高強度非調質棒鋼 - KOBELCO 神戸製鋼

1 FEATURE : Materials for Automotive Industry .. High Strength Microalloyed Steels . Masakazu Ikeda Gorou Anan Microalloyed steels have been developed and put into practical use to simplify the manufacturing process of automobile parts and to reduce manufacturing costs. In particular, high strength microalloyed steels have been applied to reduce the automobile weight. In this paper, the characteristics of high strength micro- alloyed steels and high strength/high toughness micro-alloyed steels, as well as automobile part application examples are introduced.. 2 .. 4 . 3 700 800 MPa V .. V .. Mn Cr .. 4 ,5 .. 1 . 2 .. 2 . 1 . 1 .. 2 .. 3 .. 1 . 3 .. /Vol. 52 No. 3 Dec. 2002 47. Conventional steel Conventional process Bar - Hot forging - Quenching and tempering - Machining High toughness steel New process Bar - Hot forging - Machining Hot forging steel High strength steel Microalloyed High strength and Conventional process Bar - Hot forging - Quenching and tempering - Machining steel high toughness steel New process Bar - Hot forging (Rapid cooling in part) - Machining Bar - Spheroidizing - Cold forging - Quenching and tempering - Conventional process Machining - (Induction hardening).

2 Cold forging steel Bar - Cold forging New process Cold working Machining - (Induction hardening). steel Wire - Spheroidizing - Drawing - Cold heading - Conventional process Quenching and tempering - Plating - Baking Cold heading steel Wire - Drawing - Cold heading - New process - Plating - Baking Bar - Quenching and tempering - Machining - Conventional process Direct cutting (Induction hardening). steel Bar - Machining - New process (Induction hardening). 1 3 . Fig. 1 Classification of microalloyed steels Si Si . Hardness (HB) . 226 270 340. 200 P P . Replacing of Replacing of carbon steels alloy steels . Ferrite Pearlite . High strength and 150 Martensite high toughness steel . Impact value (J/cm2 ). Bainite . High toughness steel Si P V . 100 High strength and high toughness steel Si.

3 50 Conventional . High strength steel steel . 90 . 0 KNF33M 100 KNF35M. 700 800 900 1 000 1 100 1 200. Tensile strength (MPa) 1 . 2 2 . 2 3 . Fig. 2 Relationship between tensile strength and toughness in 2 2 1 . microalloyed steels 2 KNF33M .. 3 . 6 . C Si P V 2 2 2 . C C 4 . Pb . Fatigue limit ratio Yield ratio 3 C Si P V . Fig. 3 Effect of C, Si, P, V contents on yield ratio and fatigue limit ratio C (mass ) Si (mass ) P (mass ) V (mass ). 48 KOBE STEEL ENGINEERING REPORTS/Vol. 52 No. 3 Dec. 2002 . (mass ). 1 C Si Mn S Cr V B. KNF33M High strength . microalloyed steel KNF35M Table 1 Chemical composition of High strength high strength microalloyed steel and high strength and and high toughness KNF5MC added microalloyed steel high toughness microalloyed steel Conventional KNF43.

4 Microalloyed steel JIS S55C . Notes on Lead (Pb), Sulfur (S) content : S1' S2'. , L1'. , L2'. , may be present after the steel grade to indicate the presence of Lead (L1: , L2: ) or Sulfer (S1: , S2: ). 2 3 Mechanical properties Impact properties Table 2 Mechanical properties of high strength Hardness PS TS El. RA uE20. microalloyed steel (HB). (MPa) (MPa) ( ) ( ) (J/cm2). High strength microalloyed steel 280 676 911 22 50 50. (KNF33M). Conventional 258 554 847 19 38 38. microalloyed steel JIS S55C 248 465 818 26 57 76. KNF43 KNF33 KNF35 . 6 . 2 . 2 3 7 . 5 . KNF35 S Pb . 1 000 KNF35MS1L2. Pb . KNF43 KNF35 500 KNF43L1.. 200.. Tool life (cm). 2 . 3 100.. 50.. 20. Cutting condition 10 Tool : SKH51, 10. Feed rate : 5 Cutting fluid : Dry 3 Criteria of tool life : Melted 2.

5 3 . 1 2 5 10 20 50 100. Cutting speed (m/min). 900 MPa . 5 . Fig. 5 Results of tool life test in drilling 650. 600. Stress amplitude (MPa). 550 Martensite Strength & Bainite 500. Strength Toughness 450. KNF35 HV310 about Ferrite 400 times & Pearlite KNF33 HV280. Toughness 350 KNF43L1 HV230. 300. 4 5 6 7. 10 10 10 10 Carbon content Number of cycles 6 6 . 4 Fig. 6 Schematic representation on relationship between strength Fig. 4 Results of rotating bending fatigue test and toughness and carbon content /Vol. 52 No. 3 Dec. 2002 49. C .. KNF. 5MC 1 .. 3 . 2 . 3 . 2 1 . 7 KNF5MC .. S45C SCr440 . 7 . 1 . 1 a JIS SCr440 . 1 m . JIS S45C . 1 2 m . 2 . 3 . 2 2 . 8 KNF5MC . JIS SCr440 . KNF5MC .. SCr440 . 3 . 3 .. 10 15 . 5 .. 350. WQ. OQ This study 300 AC. SCr440 QT.

6 1 b S45C QT. AC. 250. Impact value (J/cm2).. 200.. 150. (a) (b). 100. 50. 0. 10 m Tensile strength (GPa). (a) Martensite (b) Bainite 7 6 . 1 Fig. 7 Relationship between impact value and tensile strength in Photo 1 SEM micrographs of high strength and high toughness high strength and high toughness microalloyed steels and microalloyed steels medium carbon steels 50 KOBE STEEL ENGINEERING REPORTS/Vol. 52 No. 3 Dec. 2002 .. KNF5MC. 1 000 . SCr440.. 500.. Cutting condition Tool : SKH51 . 200 (TiN coated), 10. Feed rate : . 100 Cutting fluid : Dry . Tool life (cm). Criteria of tool life : 50. Melted or failure .. 20.. 10 1 1993 , 2 , 1985 , 5 3 R D , 1997 , 4 1990 , 5 , 1987 , 2. 5 10 20 50 100 200 6 1992 , Cutting speed (m/min) 7 , 1992 , 8 . Fig. 8 Results of tool life test in drilling.

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