A High shear technique for liquidus boundary measurements
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298 i
373 I
I
TEMPERATURE 473 I
(K)
573 I
673 I e~
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•
5
4_ ~ - e . . . . . •
-4
III
4340
3
z
- o
z
~
I ,°, - / '' "- - x " ' "
25
o 4130A
o~
* 4130B
u_
x 4130C I AS {3
N
I 100
I
TEMPERING
I 200
I
I 300
TEMPERATURE
I
I 400
(°C)
F i g . 3 - - R e s u l t s of MES determination of fraction of r e t a i n e d austenite ( s o l i d lines) and cementite ( d a s h e d l i n e s ) a s a f u n c tion of tempering for 4130 and 4340 type s t e e l s . T h e volume fraction of a u s t e n i t e w a s converted from the MES d e t e r m i n a tion of atomic fraction with l a t t i c e p a r a m e t e r s of austenite and m a r t e n s i t e g i v e n in Ref. 2 . Typical s t a t i s t i c a l uncertainty from the computer fits a r e indicated by e r r o r b a r s for austenite (left) and cementite (right). T h e l i n e s through the data a r e d r a w n t o guide the eye.
T h e M E S p a r a m e t e r w h i c h is best used t o c h a r a c t e r i z e t h e c a r b i d e C i s t h e s e p a r a t i o n of t h e t w o r e s o l v e d c a r b i d e l i n e s s e e n in Fig. 2 f o r t h e s p e c i m e n t e m p e r e d a t 4 5 0 ° C . F r o m t h i s s e p a r a t i o n we c a l c u l a t e t h e i n t e r n a l m a g n e t i c f i e l d s H l i s t e d i n T a b l e II. H i s f o u n d t o be t h e s a m e f o r a l l s p e c i m e n s i n w h i c h t h e C r e s o n a n c e is d e t e c t e d a n d is in a g r e e m e n t w i t h i n t e r n a l f i e l d s c h a r a c t e r i s t i c of c e m e n t i t e , F e 3 C . 13,~4 F i g u r e 3 s h o w s a l l of t h e M E S d e t e r m i n a t i o n s of r e t a i n e d a u s t e n i t e a n d c e m e n t i t e in t h e v a r i o u s s t e e l s as a f u n c t i o n of t e m p e r i n g . W e n o t e t h e f o l l o w i n g s y s t e m atics: 1) L a r g e r a m o u n t s o f r e t a i n e d a u s t e n i t e a r e o b s e r v e d i n t h e 4340 type s t e e l s r e l a t i v e t o t h e 4130 s t e e l s . T h i s is c o n s i s t e n t w i t h t h e h i g h e r c a r b o n a n d n i c k e l c o n t e n t s o f t h e 4340 s t e e l . T h e h i g h e r c a r b o n also e x p l a i n s t h e l a r g e r f r a c t i o n o f c e m e n t i t e obs e r v e d f o r the 4340 s t e e l s . T h e a m o u n t of r e t a i n e d a u s t e n i t e m e a s u r e d i n t h e 4340 s t e e l i s c o m p a r a b l e t o t h a t r e c e n t l y m e a s u r e d17 by a m a g n e t i c t e c h n i q u e f o r a n o t h e r 4340 h e a t . 2) I n c r e a s i n g the M o c o n t e n t i n t h e 4130 type s t e e l s has no v i s i b l e effects on retained austenite; however, a s y s t e m a t i c d e c r e a s e i n c e m e n t i t e c a n be s e e n . 3) T h e t e m p e r a t u r e r a n g e f o r the d i s a p p e a r a n c e o f r e t a i n e d a u s t e n i t e a n d t h e f o r m a t i o n o f c e m e n t i t e lies i n the r a t h e r n a r r o w r a n g e b e t w e e n 2 5 0 ° C a n d 3 0 0 ° C . T h e amounts of c a r b i d e o b s e r v e d a f t e r the final t
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