46 6 Vol.46 No.6 2010 6 687 694 ACTA METALLURGICA SINICA Jun. 2010 pp.687 694 1500 MPa Í Ç Æ É Æ ( ß Ó ĐÃ Æ ÅÚ, ß 100083) Ì Ä ØÝ 1500 MPa Si Mn Cr Ni Mo ¹ÏÍ ÖË Ó, ¾± Ä + (TMCP) + + Ü + Ü +250 ² 4 ³ º¾ Ú¹ Æ Đ.»Ù: Ü ¼», 1890 MPa,»Ã 1280 MPa, Î 13%; 250 ² 30 min ¼ 1820 MPa,»Ã 1350 MPa, É Ñß Á Ó ²Ç É Ã Ô Ô É ε Ç ± ½ ; É TMCP º¹ Ô + Ô + ÇÂ Ã Ô Ç ¹, Ô Ô Đ, ÀÅ «Đ. Ô Þ C., ² Ù Ã Ô, C Ô» Ô Ô. ÚÙÄ Ó É Ô «ß, Ç Ù, Ô» Ô Â É Û. È ÖË, Ü, Ô, Ô, Ã Ô ÅÕÃÅ Ì TG142.1 ÙÝ A Ù Ì 0412 1961(2010)06 0687 08 MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 1500 MPa GRADE ULTRA HIGH STRENGTH LOW ALLOY STEEL WANG Lijun, CAI Qingwu, YU Wei, WU Huibin, LEI Aidi National Engineering Research Center for Advanced Rolling Technology, University of Science and Technology Beijing, Beijing 100083 Correspondent: WANG Lijun, Tel: 13581975476, E-mail: wangljustb@126.com Supported by Project of Scientific and Technical Supporting Program of China during the 11th Five Year Plan (No.2006BAE03A06) Manuscript received 2009 12 23, in revised form 2010 03 19 ABSTRACT A novel sort of 1500 MPa grade ultra high strength low alloy structural steel with multi element of Si Mn Cr Ni Mo was designed. Effects of four different processes of TMCP (thermo mechanical controlled processing), controlled rolling+air cooled, controlled rolling + direct quenching and controlled rolling+direct quenching+tempering at 250 on the microstructure and mechanical properties were investigated. The results indicate that the directly quenched steel has a maximum tensile strength of 1890 MPa, yield strength of 1280 MPa and elongation of 13%. After tempered at 250 for 30 min, the tensile strength of the steel decreased to 1820 MPa, while the yield strength increased to 1350 MPa, which is ascribed to the comprehensive effect of the softening mechanism due to the recovery of dislocation sub structure and the strengthening mechanism due to the decomposition of retained austenite and ε carbide precipitation. Duplex phase microstructure involving lath bainite, martensite segmented by bainite, and retained austenite was obtained by the process of air cooling and TMCP, so that it has excellent strength and plasticity. Carbon diffusion phenomenon exists in the quenching process of low carbon steel. Both the decomposition of retained austenite and the carbon partitioning into austenite from martensite or bainite were found during tempering process. The paper demonstrates that the precipitation particles of cubic structure nucleated in austenite, growing up * Æ Ä ÝÏ 2006BAE03A06 Ù : 2009 12 23, Ù Ì : 2010 03 19 ½ÐÉÒ :,, 1981, Ñ DOI: 10.3724/SP.J.1037.2009.00855
688 Ô Ý 46 and coarsening during the whole cooling process. Futhermore, the emergence of a large number of second phase precipitation cores was not found in martensite or bainite after phase transformation. KEY WORDS ultra high strength low alloy steel, direct quenching, martensite, bainite, retained austenite Ü ¾, Å Ð, Ç, Ì ± ( ½± Ƽ Ü 1500 MPa ¹Å) Ý Â Â Ò ± ÎÍ, ¾ µ ÛÅ ¼½ ± Á [1,2]. ÓµÌ ± AF1410, HY180, AerMet100 [3 6], Ã Å Đ»È,  ² Ã. Ì ± 300M 4340 [7 9] 1.8%( Ã, )Ni, Ð,  ÞÛ. Ü ¾, [10] ³Ç [11]» 1500 MPa 0.2C 2Mn 1Si 0.5Cr ( Ã, %) Ä È Õ / Õ È, È [12] 4340 ¾ÐÅ» 2200 MPa Ì ±, ¹ ± [13,14] ¼Ù Si Mn Ni Cr Î 1400 MPa Æ º«Þ»,» È, Đ¹Ê» à ± ². Ö, Í Åµ 1500 MPa Þ Ì ±, ¾ Í : (1) µõý Û,, C ÃÒ 0.4%; (2) Å Â 1% ¼ Ê Si, ÍÃ, ±Ý ; (3) ² È Å Mn, Ni, Cr Mo ±, È ¾  µ Ô, ÅÝ, Õ M s, Mo  Íó Û, ¹ ÆÕ º Mn Ni Å ÄÆÕ Ã Á±, Â, Å Nb, ¾ÂÊ Ó È, ÆÕ Þ È, Ûµ ± ; (4) È Ò, º Õ Õ ÄÆÕ È ºÐ, ¹ Ì ± Ê. Ö, ± ² Ã, ² É ÃÌ ±», ½ + (TMCP) + (CR+AC) + Đ Ý (CR+DQ) + Đ Ý +250 ³ 30 min(cr+dq+t)4» ۺРÅ, ¹ ¼Â». 1 ÄÂ Í ( Ã, %) : C 0.24, Si 1.8, Mn 1.5, Cr 1.0, Ni 0.7, Mo 0.35, Nb 0.05, V 0.04, Ti 0.017, B 0.004, Fe ÄÃ. 50 kg Ó Î, Ó, º 90 mm 90 mm 120 mm, 1230 Å Á», 12 mm. Þ ºÆ  1000, È, Þº 950. º «Ã  60%, Æ 850. ½¹ Đ Ý Ö 3» ÛÐ. Å 17 /s, Æ 460, Þ Ö ; Ï Đ Ý 250 ³ 30 min. 4» ¹ 1 Ð. ½Ï GB/T228 2002 CMT 4105 Þ Ø ÅÛÐ, Ø ÐÈ 42 mm, º«½ 30 mm, ¹ 2 Ð. ½ Å GB/T229 1994 JB 30B Þ ½Ø ÅÛÐ, Charpy V Þ Ø, Ø Þ 10 mm 10 mm 55 mm, 20. LEO 1450 ÞÀ (SEM) Û ÀØ ºÐ ½½ Ñ. SEM Ø Ý «Ü 4% РгÝ. JEM 2000FX ÊÞ É (TEM) ÛÀØ Ð ºÐ Ñ. TEM Ø Æ Ë, ³ 9% г, Æ «15 20 V, 40. Ê ½ ÈÞ Ð, JEM 2010 Þ ¹ É ÛÐÛÀ. Ö 1 ³ º Fig.1 Schmatic diagram of processes of thermo mechanical controlled processing (TMCP), controlled rolling+ air cooled (CR+AC), controlled rolling+direct quenching (CR+DQ) and controlled rolling+direct quenching+tempering at 250 (CR+DQ+T) Ö 2 ¼Î Fig.2 Dimension of tensile sample (unit: mm)
6 : 1500 MPa ÕÊ Ù ßÈ 689 Ø» Å½Đ 15 mm 10 mm Ø, Ý «Ü 10% ³ Ý ¾, D5000 X É É (XRD) à ÄÆÕ. XRD ± ɹ ¹ 3 Ð. ÄÆÕ ÃÅ Æ [15] : V γ = 1.4I γ /(I α + 1.4I γ ) (1), V γ Ó ÄÆÕ ; I γ Ó fcc ÆÕ γ {200}, {220} {311}ÞÖ ÉÀ Æ ± ; I α Ó bcc α( Õ ± Õ ) {211}Þ Ö ÉÀ ±. 2 Ë Ò 2.1 ĐÐ ¼ 1 Å TMCP, CR+AC, CR+DQ CR+DQ+T 4» Å. Í, Å, ½± ¼Ä± Æ,. CR+DQ ½± ¼, 1890 MPa, ½ Ï ¼, Ú 13.0%; 250 ³ 30 min ± 1820 MPa, Ï 15.0%. CR+AC ½± ¼, Ú 1460 MPa, TMCP ÓÂ Đ Ý ÞÈ, 1510 MPa. ¼Ä± Å ¹Ò ½±. Ö ¹, CR+DQ 250 ³ 30 min ½±, ¼Ä± 1280 MPa 1320 MPa, ¼ ¹Ò, Ú Ê ½± ß µ± Ø, ʼı ÄĐ Î. Intensity, a.u. 200 220 211 311 40 50 60 70 80 90 100 2, deg Ö 3 XRD Fig.3 XRD spectrum of the tested steel 1 ³ º Đ Table 1 Mechanical properties of the tested steel at various process Process σ b, MPa σ s, MPa HB δ, % A kv, J TMCP 1510 980 440 16.0 22 CR+AC 1460 910 420 17.5 26 CR+DQ 1890 1280 490 13.0 18 CR+DQ+T 1820 1320 475 15.0 20 2.2 ØÊ Ó ¹ 4 5 ½ 4» SEM TEM. ¹, TMCP»º ºÐ Õ Õ ÄÆÕ È ºÐ. Õ ÐÞØ È, ÄÆÕ ¹Ü Â Õ Ð, Þ ½ º Ô,, Đ ÂÞ, ÅÞ. ع 5a TEM ¹ Æ, Õ ² 0.2 µm, ÄÆÕ Ü² 0.05 0.1 µm. SEM Ð TMCP ºÐ Î ÅÍ, ÒÓ Â Õ Ê ÄÆÕ, ¼ C à Â, 4% Ð Ð³Ý ¼ Æ Ð. Ý Æ Ó Ð ÞÐ º., Õ Ð ÄÆÕ Æ, Á; Õ Â C Ã, Á. ع 4a, ÆÕ ÞÐ Ë ¹, Ú TMCP» Å 17 /s, ² Þ, Õ. Ò Ë Â Si, Mn, Ni, Mo ¾, ÅÝ, Ź Þ ±. TMCP» ÆÕ «ÆÕ ß Â Õ ¼ Õ È, Ò Â ÛÌ ±. ¹ 4b 5b Ð CR+AC» ºÐ Ô ± Õ ÄÆÕ. Gregg Bhadeshia [16] Ô ± Þ Õ ±, Ë ± ÜÆÌÜ Õ ÜÆ ¹ È,., ¹ ź CR+AC» ºÐ µ ¾ Õ Ê ÄÆÕ ºÐ. ÂÔ ±, Þ Õ ºÐ Æ ¾, Õ È, źÐ. ÊÅ TMCP» Ó, CR+AC» ºÐ ³, C ¹ Ù, ºÐ., ¹ 4b ºÐ µ, C ¹ ²», 0.3 µm, Ð Û, ºÐ ÅÆ. Ö, CR+AC» ² TMCP» ÍÃ, ±. ¹ 4c ¼Ú CR+DQ» ºÐ È Õ Èà ÄÆÕ. Õ Ê ÄÆÕ Ü Î «, ¾¹½, Õ Ð º Û, ÒÓ Â Õ ßÂĹ Þ, ÊÆÕ, Õ ÐÖÊÞ Â Ò, ¾ Æ Ë. ÅÓ, Ì ¹ÛÀÆ Õ ÎÍ Õ È Þ ½ Ô, ÔÈ Đ, Ô Ð È. ¹ 5c Ð ² 0.15 µm, Ü ÄÆÕ È, ³
690 p y 46 r 4 8'j."VYe Z SEM f Fig.4 SEM images of the tested steel at various processes of TMCP (a), CR+AC (b), CR+DQ (c) and CR+DQ+T (d) r 5 8'j."VYe Z TEM f Fig.5 TEM images of the tested steel at various processes of TMCP (a), CR+AC (b), CR+DQ (c) and CR+DQ+T (d) a, [ 0.05 µm. 7 8, CR+DQ k / [ w 0 ^ i %, 0 ^, : 0. t - 4d - i, d y, ~ 250 E ', 30 min, < G i q # =['P 5 * ". C iq a E ', ~ C 9PWX - G 7 ug:, C p,, #*l Xm^. - 5d \l #&, n9 ), <G # 5 &, [ 0.2 0.3 µm. SEM g\ l', i q b l rr z V, b 3 y, v\, v ', ^ P WX - Gh b l z Z G J 9 ). r 4, R- 4c b &, - 4d Y Æ q zlh =+ i, 5 ' i q Yf D i, #\ ^ +. ",.} h =Æ, 0 ^= ^, 1 %,. J ', 0L%, ^, n 7J ', ^ C L Æq Gk =i q ' R i " P %"4 2B. - 6 =', #iq Ri "Pj, Ev L b L b 5 i. Q \ l R1 = R2, H` = 60, bz [uvw]=[001], zr (h1k1 l1)= (11 0), (h2 k2 l2 )=(100), 0 v # " P=[ Dip, := ε "P, 8Eu^Vip Fe3 C w b, n3 : ag G<. H {e - 7 = TMCP, CR+AC CR+DQ 3 9(k /Zf [ f11 # SEM g. E- 7a U, TMCP k / [ 1 # a, - k 8 1 Q=, 5 G P K : K {a, :Ka", # a&. - 7b \l CR+AC k/[ 1 Q= k 8 : 1 Q P q "1 Q 4, 1 r 3 2.3
6= : 1500 MPa ; qr\#y 9u,{PB ~ 691 9, {a)%:k, R TMCP k/[b&, <G:Ka aev, -G' hxc %K Heb.}p X, # a n, v 1 Qm h5 f 1l. - 7c \ l Z. * o, }!A}v/ -a.} M% K "T CR+DQ k / [ 1 Q= k 8 4, 1 r ^ 9, 1 1(= bcc!q Riq, 3J9(z ip γ #QH =G, v { a) % ;D 7, n o EJ y,[ br α b -m XRD A}w}G%. {acl;d,.}9æ ; '1#R&q&/ ", AB XRD A}5i j (1) DÆek/Z C L Æ?? 1 Q m f 1 K0. q K ( 6G ), i U0 2. 0 2 \l, CR+AC k / [ C L Æ q K0 ^, 26.5%. - 8 = C L Æ 2.4 = 8lpDGb>GWhvG} SEM TEM.} w H0 v, 9 ( k /# W ZÆ { q TEM g. U, C L Æ q - x Æ G : J a# bcc b α( +iq!q % ) fcc bæq γ. [ D Reb.} 9 Kp & b t. 78, vg M~% G R e b.} 3 = d, N 6blek/Z.}, 4 9 RD 6 r 7 8'j.e Z 0"{l Fig.7 Fracture morphology of the tested steel at at various processes of TMCP (a), CR+AC (b) and CR+ DQ (c) ; 8'j.Ye Z BK p 5F 8 J 2 C Table 2 Volume fraction and carbon content of retained austenite in the tested steel at various processes r6 &+ 30 min "hp Qh ε!o{l Morphology of ε carbide precipitations in lath martensite tempered at 250 for 30 min 250 Fig.6 (a) bright field (b) dark field (c) SAD pattern and index (%) Process Volume fraction TMCP 23.1 Carbon content 0.96 CR+AC 26.5 0.84 CR+DQ 4.2 0.57 CR+DQ+T 3.0 1.02
692 Ô Ý 46 Ö 8 CR+AC º Ã Ô TEM Fig.8 TEM morphology of retained austenite at CR+AC process (a) bright field (b) dark field (c) corresponding diffraction pattern and index Õ È, ÄÆÕ 0.1 µm. º ɼÚ, Õ Þ [uvw] α =[111], ÆÕ [uvw] γ =[110], ÛÅ Õ (α ) ÊÆÕ (γ ) Þ Èß {110} α /{111} γ, 111 α / 101 γ ½ ØÎ, Á K S ØÎ. TMCP» ÄÆÕ Ã Â CR+AC», 23.1%. Đ Ý ÄÆ Õ Ã, Ú 4.2%, ³ ÄÆÕ Ã 3.0%, ¼Ú³ ÄÆÕ Õ, Ø ¼Ä±. ¼ 1 2 ¼Ú ÄÆÕ Ê Ø. µ ÄÆÕ Íà [17] : ÉÀÎÆ ÄÆÕ Ü, ÉÀ¹ Đ, ¹ Ð; ÄÆÕ ¾, ÉÀǹ À ; γ Ê α Ò ÐÖ, ÂÉÀ¹. ÄÆÕ ÍÃ, Å Â ÄÆÕ ß Â Á ºÐ, ³ ¼Ü Å ¹Ò, Ö, ± ÄÆÕ Ã, À ÄÆÕ Á±. ÄÆÕ Á± ÄÆÕ C à РÑ, ÄÆÕ C ü. Å ÂÐ Ð Đ¹Ð ± ÄÆÕ C Ã, ÕÆ Ê ÄÆÕ C à ØÎ [18] ÛÐÕÆ: a = 3.571 + 0.044w C (2), w C ÄÆÕ C à ( Ã, %), a Ä ÆÕ ÕÆ, Å {311}ÞÖ Æ a = λ h2 + k 2sin θ 2 + l 2 (3) (2) Ñ, Ð ± È ÄÆÕ C Ã, Å Æ Ê ÄÆ Õ ÉÀÀ, ¹¾» ÄÆ Õ C à ¹Ò. Æ Í¼ 2. ؼ 2 ¹, TMCP» ÄÆÕ C à 0.96%, CR+AC» 0.84%. Í, ÄÆÕ Ê C Á± Ö. Ö, Ò 2» ÄÆÕ Æ Â 20%, ³ C à 0.24%, ¼Ú ÄÆÕ µ Å C Ã. Ö ¹½± TMCP CR+AC» Õ ºÐ C,, Ò 2» ¹ Õ ¾ Õ ±. Ò, ½ Æ Ó, CR+DQ» ÄÆ Õ C à 0.57%,  ³ à (0.24%), Û Å [19] Ø C Õ ß C ¹. 250 ³ 30 min, ÄÆÕ C ÃÅ 1.02%, Ú³ Ú ÄÆÕ ( ³ ÄÆÕ ÃËÈű), C Ø Õ ¼ Õ ÆÕ (¹ ). 2.5 ÁÞÑ ÎÛÜ «TMCP, CR+AC CR+DQ+T» ÑÛÐÛÀ, ¹ 9 Ð. Í, 3» Ê Æ Ü, Å Ò. CR+AC» Å, Ê ÈÈ ¹ È, ¼ ¼ Ú, Æ Ð 70 nm; CR+DQ+T» 250 ³ 30 min, C Æ È ¹ Ú, ¾ Ý Ê È Ñ, ¼ Ò, Æ Ð 15 nm; TMCP» Ó CR+AC CR+DQ+T È, 50 nm. [20] ¼Ú, È ÆÕ Ê
6 : 1500 MPa ÕÊ Ù ßÈ 693 Ö 9 ³ º Î É ßÐ Fig.9 Morphology of precipitation particles in the tested steel at various processes of TMCP (a), CR+AC (b) and CR+DQ+T (c), ÊÆÕ ÞÈß Ð ØÎ: 001 M(C,N) /001 γ, [010] M(C,N) /[010] γ. Ò Ð½ ØÎ, Ê Þ ÊÆÕ Þ 3 ÔĐ Å Đ. Ò Ê µ ÆÕ Ê, ³ ¼ 3 ÔĐ Å Æ È. Ö, ÆÕ Ê È ¼Ü. α Fe, Ê È Ê¾ ß Ø [20] : 001 M(C,N) /001 α Fe, [010] M(C,N) /[110] α Fe, Ò ½ ØÎ, Ê Þ Ê α Fe Þ 3 ÔĐ Å Đ, ÖÊ È ¹½ ¼ Þ. ÃÊ È, Ö ¹»½ Ô Ê ¾ ÆÕ, Ø È Ú, Õ ¼ Õ Ã Ê Ü. 3 (1) ² TMCP, CR+AC, CR+DQ CR+ DR+T 4», 2» Å ² Å, Đ Ý ½± 1890 MPa, ¼Ä± 1280 MPa, Ï 13.0%; 250 ³ 30 min ½± 1820 MPa, ¼Ä± 1350 MPa, Ï 15.0%. Ê ½± ß Ø, ʼı ÄĐ Î. (2) TMCP»º ºÐ Õ Õ ÄÆÕ È ºÐ; CR+AC» ºÐ Ô ± Õ ÄÆÕ ; CR+DQ» ºÐ È Õ Èà ÄÆÕ ; CR+DQ+T», Õ ³ÈÊ, Ê Ô ε È. (3) TMCP» ½, ¹ ½É, Èà Ãß, Ã, ²; CR+AC» ½É ½ÉÈ Õ ½É, ½Ö, Ã, Ò; CR+DQ» ½É, ½Ö, ½ ÉÀ, Ê²Õ ²». (4) TMCP CR+AC» Õ ºÐ C, Õ ¾ Õ ±. C Õ ß C ¹., ³ Ú ÄÆÕ, C Ø Õ ¼ Õ ÆÕ (¹ ). ³ ½±, ¼Ä±, Ò Â Đ Ô ³È ÄÆÕ Ê È Ê ± ² ¾. (5) CR+AC» Ê È È Æ Ð 70 nm; CR+DQ+T» 15 nm; TMCP 50 nm. Ô Ê ¾ ÆÕ, Ø È Ú, Õ ¼ Õ Ã Ê Ü. ÙÝ [1] Fan C G, Dong H, Yong Q L, Weng Y Q, Wang M Q, Shi J, Hui W J. Mater Mech Eng, 2006; 30: 1 (ÇÏ,,, Â˵,,,. Ö Æ, 2006; 30: 1) [2] Guo J W, Sun J B, Li H B, Rong S F. J Jiamusi Univ, 2002; 20: 23 (,,, Û. Áß, 2002; 20: 23) [3] Garrison Jr W M, Maloney J L. Mater Sci Eng, 2005; A403: 299 [4] Maloney J L, Garrison Jr W M. Acta Mater, 2005; 53: 533 [5] Ji G L, Li F G, Li Q H, Li H Q, Li Z. Mater Sci Eng, 2010; A527: 1165 [6] Li J, Guo F, Li Z, Wang J L, Yan M G. J Iron Steel Res
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