The effect of prior deformation on the strength and annealing of reverted austenite
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an a l l o y with an M s below r o o m t e m p e r a t u r e and b e c a u s e of the l a r g e amount of b a c k g r o u n d l i t e r a t u r e on the s t r e n g t h and s t r u c t u r e of r e v e r t e d a u s t e n i t e s in F e - N i a l l o y s , 5-9 t h i s type of a l l o y w a s s e l e c t e d for e x perimentation. EXPERIMENTAL
PROCEDURE
The alloy used in this investigation was prepared by vacuum melting and had an analyzed composition of Fe-31.4 pct Ni-0.03 pct C. This composition was selected because of its M s temperature, which was experimentally found to be in the -60 ~ to -70~ range. The 1 alloy was hot rolled into 1 in. wide by ~- in. thick bars and surface machined to remove existing scale. After a homogenization treatment at 2000~ for 4 h and a deformation-recrystallization treatment, the samples were water quenched from 1800~ cooled in liquid nitrogen, and w a r m e d to r o o m temperature. X-ray diffraction measurements of the type described by CullityI~ and Lindgren n indicated that 88 pet of the austenire had been transformed to martensite; integrated intensities of the (200) and (211) r e f l e c t i o n s of the m a r t e n s i t e a n d / o r f e r r i t e p h a s e and the (200) and (220) r e f l e c t i o n s of the a u s t e n i t e p h a s e w e r e u s e d for this d e t e r m i n a t i o n . S a m p l e s w e r e then r o l l e d e i t h e r 80, 50, 20, or 0 p c t r e d u c t i o n in a r e a ; the final t h i c k n e s s was held c o n s t a n t a t 0.020 in. T h e t e m p e r a t u r e , A / , a t which the m a r t e n s i t e r e v e r s i o n to a u s t e n i t e is c o m p l e t e d was d e t e r m i n e d to be 874~ using d i l a t o m e t r y m e a s u r e m e n t s . S a m p l e s that had been i m m e r s e d in liquid n i t r o g e n and d e f o r m e d 0, 20, 50, and 80 p c t r e d u c t i o n in a r e a w e r e i m m e r s e d in a liquid s a l t bath a t 900~ for 1 min and a i r c o o l e d . X - r a y d i f f r a c t i o n m e a s u r e m e n t s of the type d e s c r i b e d above i n d i c a t e d that the r e v e r s i o n to a n s t e n i t e w a s c o m p l e t e d (> 99 pct) by this h e a t t r e a t m e n t . T e n s i l e m e a s u r e m e n t s w e r e m a d e with s a m p l e s h a v ing a 2 in. gage length. The t e s t s w e r e m a d e at r o o m t e m p e r a t u r e on an l n s t r o n t e s t i n g m a c h i n e a t a c r o s s VOLUME 3, NOVEMBER 1 9 7 2 - 2 9 6 5
120
f [ / ~
log
Table I. Comparison of Tensile Properties for Annealed and Reverted Samples -
'
\ANNEALED + LIQUID NITROGEN + 807. DEFORMATI(AN
+
REVERSION
I I + ILIQUIDI NITROGEN I I + REVERSION I
Yield Strength, ks]
Tensile Strength, ksi
24.6 67.0
64.0 79.6
84.9
106.3
29.9 61.6
58.1 75.0
Present Investigation:
60
I f
Annealed (quenched from 1800~ Annealed + liquid nitrogen + reverted at 900~ Annealed + hquid Nitrogen + 80 pet deformation + reverted at 900~
I
f
f 40[
/
/
\IA~AL~D
Krauss and Cohen s Annealed (quenched from 2012 ~F) Annealed + liqmd nitrogen +
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