or TTT curve) for eutectoid carbon steel illustrates the relationship between the transformation temperature, time, and transformation products when the steel is in a supercooled austenitic state.

 

Division of C-Curve Regions

Supercooled Austenite Zone:Nyob rau sab laug ntawm txoj kab pib hloov pauv ntawm C-kov, thaj tsam no sawv cev rau thaj chaw uas supercooled austenite tseem tsis tau hloov pauv.

 

Transformation Products Zone:Nyob rau sab xis ntawm txoj kab kev hloov pauv kawg thiab saum toj ntawm Ms point, thaj chaw no qhia tias qhov twg supercooled austenite tau hloov mus rau hauv nws cov khoom.

 

Transformation Progress Zone:Thaj chaw no nyob nruab nrab ntawm cov kab pib hloov pauv thiab xaus, qhia txog cov txheej txheem hloov pauv txuas ntxiv ntawm supercooled austenite.

 

Cov kab ntawm C-Curve thiab lawv lub cev tseem ceeb

Transformation Pib Kab:Ib qho nkhaus txuas cov ntsiab lus uas lub supercooled austenite pib hloov pauv, qhia lub sijhawm nws siv rau austenite pib hloov pauv ntawm qhov kub sib txawv.

 

Transformation kawg kab:Qhia txog lub sijhawm xav tau rau austenite kom ua tiav nws qhov kev hloov pauv ntawm qhov kub sib txawv.

Ms Kab: Kab kab rov tav qhia qhov pib kub rau martensitic transformation, kos lub ntsiab lus uas austenite pib hloov mus rau martensite.

 

Mf Kab (qee zaus hu ua Mf Point):Kab rov tav kab sawv cev rau qhov kawg kub rau martensitic transformation, qhov twg austenite kiag li transforms rau hauv martensite.

 

Qhov tseem ceeb ntawm C-Curve's Nose

Nyob ntawm kwv yees li 550 degree, C-kov ntawm eutectoid carbon steel qhia tau hais tias khoov lub npe hu ua nkhaus lub qhov ntswg. Qhov ntsuas kub sib thooj yog hu ua qhov ntswg qhov ntswg, qhov twg qhov kev hloov pauv ntawm austenite yog qhov ceev tshaj plaws. Saum toj no lub qhov ntswg, austenite feem ntau undergoes pearlitic transformation; hauv qab no lub qhov ntswg, bainitic transformation tshwm sim; thiab hauv qab ntawm Ms point, martensitic transformation tshwm sim.

 

Cov ntsiab lus tseem ceeb cuam tshuam rau cov duab thiab txoj hauj lwm ntawm C-Curve

Chemical Composition ntawm Steel:Cov ntsiab lus carbon thiab alloying cuam tshuam rau kev ruaj ntseg thiab kev hloov pauv ntawm austenite. Feem ntau, kev nce hauv cov ntsiab lus carbon hloov pauv C-kov mus rau sab xis, thaum cov ntsiab lus alloying (tshwj tsis yog Co thiab Al) ua rau kom muaj kev ruaj ntseg ntawm austenite thiab hloov C-khoov cov duab.

 

Microstructure ntawm Austenite:Finer austenitic grains muab ntau qhov ciam teb rau ib cheeb tsam hauv cheeb tsam, ua kom yooj yim rau nucleation thiab kev loj hlob ntawm cov khoom hloov pauv, yog li cuam tshuam rau C-curve txoj hauj lwm thiab cov duab.

 

Austenitization Kub thiab Tuav Sijhawm:Kev kub siab austenitization ntau dua thiab ntev tuav lub sij hawm ua rau coarser austenitic nplej, hloov C-nqaj ntxiv mus rau sab xis.

 

 

III Nruam Txias Hloov Hloov Kab Ntsig ntawm Supercooled Austenite

 

▲ Nruam Txias Hloov Hloov Kab Ntsig ntawm Supercooled Austenite

 

▲ Cov tsis sib xws rau txhua tsab ntawv

 

Continuous Cooling Transformation Curve (CCT nkhaus) yog ib qho cuab yeej tseem ceeb uas siv los piav txog cov txheej txheem hloov pauv theem ntawm supercooled austenite nyob rau hauv cov cua txias tas li. Nws qhia txog cov qauv kev hloov pauv ntawm supercooled austenite ntawm qhov sib txawv ntawm cov cua txias thiab ua lub hauv paus rau kev tshuaj xyuas microstructure thiab kev ua haujlwm ntawm cov khoom hloov pauv. Nws kuj yog ib qho tseem ceeb siv rau kev tsim cov txheej txheem kho cua sov.

 

Kev txhais thiab qhov tseem ceeb ntawm CCT Curve

Lub CCT nkhaus, los yog Continuous Cooling Transformation nkhaus, sau qhov pib thiab xaus qhov kub thiab txias thiab lub sij hawm uas supercooled austenite hloov mus rau ntau theem (xws li pearlite, bainite, martensite, thiab lwm yam) nyob rau hauv cov nqi sib txawv. Qhov kev nkhaus no yog qhov tseem ceeb rau kev nkag siab txog theem kev hloov pauv ntawm cov hlau, txhim kho cov txheej txheem kho cua sov, thiab kwv yees cov khoom ntawm cov khoom steel.

 

Txoj Kev Txiav Txim CCT Curve

Txoj kev txiav txim siab CCT nkhaus feem ntau suav nrog cov kauj ruam hauv qab no:

 

Kev npaj ua qauv:Xaiv cov qauv hlau sawv cev thiab muab lawv rau kev kho austenitizing kom ntseeg tau tias txhua qhov qauv muaj tib lub microstructure ua ntej ntsuas.

 

Kev ua kom txias tsis tu ncua:Tsis tu ncua txias cov qauv austenitized ntawm qhov sib txawv tas li thaum sau cov ntaub ntawv kub thiab lub sijhawm thaum lub caij txias.

 

Transformation Product Analysis:Thaum lub sij hawm los yog tom qab txias, txiav txim seb hom thiab ntau npaum li cas ntawm transformation khoom los ntawm metallographic tsom xam los yog lwm txoj kev.

 

Curve Plotting:Npaj cov ntaub ntawv pib thiab xaus qhov kub thiab lub sijhawm rau kev hloov pauv ntawm qhov sib txawv ntawm qhov sib txawv ntawm qhov sib txawv ntawm "kub-lub sij hawm logarithmic" kev sib koom ua ke daim ntawv los tsim CCT nkhaus.

 

Cov yam ntxwv ntawm CCT Curve

Kev hloov pauv thaj tsam:CCT nkhaus feem ntau suav nrog thaj tsam rau kev hloov pauv pearlite, bainite hloov pauv (rau qee yam hlau), thiab kev hloov pauv martensite. Cov cheeb tsam no sib raug rau cov txheej txheem hloov pauv theem tshwm sim ntawm qhov sib txawv ntawm qhov txias txias.

 

Cov nqi cua txias tseem ceeb:Ob qhov tseem ceeb tseem ceeb ntawm qhov txias txias muaj nyob hauv CCT nkhaus: qhov siab tshaj qhov txias txias (Vk) thiab qis dua qhov ntsuas cua txias (Vk'). Qhov ntsuas kub tseem ceeb tshaj plaws yog qhov tsawg kawg nkaus uas yuav tsum tau ua kom ntseeg tau tias austenite tsis decompose thaum lub caij txias tas mus li thiab yog tag nrho supercooled rau hauv thaj av martensite. Qhov qis dua qhov tseem ceeb ntawm qhov txias txias yog qhov siab tshaj plaws uas ua kom cov austenite tag nrho decomposes yam tsis muaj kev hloov pauv martensitic thaum lub sijhawm txias tas mus li.

 

Transformation complexity:Continuous cooling transformation yog complex dua isothermal transformation. Txij li cov txheej txheem txias tas mus li dhau los ntawm ntau qhov kev hloov pauv kub hauv cheeb tsam sib txuas, ntau qhov kev hloov pauv yuav tshwm sim nyob rau hauv ib ntus, thiab cov cua txias sib txawv yuav ua rau cov khoom sib txawv thiab cov khoom sib txawv.

 

Kev siv ntawm CCT Curve

Kev kho cua sov txheej txheem Formulation:CCT nkhaus tuaj yeem muab kev nkag siab txog cov khoom hloov pauv thiab kev ua haujlwm ntawm cov hlau ntawm cov cua txias sib txawv, tso cai rau kev tsim cov kev kho cua sov uas tsim nyog xws li cua sov, tuav lub sij hawm, thiab cua txias.

 

Kev Ua Haujlwm Zoo:CCT nkhaus tuaj yeem siv los kwv yees cov khoom ntawm cov khoom siv hlau nyob rau hauv cov kev kho cua sov tshwj xeeb, xws li hardness, lub zog, thiab toughness.

 

Kev xaiv khoom siv:Thaum xaiv cov khoom siv, CCT nkhaus ntawm cov khoom sib txawv tuaj yeem muab piv rau kev ntsuas lawv cov kev kho cua sov thiab cov kev siv tau.

 

 

IV Hom Txias Hloov Hloov

 

▲ Kev hloov pauv sib txawv hauv qab A kub

 

▲ Kev hloov pauv sib txawv hauv qab A kub

 

Kev hloov pauv txias ntawm cov hlau feem ntau suav nrog pearlite transformation, bainite transformation, thiab martensite transformation.

 

Pearlite Transformation:Qhov kub-kub diffusion transformation yog ua tiav los ntawm nucleation thiab kev loj hlob txheej txheem. Lub morphology ntawm pearlite hloov nrog txo qhov tsim kub; Qhov sib txawv ntawm interlamellar txo qis, thiab lub zog thiab hardness nce thaum tuav zoo ductility thiab toughness.

 

Kev hloov pauv hauv Bainite:tshwm sim nyob rau hauv nruab nrab kub ntau yam, bainite transformation yog ib tug semi-diffusion transformation. Bainite muaj nyob rau hauv ntau hom, xws li sab sauv bainite thiab qis bainite, thiab nws cov khoom nyob nruab nrab ntawm cov pearlite thiab martensite.

 

Kev hloov pauv Martensite:Qhov kub-kub, tsis-diffusion transformation tshwm sim nyob rau hauv martensite yam ntxwv los ntawm siab hardness thiab lub zog tab sis qis ductility thiab toughness. Martensite tuaj yeem ua lath-zoo li lossis phaj-zoo li, sib haum rau cov pa roj carbon tsawg thiab cov pa roj carbon siab, feem.

 

 

V Kev sib raug zoo ntawm kev hloov pauv tsis tu ncua txias thiab isothermal hloov pauv

 

▲ Kev sib piv ntawm Isothermal Cooling Transformation Curve ntawm Eutectoid Steel thiab Transformation Structure

 

Kev sib raug zoo

Ob qho kev hloov pauv tsis tu ncua thiab kev hloov pauv isothermal yog txoj hauv kev tseem ceeb ntawm kev hloov pauv ntawm austenite hauv kev kho cua sov. Lawv yog ib qho tseem ceeb rau kev nkag siab txog theem hloov pauv tus cwj pwm ntawm cov ntaub ntawv, tsim cov txheej txheem kho cua sov, thiab kwv yees cov khoom siv. Qee qhov xwm txheej, cov txheej txheem hloov pauv hloov pauv tas li tuaj yeem kwv yees kwv yees siv cov isothermal transformation diagram (C nkhaus) vim qhov nyuaj ntawm kev txiav txim siab qhov kev hloov pauv hloov pauv tas li.

 

Qhov txawv

Kev hloov pauv hloov:Kev hloov pauv tsis tu ncua txias tshwm sim nyob rau hauv qhov kev hloov pauv kub tsis tu ncua, thaum isothermal transformation tshwm sim ntawm qhov ntsuas kub tsis tu ncua.

 

Txheej txheem kev hloov pauv:Thaum lub sijhawm txias tas mus li, supercooled austenite ua tiav nws cov theem hloov pauv hauv qhov kub thiab txias, uas ua rau muaj kev hloov pauv tsis sib xws. Lub hauv paus hloov microstructure yuav coarser, thaum tom qab-transformed microstructure tej zaum yuav finer, feem ntau ua rau ib tug sib tov ntawm ntau yam microstructures. Isothermal transformation, ntawm qhov tod tes, tshwm sim nyob rau hauv qhov kub thiab txias, uas ua rau cov theem sib xws.

 

Cov khoom siv hloov pauv:Vim muaj qhov sib txawv ntawm kev hloov pauv, hom thiab qhov sib faib ntawm cov khoom hloov pauv tau los ntawm ob txoj kev tuaj yeem sib txawv. Piv txwv li, nyob rau hauv eutectoid steel, tas mus li txias yuav ua tau tsuas yog nyob rau hauv pearlitic transformation tsis muaj bainite, thaum isothermal transformation tej yam kev mob yuav ua tau ib tug nplua nuj ntau yam ntawm theem transformation khoom.

 

Cov ntawv thov thiab xaiv

Hauv kev tsim cov tswv yim, kev xaiv ntawm kev hloov pauv tsis tu ncua thiab kev hloov pauv isothermal nyob ntawm cov khoom tshwj xeeb cov tshuaj muaj pes tsawg leeg, microstructure, thiab qhov xav tau kev kho cua sov cuam tshuam thiab kev ua tau zoo. Kev hloov pauv tsis tu ncua txias yog feem ntau yog siv hauv kev tsim khoom loj thiab kev ua haujlwm tas mus li vim nws qhov yooj yim thiab tus nqi qis. Nyob rau hauv sib piv, isothermal transformation yog ntau haum rau scenarios uas yuav tsum tau meej tswj nyob rau hauv lub theem transformation txheej txheem thiab cov khoom hom, xws li nyob rau hauv kev npaj ntawm high-end cov ntaub ntawv thiab zus tau tej cov qhov chaw uas yuav tsum tau tshwj xeeb kev ua tau zoo.

 

 

VI. Cov yam ntxwv cuam tshuam rau kev hloov pauv cua txias

 

Austenite Composition

Cov ntsiab lus carbon thiab cov ntsiab lus alloying cuam tshuam rau kev ruaj ntseg thiab kev hloov pauv ntawm austenite. Piv txwv li, nce cov ntsiab lus carbon hloov C nkhaus mus rau sab xis, thiab cov ntsiab lus alloying (tshwj tsis yog Co thiab Al) yaj hauv austenite txhim kho nws txoj kev ruaj ntseg thiab hloov cov duab ntawm C nkhaus.

 

Austenite Microstructure

Finer austenite nplej, nrog ntau cov qoob loo ciam teb ib cheeb tsam, pab txhawb cov nucleation thiab kev loj hlob ntawm cov khoom hloov pauv.

 

Kev nyuaj siab thiab yas deformation

Supercooled austenite nyob rau hauv tensile kev nyuaj siab accelerates transformation, whereas compressive kev nyuaj siab muaj opposite nyhuv. Yas deformation kuj accelerates lub transformation ntawm austenite.

 

 

VII. Daim ntawv thov ntawm Txias Transformation

 

Nkag siab txog kev hloov pauv cua txias ntawm cov hlau yog qhov tseem ceeb rau kev tsim cov txheej txheem kho cua sov. Los ntawm kev tswj cov txheej txheem txias thiab tus nqi, cov hlau nrog cov microstructures sib txawv thiab cov khoom tuaj yeem ua tau raws li ntau yam kev xav tau. Piv txwv li, cov txheej txheem quenching sai txias cov hlau los tsim cov qauv martensitic, yog li ua kom tawv thiab lub zog; cov txheej txheem tempering muaj cua sov thiab tuav tom qab quenching los txo cov kev ntxhov siab sab hauv thiab txhim kho toughness.

 

Kev hloov pauv cua txias hauv cov hlau yog qhov tseem ceeb ntawm cov txheej txheem kev kho cua sov, cuam tshuam los ntawm ntau yam thiab nyuaj. Hauv kev siv tswv yim, xaiv txoj kev ua kom txias thiab tus nqi raws li cov xwm txheej tshwj xeeb yog tsim nyog kom ua tiav qhov xav tau microstructure thiab cov khoom.