Effect of Microstructure on Dynamic Tensile Characteristics of SPRC440 Sheet

G

穢剳暒昷儆击穟箒滆V洢YW劒G 洢[笾SGYWXX噊VZW`G

G

SPRC440

瞿昷櫖 惾獞垚 欇窫

G

決昷籲

· 沊欇徯

· 決洛筞

· 卆汾愶

· 卆檗壊

G

Effect of Microstructure on Dynamic Tensile Characteristics of SPRC440 Sheet

G

S. H. Lee, Y. M. Rhyim, J. H. Lee, I. B. Kim, Y. D. Kim

(Received April 14, 2011 / Revised May 27, 2011 / Accepted May 27, 2011) G

Abstract

The behavior of metallic materials at high strain rates shows different characteristics from those in quasi-static deformation. Therefore, the strain rate should be considered when simulating crash events. The objective of this paper is to evaluate the dynamic tensile characteristics of SPRC440 as a function of the volume fraction of phases. As-received SPRC440 is composed of ferrite and pearlite phases. However, ferrite and martensite phases were observed after heat treatment at 730ଇ and 780ଇ for 5 minutes, as expected by calculations based on the curves from dilatometry tests.

High cross-head speed tensile tests were performed to acquire strain-stress curves at various strain rates ranging from 0.001 to 300 s^-1, which are typical in real vehicle crashes. It was observed that the flow stress increases with the strain rate and this trend was more pronounced in the as-received specimens consisting of ferrite and pearlite phases. It is speculated that the dislocation density in each phase has an influence on the strain rate sensitivity.

G G

Keywords : Dynamic Tensile Test, Strain Rate Sensitivity, Flow Stress, Dislocation Density, Microstructure G

G

41# ⇆# ᤊG G

㾲⁒ 㠦⍞㰖ȡ䢮ἓⶎ㩲Ṗ ㌂䣢㩗㧎 㭒㣪 ὖ㕂㌂⪲

⟶㡺⯊Ⳋ㍲ 㑮㏷₆₆㦮 㡆゚䟻㌗㦚 㥚䞲 ἓ⨟䢪㠦

╖䞲 ὖ㕂㧊 ⏨㞚㰖ἶ 㧞┺. 㑮㏷₆₆㦮 ἓ⨟䢪⓪ 㿿☢㠦 ╖䞲 㞞㩚㎇㧊 Ỗ㯳♲ ㌗䌲㠦㍲ 㧊⭚㪎㟒 䞮⓪◆, 㧒⹮㩗㦒⪲ ⁞㏣㨂⬢⓪ 㩫㩗㧎 㫆Ịὒ ☯ 㩗㧎 㫆Ị㠦㍲ ⼖䡫Ệ☯㧊 ┺⯊Ⳇ, ⡦䞲 ⁎ 㩫☚Ṗ 㨂⬢Ⱎ┺ ┺⯊₆ ➢ⶎ㠦 㞞㩚㎇㦚 ╊⽊䞮⓪ ㍺Ἒ

⯒ 㥚䟊㍲⓪ ㍺Ἒ 䟊㍳㠦 ㌂㣿♶ ☯㩗 ⶒ㎇䂮⯒

㔺䠮㦚 䐋䟊㍲ 㩫䢫䧞 ῂ䞶 䞚㣪Ṗ 㧞┺.

䡚㨂 ㌂㣿♮ἶ 㧞⓪ ἶ㏣ 㧎㧻 㔲䠮₆⓪ 䋂Ợ

⚦ Ṗ㰖⪲, Kolsky 㦮 1 㹾㤦 䌚㎇䕢 㧊⪶㠦 ⁒Ệ䞮 㡂 㑮㻲/s 㧊㌗㦮 ἶ⼖䡫⮶ ㏣☚㠦㍲㦮 ⼖䡫Ệ☯㦚 㔺䠮䞮⓪ 䢟䋾㓾 ⹪ 㔲䠮₆[1-4]㢖 㟓 1/s~㑮⺇/s ⼖ 䡫⮶ ㏣☚㠦㍲㦮 㔲䠮㧊 Ṗ⓻䞮☚⪳ ₆㫊㦮 㥶㞫 㔳 㧎㧻 㔲䠮₆⯒ Ṳ⨟[5-7]䞲 ộ㧊 ╖䚲㩗㧊┺.

⁞㏣䞯㩗 ὖ㩦㠦㍲ 㧎㧻ⶒ㎇㠦 ⹎䂮⓪ ⹎㎎㫆㰗 㠦 ╖䞲 㡆ῂ⓪ ╖⿖⿚ 㭖 㩫㩗 ⼖䡫⮶ ㏣☚㠦㍲

㧊⬾㠊㪎 㢪㦒Ⳇ, ἶ㏣㠦㍲㦮 ☯㩗 㧎㧻 㔺䠮㠦 ╖ 䞲 ἆὒ⓪ ㌗╖㩗㦒⪲ ⁎ 㩫⽊Ṗ ⹎⹎䞲 䘎㧊┺.

⡦䞲 ⹎㎎㫆㰗 ῂ㎇㧊 ☯㩗 㧎㧻 ἆὒ㠦 ⹎䂮⓪ 㡗䟻㠦 ╖䞲 㡆ῂ☚ 㫆㎇㧊 ┺⯎ 㧊㫛㏢㨂⯒ 㧊㣿 䞲 ἓ㤆Ṗ ╖⿖⿚㧊Ⳇ, 㧊 ἓ㤆 ṗ ㌗㦮 ゚㥾 㣎㠦

XUG ⿖㌆╖䞯ᾦG 㨂⬢Ὃ䞯ὒG YUG 䞲ῃ₆Ἒ㡆ῂ㤦G ⿖㍺G 㨂⬢㡆ῂ㏢G

JG ᾦ㔶㩖㧦G aG 㨂⬢䘟Ṗ㡆ῂ⁎⭏SGlT”ˆ“aG™ ”g’”šU™ŒU’™G

ZXWGV穢剳暒昷儆击穟箒滆V洢YW劒G 洢[笾SGYWXX噊G

G

0.015 0.016 0.017 0.018 0.019

0 1 2 3 4 5 6

data from loadcell

Load (kN)

Time (s) (a)

0.015 0.016 0.017 0.018 0.019

0 1 2 3 4 5 6

data from straingage

Load (kN)

Time (s) (b)

㏢㨂 ⼚ 䢪䞯㫆㎇ ⹥ 㩲㫆Ὃ㩫 㧊⩻㠦 ➆⯎ 㡗䟻 㧊 㿿⿚䧞 ⺆㩲♮㠞┺ἶ ⽊₆ 㠊⪋┺.

➆⧒㍲ ⽎ ⏒ⶎ㠦㍲⓪ 㧦☯㹾㣿 㣎䕦㨂⪲ ㌂㣿

♮ἶ 㧞⓪ ṫ䕦㨂 㭧㠦㍲ SPRC440 ㏢㨂⯒ ㍶䌳䞮 㡂 ☯㧒䞲 䢪䞯㩗 㫆㎇㦚 Ṗ㰖Ⳋ㍲ 㡊㻮Ⰲ⯒ 䞮㡂

㌗㦮 㫛⮮ ⹥ ゚㥾㦚 ⼖䢪㔲䋾 ㏢㨂⪲ Ⱒ✺㠞┺.

㡊㻮Ⰲ⯒ 䐋䟊 ṫ䢪㌗㧎 䗚⧒㧊䔎⪲㢖 Ⱎ⯊䎦㌂㧊 䔎㦮 㫊㨂 㡂⿖ ⹥ ⁎ ゚㥾㧊 ἶ㏣ ⼖䡫 Ệ☯㠦

⹎䂮⓪ 㡗䟻㠦 ╖䟊 㞢㞚⽊ἶ㧦 䞮㡖┺.

51# ⎎㚂# ᳓ᴿ#

#

⽎ 㡆ῂ㠦 ㌂㣿♲ SPRC440㦮 㫆㎇㦖 Table 1ὒ ṯ┺.

Table 1 Chemical composition of SPRC440 (wt%)

C Si Mn P S Fe

0.079 0.13 1.28 0.010 0.002 bal.

⹎㎎㫆㰗 ῂ㎇㦚 ⼖䢪㔲䋺⓪◆ 㧞㠊 䞚㣪䞲 ₆ 㽞㧦⬢⯒ 㠑₆ 㥚䞮㡂 ❲⧒䏶⹎䎆⯒ 㧊㣿䞮㡂 㡾

☚㠦 ➆⯎ ₎㧊⼖䢪⯒ 䁷㩫䞮㡂 㭒㣪 ⼖䌲㩦ὒ 㡾

☚㠦 ➆⯎ ㌗⿚㥾㦚 ☚㿲䞮㡖┺. 䁷㩫㧻゚⪲⓪ Theta Industries. INC ㌂㦮 Dilatronicฌ⯒ ㌂㣿䞮㡖㦒 Ⳇ, 䙃㧊 3mm, ₎㧊Ṗ 20mm 㧎 䕦㌗㔲䘎㦚 ㌂㣿 䞮㡖┺. 㔏㡾 ㏣☚⓪ 㽞╏ 5ଇ㡖㦒Ⳇ 1100ଇ㠦㍲

10⿚Ṛ 㥶㰖 䞮㡖┺. ❲⧒䏶⹎䎆 㔺䠮 ἆὒ⪲⿖䎆 㠑㦖 䖓㺓 ἷ㍶㦚 㧊㣿䞮㡂 ㌗⼖䌲 Ṳ㔲㡾☚⿖䎆 㫛⬢㡾☚₢㰖 㡺㓺䎢⋮㧊䔎㢖 䗮⧒㧊䔎㦮 ㌗⿚㥾 㦚 Ἒ㌆䞲 䤚, 㧊⯒ ⹪䌫㦒⪲ 6Ṳ㦮 㡊㻮Ⰲ ῂṚ㦚

㍺㩫䞮㡖┺. 㡊㻮Ⰲ⓪ Thermvac Engineering ㌂㦮 ἶ㡾 㡒㣫⪲⯒ ㌂㣿䞮㡖㦒Ⳇ ṗṗ㦮 㡾☚㠦㍲ 5⿚

Ṛ 㥶㰖 䤚 㑮⌟䞮㡖┺.

㡊㻮Ⰲ 㩚ὒ 䤚㦮 ⹎㎎㫆㰗 ㌗ ⿚㥾[8]ὒ ἆ㩫Ⱃ 䋂₆[9]⯒ 䁷㩫䞮₆ 㥚䞮㡂 㔲䘎㦚 ἓⳊ 㡆Ⱎ䞲 䤚 4% Nital 㣿㞷㦒⪲ 㑮㽞Ṛ 㠦䃃䞮㡂 ὧ䞯䡚⹎ἓὒ 㭒㌂㩚㧦䡚⹎ἓ㦚 㧊㣿䞮㡂 ⹎㎎㫆㰗㦚 ὖ㺆䞮㡖

┺.

⼖䡫Ệ☯㦚 ㌊䘊⽊₆ 㥚䞮㡂 㭖 㩫㩗 ⼖䡫⮶ ㏣

☚㧎 0.001/s 㫆Ị㠦㍲⓪ 㧒⹮ 㧎㧻 㔲䠮₆⯒ ㌂㣿 䞮㡖ἶ 1/s, 10/s, 100/s, 200/s, 300/s㦮 ⼖䡫⮶ ㏣☚㠦

㍲⓪ ἶ㏣ 㧎㧻 㔲䠮₆⯒ ㌂㣿䞮㡖┺.

⽎ 㡆 ῂ 㠦 ㍲ ㌂ 㣿 䞲 ἶ ㏣ 㧎 㧻 㔲 䠮 㧻 ゚ ⓪ Instron ㌂㦮 VHS-65/80-25 ⳾◎⪲ 㔲䠮 Ṗ⓻䞲 㡗

Fig. 1 Dimension of specimen for high strain rate tensile test

Fig. 2 Time-load curves at strain rate of 94/s : (a) data obtained by loadcell and (b) data obtained by strain gage

㡃㦖 0.1m/s~25m/s 㧊┺. ἶ㏣ 㧎㧻 㔲䠮 㔲 㞷䁚 㠦㧊䎆Ṗ ⳿䚲䞲 ㏣☚㠦 ☚╂䞲 䤚 㔲䘎㠦 䞮㭧㦚

⿖ὒ䞮₆ 㥚䟊 䕾㓺䔎-㫆 ⁎Ⱃ㦚 ㌂㣿䞮㡖┺. 㧊

⁎Ⱃ㦖 㔲䠮 㩚 ㌗䌲㠦㍲⓪ 䞮⿖ ⁎Ⱃ㧊 㔲䘎㦚 ῂ㏣䞮㰖 㞠㦖 ㌗䌲㧊⋮, 㔲䠮 㔲㧧 䤚 㞷䁚㠦㧊䎆 Ṗ Ṗ㏣♲ ㌗䌲㠦㍲ ⍟-㞚㤙 㥑㰖Ṗ 㩲Ệ♮⓪ 㑲Ṛ

⹎Ⰲ Ỏ㠊⚦㠞▮ 㧪⮮ 㦧⩻㦒⪲ 㧎䟊 ⁎Ⱃ㧊 㔲䘎 㦚 ῂ㏣䞮Ợ ♲┺. 㞷䁚㠦㧊䎆Ṗ 㰖㔲䞲 ㏣☚㠦 ☚

╂䞲 䤚 㔲䘎㦚 ῂ㏣䞮₆ ➢ⶎ㠦 ⁎ ㏣☚㠦 ☚╂

䞮₆ 㥚䞲 Ṗ㏣ῂṚ㧊 䞚㣪䞮⸖⪲ 㔲䘎㦖 Fig. 1ὒ ṯ㧊 䞲 㴓 ⿖⿚㦚 ₎Ợ ㍺Ἒ䞮㡖┺.

ἶ㏣G 㧎㧻G 㔲䠮㦖G 㩫㰖G ㌗䌲㠦㍲G ⰺ㤆G ザ⯎G ㏣

☚⪲G 㔲䘎㦚G 㧎㧻㔲䋺₆G ➢ⶎ㠦G 㔲䘎㠦G 㧧㣿䞮⓪G

穢剳暒昷儆击穟箒滆V洢YW劒G 洢[笾SGYWXX噊VZXXG

G

J D

J e e f e

L L

L V L

'

 '

'

 '

0 200 400 600 800 1000 1200

0.000 0.004 0.008 0.012 0.016

'L (mm)

Temperature (°c)

L_e^

Le

L

720 740 760 780 800 820 840 860 880

0 20 40 60 80 100

Austenite Ferrite

Volume Fraction (%)

Temperature (°c)

720 730 740 750 760 770 780 790 800 810 0

10 20 30 40

Dilatation curve Salt bath

Volume Fraction (%)

Temperature (°c) 㑲ṚṖ㏣☚ṖG ⏨㞚㰖Ⳋ㍲G ⹲㌳䞲G 䧮㦮G ⿞‶䡫㦒⪲G

㧎䟊G 㔲䘎ὒG 㰖⁎ṖG 㰚☯㦚G 䞲┺[10]. 㧊⩂䞲G 䞮㭧G

⟾Ⱂ㦖G 㩫䢫䞲G 㥶☯ἷ㍶㦚G 㠑⓪◆G 㧻㞶ṖG ♮⸖⪲G 㧊⯒G 㾲㏢䢪䞮₆G 㥚䞮㡂G 㔲䘎㦮G ㌗⿖G ⁎Ⱃ⿖㠦G 䞮 㭧䁷㩫㦚G 㥚䞲G ⼖䡫Ợ㧊㰖(strain gage)⯒G 㿪Ṗ⪲G ⿖ 㹿䞮㡂G 㔲䠮㦚 㔺㔲䞮㡖┺.

Fig. 2⓪ 94/s㠦㍲㦮 ἶ㏣ 㧎㧻 㔺䠮 ἆὒ⪲ 㔲Ṛ

╏ ⹱⓪ ◆㧊䎆䙂㧎䔎㦮 Ṳ㑮⓪ ⡧ṯ㦢㠦☚ ⿞ῂ 䞮ἶ Fig. 2(a)㢖 ṯ㧊 㞫㩚⪲✲㎖㠦㍲ 㠑㦖 䞮㭧◆

㧊䎆⓪ 䞮㭧 ⟾ⰒG 䡚㌗㧊G 㕂䞮ỢG ⋮䌖⌂㦒⋮SG Fig.

2(b)㢖G ṯ㧊G ⼖䡫Ợ㧊㰖⪲⿖䎆G 㠑㦖G ⼖䡫G 㔶䢎⯒G 䞮㭧㦒⪲G 䢮㌆䞲G ἆὒ㠦㍲⓪G ⁎G 䡚㌗㧊G 㢚䢪♲G ộ 㦚G ⽒G 㑮G 㧞┺UG G

㧊⓪G 㔲䘎㦮G ⁎Ⱃ⿖㠦G ⼖䡫Ợ㧊㰖⯒G ⿖㹿䞲G ἓ 㤆SG 䞮㭧㦚G 㔲䘎㠦㍲G 㰗㩧G 䁷㩫䞮₆G ➢ⶎ㠦G 㔲䘎㦮G 㰚☯㦒⪲G 㧎䞲G 䞮㭧G ⟾ⰒG 㣎㠦G 㰖⁎G ⴎ㼊SG 㔲䘎ὒG 㰖⁎㦮G ἚⳊG ⹥G 㰖⁎㢖G ⪲✲㎖㦮G ἚⳊG ❇㠦㍲G 㥶

⹲♮⓪G ⟾ⰒG 䡚㌗㧊G ⺆㩲♮₆G ➢ⶎ㧎G ộ㦒⪲G 䕦┾

♲┺UG ➆⧒㍲G ⽎G 㔺䠮㠦㍲⓪G 䞮㭧G ⟾ⰒG 䡚㌗㧊G 㾲

㏢䢪G ♲G 㧎㧻G ἆὒ⯒G 㠑₆G 㥚䞮㡂G ⼖䡫Ợ㧊㰖⯒G

⿖㹿䞮㡂G 㔺䠮㦚G 㔺㔲䞮㡖┺U

G G G

61# ⎎㚂# ൚ඦ#

#

SPRC440㦚 1100ଇ₢㰖 Ṗ㡊䞮⓪ ☯㞞 㔲䘎㦮

₎㧊 ⼖䢪⯒ 㡾☚㦮 䞾㑮⪲ Fig. 3㠦 ⋮䌖⌞┺. BCC ῂ㫆㠦㍲ FCCῂ㫆⪲ 㫆⹖䢪♾㠦 ➆⧒ ⼖㥚Ṗ Ṧ

㏢䞮₆ 㔲㧧䞮⓪ 725ଇ㠦㍲ 㡺㓺䎢⋮㧊䔎 ㌗㦒⪲

㦮 ⼖䌲Ṗ Ṳ㔲♮⓪ ộ㦚 㞢 㑮 㧞ἶ, 862ଇ㠦㍲

⼖㥚Ṗ ┺㔲 㯳Ṗ䞮⓪ ộ㦒⪲ ⽊㞚 ㌗⼖䌲Ṗ 㢚

⬢♮㠞㦢㦚 㥶㿪䞶 㑮 㧞┺.

㧊㢖 ṯ㦖 䖓㺓ἷ㍶㦒⪲⿖䎆 㡾☚㠦 ➆⯎ ㌗ ⿚ 㥾㦚 㡞䁷䞮₆ 㥚䞮㡂 ㌗⼖䌲 Ṳ㔲㡾☚⿖䎆 㫛⬢

㡾☚₢㰖 T.A.Kop[11] Ṗ 㩲㞞䞲 㔳(1)㦚 㧊㣿䞮㡂 䗮⧒㧊䔎㢖 㡺㓺䎢⋮㧊䔎㦮 ㌗╖㩗㧎 ⿚㥾㦚 Ἒ㌆

䞮㡂 Fig. 4㠦 ⋮䌖⌞┺.

(1)

Fig. 5⓪ ❲⧒䏶⹎䎆 㔺䠮 ἆὒ⪲⿖䎆 Ἒ㌆䞲 Ⱎ

⯊䎦㌂㧊䔎㦮 ⿖䞒 ⿚㥾ὒ 㡒㣫⪲㠦㍲ 㡊㻮Ⰲ⯒

䞲 䤚 ⹎㎎㫆㰗ὖ㺆㦚 䐋䟊 㔺㩲 䁷㩫䞲 Ⱎ⯊䎦㌂

㧊䔎㦮 ⿖䞒⿚㥾㦚 ゚ᾦ䞲 ⁎⧮䝚㧊┺. A1 ⼖䌲㩦 㧊㌗㦮 㡾☚㠦㍲  ⌟䞮㡖㦚 ➢ 㠑㠊㰖⓪ Ⱎ⯊䎦

Fig. 3 Dilatation curve of SPRC440

Fig. 4 Calculated volume fraction of austenite and ferrite

Fig. 5 Changes of the martensite volume fraction depending on the quenching temperature

㌂㧊䔎㦮 ⿖䞒 ⿚㥾㦖 㡺㓺䎢⋮㧊䔎䢪 㡾☚㠦㍲

䡫㎇♲ 㡺㓺䎢⋮㧊䔎㦮 ⿖䞒 ⿚㥾ὒ ゚⪖䞲┺ἶ 㞢⩺㪎 㧞㦒⋮, Fig. 5㠦 ⋮䌖⋲ ⹪㢖 ṯ㧊 㔺䁷䞲 Ⱎ⯊䎦㌂㧊䔎 ⿚㥾ὒ 㔳 (1)㦚 㧊㣿䞮㡂 Ἒ㌆䞲 ⿚ 㥾㦖 㟓 10% 㩫☚㦮 㹾㧊Ṗ 㧞㠞┺. 㧊ộ㦖 Ἒ㌆

♲ ⿚㥾㦖 㧊⪶㩗㦒⪲ 㡞䁷䞲 ộ㦒⪲ 㔺䁷ὒ 㹾㧊 Ṗ 㧞㦚 㑮 㧞㦒Ⳇ, ⡦䞲 㡒㣫⪲⓪ ┺⯎ Ṗ㡊⪲㠦

ZXYGV穢剳暒昷儆击穟箒滆V洢YW劒G 洢[笾SGYWXX噊G

G

Fig. 6 Micrographs of SPRC440

゚䟊 ㌗╖㩗㦒⪲ ‶㧒䞲 㡾☚ ⿚䙂⯒ 㥶㰖䞶 㑮 㧞㰖Ⱒ 㢚⼓䞮Ợ 㡾☚⯒ 㩲㠊䞶 㑮 㧞⓪ ộ㦖 㞚

┞⸖⪲ ⚦ Ṳ㦮 ἆὒ㠦 㹾㧊Ṗ ⋮⓪ ộ㦒⪲ 㡂Ỿ 㰚┺.

SPRC440㦖 12%㦮 䗚⧒㧊䔎 ⿚㥾㦚 Ṗ㰖⸖⪲ ☯ 㧒䞲 ⿚㥾㦮 Ⱎ⯊䎦㌂㧊䔎⯒ Ⱒ✺₆ 㥚䟊㍲⓪ 760ଇ㠦㍲ 㡊㻮Ⰲ⯒ 㔺㔲䞮Ⳋ ♶ ộ㦒⪲ 㡞㌗䞮㡖 㦒⋮ 㔺㩲 760ଇ㠦㍲ 㡊㻮Ⰲ 䤚 䁷㩫䞲 Ⱎ⯊䎦㌂

㧊䔎㌗㦮 ⿚㥾㦖 27%⪲ ⋮䌖⌂㦒Ⳇ 730ଇ㠦㍲ 㡊 㻮Ⰲ䞲 ἓ㤆 㟓 17%㦮 Ⱎ⯊䎦㌂㧊䔎Ṗ 㫊㨂䞮⓪ ộ㦒⪲ ⋮䌖⌂┺. Ⱎ⯊䎦㌂㧊䔎㦮 ⿚㥾㧊 ☯㩗 㧎 㧻 䔏㎇㠦 ⹎䂮⓪ 㡗䟻㦚 㞢㞚⽊ἶ㧦 17% ⽊┺ ⍞

⏨㦖 ⿚㥾㦮 Ⱎ⯊䎦㌂㧊䔎⯒ 㠑₆ 㥚䞮㡂 780ଇ㠦

㍲ 㡊㻮Ⰲ䞮㡂 㟓 31%㦮 Ⱎ⯊䎦㌂㧊䔎Ṗ 㫊㨂䞮⓪ 㔲䘎☚ 㩲㫆䞮㡖┺.G G

Fig. 6㦖 SPRC440㦮 㡊㻮Ⰲ 㩚ὒ 䤚㦮 ⹎㎎㫆㰗 㦚 ὧ䞯䡚⹎ἓὒ 㭒㌂㩚㧦䡚⹎ἓ㦒⪲ ὖ㺆䞲 ἆὒ 㧊┺. 㧛㑮㌗䌲㦮 SPRC440㦖 䗮⧒㧊䔎㢖 䗚⧒㧊䔎

⪲ ῂ㎇♮㠊 㧞㦒Ⳇ, 㡊㻮Ⰲ 䤚㠦⓪ 㡞㌗䞲 ⹪㢖 ṯ㧊 䗮⧒㧊䔎㢖 Ⱎ⯊䎦㌂㧊䔎⯒ 㠑㦚 㑮 㧞㠞┺.

Table 2⓪ ἆ㩫Ⱃ 䋂₆⯒ 䁷㩫䞲 ἆὒ⪲ 䗮⧒㧊 䔎 ἆ㩫Ⱃ 䋂₆⓪ 㡊㻮Ⰲ 㩚ὒ 䤚㦮 㹾㧊Ṗ Ệ㦮 㠜⓪ ộ㦒⪲ ⋮䌖⌂┺.

⹎㎎㫆㰗㦮 ῂ㎇㦚 ╂Ⰲ䞲 ṗ 㔲䘎㦮 㭖 㩫㩗

⼖䡫⮶ ㏣☚ 㧎㧻 㔺䠮 ἆὒ⯒ Table 3㠦 ⋮䌖⌞┺.

䗮⧒㧊䔎㢖 䗚⧒㧊䔎⪲ ῂ㎇♲ 㔲䘎⽊┺ 䗮⧒㧊䔎 㢖 Ⱎ⯊䎦㌂㧊䔎⪲ ῂ㎇♲ 㔲䘎㦮 㾲╖ 㧎㧻 ṫ☚

Ṩ㧊 ▪ ⏨㦖 ộ㦚 㞢 㑮 㧞㦒Ⳇ, 㧊⓪ Ⱎ⯊䎦㌂㧊 䔎㦮 ⹎㎎䞲 㕣㩫ῂ㫆㢖 ⏨㦖 㩚㥚 ⹖☚Ṗ 㩚㥚㦮 㧊☯㦚 䣾ὒ㩗㦒⪲ ⹿䟊䞾㦒⪲㖾 ṫ☚⯒ ⏨㧊₆

➢ⶎ㧊┺[12].

Fig. 7㦖G ┺㟧䞲G ⼖䡫⮶G ㏣☚㠦㍲㦮G 㰚G ⼖䡫⮶T 㦧⩻G ㍶☚⯒G ⋮䌖⌎G ộ㦒⪲SG ṖὋἓ䢪㠦G 㦮䞮㡂G 㦧

⩻㧊G 㯳Ṗ䞮⓪G ộ㦚G 䢫㧎G 䞶G 㑮G 㧞┺UG ⡦䞲SG ⹎㎎

㫆㰗㦮G ῂ㎇㠦G ㌗ὖ㠜㧊G ⼖䡫⮶G ㏣☚ṖG 㯳Ṗ䞶㑮

⪳G 㥶☯㦧⩻㧊G 㯳ṖG 䞮⓪G ộ㦚G 㞢G 㑮G 㧞┺UG ⼖䡫⮶G

㏣☚ṖG ゾ⧒㰖ⳊG 䢲㎇䢪♮⓪ 㩚㥚㤦㦮 㑮Ṗ 㯳Ṗ 䞮㡂 㩚㥚 ⹖☚Ṗ ⏨㞚㰖⸖⪲[13,14] 㩚㥚㦮 㤖㰗 㧚㧊 ⹿䟊⯒ ⹱₆ ➢ⶎ㠦 㥶☯㦧⩻㧊 ⏨㞚㰚┺.G Fig. 8㦖 ☯㧒䞲 ⼖䡫⨟㧒 ➢ ṗṗ㦮 ⼖䡫⮶ ㏣☚

㠦㍲㦮 㥶☯㦧⩻㦚 ☚㔲䞲 ộ㦒⪲, ⁎⧮䝚㦮 ₆㤎

₆Ṗ 䄺㰚┺⓪ ộ㦖 ⼖䡫⮶ ㏣☚Ṗ 㯳Ṗ䞶㑮⪳

☯㧒 ⼖䡫⨟㠦㍲㦮 㥶☯㦧⩻㧊 㯳Ṗ䞮⓪ ゚㥾㧊 䄺㰖⓪ ộ㧊⸖⪲ ⼖䡫⮶ ㏣☚㠦 ╖䞲 ⹒Ṧ☚Ṗ ㌗

╖㩗㦒⪲ 䋂┺⓪ ộ㦚 㦮⹎䞲┺.

Table 4⓪ 㡆㔶㥾㧊 10%㧒 ➢ ⼖䡫⮶ ㏣☚Ṗ 䔎

㌗㦮 ṫ䢪䣾ὒ⪲ 㧎䟊 㥶☯㦧⩻㦖 㯳Ṗ䞮㡖㦒⋮

1 7 % Ⱎ ⯊ 䎦 ㌂ 㧊 䔎 ⪲ ῂ ㎇ ♲ 㔲 䘎 ὒ ゚ ᾦ 䞮 㡂 0.001/s 㢖 300/s 㦮 㥶☯㦧⩻ὒ ⁎ 㯳Ṗ⨟㦚 ⋮䌖

Table 2 Variation of volume fraction and grain size depending on heat treatment

Ferrite Pearlite Martensite

Volume Fraction (%)

Grain Size (ໃ)

Volume Fraction (%)

Grain Size (ໃ)

Volume Fraction (%)

Grain Size (ໃ)

As-received 89 10.3 11 1.4 - -

730 ଇW.Q 83 12.4 - - 17 2.2

780 ଇW.Q 69 12.2 - - 31 2.3

穢剳暒昷儆击穟箒滆V洢YW劒G 洢[笾SGYWXX噊VZXZG

G

0.05 0.10 0.15 0.20 0.25

0 200 400 600 800 1000

0.001/s 1/s 10/s 104/s 195/s 305/s

True Stress (MPa)

True Strain

0.05 0.10 0.15 0.20

0 200 400 600 800 1000

0.001/s 1/s 10/s 91/s 194/s 301/s

True Stress (MPa)

True Strain

(a) (b)

0.05 0.10 0.15 0.20

0 200 400 600 800 1000

0.001/s 1/s 10/s 94/s 195/s 301/s

True Stress (MPa)

True Srtain

(c)

1E-4 1E-3 0.01 0.1 1 10 100 1000

0 200 400 600 800 1000

e=0.05 e=0.10 e=0.15 e=0.20

Flow Stress (MPa)

Strain Rate (/s)

1E-4 1E-3 0.01 0.1 1 10 100 1000

0 200 400 600 800 1000

e=0.05 e=0.10 e=0.15 e=0.20

Flow Stress (MPa)

Strain Rate (/s)

(a) (b)

1E-4 1E-3 0.01 0.1 1 10 100 1000

0 200 400 600 800 1000

e=0.05 e=0.10 e=0.15

Flow Stress (MPa)

Strain Rate (/s)

(c) Table 3 Material properties acquired from quasi-static

tensile tests

UTS (MPa) Elongation

12% Pearlite 474 0.35 17% Martensite 610 0.26 31% Martensite 736 0.17

⌎ ộ㦒⪲ 䗮⧒㧊䔎㢖 䗚⧒㧊䔎⪲ ῂ㎇♲ 㔲䘎㦖

⼖䡫⮶ ㏣☚Ṗ 㯳Ṗ䞾㠦 ➆⧒ 㦧⩻㦮 ⼖䢪⨟㦖 䋂 ἶ, 䗮⧒㧊䔎㢖 Ⱎ⯊䎦㌂㧊䔎⪲ ῂ㎇♲ 㔲䘎㦮 㦧

⩻ ⼖䢪⨟㧊 ㌗╖㩗㦒⪲ 㧧㦖 ộ㦚 㞢 㑮 㧞┺.

㥶☯㦧⩻㧊 㯳Ṗ䞮㡖┺⓪ ộ㦖 㩚㥚㦮 㤖㰗㧚㧊

⹿䟊 ♮㠞┺⓪ ộ㦚 㦮⹎䞮⓪◆, 㧒⹮㩗㦒⪲ ἶ㏣

⼖䡫㠦㍲ 㥶☯㦧⩻㧊 㯳Ṗ䞮⓪ 㤦㧎㦖 㩚㑶䞲 ⹪ 㢖 ṯ㧊 ⼖䡫⮶ ㏣☚Ṗ 㯳Ṗ䞾㠦 ➆⧒ 䢲㎇䢪 ♮

⓪ 㩚㥚㤦㦮 㑮Ṗ 㯳Ṗ䞮㡂 㩚㥚 ⹖☚Ṗ ⏨㞚㰖₆

➢ⶎ㦒⪲ 㞢⩺㪎 㧞┺[15]. ➆⧒㍲ ㌗⿚㥾㠦 ➆⯎

㥶☯㦧⩻ ⼖䢪⨟㦮 㹾㧊⓪ ⼖䡫㦚 䞮₆ 㩚㧎 㽞₆ 㠦 Ṭἶ 㧞⓪ 㩚㥚 ⹖☚㦮 㹾㧊㠦㍲ ₆㧎 ♲ ộ㦒

⪲ ㌂⬢♲┺.

⁞㏣㦖 㧊㩚㦮 㧊⩻㠦 ➆⧒㍲ ⰺ㤆 ┺⯎ 㩚㥚 ⹖

☚⯒ Ṗ㰖⓪◆, 㢚㩚䧞 㠊┦Ⱇ♲ ⁞㏣㦖 10⁴/mm²~ 10⁶/mm² 㩫☚㦮 㩚㥚 ⹖☚⯒ Ṭἶ 㧞⓪ ⹮Ⳋ 㕂䞮 Ợ ⌟Ṛ ṖὋ♲ ⁞㏣㦖 10⁹/mm²~10¹⁰/mm² 㩫☚㦮 㩚㥚 ⹖☚⯒ Ṗ㰖Ⳇ Ⱎ⯊䎦㌂㧊䔎 㫆㰗㦖 㕂䞮Ợ

⼖䡫♲ ⁞㏣㠦㍲㢖 ゚㔍䞲 ⏨㦖 㩚㥚 ⹖☚⯒ Ṗ㰖

⓪ ộ㦒⪲ 㞢⩺㪎 㧞┺[12,16]. ⡦䞲 䗚⧒㧊䔎⓪ 㽞

₆㠦 㟓 10⁸/mm² 㩫☚㦮 㩚㥚⹖☚⯒ Ṗ㰖Ⳇ[17] 10%

‶㧒⼖䡫㧊 㧒㠊⌂㦚 ➢ 䗚⧒㧊䔎㦮 㩚㥚⹖☚Ṗ Ⱎ⯊䎦㌂㧊䔎㦮 㽞₆ 㩚㥚⹖☚㢖 ゚㔍䞲 ộ㦒⪲

⽊ἶ♲G ⹪G 㧞┺[17,18].G G

➆⧒㍲G 䗮⧒㧊䔎㢖G Ⱎ⯊䎦㌂㧊䔎⪲G ῂ㎇♲G 㔲䘎 㦖G Ⱎ⯊䎦㌂㧊䔎ṖG 㽞₆⿖䎆G ⏨㦖G 㩚㥚G ⹖☚⯒G Ṗ 㰖₆G ➢ⶎ㠦G ⼖䡫⮶G ㏣☚ṖG 㯳Ṗ䞮㡂☚G 㩚㥚⹖☚G 㯳Ṗ⨟㧊G ㌗╖㩗㦒⪲G 㧧㦒⸖⪲G ㏣☚G ⹒Ṧ☚ṖG ⌄ 㦖G ⹮ⳊSG 䗮⧒㧊䔎㢖G 䗚⧒㧊䔎⪲G ῂ㎇♲G 㔲䘎㦖G 㽞

₆㠦G ㌗╖㩗㦒⪲G ⌄㦖G 㩚㥚⹖☚⯒G Ṭ₆G ➢ⶎ㠦G ⼖ 䡫⮶G ㏣☚ṖG 㯳Ṗ䞾㠦G ➆⧒G 㩚㥚G ⹖☚㦮G 㯳Ṗ⨟G 㧊G 䄺㰖⸖⪲G ㏣☚G ⹒Ṧ☚ṖG ⏨㦖G ộ㦒⪲G 䕦┾♲┺UG 31%㦮 Ⱎ⯊䎦㌂㧊䔎⪲ ῂ㎇♲ 㔲䘎㦖 Ⱎ⯊䎦㌂㧊

⽊Ⳋ ⼖䡫⮶ ㏣☚ ⹒Ṧ☚⓪ 䋂Ợ 㹾㧊Ṗ 㠜⓪ ộ 㦒⪲ ⋮䌖⌂┺. 㧊ộ㦖 17%㩫☚㦮 Ⱎ⯊䎦㌂㧊䔎㠦

㍲ 㧊⹎ 㿿⿚䧞 ⽋㧷䞮ἶ ἂἶ䞲 㩚㥚 ῂ㫆⯒ 䡫

Fig. 7 True strain-stress curves at various strain rate : (a) Ferrite+12% Pearlite, (b) Ferrite+17% Martensite and (c) Ferrite+31% Martensite

Fig. 8 Strain rate sensitivity at various strain rate : (a) Ferrite+12% Pearlite, (b) Ferrite+17% Martensite and (c)

Ferrite+31% Martensite

ZX[GV穢剳暒昷儆击穟箒滆V洢YW劒G 洢[笾SGYWXX噊G

G

1E-4 1E-3 0.01 0.1 1 10 100 1000

0 200 400 600 800 1000

12 % pearlite + ferrite 17% martensite + ferrite 31% martensite + ferrite

Engineering stress (MPa)

Strain rate (/s)

Table 4 The increase ratio of tensile strength at 0.001/s and 300/s at strain of 10%

0.001/s flow stress

300/s flow stress

increase rate 12% Pearlite 511 MPa 635 MPa 24%

17% Martensite 655 MPa 721 MPa 10%

31% Martensite 808 MPa 877 MPa 9%

Fig. 9 Variation of UTS depending on the strain rate and heat treatment

㎇䞾㦒⪲㖾 ⼖䡫⮶ ㏣☚ 㯳Ṗ㠦 ➆⯎ 䢲㎇䢪♲ 㩚G 㥚㤦㦮G 㯳ṖG 㡗䟻㧊G ⹎⹎䟞₆G ➢ⶎ㦒⪲G 䕦┾♲┺UG 㧊⩂䞲G ἆὒ⓪G Yoon ❇㧊G 㡆ῂ䞲G ⼖䡫⮶G ㏣☚㠦G

➆⯎G SPCC ṫὒG TRIPG ṫ㦮G ⼖䡫⮶G ㏣☚G ἓ䢪㠦G

╖䞲G 㡆ῂG ἆὒ[19]㢖☚G 㧒䂮䞲┺UG

Fig. 9⓪ ṗ ⼖䡫⮶ ㏣☚㠦㍲㦮 㾲╖ 㧎㧻 ṫ☚

Ṩ㦚 ☚㔲䞲 ộ㧊┺. 䗮⧒㧊䔎㢖 䗚⧒㧊䔎⪲ ῂ㎇

♲ 㔲䘎㦖 ⼖䡫⮶ ㏣☚Ṗ 301/s㠦㍲ 㾲╖ 㧎㧻 ṫ

☚ Ṩ㧊 581MPa㧊Ⳇ, Ⱎ⯊䎦㌂㧊䔎Ṗ 17% 䙂䞾♲

㔲䘎㦖 ⼖䡫⮶ ㏣☚Ṗ 0.001/s 㧒 ➢ 㾲╖ 㧎㧻 ṫ

☚ Ṩ㧊 610MPa㧊┺. ⡦䞲 17%㦮 Ⱎ⯊䎦㌂㧊䔎Ṗ 䙂䞾♲ 㔲䘎㦮 301/s㦮 ⼖䡫⮶ ㏣☚㠦㍲㦮 㾲╖

㧎㧻 ṫ☚ Ṩ㦖 671MPa㧊Ⳇ 31% Ⱎ⯊䎦㌂㧊䔎Ṗ 䙂䞾♲ 㔲䘎㦮 0.001/s㦮 㾲╖ 㧎㧻 ṫ☚ Ṩ㦖 736MPa㧊┺. ⽎ 㡆ῂ㠦㍲ 㔲䠮䞲 ⻪㥚 ⌊㠦㍲⓪

⼖䡫⮶ ㏣☚Ṗ ゾ⧒㰖Ⳋ㍲ 㩚㥚 ⹖☚ 㯳Ṗ⪲ 㧎䞲 ṫ䢪 䣾ὒ⽊┺ Ⱎ⯊䎦㌂㧊䔎 ㌗㠦 㦮䞲 ṫ䢪 䣾ὒ Ṗ ▪ 䋆 ộ㦚 㦮⹎䞲┺.G

G

71# ൚# ᤊ#

#

⽎ 㡆ῂ㠦㍲⓪ 㧦☯㹾㣿 ṫ䕦㠦 ╖䞮㡂 ☯㧒䞲

䢪䞯㩗 㫆㎇㦚 Ṗ㰖Ⳋ㍲☚ ⹎㎎㫆㰗㦮 ㌗ὒ ⁎ ⿚ 㥾㧊 ┺⯒ ➢, ⼖䡫⮶㏣☚㠦 ➆⯎ ☯㩗 㧎㧻 䔏㎇

㦚 ㌊䘊⽊ἶ㧦 䞮㡖┺. 㡊㻮Ⰲ⯒ 䐋䟊 䗮⧒㧊䔎㢖 䗚⧒㧊䔎 ⹥ 䗮⧒㧊䔎㢖 Ⱎ⯊䎦㌂㧊䔎⪲ SPRC440 䕦㨂㦮 ㌗ ῂ㎇ ⹥ ⿚㥾㦚 ⼖䢪㔲䋾 䤚 0.001/s~

300/s㦮 ⼖䡫⮶㏣☚㠦㍲ ἶ㏣⼖䡫Ệ☯㦚 ὖ㺆䞾㦒

⪲㖾 ┺㦢ὒ ṯ㦖 ἆ⪶㦚 㠑㠞┺.

(1) ⽎ 㡆ῂ㦮 㔲䠮 ⻪㥚㠦 㧞㠊㍲⓪ ⹎㎎㫆㰗㦮 ῂ㎇㠦 ㌗ὖ㠜㧊 ⼖䡫⮶ ㏣☚Ṗ 㯳Ṗ䞶㑮⪳ 㩚㥚

⹖☚Ṗ 㯳Ṗ䞮㡂 㥶☯㦧⩻㧊 㯳Ṗ䞮㡖┺.

(2) 䗮⧒㧊䔎㢖 Ⱎ⯊䎦㌂㧊䔎⪲ ῂ㎇♲ 㔲䘎㠦

゚䟊 䗮⧒㧊䔎㢖 䗚⧒㧊䔎⪲ ῂ㎇♲ 㔲䘎㦮 ㏣☚

⹒Ṧ☚Ṗ 䅎㦒Ⳇ, 㧊⓪ Ⱎ⯊䎦㌂㧊䔎Ṗ ⽎㰞㩗㦒

⪲ ⏨㦖 㩚㥚 ⹖☚ ⹥ 㕣㩫 ῂ㫆 ❇㦒⪲ 㧎䟊 㩚 㥚 㤖㰗㧚㦚 䣾ὒ㩗㦒⪲ ⹿䟊䞮₆ ➢ⶎ㠦, ⼖䡫⮶

㏣☚㯳Ṗ㠦 ➆⧒ 䢲㎇䢪 ♮⓪ 㩚㥚㤦 㑮㦮 㯳Ṗ 㡗䟻㧊 ㌗╖㩗㦒⪲ 㧧₆ ➢ⶎ㧎 ộ㦒⪲ 䕦┾♲┺.

(3) ⼖䡫⮶ ㏣☚ 㯳Ṗ㠦 ➆⯎ 㩚㥚⹖☚ 㯳Ṗ⪲

㧎䞲 ṫ䢪 䣾ὒ⽊┺ 㡊㻮Ⰲ⯒ 䐋䞲 Ⱎ⯊䎦㌂㧊䔎

⼖䌲㠦 㦮䞲 ṫ䢪 䣾ὒṖ ▪ 䋂Ợ ⋮䌖⌂┺.

(4) Ⱎ⯊䎦㌂㧊䔎㦮 ⿚㥾㧊 17%㠦㍲ 31%⪲ 㯳 Ṗ䞮㡂☚ ⼖䡫⮶ ㏣☚ ⹒Ṧ☚⓪ 䋂Ợ 㹾㧊Ṗ 㠜⓪ ộ㦒⪲ ⋮䌖⌂┺.

Ⳣ# ඊ# ᯢ# 㙶#

[1] T. Nicholas, 1980, Tensile testing of materials at high rates of strain, Exper. Mech., Vol 21, pp. 177~185.

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