Cac Khai Niem Ve Gang

CHNG 8: CC KHI NIM CHUNG V GANG 8.1. KHI NIM CHUNG 8.1.1. nh ngha - Gang l hp kim ca st vi Cacbon vi thnh phn Cacbon ln hn 2,14%. - Ngoi ra cn cc nguyn t thng gp l Mn, Si, P, S. Mn v Si l hai nguyn t c tc dng iu chnh s to thnh graft v c tnh ca gang. Cn P v S l cc nguyn t c hi trong gang nn cng t cng tt.

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CHNG 8: CC KHI NIM CHUNG V GANG 8.1.2. Cc c tnh c bn ca gang

- Nhit chy thp, nn d nu chy hn thp; - D nu luyn; - Tnh c tt; - D gia cng ct (tr gang trng); - Chu nn tt.

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CHNG 8: CC KHI NIM CHUNG V GANg 8.1.3. Cc c tnh c bn ca gang - Theo t chc t vi, ngi ta phn gang lm 2 loi chnh l gang trng v gang graft + Gang trng: C t chc t vi ca gang hon ton ph hp vi gin trng thi Fe-C v lun cha hn hp cng tinh Ledeburit; + Gang c graft: L loi gang trong phn ln hoc ton b lng Cacbon nm di dng t do grafhit.

- Tu theo hnh dng ca graphit, li chia thnh 3 loi: gang xm, gang do v gang cu;- Trong t chc ca loi gang ny khng c Ledeburit nn t

chc t vi khng ph hp vi gin trng tha Fe-C.3

CHNG 8: CC KHI NIM CHUNG V GANG 8.2. GANG TRNG 8.2.1. nh ngha - Gang trng l gang m Cacbon hon ton nm di dng lin kt Hp cht Xementit (Fe3C). 8.2.2. Phn loi - Gang trng trc cng tinh c %C < 4,3%. C t chc l:

Le + XeII.

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8.2.2. Phn loi- Gang trng cng tinh c %C = 4,3% c t chc Le. - Gang trng sau cng tinh c %C > 4,3% v c t

chc l Le + XeI.+ Gang trng cng v gin

nn khng dng c trongch to c kh. + Gang trng ch yu dng

luyn thp, thnhgang do, lm bi nghin v lm mp li cy.

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CHNG 8: CC KHI NIM CHUNG V GANG 8.3. GANG XM 8.3.1. T chc t vi - Gang xm cng nh nhng loi gang c grafit khc, c t chc t vi chia lm hai phn r rt: nn kim loi v grafit. (vi gang xm: T chc t vi = nn kim loi + grafit tm

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8.3.1. T chc t vi a, Grafit tm v nn kim loi Tu thuc vo lng Xementit nhiu hay t m phn t chc cha Xementit c khc nhau: - Ferit khi khng c Xementit (Fe3C); - Ferit + Feclit khi c t Fe3C (khong 0,1 - 0,6%); - Peclit khi c kh nhiu Fe3C (khong 0,6 0,8%). Phn t chc c cha Ferit, Ferit + Peclit hoc Peclit gi l nn kim loi.

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8.3.1. T chc t vi Cc loi gang xm: - Gang xm Ferit c t chc t vi l grafit tm phn b trn nn Ferit; - Gang xm Peclit c t chc t vi gm grafit tm phn b trn nn kim loi Ferit + Peclit, lng Fe3C (khong 0,1 - 0,6%); - Gang xm Peclt c t chc t vi gm grafit tm phn b trn nn kim loi Peclit, lng Fe3C (khong 0,6 0,8%).

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8.3. GANG XM 8.3.2. Thnh phn ho hc + Cacbon - Lng Cacbon cng nhiu kh nng grafit ho cng mnh, nhit chy thp nn d c, c tnh km; - Lng Cacbon c khng ch vo khong 2,8 3,5%. + Silic - L nguyn t thc y s to thnh grafit trong gang. Silic l nguyn t quan trng sau Fe v C; - Hm lng khng ch trong khong 1,5 3%. + Mangan - L nguyn t cn tr s to thnh grafit; - Lm tng cng, bn ca gang; - Hm lng khng ch trong khong 0,5 1,0%.9

8.3.2. Thnh phn ho hc

+ Phtpho - Lm tng chy long; - Lm tng tnh chng mi mn; - Lng P c khng ch vo khong 0,1 0,2% n 0,5%. Hm lng qu nhiu P gang s gin.+ Lu hunh - L nguyn t cn tr mnh s to thnh grafit; - Lm xu tnh c, gim chy long; - L nguyn t c hi, lng S khng ch trong khong 0,06 0.12%. Ngoi ra cn c mt s nguyn t khc nh Cr, Ni, Mo,c tc dng ring.10

8.3. GANG XM 8.3.3. C tnh, cc yu t nh hng v nhng bin php nng cao c tnh a, C tnh

- bn rt thp: k = 150 400MPa (= thp thng dng);- cng thp trong khong 150 250HB; - do, dai u thp; - Chng mi mn tt; - Graphit c kh nng lm tt dao ng.

+ Gang xm c t chc grafit mm.

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8.3. GANG XM b, Cc yu t nh hng n c tnh Grafit - S lng, ln, hnh dng v s phn b ca grafit. Nn kim loi

- Nn kim loi c c tnh cao th gang xm cng c c tnh cao;gang xm Ferit.

gang xm Ferit - Peclit cng

gang xm Peclit

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8.3. GANG XM

c, Cc bin php nng cao c tnh- Gim lng cacbon ca gang (2,2 2,5%); - Lm nh mn grafit bng phng php bin tnh;

- Hp kim ho;- Nhit luyn. 8.3.4. K hiu v cng dng

- Theo tiu chun ca Lin X: Cxx xx;- Theo tiu chun TCVN ca Vit Nam: GXxx xx. V d

GX15 32 hoc C15-32 k = 150N/mm2 u = 320N/mm2

k

u

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8.3.4. K hiu v cng dng - Cc mc c bn thp, k = 100 150MPa Gm: GX10 GX15 (C10 C15) Gang xm Ferit

Dng lm chi tit v, np khng chu lc.- Cc mc c bn trung bnh, k = 150 250MPa Gm: GX15 GX25 (C15 C25). Gang xm Ferit - Peclit Dng lm cc chi tit chu ti nh: v hp gim tc, mt bch,... - Cc mc c bn tng i cao, k = 250 300MPa Gm: GX25 GX30 (C25 C30). Gang xm Peclit vi grafit nh mn. Dng lm cc chi tit chu ti trng cao: bnh rng, bnh , thn my quan trng, xc mng,...14

8.3.4. K hiu v cng dng - Cc mc c bn cao, k 300MPa Gm: GX30 GX40 (C30 C40). gang xm Peclit vi grafit rt nh mn.

Dng lm cc chi tit chu trng cao, chu mi mn nh bnh rng ch V, trc chnh, v bm thu lc ,...Kt lun - Gang xm dng lm cc chi tit chu nn, trnh dng vo cc b phn chu ko cao; - Dng lm trt v grafit c tnh bi trn tt. + Gang xm bin trng - Gang c b mt ca chi tit b bin trng, mt s chi tit cn tnh chng mi mn lp b mt cao nh bi nghin, trc cn, trc nghin,...15

CHNG 8: CC KHI NIM CHUNG V GANG

8.4. GANG CU8.4.1. T chc t vi

- Gang cu l mt loi gang c t chc nn kim loi v grafit. grafit ca n c dng qu cu trn. - T chc t vi ca gang cu cba loi nn kim loi l: Ferit, Ferit Peclit v Peclit.

Tng cng c ba loi gangcu Ferit, gang cu Ferit Peclit v gang cu Peclit.16

8.4. GANG CU

8.4.2. Thnh phn ho hc- Dng Mg hoc Ce cho vo gang xm lng to ra gang cu . C thnh phn ho hc ging gang xm. + Cht bin tnh cn khng ch vi lng nh: 0,04 0,08%; + Cc nguyn t cn tr s cu ho khong mc 0,01% (S).

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8.4. GANG CU

8.4.3. C tnh v bin php nng cao c tnha, C tnh - Gang cu c c tnh cao hn gang xm nhiu; + bn: k = 400 1000MPa; 0,2 = 250 600MPa + do, dai: = 5 15%; ak = 300 600 KJ/m2 + cng khong 200HB b, Cc bin php nng cao c tnh

- Dng Niken ho bn pha Ferit;- Ti ng nhit bin thnh Bainit.18

8.4. GANG CU 8.4.4. K hiu v cng dng - Theo tiu chun ca Lin X: Bxx xx; - Theo tiu chun TCVN ca Vit Nam: GCxx xx. k V d: B455 (GC455 ) C: k = 450MPa; = 5% + Gang cu Ferit: - B3817; B4212 (GC3817; GC4212); - C bn thp t dng.19

8.4.4. K hiu v cng dng + Gang cu Peclit: - B502; B602 (GC502; GC602). - C bn tt ch yu dng lm trc khuu, trc cn, + Gang cu Peclit: - B502; B602 (GC502; GC602).;

- C bn tt ch yu dng lm trc khuu, trc cn, + Gang cu nhit luyn Bainit:- B703; B1004 (GC3817; GC4212); - C bn cao dng lm cc chi tit quan trng20


8.5. GANG DO8.5.1. T chc t vi - Gang do l mt loi gang c t chc nn kim loi v grafit. grafit ca n c hnh dng cm nh cm bng . - Gang do c 3 loi l:

+ Gang do Ferit;+ Gang do Ferit Peclit; + Gang do Peclit.

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8.5. GANG DO 8.5.2. Thnh phn ho hc- Gang do c t gang trng nn thnh phn ho hc c bn cng ging gang trng. + Lng cacbon trong gang do khong 2,2 2,8%

t grafit ho tnh do cao. + Lng Silic c th ly t 0,8 1,4%.

8.5.3. C tnh+ bn: k = 300 600MPa; 0,2 = 200 450MPa + do: = 5 15%.22

8.5. GANG DO

8.5.4. K hiu v cng dng- Theo tiu chun ca Lin X: xx xx; - Theo tiu chun TCVN ca Vit Nam: GZxx xx. k V d: 456 (GZ456 )

C: k = 450MPa; = 6%Cc mc thng dng + 306; 338; 3510; 3712 Gang do Ferit + 457; 505; 554; 603 Gang do Peclit23

8.5.4. K hiu v cng dng Cng dng Gang do ch to cc chi tit i hi ng thi cc tnh cht sau: + Hnh dng phc tp; + Tit din thnh mng;

+ Chu va p. c s dng nhiu lm cc chi tit trong t, cc my nng nghip, my ko, my dt.

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8.6. GANG HP KIM- Gang cha mt lng ln cc nguyn t nh Cr, Ni, Mn, Ti, Mo, c c tnh cao gi l gang hp kim. Cc nguyn t hp kim lm tng c tnh ca gang do:

+ Khi ho tan vo Ferit lm tng c tnh ca pha ny;+ Lm nh mn t chc Peclit khi c; + Lm tng hiu qu nhit luyn bng cch ti v ram.

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8.7. NHIT LUYN GANG8.7.1. grafit ho+ gang xm c lp v b bin trng.

T0u = 850 8800C; tu = 2 3 giFe3C + G Lp b mt c nn kim loi l Ferit hay Ferit Peclit + thay i nn kim loi - lm gim cacbon lin kt; T0u = 7000C

Fe3C F + G- lm tng cacbon lin kt; T0u > Ac3 Grafit ho tan vo Austenit26

8.7. NHIT LUYN GANG

8.7.2. Ti v ram gang+ Mc ch ca ti v ram:- Lm tng bn, cng v tnh chng mi mn

+ Ti Gang (nn kim loi v Grafit)+ Ram - Ram thp (150 2500C), t chc Mram + G;nung

+G

ti

M + d + G

- Ram trung bnh (300 4500C), t chc Tram + G;- Ram cao (500 6500C), t chc Xram + G.27

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Cac Khai Niem Ve Gang