NGHIÊN CỨU ẢNH HƯỞNG CỦA CÁC YẾU TỐ CHÍNH NHẰM ỔN ĐỊNH CÔNG NGHỆ THẤM NITƠ THỂ KHÍ LÊN MỘT SỐ LOẠI THÉP THÔNG DỤNG Ở VIỆT NAM

Header Page of 89 B GIO DC V O TO TRNG I HC BCH KHOA H NI NGUYN NGC MINH NGHIấN CU NH HNG CA CC YU T CHNH NHM N NH CễNG NGH THM NIT TH KH LấN MT S LOI THẫP THễNG DNG VIT NAM LUN N TIN S KHOA HC VT LIU H Ni 2015 Footer Page of 89 Header Page of 89 B GIO DC V O TO TRNG I HC BCH KHOA H NI NGUYN NGC MINH NGHIấN CU NH HNG CA CC YU T CHNH NHM N NH CễNG NGH THM NIT TH KH LấN MT S LOI THẫP THễNG DNG VIT NAM Chuyờn ngnh: Mó s: Kim loi hc 62440129 LUN N TIN S KHOA HC VT LIU NGI HNG DN KHOA HC: PGS TS Nguyn Vn T TS Nguyn Vn Hin Footer Page of 89 Header Page of 89 LI CM N Tụi xin chõn thnh cỏm n PGS TS Nguyn Vn T v TS Nguyn Vn Hin, nhng ngi Thy ó tn tỡnh hng dn, giỳp , ch bo v ng viờn tụi sut quỏ trỡnh thc hin lun ỏn Tụi xin chõn thnh cỏm n B mụn Vt liu hc, X lý nhit v B mt, cỏc B mụn chuyờn mụn khỏc thuc Vin Khoa hc v K thut Vt liu, Vin o to sau i hc ó to iu kin tụi cú th hon thnh lun ỏn Tụi xin chõn thnh cỏm n Ban lónh o Vin Khoa hc v K thut Vt liu ó to iu kin tụi hon thnh lun ỏn Xin cm n cỏc Anh, Ch, Em v Cỏc bn ng nghip ti Vin Khoa hc v K thut Vt liu c bit l ti B mụn Vt liu hc- X lý nhit v B mt, ó giỳp tụi rt nhiu vic hon thnh phn thc nghim ca lun ỏn ny Cui cựng tụi xin gi li cm n chõn thnh ti bn bố, gia ỡnh v ngi thõn ó luụn bờn, ng viờn v khớch l tụi sm hon thnh lun ỏn Footer Page of 89 Header Page of 89 LI CAM OAN Tụi xin cam oan õy l cụng trỡnh nghiờn cu ca riờng tụi Cỏc s liu, kt qu lun ỏn l trung thc v cha tng c cụng b bt c mt cụng trỡnh no khỏc NGI HNG DN KHOA HC: PGS.TS Nguyn Vn T TS Nguyn Vn Hin Footer Page of 89 TC GI Nguyn Ngc Minh Header Page of 89 MC LC Trang Trang ph bỡa Li cm n Li cam oan i Mc lc Danh mc cỏc bng biu v hỡnh v iv Danh mc cỏc ký hiu v ch vit tt ix M u Chng 1: Tỡnh hỡnh nghiờn cu v ng dng cụng ngh thm nit 1 Cụng ngh thm nit trờn th gii v ti Vit nam 1.1.1 Cụng ngh thm nit trờn th gii 1.1.2 Cụng ngh thm nit ti Vit nam 1.2 Cỏc phng phỏp thm nit 1.2.1 Phng phỏp thm nit th khớ 1.2.2 Phng phỏp thm nit th lng 1.2.3 Phng phỏp thm nit plasma 1.3 u nhc im ca cỏc loi hỡnh cụng ngh 13 1.4 Mc tiờu, i tng v ni dung nghiờn cu 14 1.4.1 Mc tiờu nghiờn cu 14 1.4.2 i tng nghiờn cu 15 1.4.3 Ni dung nghiờn cu 15 Chng 2: C s lý thuyt thm nit th khớ 16 2.1 C s quỏ trỡnh thm nit th khớ 16 2.1.1 Th nit ca quỏ trỡnh thm 16 2.1.2 Hot nit ca mụi trng thm 17 2.1.3 Hot nit thộp 19 2.1.4 H s truyn nit 19 2.2 Cu trỳc lp thm nit th khớ 20 2.3 nh hng ca cỏc yu t cụng ngh chớnh n s hỡnh thnh lp thm 24 2.3.1 nh hng ca nhit 24 2.3.2 nh hng ca th thm Kn 26 Footer Page of 89 i Header Page of 89 2.3.2.1 nh hng ca thnh phn cht thm 26 2.3.3.2 nh hng ca thi gian lu 28 2.3.3 nh hng ca thi gian thm v yu t khỏc 29 Chng 3: Thit b v phng phỏp nghiờn cu 32 3.1 Nguyờn vt liu s dng 33 3.2 Thit b s dng 34 3.2.1 Thit b o phõn hy NH3 34 3.2.2 Thit b ỏnh giỏ t chc v tớnh cht lp thm 35 3.2.3 Thit b thc nghim 37 39 3.3 Phng phỏp nghiờn cu 3.3.1 ỏnh giỏ mc khuych tỏn nit v s tit pha nitrit 39 3.3.2 Phng phỏp xỏc nh h s truyn 39 3.3.3 Phng phỏp xỏc nh nh hng ca cỏc thụng s cụng ngh 40 40 3.4 Cỏc quy trỡnh thc nghim 3.4.1 Quy trỡnh x lý nhit luyn trc thm 40 3.4.2 Quy trỡnh thm 42 Chng 4: Kt qu v bn lun 44 4.1 Kt qu phõn tớch ỏnh giỏ mu trc thm 44 4.1.1 Kt qu nh hin vi quang hc 44 4.1.2 Kt qu phõn tớch hin vi in t quột 45 4.1.3 Kt qu phõn tớch nhiu x Rn ghen 49 4.2 Kt qu phõn tớch ỏnh giỏ mu sau thm 50 4.2.1 Kt qu quan sỏt hin vi quang hc 50 4.2.2 Kt qu phõn tớch trờn hin vi in t quột 51 4.2.3 Kt qu phõn tớch nhiu x Rn ghen 63 65 4.3 S hỡnh thnh v phỏt trin lp thm 4.3.1 S hỡnh thnh v phỏt trin lp thm trờn thộp C20 65 4.3.2 S hỡnh thnh v phỏt trin lp thm trờn thộp SKD61 68 4.3.3 S tn ti l xp lp trng 73 4.4 nh hng ca cỏc thụng s chớnh u vo n th thm Kn 74 4.4.1 nh hng ca nhit 74 4.4.2 nh hng ca thi gian lu 75 4.4.3 nh hng ca thnh phn khớ thm 76 Footer Page of 89 ii Header Page of 89 77 4.5 H s truyn cht () 4.5.1 nh hng ca th thm 80 4.5.2 nh hng ca nhit 82 4.6 nh hng ca cỏc yu t cụng ngh chớnh n t chc v tớnh cht lp thm 83 4.6.1 nh hng ca nhit 83 4.6.2 nh hng ca th thm Kn 86 4.6.2.1 nh hng ca thi gian lu 87 4.6.2.2 nh hng ca thnh phn khớ thm 89 94 4.6.3 nh hng ca thi gian thm Kt lun chung v kin ngh 104 Danh mc cỏc cụng trỡnh khoa hc liờn quan n lun ỏn ó cụng b 107 Ti liu tham kho 108 Footer Page of 89 iii Header Page of 89 DANH MC CC BNG, HèNH V, TH Danh mc cỏc bng Bng 1.1 : Bng 2.1: Bng 2.2: Bng 2.3: Bng 3.1: Bng 4.1: Bng 4.2: So sỏnh u nhc im ca cỏc cụng ngh thm nit hin [25] Cỏc pha thng gp h Fe-N [16,20,89] H s khuych tỏn nit , v ti cỏc nhit khỏc [68] Tha s nhit theo cụng thc Harries [55] Thnh phn húa hc ca cỏc mỏc thộp nghiờn cu Nng lng nhit hỡnh thnh mt s hp cht ti 298.15K, Hf, kJ mol-1[25,54] Bng giỏ tr phõn b nng cỏc nguyờn t ti mt s v trớ trờn vựng khuch tỏn ca lp thm nit trờn thộp SKD61(s liu ch mang tớnh tham kho vỡ kt qu phõn tớch chu nh hng ca vựng lõn cn) Bng 4.3: Tớnh toỏn thnh phn Xờmentit (Fe3C)/Ferrit (Fe) cho vựng nn Bng 4.4: Cu trỳc tinh th ca Fe(C), mt s cacbit v nitrit [25,26,75,77,79] Bng Bng Bng Bng nh hng ca nhit n th thm Kn nh hng ca thi gian lu n th thm Kn nh hng ca thnh phn khớ thm n th thm Kn 4.5: 4.6: 4.7: 4.8: Bng 4.9: Bng 4.10: Bng 4.11: Bng Bng Bng Bng Bng Bng Bng Bng Bng 4.12: 4.13: 4.14: 4.15: 4.16: 4.17: 4.18: 4.19: 4.20: Bng 4.21: Bng 4.22: Bng 4.23: Bng 4.24: Bng 4.25: Footer Page of 89 Cỏc ch thm thc nghim xỏc nh h s truyn cht () Khi lng nit khuch tỏn cỏc lỏ thộp mng thc nghim Bng giỏ tr tớnh toỏn th thm, hot ca nit mụi trng thm v lỏ thộp mng tớnh toỏn bng chng trỡnh Thermo-calc H s truyn cht () trờn cỏc mỏc thộp nghiờn cu Bng giỏ tr cng ca cỏc mu thộp ph thuc vo nh hng ca nhit Cỏc thụng s ỏnh giỏ nh hng ca thi gian lu Bng giỏ tr cng ca cỏc mu thộp ph thuc thi gian lu Cỏc ch pha loóng khớ thm s dng N2 v phõn hy o c Bng kt qu phõn b cng ph thuc thnh phn khớ thm Cỏc giỏ tr th thm s dng khớ pha loóng N2 vi p=1.2at Cỏc thụng s thm nit th khớ cho tng nhúm thộp thc nghim Bng kt qu phõn b cng ph thuc thi gian thm nh hng ca thi gian thm n chiu sõu lp thm hiu qu trờn cỏc loi thộp thc nghim S liu thng kờ tớnh giỏ tr K cho thộp C20 Cỏc giỏ tr tớnh toỏn h s Herries-K ca tng loi thộp theo thc nghim nh hng ca thi gian thm n chiu sõu lp thm hiu qu trờn thộp C20 ti nhit thm 510oC theo thc nghim v theo lý thuyt tớnh toỏn Bng kt qu phõn b cng thm ti 510oC, 530oC v 550oC Bng tng kt cỏc thụng s cụng ngh nhm n nh quy trỡnh thm nit th khớ cho tng nhúm thộp thc nghim iv Header Page of 89 Danh mc cỏc hỡnh v th Hỡnh 1.1: Hỡnh 1.2: Hỡnh 1.3: Hỡnh 1.4: Hỡnh 1.5: Hỡnh 1.6: Hỡnh 1.7: Hỡnh 1.8: Hỡnh 2.1: Hỡnh 2.2: Hỡnh 2.3: Hỡnh 2.4: Hỡnh 2.5: Hỡnh 2.6: Hỡnh 2.7: Hỡnh 2.8: Hỡnh 2.9: Hỡnh 2.10: Hỡnh 2.11: Hỡnh 3.1: Hỡnh 3.2: Hỡnh 3.3: Hỡnh 3.4: Hỡnh 3.5: Hỡnh 3.6: Hỡnh 3.7: Hỡnh 3.8: Hỡnh 3.9: Hỡnh 3.10: Footer Page of 89 Mt kiu s h thng thm nit plasma [65] c trng gia in ỏp v dũng in mt chiu phỏt quang [23] Mụ hỡnh s hỡnh thnh lp b mt thm nit plasma [80] nh hng ca thnh phn khớ n cu trỳc lp thm nit plasma [65] S mụ t k thut tng núng v tng lnh [41] S h thng phng phỏp ASPN [28] S h thng phng phỏp PDN [5] S h thng phng phỏp PPN [37] S hỡnh thnh lp thm nit th khớ [1,88] S mụ t s thay i hot N t mụi trng thm vo thộp Gin pha Fe-N [89] Gin Lehrer th hin s n nh ca cỏc pha gia Fe-N [49] Mi quan h gia gin pha Fe-N v nng /chiu sõu i vi s phỏt trin cỏc lp n pha -Fe2N1-x v -Fe4N trờn nn -Fe [55] S cu trỳc lp thm nit th khớ [43] nh hng ca nhit n mc phõn hy NH3 ti cỏc lu lng khớ khỏc Thc nghim trờn lũ ging kớch thc trung bỡnh Khớ s dng 100% NH3 [25] S bin i ca th thm nit (Kn) vi mc phõn hy NH3 mụi trng thm (NH3 + N2 + 5%CO2) ti 5800C [25] nh hng ca tc dũng NH3 n giỏ tr cng ln nht v chiu dy lp thm nit th khớ thc hin trờn thộp cacbon cc thp cú hp kim húa thờm titan [42] Mi quan h gia chiu sõu lp thm v thi gian thm nh hng ca cỏc nguyờn t hp kim (a) - nh hng ca cỏc nguyờn t hp kim n cng ln nht trờn thộp thm nit, thc hin ti 5240C-48h; (b) - nh hng ca cỏc nguyờn t hp kim n chiu dy ln trng, thc hin ti 5500C24h [47] S mụ t trỡnh t nghiờn cu trờn cỏc mu thm nit th khớ S nguyờn lý hot ng ca sensor hydro [86] Sensor Sensor connection KF16 TCD Gas Analyzer Gasboard-7000 Kớnh hin vi quang hc Axiovert 25A Mỏy o cng Struers Duramin-2 Hin vi in t quột bc x trng (FESEM) Thit b nhiu x tia X (D5005) Lũ nhit luyn mu trc thm Thit b lũ thm nit v Header Page 10 of 89 Hỡnh 3.11: Hỡnh 3.12: Hỡnh 3.13: Hỡnh 3.14: Hỡnh 3.15: Hỡnh 4.1: Hỡnh 4.2: Hỡnh 4.3: Hỡnh 4.4: Hỡnh 4.5: Hỡnh 4.6: Hỡnh 4.7: Hỡnh 4.8 Hỡnh 4.9 Hỡnh 4.10: Hỡnh 4.11: Hỡnh 4.12: Footer Page 10 of 89 S b trớ thit b cung cp khớ v kim soỏt mc phõn hy nhit NH3 Quy trỡnh thng húa mu 20CrMo v C20 trc thm Quy trỡnh nhit luyn húa tt cho thộp SKD61 [79] Quy trỡnh nhit luyn húa tt thộp 30CrNi2MoVA [80] Quy trỡnh thm nit th khớ nh t chc t vi ca cỏc mu x lý nhit luyn trc thm vi phúng i 500 ln: (a) thộp C20, (b) thộp 20CrMo, (c) thộp 30CrNi2MoVA v (d) thộp SKD61 nh hin vi in t quột trờn mu thộp SKD61 sau tụi (a) v ph EDX xỏc nh thnh phn ca cỏc ht cacbit (b) Phõn b nguyờn t trờn thộp SKD61 sau tụi bng ph mapping: (a) b mt thc mu thộp, (b) phõn b hm lng Fe, (c) phõn b hm lng Cr, (d) phõn b hm lng V, (e) phõn b hm lng Mo v (f) phõn b hm lng C (a) nh hin vi in t quột v (b) nh tm thc mu hin cỏcbit phúng i 1000 ln trờn mu thộp SKD61 sau ram Phõn b nguyờn t trờn thộp SKD61 sau ram bng ph mapping: (a) nh SEM t chc t vi ca thộp, (b) phõn b hm lng Fe, (c) phõn b hm lng C, (d) phõn b hm lng Cr, (e) phõn b hm lng V v (f) phõn b hm lng Mo Kt qu nhiu x tia X vi cỏc mu thộp trc thm (a) - thộp C20; (b) - thộp 20CrMo; (c) thộp 30CrNi2MoVA; (d) thộp SKD61 nh hin vi quang hc quan sỏt t chc lp thm hỡnh thnh trờn b mt cỏc mu thộp vi phúng i 500 ln Mu c thm ti 550 oC s dng 100% NH3 vi Kn = 1,6 v thi gian thm 8h: (a) mu thộp C20; (b) mu thộp 20CrMo; (c) mu thộp 30CrNi2MoVA; (d) mu thộp SKD61 v (e) mu thộp c úng rn bng bt nha nh hin vi in t quột quan sỏt t chc lp thm hỡnh thnh trờn b mt cỏc mu thộp mng Mu c thm ti 550 oC s dng 100% NH3 vi Kn = 0,7 v thi gian thm 8h: (a) mu thộp C20; (b) mu thộp 20CrMo; (c) mu thộp 30CrNi2MoVA; (d) mu thộp SKD61 v (e) mu thộp c úng rn bng keo úng rn epoxy Ph phõn b hm lng nguyờn t trờn tit din ngang mu mng C20 sau thm ti 550oC s dng 100% NH3 vi Kn = 0,7 v thi gian thm 8h: (a) din tớch quột trờn b mt mu thc; (b) phõn b hm lng nit v (c) phõn b hm lng st Ph phõn b hm lng nguyờn t trờn tit din ngang mu mng 20CrMo sau thm ti 550 oC s dng 100% NH3 vi Kn = 0,7 v thi gian thm 8h: (e) din tớch quột trờn b mt mu thc; (a) phõn b hm lng nit; (b) phõn b hm lng st; (c) phõn b hm lng Mo v (d) phõn b hm lng Cr Ph phõn b hm lng nguyờn t trờn tit din ngang mu 20CrMo sau tụi ti 920oC: (a) din tớch quột trờn b mt mu thc; (b) phõn b hm lng st; (c) phõn b hm lng cỏcbon; (d) phõn b hm lng M v (e) phõn b hm lng Cr Ph phõn b hm lng nguyờn t trờn tit din ngang mu 20CrMo sau tụi vi Header Page 113 of 89 Trong ú: T l giỏ tr trung bỡnh ca ti v K l gi thuyt cn kim nh (trong trng hp ny, cn chng minh K luụn tn ti nờn K0 ) Khi ú, ta cú ti hn vi mc (min i xng) B M tn : M tn tn2,1 (4.13) Vi vic chn khong tin cy 99% (tng ng vi =0,01), ú ta s tin hnh kim nh gi thuyt H0: K = v gi thuyt H1: K vi vic s dng phõn phi t-Student n Da vo bng s liu (4.21) cú th tớnh c s = 19,3483 v i = 2,2128 ti T Vi tiờu chun phớa trờn, ta cú: M tn 25400.0, 0026 2, 2128 7,55 19,3483 Phõn phi t-Student ú c tra bng cú giỏ tr: tn 2,1 t52,10,01 t3;0,995 =5,841 Nh vy: M tn > tn 2,1 ú gi thuyt H0 b bỏc b v giỏ tr K luụn tn ti Kt qu ny ó chng t vic xõy dng ng hi quy dng (4.6) v cỏc h s c xỏc nh bng vic s dng phng phỏp bỡnh phng cc tiu l phự hp Bng vic tớnh toỏn tng t cho phộp xỏc nh giỏ tr K ca cỏc mỏc thộp cũn li Bng tng hp kt qu tớnh toỏn c th hin bng 4.22 Bng 4.22: Cỏc giỏ tr tớnh toỏn h s Herries - K ca tng loi thộp theo thc nghim Giỏ tr h s Herries - K (m/h1/2) Thm ti 510oC K Thm ti 550oC Thộp C20 Thộp 20CrMo Thộp 30CrNi2MoVA Thộp SKD61 0,0026 0,0024 0,0025 0,0020 Qua bng 4.22 cho thy: giỏ tr h s Herries-K ti 510oC vi thộp C20 v 20CrMo ln lt l 0,0026 v 0,0024 (n v l m/h1/2) cng thờm mt ln na khng nh v vai trũ ca cỏc nguyờn t hp kim vic quyt nh n mc phỏt trin chiu sõu lp thm cựng nhit thm, giỏ tr K ln s cho phộp nhn c lp thm cú chiu sõu ln hn S cú mt ca cỏc nguyờn t hp kim d to nitrit thộp lm gim ỏng k giỏ tr h s Herries - K, qua ú lm gim chiu sõu lp thm Giỏ tr tớnh toỏn h s Herries ti 550oC cho mỏc thộp 30CrNi2MoVA v SKD61 ln lt l 0,0025 v 0,0020 (n v l m/h1/2) ó khng nh: cỏc nguyờn t hp kim ngoi vic lm gim h s khuch tỏn v h s Herries-K, tng hm lng cỏc nguyờn t hp kim tng cng s lm gim giỏ tr h s nhit Footer Page 113 of 89 99 Header Page 114 of 89 (K) õy l h qu dn n chiu dy lp thm t c ca c mỏc thộp ny u nh hn thộp C20 v 20CrMo Khong thi gian thm t ti chiu dy hiu qu ca nhúm thộp nhit luyn húa tt l gi tỡm hiu rừ hn quy lut v s phỏt trin theo thi gian ca lp thm, nh hng ca thi gian thm n chiu sõu lp thm hiu qu ca thộp C20 ó c s dng ỏnh giỏ Cỏc thụng s t c nghiờn cu th hin qua bng 4.23 sau õy: Bng 4.23: nh hng ca thi gian thm n chiu sõu lp thm hiu qu trờn thộp C20 ti nhit thm 510oC theo thc nghim v theo lý thuyt tớnh toỏn Chiu sõu lp thm hiu qu (m) t c sau thi gian thm Mỏc thộp C20 Kt qu thc nghim 0h 4h 5h 6h 8h 105 155 180 185 132 147 161 186 Kt qu theo lý thuyt C ( X KC510 20 25400 t ) o o KC51020 C l h s Herries ca thộp C20 ti 510oC Nh vy, vi cỏc s liu thc nghim ca thộp C20 ó cp phớa trờn th biu din mi quan h gia chiu sõu lp thm (m) v thi gian thm (h) c th hin trờn hỡnh 4.36 ng xõy dng theo lý thuyt Chiu sõu lp thm hiu qu (àm) 250 X=25400.KC20 t 200 150 Cỏc kt qu thc nghim 100 50 Th gian thm (h) 0 10 Hỡnh 4.36: th biu din mi quan h gia chiu sõu lp thm v thi gian thm ca thộp C20 thm ti 510oC Cỏc kt qu biu din trờn hỡnh 4.36 i vi thộp C20 cho thy: s phỏt trin lp thm theo thi gian tuõn theo quy lut parabol (4.6) Vi cỏc ch thm ó la chn cho cỏc mỏc thộp nh ó trỡnh by bng 4.18 v thi gian hp lý lp thm hỡnh thnh tng ng l gi (vi nhúm thộp C20 v Footer Page 114 of 89 100 Header Page 115 of 89 20CrMo) v gi (vi nhúm thộp 30CrNi2MoVA v SKD61) Vic kim tra kt qu thm cng ó c tin hnh th nghim ti nhit 530oC Bng kt qu o cng v phõn b cng thu c ca lp b mt c th hin ln lt quan bng 4.24 v hỡnh 4.37 Bng 4.24: Bng kt qu phõn b cng thm ti 510oC, 530oC v 550oC Khong cỏch v v trớ cỏc vt o tớnh t b mt (mm) Thi gian thm 30 60 90 120 150 180 210 C20/510oC 6h 239 245 243 237 232 229 220 215 211 C20/530oC 6h 236 241 239 239 230 230 224 219 214 20CrMo/510oC 6h 829 882 782 659 456 375 281 255 234 20CrMo/530oC 6h 812 851 779 681 501 419 321 - - 30CrNi2MoVA/550oC 5h 851 862 812 751 551 529 498 471 482 30CrNi2MoVA/530oC 5h 882 891 824 699 628 579 472 473 - SKD61/550oC 5h 1051 984 791 583 571 532 528 - - SKD61/530oC 5h 1073 1027 731 584 546 534 529 - - Mỏc thộp/Nhit thm 240 270 Kt qu so sỏnh phõn b cng ca thộp C20 v 20CrMo (hỡnh 4.37a v 4.37b) cho thy: iu kin trỡ th thm n nh, tng nhit thm t 510oC lờn 530oC thỡ giỏ tr cng ln nht ca lp b mt gim Nguyờn nhõn l tng nhit thm s lm tng mc khuch tỏn nit vo sõu b mt thộp nhanh hn, qua ú lm gim hm lng nit vựng gn b mt, ú cng gim Vi thộp C20 v 20CrMo: ch thm gi, mc dự thm ti nhit 530oC cho phộp chiu dy lp thm cú ci thin ụi chỳt Tuy nhiờn kt qu thm ti 510oC sau gi cng ó cho thy li th v giỏ tr cng tt hn hn v chiu sõu lp thm hiu qu t c trng hp ny (khong 180 m cho thộp C20 v khong 160 m cho thộp 20CrMo) cng khụng chờnh lch nhiu so vi trng hp thm ti 530oC Vỡ lý ú, thộp C20 v 20CrMo hon ton cú th thm ti vựng nhit thp ( 530oC) Nh vy, sau thi gian thm 5h, chiu sõu lp thm t c khong 150 m vi thộp 30CrNi2MoVA v 120 m vi thộp SKD61 ó cho phộp xỏc nh c tc phỏt trin lp thm ca thộp 30CrNi2MoVA v SKD61 ln lt l 30m/h v 24m/h Kt lun: nh hng ca cỏc yu t chớnh quỏ trỡnh thm nit ó c lm sỏng t Nhit thm, th thm (thụng qua thi gian lu, thnh phn khớ thm) thay i u tỏc ng trc tip n th thm (Kn), qua ú nh hng n cu trỳc lp thm hỡnh thnh Thi gian thm cng di, s phỏt trin lp thm tip tc v tc phỏt trin lp thm s tuõn theo quy lut parabol Qua cỏc phõn tớch v ỏnh giỏ v nh hng ca cỏc thụng s cụng ngh chớnh Quy trỡnh thm nit th khớ cho mt s loi thộp ó cp cú th c tng kt li bng 4.25 Bng 4.25: Bng tng kt cỏc thụng s cụng ngh nhm n nh quy trỡnh thm nit th khớ cho tng nhúm thộp thc nghim C20 Vựng nhit thm (oC) Cỏc thụng s u vo Thnh phn khớ thm 20CrMo SKD61 510 - 530 530 - 550 NH3 + N2 (55 %) NH3 + N2 (75%) Thi gian lu (phỳt) Cỏc thụng s cụng ngh chớnh 30CrNi2MoVA ~ 12 Vựng nhit thm (oC) 510 - 530 530 - 550 Th thm (Kn) 0,5 - 1,4 0,4 - 2,1 Thi gian thm ti tiu (gi) Chiu sõu lp thm t c (m) 180 160 150 120 Giỏ tr cng ln nht (HV) 245 882 862 1051 Footer Page 117 of 89 103 Header Page 118 of 89 KT LUN CHUNG V KIN NGH Kt lun chung: Lun ỏn ó t c mt s kt qu chớnh nh sau: Vic ỏp dng cụng ngh thm nit nc ta cũn tn ti mt s nhc im nh: cụng ngh thm nit da trờn cỏc thit b nhp ngoi nờn thng ch ỏp dng c cú hiu qu cho mt s loi sn phm c th Do ú khụng th ỏp dng vi hiu qu cao cho cỏc loi sn phm v chng loi vt liu khỏc Do cha ch ng hon ton v cụng ngh thm m cht lng lp thm khụng cao, khụng n nh, cha khai thỏc ht nng lc ca thit b cng cha s dng thit b vi hiu qu cao Do ú, vic nghiờn cu cỏc yu t cụng ngh chớnh nhm n nh v thun húa cụng ngh thm nit th khớ ti Vit nam l iu vic cp thit Vic lm rừ li nh hng ca cỏc thụng s u vo (nhit , thi gian lu v thnh phn khớ thm) n giỏ tr th thm (Kn), qua ú xỏc nh cỏc thụng s cụng ngh chớnh cú nh hng n thm nit th khớ l nhit , th thm v thi gian thm ó cho thy mc nm bt cụng ngh kp thi vi xu th phỏt trin ca cụng ngh thm nit tiờn tin hin trờn th gii i vi cỏc loi thộp v nhit thm nghiờn cu thỡ kt qu nghiờn cu u khng nh s hỡnh thnh lp thm l khuch tỏn nit dc theo biờn ht chim u th i vi thộp C20 v 20CrMo, vỡ cú ht tinh th khỏ ln, nit khuch tỏn ch yu i sõu vo phớa Vic khuch tỏn xõm ln vo ht tinh th din vi tc rt chm vỡ vy lp thm giu nit trờn b mt thộp cng phỏt trin chm Kt qu nghiờn cu cho thy, tc phỏt trin lp thm giu nit (lp +) ch t khong 0,56 m/h Khi thm ti vựng nhit thp (510oC-530oC), tc phỏt trin dc theo biờn ht rt cao khong 30 m/h i vi thộp C20 v khong 27 m/h i vi thộp 20CrMo i vi thộp hp kim, s khuch tỏn nit dc theo biờn ht c tng cng nh quỏ trỡnh hỡnh thnh hp cht cacbonitrit dc theo biờn gii ht ng thi loi thộp ny thng thm nit sau nhit luyn húa tt - cú t chc thộp kộm n nh nhit thm v ht tinh th thỡ rt nh Do ú quỏ trỡnh xõm ln nit vo ht tinh th xy nhanh, thm ti vựng nhit cao (530oC-550oC) tc phỏt trin lp thm nh ú m t khỏ ln khong 30 m/h thm lờn 30CrNi2MoVA v khong 24 m/h thm lờn SKD61 Th thm nit (Kn) l i lng quyt nh n s hỡnh thnh v cht lng lp thm Kt qu nghiờn cu khng nh: thm lờn thộp C20 t hiu qu thỡ cn th thm khong (0,51,4); i vi thộp SKD61 thỡ khong th thm mang li hiu qu l (0,42,1) Nhit thm l thụng s cụng ngh cú nh hng quan trng n quỏ trỡnh thm i vi thộp C20 v 20CrMo, nhit thm ch nờn nm khong 510oC-530oC i vi cỏc loi thộp 30CrNi2MoVA, SKD61 thỡ nhit thm nm khong 530oC550oC Thi gian lu thớch hp cho cỏc loi lũ thm hỡnh tr t thng ng, thm cho cỏc loi khuụn (hỡnh dng n gin, kớch thc di 300mm, thộp thm l SKD61) nm khong t n 12 phỳt Footer Page 118 of 89 104 Header Page 119 of 89 S phỏt trin ca lp thm theo thi gian tuõn theo quy lut parabol (X = K t ) Giỏ tr K phn ỏnh vai trũ ca nguyờn t hp kim v s khuch tỏn n s phỏt trin lp thm Giỏ tr K cng ln thỡ thm cng nhanh, hiu qu ca quỏ trỡnh thm cng cao Footer Page 119 of 89 105 Header Page 120 of 89 Cỏc kin ngh: Trong tng lai, vic thc hin quy trỡnh thm ti vựng nhit thp hn gim thiu mc nh hng ca nhit n tớnh cht ca nn thộp s l mt nhng hng i ỏng quan tõm lnh vc thm nit th khớ Tuy nhiờn vic thm ti nhit thp s lm cho tc khuch tỏn nit rt nh v thi gian thm s phi kộo rt di Do ú, vic tỡm cỏc bin phỏp lm tng mc hot húa b mt thộp trc thm ci thin mc hp th v khuch tỏn nit nguyờn t l mt hng i rt ỏng quan tõm tng lai T ng húa iu khin chớnh xỏc cỏc thụng s quỏ trỡnh thm ang l xu th phỏt trin chung thi i ngy Do ú, vic xõy dng quy trỡnh thm nit th khớ cú iu khin vi vic ỏp dng cỏc thit b lm vic t ng nh van t, sens s l mt hng i nhm n nh cht lng lp thm rt thit thc v tim nng Footer Page 120 of 89 106 Header Page 121 of 89 DANH MC CễNG TRèNH CễNG B CA LUN N Cỏc cụng trỡnh ng trờn cỏc khoa hc Hong Anh Tun, Nguyn Ngc Minh (2013) 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NỘI NGUYỄN NGỌC MINH NGHIÊN CỨU ẢNH HƯỞNG CỦA CÁC YẾU TỐ CHÍNH NHẰM ỔN ĐỊNH CÔNG NGHỆ THẤM NITƠ THỂ KHÍ LÊN MỘT SỐ LOẠI THÉP THÔNG DỤNG Ở VIỆT NAM Chuyên ngành: Mã số: Kim loại học 62440129 LUẬN... Mở đầu Chương 1: Tình hình nghiên cứu ứng dụng công nghệ thấm nitơ 1 Công nghệ thấm nitơ giới Việt nam 1.1.1 Công nghệ thấm nitơ giới 1.1.2 Công nghệ thấm nitơ Việt nam 1.2 Các phương pháp thấm. .. trắng thấm nitơ thể khí [86] Ảnh hưởng nhiệt độ đến thấm Kn Ảnh hưởng thời gian lưu đến thấm Kn 550oC Ảnh hưởng thành phần khí thấm đến thấm Kn 550oC Ảnh hưởng thấm nitơ đến hệ số truyền: (a) thấm