BO CO NHM 3 TRNG H S PHM K THUT TPHCM KHOA C KH CH TO MY

1. KHI NIM CHUNG1.1. 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.

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

- Theo t chc t vi, ngi ta phn gang lm 2 loi chnh l gang trng v gang graphite + 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 graphite: L loi gang trong phn ln hoc ton b lng Cacbon nm di dng t do graphite - 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. 1.3. Cc c tnh c bn ca gang

2. GANG TRNG2.1. nh ngha- Gang trng l gang m Cacbon hon ton nm di dng lin kt Hp cht Xementit (Fe3C).- Gang trng trc cng tinh c %C < 4,3%. C t chc l: Le + XeII.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 trong ch to c kh. + Gang trng ch yu dng luyn thp, thnh gang do, lm bi nghin v lm mp li cy.

3. GANG XM3.1. T chc t vi- Gang xm cng nh nhng loi gang c graphite khc, c t chc t vi chia lm hai phn r rt: nn kim loi v graphite. (vi gang xm: T chc t vi = nn kim loi + graphite tm

- Ferit khi khng c Xementit (Fe3C);a, Grafit tm v nn kim loi - 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.Tu thuc vo lng Xementit nhiu hay t m phn t chc cha Xementit c khc nhau:

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

3.2. Thnh phn ho hc+ Cacbon - Lng Cacbon cng nhiu kh nng graphite 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 graphite 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 graphite- Lm tng cng, bn ca gang;- Hm lng khng ch trong khong 0,5 1,0%.

+ 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 graphite- 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.

3.3. C tnh, cc yu t nh hng v nhng bin php nng cao c tnha, 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 graphite mm.

b, Cc yu t nh hng n c tnh Grafit - S lng, ln, hnh dng v s phn b ca graphite Nn kim loi - Nn kim loi c c tnh cao th gang xm cng c c tnh cao;

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.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/mm2u = 320N/mm2

- 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,...

- 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 ,...- 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.Kt lun+ 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,...

4. GANG CU4.1. 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 c ba loi nn kim loi l: Ferit, Ferit Peclit v Peclit. Tng cng c ba loi gang cu Ferit, gang cu Ferit Peclit v gang cu Peclit.

4.2. Thnh phn ho hc- Dng Mg hoc Ce cho vo gang xm lng to ra gang cu .+ 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). C thnh phn ho hc ging gang xm.

4.3. C tnh v bin php nng cao c tnh - Gang cu c c tnh cao hn gang xm nhiu;+ bn: k = 400 1000MPa; 0,2 = 250 600MPaa, C tnh+ 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.

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

+ Gang cu nhit luyn Bainit: - B703; B1004 (GC3817; GC4212); - C bn cao dng lm cc chi tit quan trng + 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,

5. GANG DO5.1. 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.

5.2. Thnh phn ho hc- Gang do c t gang trng nn thnh phn ho hc c bn cng ging gang trng.+ Lng Silic c th ly t 0,8 1,4%. + Lng cacbon trong gang do khong 2,2 2,8% t grafit ho tnh do cao.5.3. C tnh+ bn: k = 300 600MPa; 0,2 = 200 450MPa+ do: = 5 15%.

5.4. K hiu v cng dng+ 306; 338; 3510; 3712 Gang do Ferit - Theo tiu chun ca Lin X: xx xx;- Theo tiu chun TCVN ca Vit Nam: GZxx xx.V d: 456 (GZ456 )C: k = 450MPa; = 6%Cc mc thng dng+ 457; 505; 554; 603 Gang do Peclit

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.Cng dng

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