On the deformation behavior of dual-phase steels

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Table I. Composition (Wt. Pct) o f the Steels, Balance F e

On the Deformation Behavior of Dual-Phase Steels

Code HT-1 HT-6

C

Mn

LUIS F. RAMOS, DAVID K. MATLOCK and GEORGE KRAUSS are Graduate Student Associate Professor, and AMAX Professor of Physical Metallurgy, respectively,Department of Metallurgical Engineering, Colorado School of Mines, Golden, CO 80401. Manuscript submitted May 3 0 , 1978. METALLURGICAL

TRANSACTIONS A

V

Ti

P

AI

N

Table II. Summary o f Heat Treatments*

Sample

Steel

Heat Treat. Temp., °C

A B C D

HT-1 HT-1 HT-1 HT-I HT-1 HT-6 HT-6 HT-6

745 780 800 820 840 745 780 800

E

F G H

Mart. Volume Fraction,Pet 6 10 15 25 35 15 25 35

Pet C in Martensite 0.64 0.42 0.30 0.24 0.15 0.64 0.42 0.30

samples were heat treated for 6 rain andicedbrine quenched. Constant grain size = 0.010 mm.

*All

p e r m i t v a r i a t i o n of e i t h e r M V F o r t h e p c t C i n the m a r t e n s i t e w h i l e t h e o t h e r p a r a m e t e r w a s h e l d cons t a n t . T h e m i c r o s t r u c t u r a l p a r a m e t e r s l i s t e d in T a b l e II w e r e p r e d i c t e d f r o m t h e p h a s e d i a g r a m a n d the volume fraction of s e c o n d p h a s e was confirmed with metallography. Tensile s p e c i m e n s with a red u c e d gage l e n g t h o f 3 1 . 2 5 m m a n d a c r o s s - s e c t i o n of 6.25 × 2 m m w e r e m a c h i n e d p r i o r t o h e a t t r e a t m e n t . All tensile t e s t s were p e r f o r m e d at r o o m t e m p e r a t u r e o n a n I n s t r o n a t a s t r a i n r a t e o f 6.7 × 1O"~ s -1" T h e o b s e r v e d s t r e s s - s t r a i n d a t a , a s s h o w n in Fig. 1, c h a n g e w i t h b o t h M V F a n d p c t C i n m a r t e n s i t e . Figures 2 a n d 3 show t h a t t h e standard tensile p r o p e r t i e s a r e a f u n c t i o n o f b o t h MVF a n d p c t C in m a r t e n s i t e . Also f r o m Fig. 1, it is a p p a r e n t in s p e c i m e n s with a constant MVF, that t h e initial s t r a i n hardening c h a r a c t e r i s t i c s d e p e n d o n t h e p e t C i n m a r t e n s i t e , i.e. the martensite strength a n d / o r morphology. I n g e n e r a l , t h e d e f o r m a t i o n b e h a v i o r of a m u l t i p h a s e m i c r o s t r u c t u r e i s c h a r a c t e r i z e d by t h e d e f o r m a t i o n of e a c h p h a s e p l u s t h e i n t e r a c t i o n b e t w e e n t h e p h a s e s . In dual-phase s t e e l s , t h e deformation behavior

35 % Mart. Vol. Fract. /~

BOO

C-Mn S~ SteeLs

0.30 % C 600

ENGINEE R~NG

STRESS (MPa)

~ 400

~"

V

6JI~4%C

"030%C

15 °l. M~rL VoL Fract.

110

210

ENGINEERfNG STRAIN (%)

Fig. 1--Engineering s t r e s s - s t r a i n c u r v e s o f F e - C - M n - S i s t e e l s with d u a l - p h a s e s t r u c t u r e . Martensite c a r b o n contents and m a r t e n s i t e v o l u m e fractions a s shown.

ISSN 0360-2133/79/0211-0259500.75/0 SOCIETY FOR METALS AND T H E METALLURGICAL SOCIETY OF A1ME

© 1979 AMERICAN

S

0.052 0.90