Effect of cooling rate on ductile-brittle bend-transition temperature of chromium wir

Gilbert, A.

Klein, M. J.

English

NASA Technical Reports Server

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TIiEkWECT OF COOLIXG RATE ON THE 
DUCTI'LE-BRITTLE BE3D-TRANSITION TEMPERATURE 
OF CHBOMIUM WIRE 7 
m 
z 
0 L
A .  G 
bY 
l b e r t  and .n 
B a t t e l l e  Meniorial I n s t i t u t e  
, J .  K l e  
Metal Science Group 
Columbus Laborator ies  
Columbus , 
- *  - 
PI66 35319 
(ACCESSION NUMBER) 
IPAGEPI 
Oh i o  
/7 (CATEGO n 
Submitted as a L e t t e r  
To 
ACTA METALLURGICA 
____c- 
November, 1965 
GPO PRICE $ 
CFSTl PRICE(S) $ 
Hard copy (HC) /A 
Microfiche (MF) 
ff653 July65 
https://ntrs.nasa.gov/search.jsp?R=19660026029 2020-03-16T20:36:47+00:00Z
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Crys ta l s  of iodide-chromium were compacted , hot-extruded , swaged , 
and then cen te r l e s s  ground to  produce a rod of l / l0 - inch  diameter. The rod 
was then warm-drawn t o  w i r e  .017 inch i n  diameter,  t h e  ma te r i a l  on which 
r. 
the  experiments were conducted. 
capsule containing argon f o r  1 hour a t  1150 C, and w a s  d i r e c t l y  quenched 
A 10-inch length w a s  annealed i n  a quartz  
/ 
i n t o  water (breaking the capsule) from 1000 C. Previously,  a chromium 
1 
~ 
w i r e  .037 inch i n  diameter had been used i n  experiments t o  determine the  
(3) From the output of a 
I 
a c t u a l  cooling rate under these conditions.  
thermocouple spot-welded t o  the  specimen sur face  (recorded using a cathode- 
r ay  osci l loscope)  , the surface-cooling r a t e  w a s  found to  be 4000 C/second. 
It i s ,  therefore ,  reasonable t o  expect t h a t  the cooling rate f o r  the pre-  
s e n t  thinner  w i r e  was a t  least t h i s  high, and probably higher .  
t reatment  produced a r e c r y s t a l l i z e d  s t r u c t u r e  containing approximately 40 
gra ins  i n  a cross-sect ion a r e a ,  and chemical ana lys i s  showed the w i r e  to  
contain 50 ppm oxygen, 2 ppm hydrogen, 15 ppm carbon, and ni t rogen i n  the  
range 10-15 ppm. 
I 
The hea t  
A 152 C aging curve w a s  obtained on one-half of the  quenched w i r e ,  
taking in t e rmi t t en t  i n t e r n a l - f r i c t i o n  readings (0.7 cyc les  per second). 
Af t e r  3000 minutes , the  i n t e r n a l - f r i c t i o n  peak w a s  found t o  have decreased 
t o  the background l e v e l ,  ind ica t ing  t h a t  the n i t rogen  re ta ined  i n  super- 
s a tu ra t ed  s o l i d  s o l u t i o n  by the  high quenching ratec3) had f u l l y  aged out .  
Specimens were c u t  from the  ha l f  of the  wire  s t i l l  i n  t h e  quenched s t a t e ,  
and a l s o  from the f u l l y  aged mater ia l ,  f o r  comparative bend tests. 
of the r e l a t i v e l y  small length of w i r e  ava i l ab le ,  a 3-point bend j i g  w a s  
constructed,  which w a s  capable of t e s t i n g  specimens g rea t e r  i n  length than 
5/16 inch. 
crosshead speed on a table-model Ins t ron ,  e leva ted  temperatures being 
obtained i n  an e l e c t r i c a l l y  heated s i l i c o n e  o i l  bath.  
Because 
The specimens were electropol ished and t e s t ed  a t  0.1 inch/minute 
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The aging curve f o r  t h e  tlhromium w i r e ,  represented by the  
decreasing height  of the i n t e r n a l - f r i c t i o n  peak with increased aging 
I t i m e ,  is presented i n  Figure 1. The conversion t o  ppm ni t rogen is 
I 
obtained using Reference 3. 
Bend-test r e s u l t s  f o r  quenched and f o r  quenched and aged 
chromium wire ,: corresponding t o  the beginning and end, respec t ive ly ,  
of t he  curve of Figure 1 are l i s t e d  i n  Table 1. As has been seen pre-  
v ious ly  fo r  chromium(4), ?t w a s  found t h a t  the t r a n s i t i o n  from d u c t i l e  
t o  b r i t t l e  behavior w a s  extremely sharp,  i n  that a specimen e i t h e r  f a i l e d  
i n  a completely b r i t t l e  manner (described as b r i t t l e  i n  Table 1) o r  bent 
t o  the  maximum ex ten t  permitted by the j i g  (duc t i l e  i n  Table 1). The 
lowest temperature a t  which a quenched specimen was d u c t i l e  was 74 C 
below the lowest temperature a t  which a n  aged specimen w a s  d u c t i l e ,  and 
"- 
i 
- .  
the h ighes t  temperature a t  which a quenched specimen w a s  b r i t t l e  was 97C 
below the  equivalent  temperature fo r  aged ma te r i a l .  Thus, regard less  of 
how the  d u c t i l e - t o - b r i t t l e  t r a n s i t i o n  is  def ined,  the  quenched ma te r i a l  
has a t r a n s i t i o n  temperature between 74 and 98 C below t h a t  f o r  aged 
material. Duct i le  specimens exhibi ted y i e ld  drops on the load-time curve 
which were more pronounced f o r  quenched than f o r  aged specimens t o  the 
ex ten t  shown i n  Table 1. 
- 
Previous i n ~ e s t i g a t i o n s ( ~ - ~ )  i n t o  the  e f f e c t  of cooling rate 
on the d u c t i l e - b r i t t l e  t r a n s i t i o n  temperature of chromium1 have shown 
"quenched" ma te r i a l  t o  be more b r i t t l e  than "furnace-cooled" 
-- 
material, 
i n  con t r a s t  t o  the present  r e s u l t s .  
suggest t h a t  t h e  quenching rates used i n  previous work have been i n s u f f i c i e n t  
Recent experimental  r e s u l t s  , however, 
t o  maintain the n i t rogen  i n  so lu t ion .  This conclusion i s  based on the 
d a t a  quoted i n  Table 2(8) which shows that quenching rates of the  order 
of s eve ra l  thousand degrees centigrade per second a r e  necessary t o  
. 
L . 4 
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- . .  - TABLE 1. BEND-"SITION BEHAVIOR OF .017-INCH-DUIS.IETER CHROMIUM WIRE , 
~ _ _ _ _ ~  ~~ - 
Brit t le  
Tes t  Upper Lower Yield Frac ture  
Yield Point Yield-Point Drop , Load, Specimen Temp., Bend 
Number "C Behavior Load, l b  Load, l b  % l b  
Quenched Wire 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
.30 
53 
7 1  
85 
94 
98 
105 
113 
i29 
142 
164 
30 
105 
128 
145 
166 
192 
195 
225 
2 60 
B r i t t l e  
Duct i le  
Bri t t le  
Duc t i l e  
B r i t t l e  
D u c t i l e  
11 
I t  
I1 
II 
I t  
Britt le 
SI  
Duct i l e  
Bri t t le  
Duc t i l e  
Brittle 
Duc t i l e  
I 1  
Preliminary -- 
1.08 
1.07 
0 -96 
1.30 
1.52 
1.03 
1.12 
-- 
-- 
test; no load recorded. 
0 -84 29 
0.86 24 
0.72 33 
1.14 12 
1.32 15 
0.75 37 
0.98 14 
-- -- 
-- -- 
-- -- 
Quenched and Aged Wire 
Preliminary test; no load recorded. -- -- -- -- -- -- 
0.87 0.84 3 
0.72 0.64 12 
1.09 0.91 20 
0.89 0.78 15 
-- -- -- 
-- -- -_ 
TABLE 2. NITROGEN RETAINED I N  SOLUTION 
IN CHROMIUM AS A FUNCTION OF 
COOLING RATE 
Cooling Times and Approximate 
Cooling Rates From 1000 t o  100°C Nitrogen, 
T i m e ,  sec. Rate, 'C/sec. Ppm 
I 
0.1 
25 
200 
1,800 
i o ,  800 
-9000 
40 
5 
0.5 
0 -09 
26 
6 
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r e t a i n  even 20-30 ppm i n  so lu t ion .  The 
l a rge r  specimens used i n  previous inves t iga t ions  (5-7) together  with use 
of o i l  as a quenching medium(5y7) could not  have permitted such a high 
cooling r a t e .  
containing higher n i t rogen  concentrat ions which , aging s tud ie s  have 
Furthermore, previous work has been performed on chromium 
, increases  the  k i n e t i c s  of  n i t r i d e  p r e c i p i t a t i o n ,  and correa-  I 
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pondingly increases  the cri t ical  cooling rate necessary t o  maintain the 
n i t rogen  i n  so lu t ion .  I n  t h e  l i g h t  of these considerat ions,  i t  seems 
l i k e l y  t h a t  t h e  quenching r a t e s  used previously served pr imari ly  t o  
modify she morphology and d i s t r i b u t i o n  of the  n i t r i d e  phase r a t h e r  than 
to maintain a l l  t h e  n i t rogen  i n  so lu t ion .  This c w t a i n l y  seemed t o  be I 
the case i n  earlier work by one of the  present  au thors  (lo) in which quenched I 
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I t e n s i l e  specimens gave every indica t ion  of being d ispers ion  hardened by a 
I much f i n e r  p r e c i p i t a t e  than d id  slow-cooled specimens , a conclusion 
supported by the  t ransmission e l e c t r o n  microscopy r e s u l t s  of Yoshida , e t .  
~ 
a l .  (11), who showed o i l  quenched chromium t o  contain many p r e c i p i t a t e s  
of varying s i z e .  
I n  the present  work, however, the data i n  Figure 1, together  
w i th  the n i t rogen  ana lys i s ,  show tha t  a l l  t h e  n i t rogen  present  i n  the 
ma te r i a l  is i n  s o l i d  s o l u t i o n  as a r e s u l t  of the quench, and t h a t  a f t e r  
aging fo r  times g r e a t e r  than 3000 minutes, it is l a rge ly  present  as a 
p rec ip i r a t ed  phase i n  accordance with the pred ic t ions  of cqui l ibr ium- 
s o l u b i l i t y  data"). 
i s  l e s s  de t r imenta l  t o  d u c t i l i t y  than n i t rogen  combined i n  a second phase. 
It thus appears t h a t  n i t rogen  completely i n  so lu t ion  
-_ 
This work was performed under NASA Contract NASw-101 and AEC 
Contract W-7405-eng-92 t o  whom thpnks are due f o r  permission t o  publ ish.  
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REFEWNCES 
(1) G. T. Hahn, A .  Gi lbe r t ,  and R. I. Ja f f ee ,  "Tne E f fec t s  of Solutes  
on the  B r i t t l e - D u c t i l e  T rans i t i on  i n  Refractory Metals", Refractory 
Metals and Alloys 11, Interscience,  New York, 2 3 .  
( 2 )  M. E. DeMorton, "Measurement of Kitrogen Diffusion i n  Chromium by 
Anelas t ic  Nethods", J. Appl. Phys., 37, 2768 (1962). 
(3) M. J. Klein and A. H. Clauer, "Nitrogen-Induced I n t e r n a l  F r i c t i o n  
i n  Chromiun", Trans. AIME, 233, 1771 (1965). -
(4) A. G i lbe r t ,  C. N. Iieid, and G .  T.  Hahn, "Observation on the  Fracture  
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Chromium", Trans. M e t .  SOC. AIME, 227,  274 (1963). -
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- v  ? 
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The Effect of Cooling Rate on the Ductile- Brittle Bend-transition Temperature of Chromium Wire

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